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Sample records for cubic perovskite structure

  1. Competing structural instabilities in cubic perovskites

    CERN Document Server

    Vanderbilt, D

    1994-01-01

    We study the antiferrodistortive instability and its interaction with ferroelectricity in cubic perovskite compounds. Our first-principles calculations show that coexistence of both instabilities is very common. We develop a first-principles scheme to study the thermodynamics of these compounds when both instabilities are present, and apply it to SrTiO$_3$. We find that increased pressure enhances the antiferrodistortive instability while suppressing the ferroelectric one. Moreover, the presence of one instability tends to suppress the other. A very rich $P$--$T$ phase diagram results.

  2. First-principles prediction of structural, elastic, electronic and thermodynamic properties of the cubic SrUO{sub 3}-Perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Sahli, B. [Laboratoire de Génie Physique, Université Ibn Khaldoun, Tiaret, 14000 (Algeria); Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes 22000 (Algeria); Bouafia, H., E-mail: hamza.tssm@gmail.com [Laboratoire de Génie Physique, Université Ibn Khaldoun, Tiaret, 14000 (Algeria); Abidri, B.; Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes 22000 (Algeria); Hiadsi, S.; Akriche, A. [Laboratoire de Microscope Electronique et Sciences des Matériaux, Université des Sciences et de la Technologie Mohamed Boudiaf, département de Génie Physique, BP1505 El m’naouar, Oran (Algeria); Benkhettou, N.; Rached, D. [Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes 22000 (Algeria)

    2015-06-25

    Highlights: • The ground state properties of SrUO{sub 3}-Perovskite were investigated. • Elastic constants and their related parameters were calculated. • Electronic properties are treated using GGA-PBEsol + U approach. - Abstract: In this paper, we investigate bulk properties of the cubic SrUO{sub 3}-Perovskite in their nonmagnetic (NM), antiferromagnetic (AFM) and ferromagnetic (FM) states using all-electron self consistent Full Potential Augmented Plane Waves plus local orbital (FP-(L)APW + lo) method within PBEsol Generalized Gradiant density approximations. Our calculation allowed us to predict that the more stable magnetic state of the cubic SrUO{sub 3}-Perovskite is that of the ferromagnetic (FM). This work is the first prediction of elastic constants and their related parameters (Young modulus, shear modulus, Poisson ratio, Zener anisotropy and the Debye temperature) for this cubic compound using Mehl method. We have employed the GGA(PBEsol) and GGA(PBEsol) + U to investigate the electronic band structure, density of states and electronic charge density of SrUO{sub 3}-Perovskite. The electronic band structure calculations revealed that SrUO{sub 3} exhibits metallic behavior. On the other hand the charge density plots for [1 1 0] direction indicates a strong ionic character along the Sr–O bond while the U–O bond has strong covalent character. Finally, we have analyzed the thermodynamic properties using the quasi-harmonic Debye model to complete the fundamental characterization of cubic SrUO{sub 3}-Perovskite.

  3. Structural and optoelectronic properties of cubic perovskite RbPbF3

    Indian Academy of Sciences (India)

    K Ephraim Babu; N Murali; D Tirupathi Swamy; V Veeraiah

    2014-04-01

    The structural and optoelectronic properties of cubic perovskite RbPbF 3 are calculated using all electrons full potential linearized augmented plane wave (FP-LAPW) method. The calculated lattice constant is in good agreement with the experimental result. The calculated band structure shows a direct band gap of 3.07 eV. The contribution of different bands is analysed from the total and partial density of state curves. We identified hybridization of Pb , Pb states with F states in the valence bonding region. Calculations of the optical spectra, viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss are performed for the energy range of 0-30 eV. Based on the direct bandgap, as well as other optical properties of the compound, it is predicted that this material is useful for vacuum-ultraviolet-transparent (VUV-transparent) applications.

  4. The Coulombic Lattice Potential of Ionic Compounds: The Cubic Perovskites.

    Science.gov (United States)

    Francisco, E.; And Others

    1988-01-01

    Presents coulombic models representing the particles of a system by point charges interacting through Coulomb's law to explain coulombic lattice potential. Uses rubidium manganese trifluoride as an example of cubic perovskite structure. Discusses the effects on cluster properties. (CW)

  5. Ionic and Optical Properties of Methylammonium Lead Iodide Perovskite across the Tetragonal-Cubic Structural Phase Transition

    Energy Technology Data Exchange (ETDEWEB)

    Hoque, Md Nadim Ferdous [Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock Texas 79409 USA; Islam, Nazifah [Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock Texas 79409 USA; Li, Zhen [Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden Colorado 80401 USA; Ren, Guofeng [Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock Texas 79409 USA; Zhu, Kai [Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden Colorado 80401 USA; Fan, Zhaoyang [Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock Texas 79409 USA

    2016-09-01

    Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, dramatic changes in these properties resulting from a structural phase transition, are not well studied. Herein, we report a striking contrast at approximately 45 degrees C in the ionic/electrical properties of MAPbl3 owing to a change of the ion activation energy from 0.7 to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the 'continuous' nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature as when tetragonal-cubic structural phase transition occurs.

  6. Structural, elastic, and electronic properties of cubic perovskite BaHfO{sub 3} obtained from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Hongsheng [Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011 (China); Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Graduate School of Chinese Academy of Sciences, Beijing 100049 (China); Chang Aimin, E-mail: changam@ms.xjb.ac.c [Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011 (China); Wang Yunlan [Center for High Performance Computing, Northwestern Polytechnical University, Xi' an 710072 (China)

    2009-08-01

    We investigated the structural, elastic, and electronic properties of the cubic perovskite-type BaHfO{sub 3} using a first-principles method based on the plane-wave basis set. Analysis of the band structure shows that perovskite-type BaHfO{sub 3} is a wide gap indirect semiconductor. The band-gap is predicted to be 3.94 eV within the screened exchange local density approximation (sX-LDA). The calculated equilibrium lattice constant of this compound is in good agreement with the available experimental and theoretical data reported in the literatures. The independent elastic constants (C{sub 11}, C{sub 12}, and C{sub 44}), bulk modules B and its pressure derivatives B{sup '}, compressibility beta, shear modulus G, Young's modulus Y, Poisson's ratio nu, and Lame constants (mu,lambda) are obtained and analyzed in comparison with the available theoretical and experimental data for both the singlecrystalline and polycrystalline BaHfO{sub 3}. The bonding-charge density calculation make it clear that the covalent bonds exist between the Hf and O atoms and the ionic bonds exist between the Ba atoms and HfO{sub 3} ionic groups in BaHfO{sub 3}.

  7. First principles study of the structural and electronic properties of double perovskite Ba2YTaO6 in cubic and tetragonal phases

    Science.gov (United States)

    Deluque Toro, C. E.; Rodríguez M., Jairo Arbey; Landínez Téllez, D. A.; Moreno Salazar, N. O.; Roa-Rojas, J.

    2014-12-01

    The Ba2YTaO6 double perovskite presents a transition from cubic (Fm-3m) to tetragonal structure (I4/m) at high temperature. In this work, we present a detailed study of the structural and electronic properties of the double perovskite Ba2YTaO6 in space group Fm-3m and I4/m. Calculations were made with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations. From the minimization of energy as a function of volume and the fitting of the Murnaghan equation some structural characteristics were determined as, for example, total energy, lattice parameter (a=8.50 Å in cubic phase and a=5.985 Å and c=8.576 Å in tetragonal), bulk modulus (135.6 GPa in cubic phase and 134.1 GPa in tetragonal phase) and its derivative. The study of the electronic characteristics was performed from the analysis of the electronic density of states (DOS). We find a non-metallic behavior for this with a direct band gap of approximately 3.5 eV and we found that the Ba2YTaO6 (I4/m) phase is the most stable one. © 2013 Elsevier Science.

  8. Structural,Electronic and Elastic Properties of Cubic Perovskites SrSnO3 and SrZrO3 under Hydrostatic Pressure Effect

    Institute of Scientific and Technical Information of China (English)

    SHI Li-Wei; DUAN Yi-Feng; YANG Xian-Qing; QIN Li-Xia

    2010-01-01

    @@ Using the plane-wave pesudopotential(PWPP)method within the generalized gradient approximation(GGA),we investigate the hydrostatic pressure induced effect on the structural,electronic and elastic properties of cubic perovskites SrSnO3 and SrZrO3.The pressure dependence of the lattice constants,some indirect and direct band gaps,the upper valence bandwidths,the elastic stiffness constants and the aggregate elastic moduli,as well as the Debye temperature are investigated.Our calculated ground-state results are in good agreement with the available experimental and theoretical data.

  9. First-principles calculation of the structural, electronic, and magnetic properties of cubic perovskite RbXF3 (X = Mn, V, Co, Fe)

    Science.gov (United States)

    rehman Hashmi, Muhammad Raza ur; Zafar, Muhammad; Shakil, M.; Sattar, Atif; Ahmed, Shabbir; Ahmad, S. A.

    2016-11-01

    First-principles calculations by means of the full-potential linearized augmented plane wave method using the generalized gradient approximation with correlation effect correction (GGA+U) within the framework of spin polarized density functional theory (DFT+U) are used to study the structural, electronic, and magnetic properties of cubic perovskite compounds RbXF3 (X = Mn, V, Co, and Fe). It is found that the calculated structural parameters, i.e., lattice constant, bulk modulus, and its pressure derivative are in good agreement with the previous results. Our results reveal that the strong spin polarization of the 3d states of the X atoms is the origin of ferromagnetism in RbXF3. Cohesive energies and the magnetic moments of RbXF3 have also been calculated. The calculated electronic properties show the half-metallic nature of RbCoF3 and RbFeF3, making these materials suitable for spintronic applications.

  10. New cubic perovskites for one- and two-photon water splitting using the computational materials repository

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Landis, David; Thygesen, Kristian Sommer

    2012-01-01

    screening of around 19 000 oxides, oxynitrides, oxysulfides, oxyfluorides, and oxyfluoronitrides in the cubic perovskite structure with PEC applications in mind. We address three main applications: light absorbers for one- and two-photon water splitting and high-stability transparent shields to protect...

  11. Calculated Pourbaix Diagrams of Cubic Perovskites for Water Splitting: Stability Against Corrosion

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

    2014-01-01

    We use density functional theory calculations to investigate the stability of cubic perovskites for photo-electrochemical water splitting taking both materials in their bulk crystal structure and dissolved phases into account. The method is validated through a detailed comparison of the calculated...

  12. Post-perovskite Transition in Anti-structure.

    Science.gov (United States)

    Wang, Bosen; Ohgushi, Kenya

    2016-11-30

    The discovery of the post-perovskite transition, which is the structural transition from the perovskite to post-perovskite structure in MgSiO3 under pressure, has aroused great interests in geosciences. Despite of previous extensive studies, key factors of the post-perovsktie transition are still under hot debate primarily due to the big difficulty in performing systematic experiments under extreme conditions. Hence, search for new materials showing the post-perovskite transition under ambient pressure has been highly expected. We here report a new-type of materials Cr3AX (A = Ga, Ge; X = C, N), which exhibits the post-perovskite transition as a function of "chemical pressure" at ambient physical pressure. The detailed structural analysis indicates that the tolerance factor, which is the measure of the ionic radius mismatch, plays the key role in the post-perovskite transition. Moreover, we found a tetragonal perovskite structure with loss of inversion symmetry between the cubic perovskite and orthorhombic post-perovskite structures. This finding stimulates a search for a ferroelectric state in MgSiO3.

  13. Post-perovskite Transition in Anti-structure

    Science.gov (United States)

    Wang, Bosen; Ohgushi, Kenya

    2016-11-01

    The discovery of the post-perovskite transition, which is the structural transition from the perovskite to post-perovskite structure in MgSiO3 under pressure, has aroused great interests in geosciences. Despite of previous extensive studies, key factors of the post-perovsktie transition are still under hot debate primarily due to the big difficulty in performing systematic experiments under extreme conditions. Hence, search for new materials showing the post-perovskite transition under ambient pressure has been highly expected. We here report a new-type of materials Cr3AX (A = Ga, Ge; X = C, N), which exhibits the post-perovskite transition as a function of “chemical pressure” at ambient physical pressure. The detailed structural analysis indicates that the tolerance factor, which is the measure of the ionic radius mismatch, plays the key role in the post-perovskite transition. Moreover, we found a tetragonal perovskite structure with loss of inversion symmetry between the cubic perovskite and orthorhombic post-perovskite structures. This finding stimulates a search for a ferroelectric state in MgSiO3.

  14. Lattice dynamics and thermal equation of state of cubic CaSiO3 perovskite

    Science.gov (United States)

    Sun, T.; Wentzcovitch, R. M.

    2014-12-01

    CaSiO3 perovskite (CaPv) is believed to be the third most abundant mineral in the Earth's lower mantle and is a major component of mid-ocean ridge basalt (MORB). A well constrained thermal equation of state for CaPv is key to several geophysical problems, e.g., lower mantle composition, density contrast between mantle and plates, nature of D" region, etc. Its experimental and theoretical determination have been very challenging because the cubic structure that CaPv adopts at lower mantle conditions is unstable at low temperatures and some of its harmonic phonons have imaginary frequencies. We have used a recently developed hybrid method combining ab initio molecular dynamics with vibrational normal mode analysis to compute its free energy and thermal equation of state at lower mantle conditions. These results are essential to understand the fate of subducted MORB in the mantle. Research supported by NSF grants EAR-1319361 and EAR-1019853

  15. Magnetism and the spin state in cubic perovskite CaCo O3 synthesized under high pressure

    Science.gov (United States)

    Xia, Hailiang; Dai, Jianhong; Xu, Yuanji; Yin, Yunyu; Wang, Xiao; Liu, Zhehong; Liu, Min; McGuire, Michael A.; Li, Xiang; Li, Zongyao; Jin, Changqing; Yang, Yifeng; Zhou, Jianshi; Long, Youwen

    2017-07-01

    Cubic SrCo O3 with an intermediate spin state can only be stabilized by high pressure and high temperature (HPHT) treatment. It is metallic and ferromagnetic with the highest Curie temperature of the transition-metal perovskites. The chemical substitution by Ca on Sr sites would normally lower crystal symmetry from cubic to orthorhombic as seen in the perovskite family of Ca M O3 (M =M4 + of transition metals, G e4 + , S n4 + , and Z r4 + ) at room temperature. This structural change narrows the bandwidth, so as to further enhance the Curie temperature as the crossover to the localized electronic state is approached. We report a successful synthesis of the perovskite CaCo O3 with a HPHT treatment. Surprisingly, CaCo O3 crystallizes in a simple cubic structure that remains stable down to 20 K, the lowest temperature in the structural study. The new perovskite has been thoroughly characterized by a suite of measurements including transport, magnetization, specific heat, thermal conductivity, and thermoelectric power. Metallic CaCo O3 undergoes two successive magnetic transitions at 86 K and 54 K as temperature decreases. The magnetization at 5 K is compatible with the intermediate spin state t4e1 of C o4 + at the octahedral site. The thermal expansion of the Co-O bond length indicates that the population of high spin state t3e2 increases for T >100 K . The shortest Co-O bond length in cubic CaCo O3 is responsible for delocalizing electrons in the π*-band and itinerant-electron ferromagnetism at T <54 K . A comprehensive comparison between SrCo O3 and CaCo O3 and the justification of their physical properties by first-principles calculation have also been made in this report. Partially filled π* and σ* bands would make CaCo O3 suitable to study the Hund's coupling effect in a metal.

  16. High-pressure synthesis of 5d cubic perovskite BaOsO3 at 17 GPa: ferromagnetic evolution over 3d to 5d series.

    Science.gov (United States)

    Shi, Youguo; Guo, Yanfeng; Shirako, Yuichi; Yi, Wei; Wang, Xia; Belik, Alexei A; Matsushita, Yoshitaka; Feng, Hai Luke; Tsujimoto, Yoshihiro; Arai, Masao; Wang, Nanlin; Akaogi, Masaki; Yamaura, Kazunari

    2013-11-06

    In continuation of the series of perovskite oxides that includes 3d(4) cubic BaFeO3 and 4d(4) cubic BaRuO3, 5d(4) cubic BaOsO3 was synthesized by a solid-state reaction at a pressure of 17 GPa, and its crystal structure was investigated by synchrotron powder X-ray diffraction measurements. In addition, its magnetic susceptibility, electrical resistivity, and specific heat were measured over temperatures ranging from 2 to 400 K. The results establish a series of d(4) cubic perovskite oxides, which can help in the mapping of the itinerant ferromagnetism that is free from any complication from local lattice distortions for transitions from the 3d orbital to the 5d orbital. Such a perovskite series has never been synthesized at any d configuration to date. Although cubic BaOsO3 did not exhibit long-range ferromagnetic order unlike cubic BaFeO3 and BaRuO3, enhanced feature of paramagnetism was detected with weak temperature dependence. Orthorhombic CaOsO3 and SrOsO3 show similar magnetic behaviors. CaOsO3 is not as conducting as SrOsO3 and BaOsO3, presumably due to impact of tilting of octahedra on the width of the t2g band. These results elucidate the evolution of the magnetism of perovskite oxides not only in the 5d system but also in group 8 of the periodic table.

  17. Hybrid DFT calculations of the F centers in cubic ABO{sub 3} perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Kotomin, E A; Zhukovskii, Y F; Piskunov, S [Institute for Solid State Physics, University of Latvia, Kengaraga 8, Riga LV-1063 (Latvia); Ellis, D E [Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208 (United States)], E-mail: kotomin@latnet.lv

    2008-06-01

    We employed the hybrid DFT-LCAO approach as implemented in the CRYSTAL code for 135 atom supercell calculations of O vacancies with trapped electrons (known as the F centers) in three cubic perovskite crystals: SrTiO{sub 3}, PbTiO{sub 3} and PbZrO{sub 3}. The local lattice relaxation, charge redistribution and defect energy levels in the optical gap are compared. We demonstrate how difference in a chemical composition of host materials leads to quite different defect properties.

  18. Superhard BC(3) in cubic diamond structure.

    Science.gov (United States)

    Zhang, Miao; Liu, Hanyu; Li, Quan; Gao, Bo; Wang, Yanchao; Li, Hongdong; Chen, Changfeng; Ma, Yanming

    2015-01-01

    We solve the crystal structure of recently synthesized cubic BC(3) using an unbiased swarm structure search, which identifies a highly symmetric BC(3) phase in the cubic diamond structure (d-BC(3)) that contains a distinct B-B bonding network along the body diagonals of a large 64-atom unit cell. Simulated x-ray diffraction and Raman peaks of d-BC(3) are in excellent agreement with experimental data. Calculated stress-strain relations of d-BC(3) demonstrate its intrinsic superhard nature and reveal intriguing sequential bond-breaking modes that produce superior ductility and extended elasticity, which are unique among superhard solids. The present results establish the first boron carbide in the cubic diamond structure with remarkable properties, and these new findings also provide insights for exploring other covalent solids with complex bonding configurations.

  19. Theoretical determination of the structures of CaSiO3 perovskites.

    Science.gov (United States)

    Caracas, Razvan; Wentzcovitch, Renata M

    2006-12-01

    Density functional theory is used to determine the possible crystal structure of the CaSiO3 perovskites and their evolution under pressure. The ideal cubic perovskite is considered as a starting point for studying several possible lower-symmetry distorted structures. The theoretical lattice parameters and the atomic coordinates for all the structures are determined, and the results are discussed with respect to experimental data.

  20. Small shear modulus of cubic CaSiO3 perovskite

    Science.gov (United States)

    Kawai, Kenji; Tsuchiya, Taku

    2015-04-01

    Ca-perovskite (CaPv) is considered to be one of the most abundant minerals in the Earth's lower mantle (LM). Furthermore, previous static calculations and mean-field theory suggest that it has a much larger shear modulus than bridgmanite (MgPv). In this study, the elasticity of cubic CaPv was reinvestigated using the density functional constant-temperature first principles molecular dynamics method under the correct conditions to simulate its elasticity. Our new results clearly demonstrate that cubic CaPv has comparable bulk and slightly smaller shear moduli than Fe-bearing MgPv. This is because the boundary condition for the supercell used in this study allows for the rotational phonon motion of SiO6 octahedra under strain, which predominantly affects the decrease in C11 and C44. Acoustic wave velocities determined from the elastic moduli indicate that cubic CaPv has slower velocities and larger densities than Fe-bearing MgPv and preliminary reference Earth model in the LM. This suggests that if CaPv-rich material exists, it can accumulate in the lowermost LM and produce a seismically low-velocity anomaly.

  1. d0 Perovskite-Semiconductor Electronic Structure

    OpenAIRE

    Bistritzer, R.; Khalsa, G.; MacDonald, A. H.

    2010-01-01

    We address the low-energy effective Hamiltonian of electron doped d0 perovskite semiconductors in cubic and tetragonal phases using the k*p method. The Hamiltonian depends on the spin-orbit interaction strength, on the temperature-dependent tetragonal distortion, and on a set of effective-mass parameters whose number is determined by the symmetry of the crystal. We explain how these parameters can be extracted from angle resolved photo-emission, Raman spectroscopy, and magneto-transport measu...

  2. PbCl2-tuned inorganic cubic CsPbBr3(Cl) perovskite solar cells with enhanced electron lifetime, diffusion length and photovoltaic performance

    Science.gov (United States)

    Li, Bo; Zhang, Yanan; Zhang, Luyuan; Yin, Longwei

    2017-08-01

    Inorganic CsPbBr3 perovskite is arousing great interest following after organic-inorganic hybrid halide perovskites, and is found as a good candidate for photovoltaic devices for its prominent photoelectric property and stability. Herein, we for the first time report on PbCl2-tuned inorganic Cl-doped CsPbBr3(Cl) perovskite solar cells with adjustable crystal structure and Cl doping for enhanced carrier lifetime, extraction rate and photovoltaic performance. The effect of PbCl2 on the morphologies, structures, optical, and photovoltaic performance of CsPbBr3 perovskite solar cells is investigated systemically. Compared with orthorhombic CsPbBr3, cubic CsPbBr3 demonstrates a significant improvement for electron lifetime (from 6.7 ns to 12.3 ns) and diffusion length (from 69 nm to 197 nm), as well as the enhanced electron extraction rate from CsPbBr3 to TiO2. More importantly, Cl doping benefits the further enhancement of carrier lifetime (14.3 ns) and diffusion length (208 nm). The Cl doped cubic CsPbBr3(Cl) perovskite solar cell exhibits a Jsc of 8.47 mA cm-2 and a PCE of 6.21%, superior to that of pure orthorhombic CsPbBr3 (6.22 mA cm-2 and 3.78%). The improvement of photovoltaic performance can be attributed to enhanced carrier lifetime, diffusion length and extraction rates, as well as suppressed nonradiative recombination.

  3. The special symplectic structure of binary cubics

    CERN Document Server

    Slupinski, Marcus

    2009-01-01

    Let $k$ be a field of characteristic not 2 or 3. Let $V$ be the $k$-space of binary cubic polynomials. The natural symplectic structure on $k^2$ promotes to a symplectic structure $\\omega$ on $V$ and from the natural symplectic action of $\\textrm{Sl}(2,k)$ one obtains the symplectic module $(V,\\omega)$. We give a complete analysis of this symplectic module from the point of view of the associated moment map, its norm square $Q$ (essentially the classical discriminant) and the symplectic gradient of $Q$. Among the results are a symplectic derivation of the Cardano-Tartaglia formulas for the roots of a cubic, detailed parameters for all $\\textrm{Sl}(2,k)$ and $\\textrm{Gl}(2,k)$-orbits, in particular identifying a group structure on the set of $\\textrm{Sl}(2,k)$-orbits of fixed nonzero discriminant, and a purely symplectic generalization of the classical Eisenstein syzygy for the covariants of a binary cubic. Such fine symplectic analysis is due to the special symplectic nature inherited from the ambient excepti...

  4. Use of Pom Pons to Illustrate Cubic Crystal Structures.

    Science.gov (United States)

    Cady, Susan G.

    1997-01-01

    Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)

  5. Local atomic structure in cubic stabilized zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Villella, P.; Conradson, S. D.; Espinosa-Faller, F. J.; Foltyn, S. R.; Sickafus, K. E.; Valdez, J. A.; Degueldre, C. A.

    2001-09-01

    X-ray-absorption fine structure measurements have been used to elucidate the local atomic structure of quaternary Zr, Y, Er, Ce/U cubic stabilized zirconia. These compounds display more complicated local environments than those reported for simpler binary systems. While the shortest cation-O distances are similar to those found in the binary cubic stabilized compounds, responding to the different sizes of the cations, we have identified large distortions in the first-shell oxygen distribution involving long, 2.8--3.2 {angstrom} cation-O distances that are similar to those found in the amorphous phase of zirconium. The cation-cation distributions are also found to be quite complicated (non-Gaussian) and element specific. The U-near neighbor distances are expanded relative to the Ce ions for which it substitutes, consistent with the larger size of the actinide, and the U-cation distribution is also more complicated. In terms of the effects of this substitution on the other cation sites, the local environment around Y is altered while the Zr and Er local environments remain unchanged. These results point out the importance of collective and correlated interactions between the different pairs of cations and the host lattice that are mediated by the local strain fields generated by the different cations. The presence of pair-specific couplings has not been commonly included in previous analyses and may have implications for the stabilization mechanisms of cubic zirconia.

  6. Dynamic stabilization of cubic CaSiO3 perovskite at high temperatures and pressures from ab initio molecular dynamics

    Science.gov (United States)

    Sun, Tao; Zhang, Dong-Bo; Wentzcovitch, Renata M.

    2014-03-01

    The stability of cubic CaSiO3 perovskite (CaPv) at high temperatures and pressures is investigated by vibrational normal-mode analysis. We compute power spectra of mode autocorrelation functions using a recently developed hybrid approach combining ab initio molecular dynamics with lattice dynamics. These power spectra, together with the probability distributions of atomic displacements, indicate that cubic CaPv is stabilized at T ˜600 K and P ˜ 26 GPa. We then utilize the concept of phonon quasiparticles to characterize the vibrational properties of cubic CaPv at high temperature and obtain anharmonic phonon dispersions through the whole Brillouin zone. Such temperature-dependent phonon dispersions pave the way for more accurate calculations of free-energy, thermodynamic, and thermoelastic properties of cubic CaPv at Earth's lower mantle conditions.

  7. Designing rules and probabilistic weighting for fast materials discovery in the Perovskite structure

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Jacobsen, Karsten Wedel

    2014-01-01

    , more complex, crystals. Here, we consider a large database of calculated stabilities and bandgaps of oxides and oxynitrides in the perovskite structure. We use the database as a testing ground for existing ideas about the behavior of these types of compounds and we derive some new simple chemical......-based rules which combine structural information, like the ionic radii of the chemical elements, with electronic data, like the number of electrons and the valences of the pure elements. The rules extracted from the ABO3 cubic perovskite are then tested using the ABO2N and A2BO4 stoichiometry in the cubic...... and layered perovskite structure, respectively. These rules allow a saving in computer time of around 80%....

  8. Crystal and electronic structures of substituted halide perovskites based on density functional calculation and molecular dynamics

    Science.gov (United States)

    Takaba, Hiromitsu; Kimura, Shou; Alam, Md. Khorshed

    2017-03-01

    Durability of organo-lead halide perovskite are important issue for its practical application in a solar cells. In this study, using density functional theory (DFT) and molecular dynamics, we theoretically investigated a crystal structure, electronic structure, and ionic diffusivity of the partially substituted cubic MA0.5X0.5PbI3 (MA = CH3NH3+, X = NH4+ or (NH2)2CH+ or Cs+). Our calculation results indicate that a partial substitution of MA induces a lattice distortion, resulting in preventing MA or X from the diffusion between A sites in the perovskite. DFT calculations show that electronic structures of the investigated partially substituted perovskites were similar with that of MAPbI3, while their bandgaps slightly decrease compared to that of MAPbI3. Our results mean that partial substitution in halide perovskite is effective technique to suppress diffusion of intrinsic ions and tune the band gap.

  9. Lattice dynamics of cubic CaSiO3 perovskite at high temperatures and pressures

    Science.gov (United States)

    Sun, Tao; Zhang, Dong-Bo; Wentzcovitch, Renata M.

    2013-03-01

    Cubic CaSiO3-perovskite is a minor but important phase of the Earth's lower mantle. It is a mechanically unstable phase at low temperatures but it is stabilized at lower mantle temperatures. We have investigated its vibrational properties at high pressures and temperatures of the lower mantle. We have projected ionic velocities from ab initio molecular dynamics trajectories onto vibrational normal modes and computed the mode-mode correlation function from which we extract phonon frequencies and life times at finite temperatures. These correlations clearly indicate that normal modes with imaginary frequencies at 0 K are stabilized with increasing temperature. To overcome the finite size effect inherent in molecular dynamics simulations, a renormalized second-order force constant matrix in real space is constructed from the phonon frequencies at finite temperature and the phonon polarization vectors. Phonon dispersions and vibrational density of states are then determined by Fourier interpolation using the renormalized force matrix. These temperature dependent dispersions allow us to investigate thermodynamics and thermal elastic properties at lower mantle conditions. Supported by NSF Grants EAR-1047626 and EAR-0810272.

  10. Effect of pressure on the global and local properties of cubic perovskite crystals

    OpenAIRE

    OUAHRANI, Tarik; MERAD-BOUDIA, I.; Baltache, H.; Khenata, R.; Z. Bentalha

    2011-01-01

    The influence of pressure on the structural, elastic, thermal and bonding properties of four perovskite-type oxides AMO3 is studied from the point of view of the quantum theory of atoms in molecules. Ab initio investigations are performed by means of the full-potential linear augmented plane-wave method as implemented in the wien2k code. The integrated basin charges resulting from the topological analysis of electronic density provide a partition of the bulk modulus and compressibility into a...

  11. Effect of pressure on the global and local properties of cubic perovskite crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ouahrani, Tarik; Merad-Boudia, I; Bentalha, Z [Laboratoire de Physique Theorique, Departement de Physique. Ecole Preparatoire Sciences et Techniques, BP 230, 13000 Tlemcen (Algeria); Baltache, H; Khenata, R, E-mail: tarik_ouahrani@yahoo.fr [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Universite de Mascara, 29000 Mascara (Algeria)

    2011-08-01

    The influence of pressure on the structural, elastic, thermal and bonding properties of four perovskite-type oxides AMO{sub 3} is studied from the point of view of the quantum theory of atoms in molecules. Ab initio investigations are performed by means of the full-potential linear augmented plane-wave method as implemented in the wien2k code. The integrated basin charges resulting from the topological analysis of electronic density provide a partition of the bulk modulus and compressibility into atomic contributions. Special attention is paid to the nonlinear behaviour of the local bonding properties.

  12. P-V-T equation of state of cubic CaSiO3 perovskite from first-principles computation

    Science.gov (United States)

    Kawai, Kenji; Tsuchiya, Taku

    2014-04-01

    Ca-perovskite (Pv) is considered to be one of the most abundant minerals in the Earth's lower mantle (LM) with an ideal cubic structure at LM pressures and temperatures. In this study, a pressure-volume-temperature (P-V-T) equation of state model for Ca-Pv is constructed using density functional first-principles molecular dynamics simulations. The calculated P-V-T data yield KT0 1000 K = 203.95 GPa, V0 1000 K = 46.17 Å3/formula unit, γ0 = 1.576, and q = 0.96 within the framework of the Mie-Grüneisen-Debye formulation. We compare the density and bulk sound velocity of Ca-Pv with those of iron-bearing Mg-Pv and seismological values. Along an adiabatic temperature gradient, Ca-Pv has ~2.5% higher density and ~0.7% faster bulk sound velocity than the preliminary reference Earth model, while it has ~3.8% higher density and ~2.7% slower bulk sound velocity than iron-bearing Mg-Pv. Our results indicate that a possible lateral variation in the Ca-Pv fraction in the LM could produce an anticorrelation between VΦ and ρ.

  13. Autothermal reforming catalyst having perovskite structure

    Science.gov (United States)

    Krumpel, Michael; Liu, Di-Jia

    2009-03-24

    The invention addressed two critical issues in fuel processing for fuel cell application, i.e. catalyst cost and operating stability. The existing state-of-the-art fuel reforming catalyst uses Rh and platinum supported over refractory oxide which add significant cost to the fuel cell system. Supported metals agglomerate under elevated temperature during reforming and decrease the catalyst activity. The catalyst is a perovskite oxide or a Ruddlesden-Popper type oxide containing rare-earth elements, catalytically active firs row transition metal elements, and stabilizing elements, such that the catalyst is a single phase in high temperature oxidizing conditions and maintains a primarily perovskite or Ruddlesden-Popper structure under high temperature reducing conditions. The catalyst can also contain alkaline earth dopants, which enhance the catalytic activity of the catalyst, but do not compromise the stability of the perovskite structure.

  14. Predictive study of structural, electronic, magnetic and thermodynamic properties of XFeO3 (X = Ag, Zr and Ru multiferroic materials in cubic perovskite structure: first-principles calculations

    Directory of Open Access Journals (Sweden)

    Moulay N.

    2015-06-01

    Full Text Available The full potential linear-muffin-tin-orbital method within the spin local density approximation has been used to study the structural, electronic, magnetic and thermodynamic properties of three multiferroic compounds of XFeO3 type. Large values of bulk modulus for these compounds have been obtained, which demonstrates their hardness. The calculated total and partial density of states of these compounds shows a complex of strong hybridized 3d and 4d states at Fermi level. The two degenerate levels eg and t2g clearly demonstrate the origin of this complex. We have also investigated the effect of pressure, from 0 GPa to 55 GPa, on the magnetic moment per atom and the exchange of magnetic energy between the ferromagnetic and antiferromagnetic states. For more detailed knowledge, we have calculated the thermodynamic properties, and determined heat capacity, Debye temperature, bulk modulus and enthropy at different temperatures and pressures for the three multiferroic compounds. This is the first predictive calculation of all these properties.

  15. Size-dependent one-photon- and two-photon-pumped amplified spontaneous emission from organometal halide CH3NH3PbBr3 perovskite cubic microcrystals.

    Science.gov (United States)

    Zhang, Zhen-Yu; Wang, Hai-Yu; Zhang, Yan-Xia; Li, Kai-Jiao; Zhan, Xue-Peng; Gao, Bing-Rong; Chen, Qi-Dai; Sun, Hong-Bo

    2017-01-18

    In the past few years, organometal halide light-emitting perovskite thin films and colloidal nanocrystals (NCs) have attracted significant research interest in the field of highly purified illuminating applications. However, knowledge of photoluminescence (PL) characteristics, such as amplified spontaneous emission (ASE) of larger-sized perovskite crystals, is still relatively scarce. Here, we presented room-temperature size-dependent spontaneous emission (SE) and ASE of the organometal halide CH3NH3PbBr3 perovskite cubic microcrystals pumped through one-photon-(1P) and two-photon-(2P) excitation paradigms. The results showed that the optical properties of SE and ASE were sensitively dependent on the sizes of perovskite microcrystals irrespective of whether 1P or 2P excitation was used. Moreover, by comparing the spectral results of 1P- and 2P-pumped experiments, 2P pumping was found to be an effective paradigm to reduce thresholds by one order of magnitude. Finally, we carried out fluences-dependent time-resolved fluorescence dynamics experiments to study the underlying effects of these scale-dependent SE and ASE. We found that the photoluminescence (PL) recombination rates sensitively became faster with increasing carriers' densities, and that the ASE pumped from larger-sized CH3NH3PbBr3 perovskite cubic microcrystals showed faster lifetimes. This work shows that micro-sized perovskite cubic crystals could be the ideal patterns of perovskite materials for realizing ASE applications in the future.

  16. Ytterbium: Transition at High Pressure from Face-Centered Cubic to Body-Centered Cubic Structure.

    Science.gov (United States)

    Hall, H T; Barnett, J D; Merrill, L

    1963-01-11

    Pressure of 40,000 atmospheres at 25 degrees C induces a phase transformation in ytterbium metal; the face-centered cubic structure changes to body-centered cubic. The radius of the atom changes from 1.82 to 1.75 A. At the same time the atom's volume decreases by 11 percent and the volume, observed macroscopically, decreases 3.2 percent.

  17. Understanding the Cubic Phase Stabilization and Crystallization Kinetics in Mixed Cations and Halides Perovskite Single Crystals.

    Science.gov (United States)

    Xie, Li-Qiang; Chen, Liang; Nan, Zi-Ang; Lin, Hai-Xin; Wang, Tan; Zhan, Dong-Ping; Yan, Jia-Wei; Mao, Bing-Wei; Tian, Zhong-Qun

    2017-03-08

    The spontaneous α-to-δ phase transition of the formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by alloying with methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this Communication, we grow high-quality mixed cations and halides perovskite single crystals (FAPbI3)1-x(MAPbBr3)x to understand the principles for maintaining pure perovskite phase, which is essential to device optimization. We demonstrate that the best composition for a perfect α-phase perovskite without segregation is x = 0.1-0.15, and such a mixed perovskite exhibits carrier lifetime as long as 11.0 μs, which is over 20 times of that of FAPbI3 single crystal. Powder XRD, single crystal XRD and FT-IR results reveal that the incorporation of MA(+) is critical for tuning the effective Goldschmidt tolerance factor toward the ideal value of 1 and lowering the Gibbs free energy via unit cell contraction and cation disorder. Moreover, we find that Br incorporation can effectively control the perovskite crystallization kinetics and reduce defect density to acquire high-quality single crystals with significant inhibition of δ-phase. These findings benefit the understanding of α-phase stabilization behavior, and have led to fabrication of perovskite solar cells with highest efficiency of 19.9% via solvent management.

  18. First-principles molecular dynamics simulations of proton diffusion in cubic BaZrO $$_3$$ 3 perovskite under strain conditions

    Directory of Open Access Journals (Sweden)

    Marco Fronzi

    2016-08-01

    Full Text Available Abstract First-principles molecular dynamics simulations have been employed to analyse the proton diffusion in cubic BaZrO $$_3$$ 3 perovskite at 1300 K. A non-linear effect on the proton diffusion coefficient arising from an applied isometric strain up to 2  $$\\%$$ % of the lattice parameter, and an evident enhancement of proton diffusion under compressive conditions have been observed. The structural and electronic properties of BaZrO $$_3$$ 3 are analysed from Density Functional Theory calculations, and after an analysis of the electronic structure, we provide a possible explanation for an enhanced ionic conductivity of this bulk structure that can be caused by the formation of a preferential path for proton diffusion under compressive strain conditions. By means of Nudged Elastic Band calculations, diffusion barriers were also computed with results supporting our conclusions.

  19. AB-INITIO STUDY OF BULK MODULUS AND CHARGE DENSITY OF CUBIC SrMO3 PEROVSKITES (M = Ti, Zr, Mo, Rh, Ru

    Directory of Open Access Journals (Sweden)

    AVINASH DAGA

    2012-03-01

    Full Text Available Bulk modulus & charge density of cubic SrMO3 perovskites (M = Ti, Zr, Mo, Rh & Ru have been investigated systematically using the first principle density functional calculations. Local density approximation (LDAmethod has been used to compute the two quantities for five perovskites. It is found that the calculated bulk modulus for all the transition metal oxides are in good agreement with the available experimental data and with other theoretical results previously reported in the literature. ABINIT computer code is used to carry out all the calculations. Charge density plots for all the five cubic SrMO3 perovskites have been drawn using MATLAB. The maximum and minimum values of charge density along with the corresponding reduced coordinates are reported for all the perovskites.

  20. Thermal expansion and structural distortion of perovskite — data for NaMgF 3 perovskite. Part I

    Science.gov (United States)

    Zhao, Yusheng; Weidner, Donald J.; Parise, John B.; Cox, David E.

    1993-02-01

    The crystal structure of NaMgF 3 perovskite (Neighborite) has been studied at high temperature by X-ray powder diffraction. Data were collected using a position sensitive detector with a monochromatic synchroton radiation source. Changes in unit cell and atomic positions of the perovskite structure were defined using the Rietveld refinement technique. The linear and volumetric thermal expansion coefficients are observed to be αa = 4.04 × 10 -5 K -1, αb = 1.53 × 10 -5 K -1, αc = 3.06 × 10 -5 K -1, αv = 8.80 × 10 -5 K -1 for the orthorhombic Pbnm phase, and αa0 = 3.16 × 10 -5 K -1, αv0 = 9.49 × 10 -5 K -1 for the cubic Pm3m phase of NaMgF 3 perovskite, respectively. The temperature-induced linear and volumetric changes of the centrosymmetrically distorted ABX 3 perovskite structure can be empirically expressed as a combination of the change of the (BX) bond length and the change of tilting of the BX 6 octahedral framework. The considerable anisotropy of linear thermal expansion, αa > αc > αb, for the orthorhombic Pbnm phase reflects the progressive decrease of structural distortion and the development of the phase transition of the NaMgF 3 perovskite. The tilting angle of the MgF 6 octahedral framework is observed to decrease rapidly toward zero as the temperature approaches Tc = 765°C in the manner expected for a ferroelastic phase transition. More interestingly, the apparent (MgF) bond lengths of the MgF 6 octahedra shrink dramatically throughout a temperature interval of about 100°C before the phase transition. The volumetric thermal expansion increases drastically in a critical manner as the temperature approaches Tc.

  1. Facile preparation of smooth perovskite films for efficient meso/planar hybrid structured perovskite solar cells.

    Science.gov (United States)

    Zhang, Meng; Yu, Hua; Yun, Jung-Ho; Lyu, Miaoqiang; Wang, Qiong; Wang, Lianzhou

    2015-06-21

    Smooth organolead halide perovskite films for meso/planar hybrid structured perovskite solar cells were prepared by a simple compressed air blow-drying method under ambient conditions. The resultant perovskite films show high surface coverage, leading to a device power conversion efficiency of over 10% with an open circuit voltage up to 1.003 V merely using pristine poly(3-hexylthiophene) (P3HT) as a hole transporter.

  2. Lattice dynamics and the nature of structural transitions in organolead halide perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Comin, Riccardo; Crawford, Michael K.; Said, Ayman H.; Herron, Norman; Guise, William E.; Wang, Xiaoping; Whitfield, Pamela S.; Jain, Ankit; Gong, Xiwen; McGaughey, Alan J. H.; Sargent, Edward H.

    2016-09-09

    Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remarkable optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic x-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our findings confirm the displacive nature of the cubic-to-tetragonal phase transition, which is further shown, using neutron and x-ray diffraction, to be close to a tricritical point. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These findings reveal key structural properties of these materials, and also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.

  3. First-principles study of structural stability and elastic property of pre-perovskite PbTiO3

    Institute of Scientific and Technical Information of China (English)

    Liu Yong; Ni Li-Hong; Ren Zhao-Hui; Xu Gang; Li Xiang; Song Chen-Lu; Han Gao-Rong

    2012-01-01

    The structural stability and the elastic properties of a novel structure of lead titanate,which is named preperovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner,are investigated by using first-principles calculations.PP-PTO is energetically unstable compared with conventional perovskite phases,however it is mechanically stable. The equilibrium transition pressures for changing from preperovskite to cubic and tetragonal phases are -0.5 GPa and -1.4 GPa,respectively,with first-order characteristics.Further,the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network,which shows a highly anisotropic character in PP-PTO.This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite.

  4. First-principles calculation on the electronic structure and optical properties of the cubic inverse perovskite Sc3AlN%反钙钛矿晶体Sc3AlN电子结构和光学性质的第一性原理研究

    Institute of Scientific and Technical Information of China (English)

    何卫中; 方志杰

    2012-01-01

    采用基于密度泛函理论的第一性原理的分子动力学方法,对立方反钙钛矿Sc3AlN的电子结构和光学性质进行了计算.系统分析了Sc3AlN电子结构和成键情况,并利用计算的能带结构和态密度分析了Sc3AlN的介电函数实部和虚部以及由它们派生出来的光学常数,即折射率、反射谱、吸收谱、光电导率和能量损失函数等.计算结果表明Sc3AlN属于导体材料,其价带主要由Al的2s2p,Sc的3d态电子构成,导带主要由Sc的3d态电子构成,静态介电常数ε1(O)=22.1,折射率n(0)=4.7.%The electronic structure and optical properties of the cubic inverse perovskite Sc3AlN have been calculated by using the first-principle density function theory molecular dynamics method. The results of band structure show that Sc3AlN is a conductor material. The complex dielectric functions, refractive index, reflection spectra, absorption spectra, optical conductivity and energy loss function of Sc3AlN are analyzed in terms of calculated band structure and density of state. The conduction band of Sc3AlN is mainly composed of Sc 3d, 4s and the valence bands is composed of the Al 2s, 2p and N 2p. The static dielectric function ε (0)=22.1, the reflectivity n(0)=4.7.

  5. Optical studies of cubic III-nitride structures

    OpenAIRE

    Powell, Ross E L

    2014-01-01

    The properties of cubic nitrides grown by molecular beam epitaxy (MBE) on GaAs (001) have been studied using optical and electrical techniques. The aim of these studies was the improvement of the growth techniques in order to improve the quality of grown nitrides intended for bulk substrate and optoelectronic device applications. We have also characterised hexagonal nanocolumn structures incorporating indium. Firstly, bulk films of cubic AlxGa1-xN with aluminium fractions (x) spanning the ...

  6. Structural Investigation of Cesium Lead Halide Perovskites for High-Efficiency Quantum Dot Light Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Van Le, Quyet; Beom Kim, Jong; Kim, Soo Young; Lee, Byeongdu; Lee, Dong Ryeol

    2017-08-16

    We have investigated the effect of reaction temperature of hot-injection method on the structural properties of CsPbX3 (X: Br, I, Cl) perovskite nanocrystals (NCs) using the small- and wide-angle X-ray scattering. It is confirmed that the size of the NCs decreased as the reaction temperature decreased, resulting stronger quantum confinement. The cubic-phase perovskite NCs were formed despite the reaction temperatures increased from 140 to 180 °C. However, monodispersive NC cubes which are required for densely packing self-assembly film were only formed at lower temperatures. From the X-ray scattering measurements, the spin-coated film from more monodispersive perovskite nanocubes synthesized at lower temperatures resulted in more preferred orientation. This dense-packing perovskite film with preferred orientation yielded efficient light-emitting diode (LED) performance. Thus, the dense-packing structure of NC assemblies formed after spin-coating should be considered for high-efficient LEDs based on perovskite quantum dots in addition to quantum confinement effect of the quantum dots.

  7. Tackling pseudosymmetry problems in electron backscatter diffraction (EBSD) analyses of perovskite structures

    Science.gov (United States)

    Mariani, Elisabetta; Kaercher, Pamela; Mecklenburgh, Julian; Wheeler, John

    2016-04-01

    tilt and a deformation of the anion octahedron. These distortions may occur together. Common misidentifications observed in EBSD data are [100] and [001] seen as equivalent solutions, whereby these dyad symmetry axes are misidentified as tetrad axes of the cubic symmetry. In this study we investigate methods that could be applied to the EBSP automated indexing algorithm to solve the pseudosymmetry problem in perovskite structures. Attention is given to subtle angular deviations between bands and to differences in pseudosymmetric Kikuchi patterns.

  8. Perovskite oxides: Oxygen electrocatalysis and bulk structure

    Science.gov (United States)

    Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, Ernest

    1987-01-01

    Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

  9. Ultrafast structural dynamics of perovskite superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Woerner, M.; Korff Schmising, C. von; Zhavoronkov, N.; Elsaesser, T. [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Berlin (Germany); Bargheer, M. [Universitaet Potsdam, Institut fuer Physik und Astronomie, Potsdam (Germany); Vrejoiu, I.; Hesse, D.; Alexe, M. [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2009-07-15

    Femtosecond X-ray diffraction provides direct insight into the ultrafast reversible lattice dynamics of materials with a perovskite structure. Superlattice (SL) structures consisting of a sequence of nanometer-thick layer pairs allow for optically inducing a tailored stress profile that drives the lattice motions and for limiting the influence of strain propagation on the observed dynamics. We demonstrate this concept in a series of diffraction experiments with femtosecond time resolution, giving detailed information on the ultrafast lattice dynamics of ferroelectric and ferromagnetic superlattices. Anharmonically coupled lattice motions in a SrRuO{sub 3}/PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (SRO/PZT) SL lead to a switch-off of the electric polarizations on a time scale of the order of 1 ps. Ultrafast magnetostriction of photoexcited SRO layers is demonstrated in a SRO/SrTiO{sub 3} (STO) SL. (orig.)

  10. Syntheses, structures, and ionic conductivities of perovskite-structured lithium–strontium–aluminum/gallium–tantalum-oxides

    Energy Technology Data Exchange (ETDEWEB)

    Phraewphiphat, Thanya, E-mail: thanya@echem.titech.ac.jp [Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Iqbal, Muhammad, E-mail: iqbal@echem.titech.ac.jp [Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Suzuki, Kota, E-mail: ksuzuki@echem.titech.ac.jp [Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Matsuda, Yasuaki, E-mail: matsuda@chem.mie-u.ac.jp [Department of Chemistry, Mie University, 1577 Kurimamachiyacho, Tsu, Mie 514-8507 (Japan); Yonemura, Masao, E-mail: masao.yonemura@kek.jp [High Energy Accelerator Research Organization, Tokai-mura, Naka-gun, Ibaraki 319-1106 (Japan); Hirayama, Masaaki, E-mail: hirayama@echem.titech.ac.jp [Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8502 (Japan); Kanno, Ryoji, E-mail: kanno@echem.titech.ac.jp [Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8502 (Japan)

    2015-05-15

    The ionic conductivities of new perovskite-structured lithium–strontium–aluminum/gallium–tantalum oxides were investigated. Solid solutions of the new perovskite oxides, (Li{sub x}Sr{sub 1−x})(Al{sub (1−x)/2}Ta{sub (1+x)/2})O{sub 3} and (Li{sub x}Sr{sub 1−x})(Ga{sub (1−x)/2}Ta{sub (1+x)/2})O{sub 3}, were synthesized using a ball-milled-assisted solid-state method. The partial substitution of the smaller Ga{sup +3} for Ta{sup +5} resulted in new compositions, the structures of which were determined by neutron diffraction measurements using a cubic perovskite structural model with the Pm−3m space group. Vacancies were introduced into the Sr(Li) sites by the formation of solid solutions with compositions (Li{sub x}Sr{sub 1−x−y}☐{sub y})(Ga{sub [(1−x)/2]−y}Ta{sub [(1+x)/2]+y})O{sub 3}, where the composition range of 0≤y≤0.20 was examined for x=0.2 and 0.25. The highest conductivity, 1.85×10{sup −3} S cm{sup −1} at 250 °C, was obtained for (Li{sub 0.25}Sr{sub 0.625}☐{sub 0.125})(Ga{sub 0.25}Ta{sub 0.75})O{sub 3} (x=0.25, y=0.125). Enhanced ionic conductivities were achieved by the introduction of vacancies at the A-sites. - Graphical abstract: Novel lithium-conducting oxides with the cubic perovskite structure (Li{sub x}Sr{sub 1−x−y}☐{sub y})(Ga{sub [(1−x)/2]−y}Ta{sub [(1+x)/2]+y})O{sub 3} provide a specific solid-solution region with various x and y values, exhibiting the highest ionic conductivity (1.85 S cm{sup −1} at 250 °C) for (Li{sub 0.25}Sr{sub 0.625}☐{sub 0.125})(Ga{sub 0.25}Ta{sub 0.75})O{sub 3} (x=0.25, y=0.125 in (Li{sub x}Sr{sub 1−x−y}☐{sub y})(Ga{sub [(1−x)/2]−y}Ta{sub [(1+x)/2]+y})O{sub 3}). The vacancies (☐) introduced into the A-sites contribute to the enhancement of lithium diffusion in the perovskite structure because of the enlargement of the bottleneck size and suppression of the interaction between lithium and oxygen. - Highlights: • The perovskite-structured novel Li

  11. High temperature X-ray diffraction and thermo-gravimetrical analysis of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ under different atmospheres.

    Science.gov (United States)

    Sahini, M G; Tolchard, J R; Wiik, K; Grande, T

    2015-06-21

    Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) with the cubic perovskite structure is known to be metastable at low temperature under an oxidizing atmosphere. Here, the thermal and chemical expansion of BSCF were studied by in situ high temperature powder X-ray diffraction and thermo-gravimetrical analysis (TGA) in partial pressure of oxygen ranging from an inert atmosphere (∼10(-4) bar) to 10 bar O(2). The BSCF powder, heat treated at 1000 °C and quenched to ambient temperature prior to the analysis, was shown to oxidize under an oxidizing atmosphere before thermal reduction took place. With decreasing partial pressure of oxygen the initial oxidation was suppressed and only reduction of Co/Fe and loss of oxygen were observed under an inert atmosphere. The thermal expansion of BSCF under different atmospheres was determined from the thermal evolution of the cubic unit cell parameter, demonstrating that the thermal expansion of BSCF depends on the atmosphere. Chemical expansion of BSCF was also estimated based on the diffraction data and thermo-gravimetrical analysis. A hexagonal perovskite phase, coexisting with the cubic BSCF polymorph, was observed to be formed above 600 °C during heating. The phase separation leading to the formation of the hexagonal polymorph was driven by oxidation, and the unit cell of the cubic BSCF was shown to decrease with increasing amounts of the hexagonal phase. The hexagonal phase disappeared upon further heating, accompanied with an expansion of the unit cell of the cubic BSCF.

  12. Non-cubic crystal symmetry of CaSiO 3 perovskite up to 18 GPa and 1600 K

    Science.gov (United States)

    Uchida, Takeyuki; Wang, Yanbin; Nishiyama, Norimasa; Funakoshi, Ken-ichi; Kaneko, Hiroshi; Nozawa, Akifumi; Von Dreele, Robert B.; Rivers, Mark L.; Sutton, Steve R.; Yamada, Akihiro; Kunimoto, Takehiro; Irifune, Tetsuo; Inoue, Toru; Li, Baosheng

    2009-05-01

    In situ synchrotron X-ray diffraction experiments have been conducted on CaSiO 3 perovskite (CaPv) in a double-stage multianvil apparatus up to 18 GPa and 1600 K using a newly developed step-scan diffraction technique, which utilizes an energy-dispersive setup with a solid-state detector and collimator assemblies to collect angle-dispersive diffraction data over a wide range of photon energies. Superlattice reflections were resolved throughout the pressure ( P) and temperature ( T) range of the experiments, confirming that the crystal symmetry of CaPv is neither cubic nor tetragonal. A combination of analyses of the complete two-dimensional intensity datasets (photon energy from 20 to 160 keV and 2 θ angle from 3.0° to 9.0°) and Rietveld refinements at selected wavelengths revealed that the most likely space group of CaPv in the experimental P- T range, and therefore in the Earth's transition zone, is either Pbnm or Cmcm. The difference between these two space groups was too small to resolve with our technique.

  13. The Structural Disorder and Lattice Stability of (Ba,Sr)(Co,Fe)O3 Complex Perovskites

    Energy Technology Data Exchange (ETDEWEB)

    S.N.Rashkeev

    2011-05-01

    The structural disorder and lattice stability of complex perovskite (Ba,Sr)(Co,Fe)O3, a promising cathode material for solid oxide fuel cells and oxygen permeation membranes, is explored by means of first principles DFT calculations. It is predicted that Ba and Sr ions easily exchange their lattice positions (A-cation disorder) similarly to Co and Fe ions (B-cation disorder). The cation antisite defects (exchange of A- and B-type cations) have a relatively high formation energy. The BSCF is predicted to exist in an equilibrium mixture of several phases and can decompose exothermically into the Ba- and Co-rich hexagonal (Ba,Sr)CoO3 and Sr- and Fe-rich cubic (Ba,Sr)FeO3 perovskites.

  14. Halide-Dependent Electronic Structure of Organolead Perovskite Materials

    KAUST Repository

    Buin, Andrei

    2015-06-23

    © 2015 American Chemical Society. Organometal halide perovskites have recently attracted tremendous attention both at the experimental and theoretical levels. These materials, in particular methylammonium triiodide, are still limited by poor chemical and structural stability under ambient conditions. Today this represents one of the major challenges for polycrystalline perovskite-based photovoltaic technology. In addition to this, the performance of perovskite-based devices is degraded by deep localized states, or traps. To achieve better-performing devices, it is necessary to understand the nature of these states and the mechanisms that lead to their formation. Here we show that the major sources of deep traps in the different halide systems have different origin and character. Halide vacancies are shallow donors in I-based perovskites, whereas they evolve into a major source of traps in Cl-based perovskites. Lead interstitials, which can form lead dimers, are the dominant source of defects in Br-based perovskites, in line with recent experimental data. As a result, the optimal growth conditions are also different for the distinct halide perovskites: growth should be halide-rich for Br and Cl, and halide-poor for I-based perovskites. We discuss stability in relation to the reaction enthalpies of mixtures of bulk precursors with respect to final perovskite product. Methylammonium lead triiodide is characterized by the lowest reaction enthalpy, explaining its low stability. At the opposite end, the highest stability was found for the methylammonium lead trichloride, also consistent with our experimental findings which show no observable structural variations over an extended period of time.

  15. Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (Sr,Ca)FeO 2 . 5 + δ

    Science.gov (United States)

    Carlo, J. P.; Evans, M. E.; Anczarski, J. A.; Ock, J.; Boyd, K.; Pollichemi, J. R.; Leahy, I. A.; Vogel, W.; Viescas, A. J.; Papaefthymiou, G. C.

    A variety of compounds crystallize into perovskite and similar structures, making them versatile laboratories for many phenomena and applications, including multiferroicity, superconductivity, and photovoltaics. Oxygen-deficient perovskites ABOx have attracted interest for use in fuel cells and related applications due to high oxygen mobility and the possibility of charge disproportionation. Vast chemical flexibility is obtained through reductions in lattice symmetry and rotation/distortion of the BO6 octahedra, as well as ordering of oxygen vacancies. We have synthesized and studied the structural and magnetic properties of oxygen-deficient perovskites (Sr,Ca)FeO2 . 5 + δ using x-ray diffraction and Mossbauer spectroscopy. While the ideal perovskite has δ = 0.5, this requires Fe4+, and hence strongly oxidizing environments. When grown in air, Fe3+ is favored, yielding δ ~ 0. SrFeO2 . 5 + δ exhibits cubic symmetry and paramagnetism at 300K, but CaFeO2 . 5 + δ crystallizes into the orthorhombic brownmillerite structure, and is magnetically ordered at 300K. In the doped intermediaries we find coexistence of cubic/paramagnetic and orthorhombic/magnetic phases over a wide range of Ca content. Financial support from the Villanova Undergraduate Research Fellowship program and the Research Corporation for Science Advancement.

  16. Charge disproportionation and the pressure-induced insulator-metal transition in cubic perovskite PbCrO3.

    Science.gov (United States)

    Cheng, Jinguang; Kweon, K E; Larregola, S A; Ding, Yang; Shirako, Y; Marshall, L G; Li, Z-Y; Li, X; dos Santos, António M; Suchomel, M R; Matsubayashi, K; Uwatoko, Y; Hwang, G S; Goodenough, John B; Zhou, J-S

    2015-02-10

    The perovskite PbCrO3 is an antiferromagnetic insulator. However, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. We report a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. We argue that a charge disproportionation 3Cr(4+) → 2Cr(3+) + Cr(6+) in association with the 6s-p hybridization on the Pb(2+) is responsible for the insulating ground state of PbCrO3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT+U) calculations.

  17. Highly Aminated Mesoporous Silica Nanoparticles with Cubic Pore Structure

    KAUST Repository

    Suteewong, Teeraporn

    2011-01-19

    Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.

  18. Numerical modeling of perovskite solar cells with a planar structure

    Science.gov (United States)

    Malyukov, S. P.; Sayenko, A. V.; Ivanova, A. V.

    2016-10-01

    The paper is devoted to the research and development of high-efficiency solar cells with a planar perovskite n-i-p structure. A numerical model of this solar cell in the drift- diffusion approximation based on Poisson equation and continuity equations provided to determine their photoelectric characteristics and design optimization. The author considers the spectral photogeneration, bulk and surface recombination, transport charge carriers in perovskite and their collection by the electron and hole transport layers. As a result of the simulation, it was obtained efficiency dependence on perovskite absorber material thickness and lifetime (diffusion length) of the charge carriers. It is found that in addition to absorption coefficient optimal perovskite thickness is determined largely by the charge carrier diffusion length, and it has the upper limit in thickness of 500-600 nm.

  19. Elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 under pressure

    Science.gov (United States)

    Soleimanpour, Sh; Kanjouri, F.

    2015-07-01

    The elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 have been calculated using the full potential linearized augmented plane wave based on density functional theory. Exchange and correlation effects are taken into account by a generalized gradient approximation and an orbital independent modified Becke-Johnson potential coupled with generalized gradient approximation. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. The results are in good agreement with the available theoretical and experimental data. The elastic properties such as elastic constants, shear modulus, Young modulus, Poisson's ratio, B/G ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and specific heat have been calculated. The pressure dependence of the elastic moduli has been also evaluated. Furthermore, elastic anisotropic properties for KCaF 3 have been analyzed in the pressure range of 0-40 GPa by calculating directional dependence of the Young's moduli in the crystal. From calculations of the electronic properties, it is found that the band gap is 10.4 (6.1) eV at the R-Γ direction in the Brillouin zone using modified Becke-Johnson potential coupled with generalized gradient approximation (generalized gradient approximation). The variation of the band gap versus pressure is well fitted to a quadratic function. The calculations show that indirect R-Γ to direct Γ -Γ band gap transition occurs at 20 GPa. Moreover, optical properties, such as the dielectric function, refractive index and extinction index, have been calculated for radiation up to 35 eV.

  20. A First-Principles Study on the Structural and Electronic Properties of Sn-Based Organic-Inorganic Halide Perovskites

    Science.gov (United States)

    Ma, Zi-Qian; Pan, Hui; Wong, Pak Kin

    2016-11-01

    Organic-inorganic halide perovskites have attracted increasing interest on solar-energy harvesting because of their outstanding electronic properties. In this work, we systematically investigate the structural and electronic properties of Sn-based hybrid perovskites MASnX3 and FASnX3 (X = I, Br) based on density-functional-theory calculations. We find that their electronic properties strongly depend on the organic molecules, halide atoms, and structures. We show that there is a general rule to predict the band gap of the Sn-based hybrid perovskite: its band gap increases as the size of halide atom decreases as well as that of organic molecule increase. The band gap of high temperature phase (cubic structure) is smaller than that of low temperature phase (orthorhombic structure). The band gap of tetragonal structure (medium-temperature phase) may be larger or smaller than that of cubic phase, depending on the orientation of the molecule. Tunable band gap within a range of 0.73-1.53 eV can be achieved by choosing halide atom and organic molecule, and controlling structure. We further show that carrier effective mass also reduces as the size of halide atom increases and that of molecule decreases. By comparing with Pb-based hybrid perovskites, the Sn-based systems show enhanced visible-light absorption and carrier mobility due to narrowed band gap and reduced carrier effective mass. These Sn-based organic-inorganic halide perovskites may find applications in solar energy harvesting with improved performance.

  1. First-principles prediction of oxygen octahedral rotations in perovskite-structure EuTiO_{3}

    OpenAIRE

    Rushchanskii, Konstantin Z.; Spaldin, Nicola A.; Marjana Le\\ueai\\u

    2012-01-01

    We present a systematic first-principles study of the structural and vibrational properties of perovskite-structure EuTiO3. Our calculated phonon spectrum of the high-symmetry cubic structural prototype shows strong M-and R-point instabilities, indicating a tendency to symmetry-lowering structural deformations composed of rotations and tilts of the oxygen octahedra. Subsequent explicit study of 14 different octahedral tilt-patterns showed that the I4/mcm, Imma, and R (3) over barc structures,...

  2. Structural properties, electric response and electronic feature of BaSnO{sub 3} perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Cuervo Farfan, J. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 14490 Bogota D.C. (Colombia); Arbey Rodriguez, J.; Fajardo, F. [Grupo de Estudios de Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota DC (Colombia); Vera Lopez, E. [Grupo de Superficies, Electroquimica y Corrosion, UPTC, Tunja (Colombia); Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 14490 Bogota D.C. (Colombia); Roa-Rojas, J., E-mail: jroar@unal.edu.c [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 14490 Bogota D.C. (Colombia)

    2009-10-01

    It has been observed that the semiconducting compound SnO{sub 2} presents very good results as gas sensor. One important development has been performed to study perovskite oxides for this relevant application. One oxide material which constitutes an excellent candidate for this technological application is BaSnO{sub 3}. Polycrystalline samples with single phase of BaSnO{sub 3} were synthesized by using the solid state reaction method. Samples were characterized structurally by means of X-ray diffraction (XRD) technique. Rietveld refinement, by using the GSAS code, reveals that this material synthesizes in a cubic perovskite, space group Pm3m (no. 221), with lattice parameter 4.1190(3)A. Electric response was examined through the impedance spectroscopy technique. Results of Bode diagram, from an equivalent circuit, evidence the semiconductor character of material. We carried out a theoretical study by means of the calculation of the bands diagram and the density of states of the BaSnO{sub 3}. Calculation was performed by employing the density functional theory (DFT), with the generalized gradient approach (GGA). DFT theory permitted to establish that BaSnO{sub 3} material has an indirect semiconducting behavior. The calculated gap for this perovskite-like stagnate is at least 0.4 eV. Bulk modulus for material was also determined to be 132 GPa.

  3. Synthesis and structure of perovskite ScMnO3.

    Science.gov (United States)

    Chen, Haiyan; Yu, Tian; Gao, Peng; Bai, Jianming; Tao, Jing; Tyson, Trevor A; Wang, Liping; Lalancette, Roger

    2013-08-19

    The rare-earth manganites RMnO3 (R = rare earth) are a class of important multiferroics with stable hexagonal structures for small R ion radius (Sc, Lu, Yb, ...). Metastable perovskite phases of these systems possess intriguing electronically driven electrical polarization, but the synthesis of the perovskite phase for the end member ScMnO3 system has proven to be elusive. We report the structure of a new monoclinic P2(1)/n perovskite phase of ScMnO3 synthesized from the hexagonal phase under high-pressure and high-temperature conditions. This extends the small ion region for so-called E-phase electronically driven ferroelectric manganese perovsites.

  4. Nonlinear structure formation in the Cubic Galileon gravity model

    CERN Document Server

    Barreira, Alexandre; Hellwing, Wojciech A; Baugh, Carlton M; Pascoli, Silvia

    2013-01-01

    We model the linear and nonlinear growth of large scale structure in the Cubic Galileon gravity model, by running a suite of N-body cosmological simulations using the {\\tt ECOSMOG} code. Our simulations include the Vainshtein screening effect, which reconciles the Cubic Galileon model with local tests of gravity. In the linear regime, the amplitude of the matter power spectrum increases by $\\sim 25%$ with respect to the standard $\\Lambda$CDM model today. The modified expansion rate accounts for $\\sim 20%$ of this enhancement, while the fifth force is responsible for only $\\sim 5%$. This is because the effective unscreened gravitational strength deviates from standard gravity only at late times, even though it can be twice as large today. In the nonlinear regime ($k \\gtrsim 0.1 h\\rm{Mpc}^{-1}$), the fifth force leads to only a modest increase ($\\lesssim 8%$) in the clustering power on all scales due to the very efficient operation of the Vainshtein mechanism. Such a strong effect is typically not seen in other...

  5. Structural determination and electronic properties of the 4d perovskite SrPdO3

    Science.gov (United States)

    He, Jiangang; Franchini, Cesare

    2014-01-01

    The structure and ground state electronic structure of the recently synthesized SrPdO3 perovskite [A. Galal et al. J. Power Sources 195, 3806 (2010), 10.1016/j.jpowsour.2009.12.091] have been studied by means of screened hybrid functional and the GW approximation with the inclusion of electron-hole interaction within the test-charge/test-charge scheme. By conducting a structural search based on lattice dynamics and group theoretical method we identify the orthorhombic phase with Pnma space group as the most stable crystal structure. The phase transition from the ideal cubic perovskite structure to the Pnma one is explained in terms of the simultaneous stabilization of the antiferrodistortive phonon modes R4+ and M3+. Our results indicate that SrPdO3 exhibits an insulating ground state, substantiated by a GW0 gap of about 1.1 eV. Spin polarized calculations suggest that SrPdO3 adopts a low spin state (t2g↑↓↑↓↑↓eg0), and is expected to exhibit spin excitations and spin state crossovers at finite temperature, analogous to the case of 3d isoelectronic LaCoO3. This would provide another playground for the study of spin state transitions in 4d oxides and an opportunity to design multifunctional materials based on the 4d Pnma building block.

  6. Structure and energetics of nanotwins in cubic boron nitrides

    Science.gov (United States)

    Zheng, Shijian; Zhang, Ruifeng; Huang, Rong; Taniguchi, Takashi; Ma, Xiuliang; Ikuhara, Yuichi; Beyerlein, Irene J.

    2016-08-01

    Recently, nanotwinned cubic boron nitrides (NT c-BN) have demonstrated extraordinary leaps in hardness. However, an understanding of the underlying mechanisms that enable nanotwins to give orders of magnitude increases in material hardness is still lacking. Here, using transmission electron microscopy, we report that the defect density of twin boundaries depends on nanotwin thickness, becoming defect-free, and hence more stable, as it decreases below 5 nm. Using ab initio density functional theory calculations, we reveal that the Shockley partials, which may dominate plastic deformation in c-BNs, show a high energetic barrier. We also report that the c-BN twin boundary has an asymmetrically charged electronic structure that would resist migration of the twin boundary under stress. These results provide important insight into possible nanotwin hardening mechanisms in c-BN, as well as how to design these nanostructured materials to reach their full potential in hardness and strength.

  7. Structure and energetics of nanotwins in cubic boron nitrides

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Shijian, E-mail: sjzheng@imr.ac.cn, E-mail: zrf@buaa.edu.cn; Ma, Xiuliang [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Zhang, Ruifeng, E-mail: sjzheng@imr.ac.cn, E-mail: zrf@buaa.edu.cn [School of Materials Science and Engineering, and International Research Institute for Multidisciplinary Science, Beihang University, Beijing 100191 (China); Huang, Rong [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062 (China); Taniguchi, Takashi [National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan); Ikuhara, Yuichi [Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587 (Japan); Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656 (Japan); Beyerlein, Irene J. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2016-08-22

    Recently, nanotwinned cubic boron nitrides (NT c-BN) have demonstrated extraordinary leaps in hardness. However, an understanding of the underlying mechanisms that enable nanotwins to give orders of magnitude increases in material hardness is still lacking. Here, using transmission electron microscopy, we report that the defect density of twin boundaries depends on nanotwin thickness, becoming defect-free, and hence more stable, as it decreases below 5 nm. Using ab initio density functional theory calculations, we reveal that the Shockley partials, which may dominate plastic deformation in c-BNs, show a high energetic barrier. We also report that the c-BN twin boundary has an asymmetrically charged electronic structure that would resist migration of the twin boundary under stress. These results provide important insight into possible nanotwin hardening mechanisms in c-BN, as well as how to design these nanostructured materials to reach their full potential in hardness and strength.

  8. New cubic structure compounds as actinide host phases

    Energy Technology Data Exchange (ETDEWEB)

    Stefanovsky, S V [SIA Radon, 7th Rostovskii lane 2/14, Moscow 119121 (Russian Federation); Yudintsev, S V; Livshits, T S, E-mail: profstef@mtu-net.ru [Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Staromonetny lane 35, Moscow 119017 (Russian Federation)

    2010-03-15

    Various compounds with fluorite (cubic zirconia) and fluorite-derived (pyrochlore, zirconolite) structures are considered as promising actinide host phases at immobilization of actinide-bearing nuclear wastes. Recently some new cubic compounds - stannate and stannate-zirconate pyrochlores, murataite and related phases, and actinide-bearing garnet structure compounds were proposed as perspective matrices for complex actinide wastes. Zirconate pyrochlore (ideally Gd{sub 2}Zr{sub 2}O{sub 7}) has excellent radiation resistance and high chemical durability but requires high temperatures (at least 1500 deg. C) to be produced by hot-pressing from sol-gel derived precursor. Partial Sn{sup 4+} substitution for Zr{sup 4+} reduces production temperature and the compounds REE{sub 2}ZrSnO{sub 7} may be hot-pressed or cold pressed and sintered at {approx}1400 deg. C. Pyrochlore, A{sub 2}B{sub 2}O{sub 7-x} (two-fold elementary fluorite unit cell), and murataite, A{sub 3}B{sub 6}C{sub 2}O{sub 20-y} (three-fold fluorite unit cell), are end-members of the polysomatic series consisting of the phases whose structures are built from alternating pyrochlore and murataite blocks (nano-sized modules) with seven- (2C/3C/2C), five- (2C/3C), eight- (3C/2C/3C) and three-fold (3C - murataite) fluorite unit cells. Actinide content in this series reduces in the row: 2C (pyrochlore) > 7C > 5C > 8C > 3C (murataite). Due to congruent melting murataite-based ceramics may be produced by melting and the firstly segregated phase at melt crystallization is that with the highest fraction of the pyrochlore modules in its structure. The melts containing up to 10 wt. % AnO{sub 2} (An = Th, U, Np, Pu) or REE/An fraction of HLW form at crystallization zoned grains composed sequentially of the 5C {yields} 8C {yields} 3C phases with the highest actinide concentration in the core and the lowest - in the rim of the grains. Radiation resistance of the 'murataite' is comparable to titanate pyrochlores. One

  9. Structural and magnetic study of the double-perovskites Ba2(Fe, B)2O6 (B = Mo, W and Re)

    Science.gov (United States)

    Rammeh, N.; Bramnik, K. G.; Ehrenberg, H.; Ritter, C.; Fuess, H.; Cheikh-Rouhou, A.

    2004-05-01

    Ceramics of Ba2(Fe,B)2O6 double-perovskites have been prepared and studied for B = Mo, W and Re. Rietveld analysis confirms that all samples crystallize in a cubic double-perovskite structure with Fmm space group. Magnetization measurements performed in the temperature range from 5 K to 350 K show a ferromagnetic behaviour for both materials Ba2(Fe,Mo)2O6 and Ba2(Fe,Re)2O6, with TC = 335 K, 318 K respectively, and antiferromagnetic behaviour for Ba2(Fe,W)2O6 with TN = 20 K.

  10. Variable-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type barium titanate phases.

    Science.gov (United States)

    Nakatani, Tomotaka; Yoshiasa, Akira; Nakatsuka, Akihiko; Hiratoko, Tatsuya; Mashimo, Tsutomu; Okube, Maki; Sasaki, Satoshi

    2016-02-01

    A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3 perovskite has been performed over the temperature range 298-778 K. A transition from a tetragonal (P4mm) to a cubic (Pm3m) phase has been revealed near 413 K. In the non-centrosymmetric P4mm symmetry group, both Ti and O atoms are displaced along the c-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti(4+) and Ba(2+) cations occupy off-center positions in the TiO6 and BaO12 polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.

  11. High-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type PbTiO3 phases.

    Science.gov (United States)

    Yoshiasa, Akira; Nakatani, Tomotaka; Nakatsuka, Akihiko; Okube, Maki; Sugiyama, Kazumasa; Mashimo, Tsutomu

    2016-06-01

    A high-temperature single-crystal X-ray diffraction study of a synthetic PbTiO3 perovskite was carried out over the wide temperature range 298-928 K. A transition from a tetragonal (P4mm) to a cubic (Pm \\bar 3 m) phase has been revealed near 753 K. In the non-centrosymmetric P4mm symmetry group, the difference in relative displacement between Pb and O along the c-axis is much larger than that between Ti and O. The Pb and Ti cations contribute sufficiently to polarization being shifted in the opposite direction compared with the shift of O atoms. Deviation from the linear changes in Debye-Waller factors and bonding distances in the tetragonal phases can be interpreted as a precursor phenomenon before the phase transition. Disturbance of the temperature factor Ueq for O is observed in the vicinity of the transition point, while Ueq values for Pb and Ti are continuously changing with increasing temperature. The O site includes the clear configurational disorder in the cubic phase. The polar local positional distortions remain in the cubic phase and are regarded as the cause of the paraelectricity. Estimated values of the Debye temperature ΘD for Pb and Ti are 154 and 467 K in the tetragonal phase and decrease 22% in the high-temperature phase. Effective potentials for Pb and Ti change significantly and become soft after the phase transition.

  12. Characterization, Microstructure, and Dielectric properties of cubic pyrochlore structural ceramics

    KAUST Repository

    Li, Yangyang

    2013-05-01

    The (BMN) bulk materials were sintered at 1050°C, 1100°C, 1150°C, 1200°C by the conventional ceramic process, and their microstructure and dielectric properties were investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM) (including the X-ray energy dispersive spectrometry EDS and high resolution transmission electron microscopy HRTEM) and dielectric impedance analyzer. We systematically investigated the structure, dielectric properties and voltage tunable property of the ceramics prepared at different sintering temperatures. The XRD patterns demonstrated that the synthesized BMN solid solutions had cubic phase pyrochlore-type structure when sintered at 1050°C or higher, and the lattice parameter (a) of the unit cell in BMN solid solution was calculated to be about 10.56Å. The vibrational peaks observed in the Raman spectra of BMN solid solutions also confirmed the cubic phase pyrochlore-type structure of the synthesized BMN. According to the Scanning Electron Microscope (SEM) images, the grain size increased with increasing sintering temperature. Additionally, it was shown that the densities of the BMN ceramic tablets vary with sintering temperature. The calculated theoretical density for the BMN ceramic tablets sintered at different temperatures is about 6.7521 . The density of the respective measured tablets is usually amounting more than 91% and 5 approaching a maximum value of 96.5% for sintering temperature of 1150°C. The microstructure was investigated by using Scanning Transmission Electron Microscope (STEM), X-ray diffraction (XRD). Combined with the results obtained from the STEM and XRD, the impact of sintering temperature on the macroscopic and microscopic structure was discussed. The relative dielectric constant ( ) and dielectric loss ( ) of the BMN solid solutions were measured to be 161-200 and (at room temperature and 100Hz-1MHz), respectively. The BMN solid

  13. Synthesis of crystalline perovskite-structured SrTiO3 nanoparticles using an alkali hydrothermal process

    Institute of Scientific and Technical Information of China (English)

    U.K.N. Din; T.H.T. Aziz; M.M. Salleh; A.A. Umar

    2016-01-01

    We report an experimental route for synthesizing perovskite-structured strontium titanate (SrTiO3) nanocubes using an alkali hydrothermal process at low temperatures without further heating. Furthermore, we studied the influence of heating time (at 180°C) on the crystallinity, morphology, and perovskite phase formation of SrTiO3. The SrTiO3 powder, which is formed via nanocube agglomeration, transforms into cubic particles with a particle size of 120–150 nm after 6 h of hydrothermal sintering. The crystallinity and percentage of the perovskite phase in the product increased with heating time. The cubic particles contained 31.24at% anatase TiO2 that originated from the precursor. By varying the weight ratio of anatase TiO2 used to react with the strontium salt precursor, we reduced the anatase-TiO2 content to 18.8at%. However, the average particle size increased when the anatase-TiO2 content decreased.

  14. Crystal structure of SrGeO3 in the high-pressure perovskite-type phase

    Directory of Open Access Journals (Sweden)

    Akihiko Nakatsuka

    2015-05-01

    Full Text Available Single crystals of the SrGeO3 (strontium germanium trioxide high-pressure phase have been synthesized successfully at 6 GPa and 1223 K. The compound crystallizes with the ideal cubic perovskite-type structure (space group Pm-3m, which consists of a network of corner-linked regular GeO6 octahedra (point-group symmetry m-3m, with the larger Sr atoms located at the centers of cavities in the form of SrO12 cuboctahedra (point-group symmetry m-3m in the network. The degrees of covalencies included in the Sr—O and the Ge—O bonds calculated from bond valences are 20.4 and 48.9%, respectively. Thus, the Ge—O bond of the GeO6 octahedron in the SrGeO3 perovskite has a strong covalency, comparable to those of the Si—O bonds of the SiO4 tetrahedra in silicates with about 50% covalency. The thermal vibrations of the O atoms in the title compound are remarkably suppressed in the directions of the Ge—O bonds. This anisotropy ranks among the largest observed in stoichiometric cubic perovskites.

  15. Structural properties of PbVO3 perovskites under hydrostatic pressure conditions up to 10.6 GPa.

    Science.gov (United States)

    Zhou, Wei; Tan, Dayong; Xiao, Wansheng; Song, Maoshuang; Chen, Ming; Xiong, Xiaolin; Xu, Jian

    2012-10-31

    High-pressure synchrotron x-ray powder diffraction experiments were performed on PbVO(3) tetragonal perovskite in a diamond anvil cell under hydrostatic pressures of up to 10.6 GPa at room temperature. The compression behavior of the PbVO(3) tetragonal phase is highly anisotropic, with the c-axis being the soft direction. A reversible tetragonal to cubic perovskite structural phase transition was observed between 2.7 and 6.4 GPa in compression and below 2.2 GPa in decompression. This transition was accompanied by a large volume collapse of 10.6% at 2.7 GPa, which was mainly due to electronic structural changes of the V(4+) ion. The polar pyramidal coordination of the V(4+) ion in the tetragonal phase changed to an isotropic octahedral coordination in the cubic phase. Fitting the observed P-V data using the Birch-Murnaghan equation of state with a fixed [Formula: see text] of 4 yielded a bulk modulus K(0) = 61(2) GPa and a volume V(0) = 67.4(1) Å(3) for the tetragonal phase, and the values of K(0) = 155(3) GPa and V(0) = 58.67(4) Å(3) for the cubic phase. The first-principles calculated results were in good agreement with our experiments.

  16. The Structure of the Cubic Coincident Site Lattice Rotation Group

    Energy Technology Data Exchange (ETDEWEB)

    Reed, B W; Minich, R W; Rudd, R E; Kumar, M

    2004-01-13

    This work is intended to be a mathematical underpinning for the field of grain boundary engineering and its relatives. The interrelationships within the set of rotations producing coincident site lattices in cubic crystals are examined in detail. Besides combining previously established but widely scattered results into a unified context, the present work details newly developed representations of the group structure in terms of strings of generators (based on quaternionic number theory, and including uniqueness proofs and rules for algebraic manipulation) as well as an easily visualized topological network model. Important results that were previously obscure or not universally understood (e.g. the {Sigma} combination rule governing triple junctions) are clarified in these frameworks. The methods also facilitate several general observations, including the very different natures of twin-limited structures in two and three dimensions, the inadequacy of the {Sigma} combination rule to determine valid quadruple nodes, and a curious link between allowable grain boundary assignments and the four-color map theorem. This kind of understanding is essential to the generation of realistic statistical models of grain boundary networks (particularly in twin-dominated systems) and is especially applicable to the field of grain boundary engineering.

  17. Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide.

    Science.gov (United States)

    Fabini, Douglas H; Stoumpos, Constantinos C; Laurita, Geneva; Kaltzoglou, Andreas; Kontos, Athanassios G; Falaras, Polycarpos; Kanatzidis, Mercouri G; Seshadri, Ram

    2016-12-05

    The structure of the hybrid perovskite HC(NH2 )2 PbI3 (formamidinium lead iodide) reflects competing interactions associated with molecular motion, hydrogen bonding tendencies, thermally activated soft octahedral rotations, and the propensity for the Pb(2+) lone pair to express its stereochemistry. High-resolution synchrotron X-ray powder diffraction reveals a continuous transition from the cubic α-phase (Pm3‾ m, #221) to a tetragonal β-phase (P4/mbm, #127) at around 285 K, followed by a first-order transition to a tetragonal γ-phase (retaining P4/mbm, #127) at 140 K. An unusual reentrant pseudosymmetry in the β-to-γ phase transition is seen that is also reflected in the photoluminescence. Around room temperature, the coefficient of volumetric thermal expansion is among the largest for any extended crystalline solid.

  18. Study of structural, elastic, electronic and thermodynamic properties of NaAlO{sub 3}-perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Bouafia, H. [Laboratoire de Microscope Electronique et Sciences des Materiaux, departement de physique, USTO, BP1505 El m' naouar, Oran (Algeria); Sahli, B. [Laboratoire de Genie Physique, Universite Ibn-Khaldoun, Tiaret 14000 (Algeria); Hiadsi, S. [Laboratoire de Microscope Electronique et Sciences des Materiaux, departement de physique, USTO, BP1505 El m' naouar, Oran (Algeria); Abidri, B., E-mail: b_abidri@hotmail.com [Laboratoire des Materiaux Magnetiques, Universite Djillali Liabes, Sidi Bel-Abbes 22000 (Algeria); Rached, D. [Laboratoire des Materiaux Magnetiques, Universite Djillali Liabes, Sidi Bel-Abbes 22000 (Algeria); Amrani, B. [Departement de Physique, Universite d' Oran es-senia (Algeria)

    2012-06-15

    The structural, elastic, electronic, and thermodynamic properties of the cubic NaAlO{sub 3}-perovskite are calculated using the full potential linearized augmented plane wave with local orbital (FP-LAPW)+lo. The exchange-correlation energy, is treated in generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) parameterization. The calculated equilibrium parameter is in good agreement with other works. The bulk modulus, elastic constants and their related parameters, such as Young modulus, shear modulus, and Poisson ratio were predicted. The electronic band structure of this compound has been calculated using the Angel-Vosko (EV) generalized gradient approximation (GGA) for the exchange correlation potential. We deduced that NaAlO{sub 3}-perovskite exhibit a wide-gap which it is an indirect from R to {Gamma} point. The analysis of the density of states (DOS) curves shows ionic and covalent character bond for Al-O and Na-O respectively. To complete the fundamental characterization of NaAlO{sub 3} material we have analyzed the thermodynamic properties using the quasi-harmonic Debye model.

  19. Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide

    Science.gov (United States)

    Whitfield, P. S.; Herron, N.; Guise, W. E.; Page, K.; Cheng, Y. Q.; Milas, I.; Crawford, M. K.

    2016-01-01

    We have examined the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q ∼ (Tc−T)β, where Tc is the critical temperature and the exponent β was close to ¼, as predicted for a tricritical phase transition. However, we also observed coexistence of the cubic and tetragonal phases over a range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI3 based solar cells. PMID:27767049

  20. Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide

    Science.gov (United States)

    Whitfield, P. S.; Herron, N.; Guise, W. E.; Page, K.; Cheng, Y. Q.; Milas, I.; Crawford, M. K.

    2016-10-01

    We have examined the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q ˜ (Tc-T)β, where Tc is the critical temperature and the exponent β was close to ¼, as predicted for a tricritical phase transition. However, we also observed coexistence of the cubic and tetragonal phases over a range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI3 based solar cells.

  1. Phase transitions and compressibility of NaMgF3 (Neighborite) in perovskite- and post-perovskite-related structures

    Science.gov (United States)

    Martin, C. David; Crichton, Wilson A.; Liu, Haozhe; Prakapenka, Vitali; Chen, Jiuhua; Parise, John B.

    2006-06-01

    Monochromatic x-ray diffraction data collected in-situ within the diamond anvil cell show perovskite structured Neighborite (NaMgF3) transforms to the CaIrO3-type post-perovskite structure between 28 and 30 GPa. Upon laser heating, the CaIrO3-type structure transforms further to an unknown structure (Pnnm, designated N-phase). Upon pressure release, N-phase NaMgF3 becomes x-ray amorphous. A structure transformation in post-perovskite MgSiO3 and MgGeO3 to N-phase may account for previous observations of extra x-ray reflections during high pressure experiments and tomographic observations of an additional boundary in the lower mantle below the D'' discontinuity.

  2. Deformation-induced structural transition in body-centred cubic molybdenum.

    Science.gov (United States)

    Wang, S J; Wang, H; Du, K; Zhang, W; Sui, M L; Mao, S X

    2014-03-07

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original -oriented body-centred cubic structure to a -oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into -oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.

  3. Deformation-induced structural transition in body-centred cubic molybdenum

    Science.gov (United States)

    Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.

    2014-03-01

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original -oriented body-centred cubic structure to a -oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into -oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.

  4. The ground states properties and the spin effect on the cubic and hexagonal perovskite manganese oxide BaMnO 3: GGA+ U calculation

    Science.gov (United States)

    Hamdad, Noura

    2011-03-01

    Particularly interesting as candidates to technological applications are the manganese perovskites with AMnO 3 formula. Their magnetic structure was described as resulting from a particular ordering of the occupied d orbitals which possess. This reflects my understanding of the structural, electronic and magnetic phenomena, which is well established only in the limit where the systems show localized or itinerant electron behavior. In general, the perovskites of ABO 3-type are well known with their (anti)ferroelectric, piezoelectric and (anti)ferromagnetism properties applied in considerable technological investigations. In my paper, I studied the ground states properties of the BaMnO 3 perovskite oxide. My structural properties are given using LSDA, GGA, LSDA+ U and GGA+ U in the aim to introduce the exchange correlation potential. In the following paper, I use the GGA+ U on the electronic and magnetic properties calculation. I show in my study the density of states, the band structures and also the charge density figures. My results such as lattice parameter, bulk modulus and its pressure derivative agree very well with available theoretical works and experimental data. I discuss the magnetic moment and the U-Hubbard effect introduced by LSDA+ U and GGA+ U on my results given in this paper.

  5. Size of oxide vacancies in fluorite and perovskite structured oxides

    DEFF Research Database (Denmark)

    Chatzichristodoulou, Christodoulos; Norby, Poul; Hendriksen, Peter Vang

    2015-01-01

    An analysis of the effective radii of vacancies and the stoichiometric expansion coefficient is performed on metal oxides with fluorite and perovskite structures. Using the hard sphere model with Shannon ion radii we find that the effective radius of the oxide vacancy in fluorites increases...... with increasing ion radius of the host cation and that it is significantly smaller than the radius of the oxide ion in all cases, from 37% smaller for HfO2 to 13 % smaller for ThO2. The perovskite structured LaGaO3 doped with Sr or Mg or both is analyzed in some detail. The results show that the effective radius...... of an oxide vacancy in doped LaGaO3 is only about 6 % smaller than the oxide ion. In spite of this the stoichiometric expansion coefficient (a kind of chemical expansion coefficient) of the similar perovskite, LaCrO3, is significantly smaller than the stoichiometric expansion coefficient of the fluorite...

  6. First-principles prediction of oxygen octahedral rotations in perovskite-structure EuTiO3

    Science.gov (United States)

    Rushchanskii, Konstantin Z.; Spaldin, Nicola A.; Ležaić, Marjana

    2012-03-01

    We present a systematic first-principles study of the structural and vibrational properties of perovskite-structure EuTiO3. Our calculated phonon spectrum of the high-symmetry cubic structural prototype shows strong M- and R-point instabilities, indicating a tendency to symmetry-lowering structural deformations composed of rotations and tilts of the oxygen octahedra. Subsequent explicit study of 14 different octahedral tilt-patterns showed that the I4/mcm, Imma, and R3¯c structures, all with antiferrodistortive rotations of the octahedra, have significantly lower total energy than the prototype Pm3¯m structure. We discuss the dynamical stability of these structures, and the influence of the antiferrodistortive structural distortions on the vibrational, optical, and magnetic properties of EuTiO3, in the context of recent unexplained experimental observations.

  7. Structural phase transitions in the ordered double perovskite Sr{sub 2}MnTeO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Ortega-San Martin, L [Departamento de Quimica Inorganica, Facultad de Ciencia y TecnologIa, Universidad del Pais Vasco (UPV/EHU), Apartado 644, E-48080 Bilbao (Spain); Chapman, J P [Departamento de Quimica Inorganica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco (UPV/EHU), Apartado 644, E-48080 Bilbao (Spain); Hernandez-Bocanegra, E [Departamento de Fisica Aplicada II, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco (UPV/EHU), Apartado 644, E-48080 Bilbao (Spain); Insausti, M [Departamento de Quimica Inorganica, Facultad de Ciencia y TecnologIa, Universidad del Pais Vasco (UPV/EHU), Apartado 644, E-48080 Bilbao (Spain); Arriortua, M I [Departamento de Mineralogia y Petrologia, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco (UPV/EHU), Apartado 644, E-48080 Bilbao (Spain); Rojo, T [Departamento de Quimica Inorganica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco (UPV/EHU), Apartado 644, E-48080 Bilbao (Spain)

    2004-06-16

    The crystal structure of the ordered double perovskite Sr{sub 2}MnTeO{sub 6} has been refined at ambient temperature from high resolution neutron and x-ray powder diffraction data in the monoclinic space group P 12{sub 1}/n 1 with a 5.7009(1) A, b = 5.6770(1) A, c = 8.0334(1) A and {beta} = 90.085(1) deg. This represents a combination of in-phase (+) and out-of-phase (-) rotations of virtually undistorted MnO{sub 6} and TeO{sub 6} octahedra in the (-+) sense about the axes of the ideal cubic perovskite. High temperature x-ray powder diffraction shows three structural phase transitions at approximately 250, 550 and 675 deg. C, each corresponding to the disappearance of rotations about one of these axes. The first transition was analysed by differential scanning calorimetry and showed a thermal hysteresis with an enthalpy of 0.55 J g{sup -1}. We propose the (P12{sub 1}/n1 {yields} I12/m1 {yields} I4/m {yields} Fm3barm) sequence of structural transitions which has not been previously reported for a double perovskite oxide.

  8. Anion order in perovskites: a group-theoretical analysis.

    Science.gov (United States)

    Talanov, M V; Shirokov, V B; Talanov, V M

    2016-03-01

    Anion ordering in the structure of cubic perovskite has been investigated by the group-theoretical method. The possibility of the existence of 261 ordered low-symmetry structures, each with a unique space-group symmetry, is established. These results include five binary and 14 ternary anion superstructures. The 261 idealized anion-ordered perovskite structures are considered as aristotypes, giving rise to different derivatives. The structures of these derivatives are formed by tilting of BO6 octahedra, distortions caused by the cooperative Jahn-Teller effect and other physical effects. Some derivatives of aristotypes exist as real substances, and some as virtual ones. A classification of aristotypes of anion superstructures in perovskite is proposed: the AX class (the simultaneous ordering of A cations and anions in cubic perovskite structure), the BX class (the simultaneous ordering of B cations and anions) and the X class (the ordering of anions only in cubic perovskite structure). In most perovskites anion ordering is accompanied by cation ordering. Therefore, the main classes of anion order in perovskites are the AX and BX classes. The calculated structures of some anion superstructures are reported. Comparison of predictions and experimentally investigated anion superstructures shows coherency of theoretical and experimental results.

  9. Impact of Atomic Structure on Absolute Energy Levels of Methylammonium Lead Iodide Perovskite

    Science.gov (United States)

    Choi, Joshua

    2015-03-01

    There has been a staggeringly rapid increase in the photovoltaic performance of methylammonium lead iodide (MAPbI3) perovskite - greater than 19 percent solar cell power conversion efficiency has been reported in less than five years since the first report in 2009. Despite the progress in device performance, structure-property relationships in MAPbI3 are still poorly understood. I will present our recent findings on the impact of changing the Pb-I bond length and Pb-I-Pb bond angle on the electronic structure of MAPbI3. By using the combination of temperature dependent X-ray scattering, ultraviolet photoelectron spectroscopy, absorbance and PL spectroscopy, we show that the energy levels of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) shift in the same direction as MAPbI3 goes through tetragonal-to-cubic structural phase transition wherein the rotational angle of PbI6 octahedra is the order parameter of the transition. Our experimental results are corroborated by density functional theory calculations which show that the lattice expansion and bond angle distortion cause different degree of orbital overlap between the Pb and I atoms and the anti-bonding orbital nature of both HOMO and LUMO results in the same direction of their shift. Moreover, through pair distribution function analysis of X-ray scattering, we discovered that the majority of MAPbI3 in thin film solar cell layer has highly disordered structure with a coherence range of only 1.4 nm. The nanostructuring correlates with a blueshift of the absorption onset and increases the photoluminescence. Our results underscore the importance of understanding the structure-property relationships in order to improve the device performance of metal-organic perovskites.

  10. Crystal Structure of Pure and Aluminous Calcium Silicate Perovskites at Mantle Related Pressure and Temperature

    Science.gov (United States)

    Chen, H.; Shim, S. H.; Leinenweber, K. D.; Meng, Y.; Prakapenka, V.

    2015-12-01

    CaSiO3-perovskite (CaPv) is believed to be the third most abundant mineral (5 wt%) in the Earth's lower mantle (LM). Subducted slabs contain 23 wt% CaPv at the LM related pressure (P) and temperature (T), where Al2O3 could be incorporated into the crystal structure of CaPv (AlCaPv). However, there remains important discrepancy between computations and experiments on the crystal structure of CaPv at high P and low T. Some computations have predicted a tetragonal I4/mcm structure with a pseudo-cubic axial ratio (cp/ap) greater than 1, while X-ray diffraction (XRD) studies have suggested a tetragonal P4/mmm structure with cp/ap ~ 0.995. Using Ne as a pressure medium, we conducted in-situ XRD of CaSiO3 and 5 wt% Al-bearing CaSiO3 in the laser heated diamond anvil cell at the GSECARS and HPCAT sectors of the Advanced Photon Source. Rietveld refinements are performed on the diffraction patterns of CaPv at 300 K and 20-60 GPa. Similar to previous studies, we observed splitting of the 200 and 211 peaks after T-quench in pure CaPv. However, unlike previous experiments, diffraction patterns were more consistent with a tetragonal I4/mcm structure with cp/ap ~ 1.005 than P4/mmm. All the previous diffraction patterns have been measured with an Ar or MgO medium, or even without a medium, while we used more hydrostatic Ne medium. Considering the small free energy differences among different perovskite structures, the crystal structure of CaPv may be very sensitive to non-hydrostatic stresses. In runs with AlCaPv, asymmetrical 200 peaks are found up to 60 GPa and 2200 K, showing that non-cubic could be still stable at mantle geotherm temperatures in AlCaPv. The extreme sensitivity of CaPv on deviatoric stresses may have important implications for the elastic properties of the mantle regions with strong deformations, because the elastic anisotropy can change with the crystal structure of CaPv.

  11. A DFT+U study of the structural, electronic, magnetic, and mechanical properties of cubic and orthorhombic SmCoO3

    Science.gov (United States)

    Olsson, Emilia; Aparicio-Anglès, Xavier; de Leeuw, Nora H.

    2016-12-01

    SmCoO3 is a perovskite material that has gained attention as a potential substitute for La1-xSrxMnO3-d as a solid oxide fuel cell cathode. However, a number of properties have remained unknown due to the complexity of the material. For example, we know from experimental evidence that this perovskite exists in two different crystal structures, cubic and orthorhombic, and that the cobalt ion changes its spin state at high temperatures, leading to a semiconductor-to-metal transition. However, little is known about the precise magnetic structure that causes the metallic behavior or the spin state of the Co centers at high temperature. Here, we therefore present a systematic DFT+U study of the magnetic properties of SmCoO3 in order to determine what magnetic ordering is the one exhibited by the metallic phase at different temperatures. Similarly, mechanical properties are difficult to measure experimentally, which is why there is a lack of data for the two different phases of SmCoO3. Taking advantage of our DFT calculations, we have determined the mechanical properties from our calculated elastic constants, finding that both polymorphs exhibit similar ductility and brittleness, but that the cubic structure is harder than the orthorhombic phase.

  12. Structural manipulation and tailoring of dielectric properties in SrTi1-xFexTaxO3 perovskites: Design of new lead free relaxors

    Science.gov (United States)

    Shukla, R.; Patwe, S. J.; Deshpande, S. K.; Achary, S. N.; Krishna, P. S. R.; Shinde, A. B.; Gopalakrishnan, J.; Tyagi, A. K.

    2016-08-01

    We report composition dependent structure evolution from SrTiO3 to SrFe0.5Ta0.5O3 by powder X-ray and neutron diffraction studies of SrTi1-2xFexTaxO3 (0.00 ≤ × ≤ 0.50) compositions. Structural studies reveal cubic (Pm3m) perovskite-type structure of the parent SrTiO3 for x up to 0.075 and cation disordered orthorhombic (Pbnm) perovskite-type structure for x ≥ 0.33. A biphasic region consisting of a mixture of cubic and orthorhombic structures is found in the range for 0.10 ≤ × ≤ 0.25. Dielectric studies reveal transformation from a normal dielectric to relaxor like properties with increasing Fe3+ and Ta5+ concentration. Dielectric response is maximum at x = 0.33 in the series. The results establish a protocol for designing new lead-free relaxor materials based on the co-substitution of Fe3+ and Ta5+ for Ti4+ in SrTiO3. A complex interplay of strain effects arising from distribution of cations at the octahedral sites of the perovskite structure controls the dielectric properties.

  13. Lateral-Structure Single-Crystal Hybrid Perovskite Solar Cells via Piezoelectric Poling.

    Science.gov (United States)

    Dong, Qingfeng; Song, Jingfeng; Fang, Yanjun; Shao, Yuchuan; Ducharme, Stephen; Huang, Jinsong

    2016-04-13

    Single-crystal perovskite solar cells with a lateral structure yield an efficiency enhancement 44-fold that of polycrystalline thin films, due to the much longer carrier diffusion length. A piezoelectric effect observed in perovskite single-crystal and the strain-generated grain-boundaries enable ion migration to form a p-i-n structure.

  14. Use of the Primitive Unit Cell in Understanding Subtle Features of the Cubic Closest-Packed Structure

    Science.gov (United States)

    Hawkins, John A.; Rittenhouse, Jeffrey L.; Soper, Linda M.; Rittenhouse, Robert C.

    2008-01-01

    One of the most important crystal structures adopted by metals is characterized by the "abcabc"...stacking of close-packed layers. This structure is commonly referred to in textbooks as the cubic close-packed (ccp) or face-centered cubic (fcc) structure, since the entire lattice can be generated by replication of a face-centered cubic unit cell…

  15. Reversible Structural Swell-Shrink and Recoverable Optical Properties in Hybrid Inorganic-Organic Perovskite.

    Science.gov (United States)

    Zhang, Yupeng; Wang, Yusheng; Xu, Zai-Quan; Liu, Jingying; Song, Jingchao; Xue, Yunzhou; Wang, Ziyu; Zheng, Jialu; Jiang, Liangcong; Zheng, Changxi; Huang, Fuzhi; Sun, Baoquan; Cheng, Yi-Bing; Bao, Qiaoliang

    2016-07-26

    Ion migration in hybrid organic-inorganic perovskites has been suggested to be an important factor for many unusual behaviors in perovskite-based optoelectronics, such as current-voltage hysteresis, low-frequency giant dielectric response, and the switchable photovoltaic effect. However, the role played by ion migration in the photoelectric conversion process of perovskites is still unclear. In this work, we provide microscale insights into the influence of ion migration on the microstructure, stability, and light-matter interaction in perovskite micro/nanowires by using spatially resolved optical characterization techniques. We observed that ion migration, especially the migration of MA(+) ions, will induce a reversible structural swell-shrink in perovskites and recoverably affect the reflective index, quantum efficiency, light-harvesting, and photoelectric properties. The maximum ion migration quantity in perovskites was as high as approximately 30%, resulting in lattice swell or shrink of approximately 4.4%. Meanwhile, the evidence shows that ion migration in perovskites could gradually accelerate the aging of perovskites because of lattice distortion in the reversible structural swell-shrink process. Knowledge regarding reversible structural swell-shrink and recoverable optical properties may shed light on the development of optoelectronic and converse piezoelectric devices based on perovskites.

  16. Magnetic coupling at perovskite and rock-salt structured interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Matvejeff, M., E-mail: mikko.matvejeff@picosun.com [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8581 Chiba (Japan); Department of Chemistry, Aalto University, Kemistintie 1, 02150 Espoo (Finland); Ahvenniemi, E. [Department of Chemistry, Aalto University, Kemistintie 1, 02150 Espoo (Finland); Takahashi, R.; Lippmaa, M. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8581 Chiba (Japan)

    2015-10-05

    We study magnetic coupling between hole-doped manganite layers separated by either a perovskite or a rock-salt barrier of variable thickness. Both the type and the quality of the interface have a strong impact on the minimum critical barrier thickness where the manganite layers become magnetically decoupled. A rock-salt barrier layer only 1 unit cell (0.5 nm) thick remains insulating and is able to magnetically de-couple the electrode layers. The technique can therefore be used for developing high-performance planar oxide electronic devices such as magnetic tunnel junctions and quantum well structures that depend on magnetically and electronically sharp heterointerfaces.

  17. Navigating Organo-Lead Halide Perovskite Phase Space via Nucleation Kinetics toward a Deeper Understanding of Perovskite Phase Transformations and Structure-Property Relationships.

    Science.gov (United States)

    Williams, Spencer T; Chueh, Chu-Chen; Jen, Alex K-Y

    2015-07-01

    Organo-lead halide perovskite photovoltaics have developed faster than our understanding of the material itself. Using the vast body of work on perovskite processing created in just the past few years, it is possible to create a better picture of this material's complex phase-transformation behavior. This concept paper summarizes and correlates the current understanding of structural intermediates, kinetic controls, and structure-property relationships of organo-lead iodide perovskites. To this end, a new way of graphically relating information is developed, allowing the simultaneous mapping of schematic kinetic relationships between all currently prevailing perovskite deposition and growth techniques.

  18. Photodetectors Based on Two-Dimensional Layer-Structured Hybrid Lead Iodide Perovskite Semiconductors.

    Science.gov (United States)

    Zhou, Jiachen; Chu, Yingli; Huang, Jia

    2016-10-05

    Hybrid lead iodide perovskite semiconductors have attracted intense research interests recently because of their easy fabrication processes and high power conversion efficiencies in photovoltaic applications. Layer-structured materials have interesting properties such as quantum confinement effect and tunable band gap due to the unique two-dimensional crystalline structures. ⟨100⟩-oriented layer-structured perovskite materials are inherited from three-dimensional ABX3 perovskite materials with a generalized formula of (RNH3)2(CH3NH3)n-1MnX3n+1, and adopt the Ruddlesden-Popper type crystalline structure. Here we report the synthesis and investigation of three layer-structured perovskite materials with different layer numbers: (C4H9NH3)2PbI4 (n = 1, one-layered perovskite), (C4H9NH3)2(CH3NH3)Pb2I7 (n = 2, two-layered perovskite) and (C4H9NH3)2(CH3NH3)2Pb3I10 (n = 3, three-layered perovskite). Their photoelectronic properties were investigated in related to their molecular structures. Photodetectors based on these two-dimensional (2D) layer-structured perovskite materials showed tunable photoresponse with short response time in milliseconds. The photodetectors based on three-layered perovskite showed better performances than those of the other two devices, in terms of output current, responsivity, Ilight/Idark ratio, and response time, because of its smaller optical band gap and more condensed microstructure comparing the other two materials. These results revealed the relationship between the molecular structures, film microstructures and the photoresponse properties of 2D layer-structured hybrid perovskites, and demonstrated their potentials as flexible, functional, and tunable semiconductors in optoelectronic applications, by taking advantage of their tunable quantum well molecular structure.

  19. Tilting structures in inverse perovskites, M3TtO (M = Ca, Sr, Ba, Eu; Tt = Si, Ge, Sn, Pb).

    Science.gov (United States)

    Nuss, Jürgen; Mühle, Claus; Hayama, Kyouhei; Abdolazimi, Vahideh; Takagi, Hidenori

    2015-06-01

    Single-crystal X-ray diffraction experiments were performed for a series of inverse perovskites, M3TtO (M = Ca, Sr, Ba, Eu; Tt = tetrel element: Si, Ge, Sn, Pb) in the temperature range 500-50 K. For Tt = Sn, Pb, they crystallize as an 'ideal' perovskite-type structure (Pm3m, cP5); however, all of them show distinct anisotropies of the displacement ellipsoids of the M atoms at room temperature. This behavior vanishes on cooling for M = Ca, Sr, Eu, and the structures can be regarded as `ideal' cubic perovskites at 50 K. The anisotropies of the displacement ellipsoids are much more enhanced in the case of the Ba compounds. Finally, their structures undergo a phase transition at ∼ 150 K. They change from cubic to orthorhombic (Ibmm, oI20) upon cooling, with slightly tilted OBa6 octahedra, and bonding angles O-Ba-O ≃ 174° (100 K). For the larger Ba(2+) cations, the structural changes are in agreement with smaller tolerance factors (t) as defined by Goldschmidt. Similar structural behavior is observed for Ca3TtO. Smaller Tt(4-) anions (Si, Ge) introduce reduced tolerance factors. Both compounds Ca3SiO and Ca3GeO with cubic structures at 500 K, change into orthorhombic (Ibmm) at room temperature. Whereby, Ca3SiO is the only representative within the M3TtO family where three polymorphs can be found within the temperature range 500-50 K: Pm3m-Ibmm-Pbnm. They show tiny differences in the tilting of the OCa6 octahedra, expressed by O-Ca-O bond angles of 180° (500 K), ∼ 174° (295 K) and 170° (100 K). For larger M (Sr, Eu, Ba), together with smaller Tt (Si, Ge) atoms, pronounced tilting of the OM6 octahedra, and bonding angles of O-M-O ≃ 160° (295 K) are observed. They crystallize in the anti-GdFeO3 type of structure (Pbnm, oP20), and no phase transitions occur between 500 and 50 K. The observed phase transitions are all accompanied by multiple twinning, in terms of pseudo-merohedry or reticular pseudo-merohedry.

  20. An experimental study of perovskite-structured mixed ionic- electronic conducting oxides and membranes

    Science.gov (United States)

    Zeng, Pingying

    In recent decades, ceramic membranes based on mixed ionic and electronic conducting (MIEC) perovskite-structured oxides have received many attentions for their applications for air separation, or as a membrane reactor for methane oxidation. While numerous perovskite oxide materials have been explored over the past two decades; there are hardly any materials with sufficient practical economic value and performance for large scale applications, which justifies continuing the search for new materials. The main purposes of this thesis study are: (1) develop several novel SrCoO3-delta based MIEC oxides, SrCoCo1-xMxO3-delta, based on which membranes exhibit excellent oxygen permeability; (2) investigate the significant effects of the species and concentration of the dopants M (metal ions with fixed valences) on the various properties of these membranes; (3) investigate the significant effects of sintering temperature on the microstructures and performance of oxygen permeation membranes; and (4) study the performance of oxygen permeation membranes as a membrane reactor for methane combustion. To stabilize the cubic phase structure of the SrCoO3-delta oxide, various amounts of scandium was doped into the B-site of SrCoO 3-delta to form a series of new perovskite oxides, SrScxCoCo 1-xO3-delta (SSCx, x = 0-0.7). The significant effects of scandium-doping concentration on the phase structure, electrical conductivity, sintering performance, thermal and structural stability, cathode performance, and oxygen permeation performance of the SSCx membranes, were systematically studied. Also for a more in-depth understanding, the rate determination steps for the oxygen transport process through the membranes were clarified by theoretical and experimental investigation. It was found that only a minor amount of scandium (5 mol%) doping into the B-site of SrCoO3-delta can effectively stabilize the cubic phase structure, and thus significantly improve the electrical conductivity and

  1. Structural characterization and optical properties of perovskite ZnZrO 3 nanoparticles

    KAUST Repository

    Zhu, Xinhua

    2014-03-17

    Perovskite ZnZrO3 nanoparticles were synthesized by hydrothermal method, and their microstructures and optical properties were characterized. The crystallinity, phase formation, morphology and composition of the as-synthesized nanoparticles were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolutiontransmission electron microscopy (HRTEM), and energy-dispersive X-ray (EDX) spectroscopy analysis, respectively. TEM images demonstrated that the average particle size of the ZnZrO3 powders was increased with increasing the Zn/Zr molar ratios in the precursors, and more large ZnZrO3 particles with cubic morphology were observed at high Zn/Zr molar ratios. In addition, the phase structures of the ZnZrO3 particles were also evolved from a cubic to tetragonal perovskite phase, as revealed by XRD and SAED patterns. HRTEM images demonstrate that surface structures of the ZnZrO3 powders synthesized at high Zn/Zr molar ratios, are composed of corners bound by the {100} mini-facets, and the surface steps lying on the {100} planes are frequently observed, whereas the (101) facet isoccasionally observed. The formation of such a rough surface structure is understood from the periodic bond chain theory. Quantitative EDX analyses demonstrated that the atomic concentrations (at.%) of Zn:Zr:O in the particles were 20.70:21.07:58.23, as close to the composition of ZnZrO3. In the optical spectra, a significant red shift of the absorption edges (for the ZnZrO3 nanopowders) from UV to visible region (from 394 to 417 nm) was observed as increasing the Zn/Zr molar ratios in the precursors, which corresponds to that the band gap energies of the ZnZrO3 nanopowders can be continuously tuned from 3.15 to 2.97 eV. This opens an easy way to tune the band gap energies of the ZnZrO3 nanopowders. © 2014 The American Ceramic Society.

  2. Perovskite-type oxides - Oxygen electrocatalysis and bulk structure

    Science.gov (United States)

    Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, E.

    1988-01-01

    Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

  3. Structure-Band Gap Relationships in Hexagonal Polytypes and Low-Dimensional Structures of Hybrid Tin Iodide Perovskites.

    Science.gov (United States)

    Stoumpos, Constantinos C; Mao, Lingling; Malliakas, Christos D; Kanatzidis, Mercouri G

    2017-01-03

    The present study deals with the structural characterization and classification of the novel compounds 1-8 into perovskite subclasses and proceeds in extracting the structure-band gap relationships between them. The compounds were obtained from the employment of small, 3-5-atom-wide organic ammonium ions seeking to discover new perovskite-like compounds. The compounds reported here adopt unique or rare structure types akin to the prototype structure perovskite. When trimethylammonium (TMA) was employed, we obtained TMASnI3 (1), which is our reference compound for a "perovskitoid" structure of face-sharing octahedra. The compounds EASnI3 (2b), GASnI3 (3a), ACASnI3 (4), and IMSnI3 (5) obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium (ACA), and imidazolium (IM) cations, respectively, represent the first entries of the so-called "hexagonal perovskite polytypes" in the hybrid halide perovskite library. The hexagonal perovskites define a new family of hybrid halide perovskites with a crystal structure that emerges from a blend of corner- and face-sharing octahedral connections in various proportions. The small organic cations can also stabilize a second structural type characterized by a crystal lattice with reduced dimensionality. These compounds include the two-dimensional (2D) perovskites GA2SnI4 (3b) and IPA3Sn2I7 (6b) and the one-dimensional (1D) perovskite IPA3SnI5 (6a). The known 2D perovskite BA2MASn2I7 (7) and the related all-inorganic 1D perovskite "RbSnF2I" (8) have also been synthesized. All compounds have been identified as medium-to-wide-band-gap semiconductors in the range of Eg = 1.90-2.40 eV, with the band gap progressively decreasing with increased corner-sharing functionality and increased torsion angle in the octahedral connectivity.

  4. Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo2O5+δ (RE= Pr, Gd, Y)

    Institute of Scientific and Technical Information of China (English)

    Hao Haoshan; Zheng Lu; Wang Yingfang; Liu Shijiang; Hu Xing

    2007-01-01

    The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5+δ, GdBaCo2O5+δ, and YBaCo2O5+δ were investigated by the thermogravimetry (TG) method in the temperature range of 400~900 ℃. The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides, such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ, whereas, the oxygen permeation flux was comparable to that of the latter, which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere (Δδ/Vmol) in these double perovskite structure oxides. The large oxygen adsorption/desorption rate constants of GdBaCo2O5+δ and PrBaCo2O5+δ made them nice catalyst coating materials, on other membrane surfaces, to improve the oxygen permeability.

  5. Intrinsic and extrinsic photoluminescence in the NH sub 4 MnCl sub 3 cubic perovskite: a spectroscopic study

    CERN Document Server

    Hernandez, I

    2003-01-01

    This work investigates the photoluminescence (PL) properties of the cubic chloroperovskite NH sub 4 MnCl sub 3. Like in most concentrated materials, the Mn sup 2 sup + PL which is located at 2.10 eV at T = 10 K strongly depends on the temperature. Optical absorption (OA), emission, and excitation spectroscopy, as well as lifetime measurements, performed on NH sub 4 MnCl sub 3 indicate that the PL is mainly intrinsic at T = 10 K and consists of a broad band located at 2.10 eV. Above this temperature, the PL gradually transforms to extrinsic PL due to exciton migration and subsequent trapping. Further temperature increase above 100 K yields transfer to killers of excitation which are responsible for the PL quenching, and hence the absence of PL at ambient conditions. The exciton traps are identified with perturbed Mn sup 2 sup + sites with the effective activation energy of 52 meV, whilst the activation energy for energy transfer is 47 meV. The existence of these traps has been directly revealed by time-resolve...

  6. Structure of the body-centered cubic phase of lipid systems.

    Science.gov (United States)

    Saludjian, P; Reiss-Husson, F

    1980-12-01

    A new model is proposed for the structure of the body-centered cubic phase of lipid systems. Infinite rods of polar groups (and water) are arranged with axes parallel to the four cubic [unk]1 1 1[unk] directions. The hydrocarbon chains fill the space between the rods to form a continuous matrix. With this unified topology, the model explains satisfactorily the x-ray diffraction patterns of strontium soaps, lecithin, galactolipids, potassium soaps, and hexadecyltrimethylammonium bromide and explains the transition between cubic/H(II) phases. The paradoxical thermal effects on the lipid cubic phase, in particular the decrease of unit cell dimensions with increasing temperature, can be explained with the proposed model by mechanisms similar to those used for the monodimensional and bidimensional (mesomorphic) phases.

  7. Structure and magnetic properties of the double-perovskites Ba2(B,Re)2O6 (B = Fe, Mn, Co and Ni)

    Science.gov (United States)

    Rammeh, N.; Ehrenberg, H.; Fuess, H.; Cheikkh-Rouhou, A.

    2006-09-01

    Structural and magnetic properties of Ba2(B,Re)2O6 (B = Fe, Mn, Co and Ni) double-perovskite oxides have been investigated. Rietveld analysis shows that all our synthesized samples are single phase and crystallize at room temperature in the cubic double-perovskite structure with Fm3m space group. Magnetization measurements versus temperature and versus magnetic applied field up to 5 T show that Ba2(Fe,Re)2O6, Ba2(Mn,Re)2O6 and Ba2(Ni,Re)2O6 are ferromagnetic at low temperature with TC = 318 K, 113 K and 32 K respectively while Ba2(Co,Re)2O6 is antiferromagnetic below TN = 25 K.

  8. Iridium double perovskite Sr2YIrO6 : A combined structural and specific heat study

    Science.gov (United States)

    Corredor, L. T.; Aslan-Cansever, G.; Sturza, M.; Manna, Kaustuv; Maljuk, A.; Gass, S.; Dey, T.; Wolter, A. U. B.; Kataeva, Olga; Zimmermann, A.; Geyer, M.; Blum, C. G. F.; Wurmehl, S.; Büchner, B.

    2017-02-01

    Recently, the iridate double perovskite Sr2YIrO6 has attracted considerable attention due to the report of unexpected magnetism in this Ir5 + (5 d4 ) material, in which according to the Jeff model, a nonmagnetic ground state is expected. However, in recent works on polycrystalline samples of the series Ba2 -xSrxYIrO6 no indication of magnetic transitions have been found. We present a structural, magnetic, and thermodynamic characterization of Sr2YIrO6 single crystals, with emphasis on the temperature and magnetic field dependence of the specific heat. As determined by x-ray diffraction, the Sr2YIrO6 single crystals have a cubic structure, with space group F m 3 ¯m . In agreement with the expected nonmagnetic ground state of Ir5 + (5d 4 ) in Sr2YIrO6 , no magnetic transition is observed down to 430 mK. Moreover, our results suggest that the low-temperature anomaly observed in the specific heat is not related to the onset of long-range magnetic order. Instead, it is identified as a Schottky anomaly caused by paramagnetic impurities present in the sample, of the order of n ˜0.5 (2 )% . These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.

  9. The local structure of mixed-ion perovskites

    CERN Document Server

    Shuvaeva, V A; Azuma, Y; Yagi, K; Sakaue, K; Terauchi, H; Raevski, I P; Zhuchkov, K; Antipin, M Y

    2003-01-01

    The temperature-dependent Nb K-edge absorption spectra of several mixed-ion Pb-containing perovskite compounds were analysed to determine the Nb displacement and to trace its changes through the phase transitions. Both extended x-ray absorption fine structure (EXAFS) and the pre-edge region of the spectra were involved in the analysis. The results show that, in the compounds studied, Nb occupies an off-centre position with symmetry lower than that implied by macroscopic symmetry. The magnitude and direction of the Nb off-centre displacement do not display any noticeable temperature change and are not affected by the change in macroscopic symmetry. The Nb-O distribution and its temperature evolution do not show any distinct dependence on the degree of compositional ordering and properties of the samples.

  10. Thermally induced structural evolution and performance of mesoporous block copolymer-directed alumina perovskite solar cells.

    Science.gov (United States)

    Tan, Kwan Wee; Moore, David T; Saliba, Michael; Sai, Hiroaki; Estroff, Lara A; Hanrath, Tobias; Snaith, Henry J; Wiesner, Ulrich

    2014-05-27

    Structure control in solution-processed hybrid perovskites is crucial to design and fabricate highly efficient solar cells. Here, we utilize in situ grazing incidence wide-angle X-ray scattering and scanning electron microscopy to investigate the structural evolution and film morphologies of methylammonium lead tri-iodide/chloride (CH3NH3PbI(3-x)Cl(x)) in mesoporous block copolymer derived alumina superstructures during thermal annealing. We show the CH3NH3PbI(3-x)Cl(x) material evolution to be characterized by three distinct structures: a crystalline precursor structure not described previously, a 3D perovskite structure, and a mixture of compounds resulting from degradation. Finally, we demonstrate how understanding the processing parameters provides the foundation needed for optimal perovskite film morphology and coverage, leading to enhanced block copolymer-directed perovskite solar cell performance.

  11. Thermally Induced Structural Evolution and Performance of Mesoporous Block Copolymer-Directed Alumina Perovskite Solar Cells

    Science.gov (United States)

    2015-01-01

    Structure control in solution-processed hybrid perovskites is crucial to design and fabricate highly efficient solar cells. Here, we utilize in situ grazing incidence wide-angle X-ray scattering and scanning electron microscopy to investigate the structural evolution and film morphologies of methylammonium lead tri-iodide/chloride (CH3NH3PbI3–xClx) in mesoporous block copolymer derived alumina superstructures during thermal annealing. We show the CH3NH3PbI3–xClx material evolution to be characterized by three distinct structures: a crystalline precursor structure not described previously, a 3D perovskite structure, and a mixture of compounds resulting from degradation. Finally, we demonstrate how understanding the processing parameters provides the foundation needed for optimal perovskite film morphology and coverage, leading to enhanced block copolymer-directed perovskite solar cell performance. PMID:24684494

  12. Thermally induced structural evolution and performance of mesoporous block copolymer-directed alumina perovskite solar cells.

    KAUST Repository

    Tan, Kwan Wee

    2014-04-11

    Structure control in solution-processed hybrid perovskites is crucial to design and fabricate highly efficient solar cells. Here, we utilize in situ grazing incidence wide-angle X-ray scattering and scanning electron microscopy to investigate the structural evolution and film morphologies of methylammonium lead tri-iodide/chloride (CH3NH3PbI(3-x)Cl(x)) in mesoporous block copolymer derived alumina superstructures during thermal annealing. We show the CH3NH3PbI(3-x)Cl(x) material evolution to be characterized by three distinct structures: a crystalline precursor structure not described previously, a 3D perovskite structure, and a mixture of compounds resulting from degradation. Finally, we demonstrate how understanding the processing parameters provides the foundation needed for optimal perovskite film morphology and coverage, leading to enhanced block copolymer-directed perovskite solar cell performance.

  13. Formation Mechanism and Binding Energy for Body-Centered Cubic Structure of He+9 Cluster

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jian-Ping; GOU Qing-Quan; LI Ping

    2004-01-01

    The formation mechanism for the body-centered cubic structure of He+9 cluster is proposed and its total energy curve is calculated by the method of a Modified Arrangement Channel Quantum Mechanics. The energy is the function of separation R between the nuclei at the center and an apex of the body-centered cubic structure. The result of the calculation shows that the curve has a minimal energy -25.6669 (a.u.) at R = 2.550ao. The binding energy of He+9 with respect to He+ + 8He was calculated to be 0.8857 a.u. This means that the cluster of He+9 may be formed in the body-centered cubic structure of R = 2.55a0.

  14. Structure and Growth Control of Organic–Inorganic Halide Perovskites for Optoelectronics: From Polycrystalline Films to Single Crystals

    Science.gov (United States)

    Chen, Yani; He, Minhong; Peng, Jiajun; Sun, Yong

    2016-01-01

    Recently, organic–inorganic halide perovskites have sparked tremendous research interest because of their ground‐breaking photovoltaic performance. The crystallization process and crystal shape of perovskites have striking impacts on their optoelectronic properties. Polycrystalline films and single crystals are two main forms of perovskites. Currently, perovskite thin films have been under intensive investigation while studies of perovskite single crystals are just in their infancy. This review article is concentrated upon the control of perovskite structures and growth, which are intimately correlated for improvements of not only solar cells but also light‐emitting diodes, lasers, and photodetectors. We begin with the survey of the film formation process of perovskites including deposition methods and morphological optimization avenues. Strategies such as the use of additives, thermal annealing, solvent annealing, atmospheric control, and solvent engineering have been successfully employed to yield high‐quality perovskite films. Next, we turn to summarize the shape evolution of perovskites single crystals from three‐dimensional large sized single crystals, two‐dimensional nanoplates, one‐dimensional nanowires, to zero‐dimensional quantum dots. Siginificant functions of perovskites single crystals are highlighted, which benefit fundamental studies of intrinsic photophysics. Then, the growth mechanisms of the previously mentioned perovskite crystals are unveiled. Lastly, perspectives for structure and growth control of perovskites are outlined towards high‐performance (opto)electronic devices.

  15. Structure and Growth Control of Organic-Inorganic Halide Perovskites for Optoelectronics: From Polycrystalline Films to Single Crystals.

    Science.gov (United States)

    Chen, Yani; He, Minhong; Peng, Jiajun; Sun, Yong; Liang, Ziqi

    2016-04-01

    Recently, organic-inorganic halide perovskites have sparked tremendous research interest because of their ground-breaking photovoltaic performance. The crystallization process and crystal shape of perovskites have striking impacts on their optoelectronic properties. Polycrystalline films and single crystals are two main forms of perovskites. Currently, perovskite thin films have been under intensive investigation while studies of perovskite single crystals are just in their infancy. This review article is concentrated upon the control of perovskite structures and growth, which are intimately correlated for improvements of not only solar cells but also light-emitting diodes, lasers, and photodetectors. We begin with the survey of the film formation process of perovskites including deposition methods and morphological optimization avenues. Strategies such as the use of additives, thermal annealing, solvent annealing, atmospheric control, and solvent engineering have been successfully employed to yield high-quality perovskite films. Next, we turn to summarize the shape evolution of perovskites single crystals from three-dimensional large sized single crystals, two-dimensional nanoplates, one-dimensional nanowires, to zero-dimensional quantum dots. Siginificant functions of perovskites single crystals are highlighted, which benefit fundamental studies of intrinsic photophysics. Then, the growth mechanisms of the previously mentioned perovskite crystals are unveiled. Lastly, perspectives for structure and growth control of perovskites are outlined towards high-performance (opto)electronic devices.

  16. A kinetic study of the decomposition of the cubic perovskite-type oxide Ba(x)Sr(1-x)Co(0.8)Fe(0.2)O(3-delta) (BSCF) (x = 0.1 and 0.5).

    Science.gov (United States)

    Mueller, David N; De Souza, Roger A; Weirich, Thomas E; Roehrens, Daniel; Mayer, Joachim; Martin, Manfred

    2010-09-21

    The decomposition of the cubic perovskite-type oxide Ba(x)Sr(1-x)Co(0.8)Fe(0.2)O(3-delta) (BSCF) into hexagonal and cubic perovskite-type phases has been examined by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) and X-Ray Diffraction (XRD). SEM and TEM measurements reveal that the new hexagonal phase grows predominantly at the grain boundaries of BSCF ceramics and that the cation composition of the newly formed hexagonal phase differs from that of the starting material. An orientational relationship between the hexagonal and the parent cubic phase was also observed. By means of ex situ XRD the phase fraction of the hexagonal phase was determined as a function of annealing time. A kinetic analysis of the data, based on Avrami-type kinetics, indicates that the decomposition is independent of the initial A-site composition, and the obtained reaction order supports the conclusion that the hexagonal phase grows at the grain boundaries in dense ceramic samples.

  17. Isolation of mitochondria with cubic membrane morphology reveals specific ionic requirements for the preservation of membrane structure.

    Science.gov (United States)

    Chong, Ketpin; Tan, Olivia Li Ling; Almsherqi, Zakaria A; Lin, Qingsong; Kohlwein, Sepp D; Deng, Yuru

    2015-03-01

    Biological membranes with cubic symmetry are a hallmark of virus-infected or diseased cells. The mechanisms of formation and specific cellular functions of cubic membranes, however, are unclear. The best-documented cubic membrane formation occurs in the free-living giant amoeba Chaos carolinense. In that system, mitochondrial inner membranes undergo a reversible structural change from tubular to cubic membrane organization upon starvation of the organism. As a prerequisite to further analyze the structural and functional features of cubic membranes, we adapted protocols for the isolation of mitochondria from starved amoeba and have identified buffer conditions that preserve cubic membrane morphology in vitro. The requirement for high concentration of ion-chelating agents in the isolation media supports the importance of a balanced ion milieu in establishing and maintaining cubic membranes in vivo.

  18. Bandgap Engineering of Double Perovskites for One- and Two-photon Water Splitting

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

    2013-01-01

    Computational screening is becoming increasingly useful in the search for new materials. We are interested in the design of new semiconductors to be used for light harvesting in a photoelectrochemical cell. In the present paper, we study the double perovskite structures obtained by combining 46...... stable cubic perovskites which was found to have a finite bandgap in a previous screening-study. The four-metal double perovskite space is too large to be investigated completely. For this reason we propose a method for combining different metals to obtain a desired bandgap. We derive some bandgap design...... rules on how to combine two cubic perovskites to generate a new combination with a larger or smaller bandgap compared with the constituent structures. Those rules are based on the type of orbitals involved in the conduction bands and on the size of the two cubic bandgaps. We also see that a change...

  19. Structural Characterization of Cubic GaN Grown on GaAs(001) Substrates

    Institute of Scientific and Technical Information of China (English)

    ZHENG Xinhe; QU Bo; WANG Yutian; YANG Hui; LIANGJunwu; HAN Jingyi

    2001-01-01

    Structural characteristics of cubic GaN epilayers grown on GaAs(001) were studied using X-ray double-crystal diffraction technique. The structure factors of cubic GaN(002) and (004) components are approximately identical. However, the integrated intensities of the rocking curve for cubic (002) components are over five times as those of (004)components. The discrepancy has been interpreted in detail considering other factors. In the conventional double crystal rocking curve, the peak broadening includes such information caused by the orientation distribution (mosaicity) and the distribution of lattice spacing. These two kinds of distributions can be distinguished by the triple-axis diffraction in which an analyzer crystal is placed in front of the detector.Moreover, the peak broadening was analyzed by reciprocal lattice construction and Eward sphere. By using triple-axis diffraction of cubic (002) and (113)components, domain size and dislocation density were estimated. The fully relaxed lattice parameter of cubic GaN was determined to be about 0.451 ± 0.001nm.

  20. Structural and Quantitative Investigation of Perovskite Pore Filling in Mesoporous Metal Oxides

    Directory of Open Access Journals (Sweden)

    Shany Gamliel

    2016-11-01

    Full Text Available In recent years, hybrid organic–inorganic perovskite light absorbers have attracted much attention in the field of solar cells due to their optoelectronic characteristics that enable high power conversion efficiencies. Perovskite-based solar cells’ efficiency has increased dramatically from 3.8% to more than 20% in just a few years, making them a promising low-cost alternative for photovoltaic applications. The deposition of perovskite into a mesoporous metal oxide is an influential factor affecting solar cell performance. Full coverage and pore filling into the porous metal oxide are important issues in the fabrication of highly-efficient mesoporous perovskite solar cells. In this work, we carry out a structural and quantitative investigation of CH3NH3PbI3 pore filling deposited via sequential two-step deposition into two different mesoporous metal oxides—TiO2 and Al2O3. We avoid using a hole conductor in the perovskite solar cells studied in this work to eliminate undesirable end results. Filling oxide pores with perovskite was characterized by Energy Dispersive X-ray Spectroscopy (EDS in Transmission Electron Microscopy (TEM on cross-sectional focused ion beam (FIB lamellae. Complete pore filling of CH3NH3PbI3 perovskite into the metal oxide pores was observed down to X-depth, showing the presence of Pb and I inside the pores. The observations reported in this work are particularly important for mesoporous Al2O3 perovskite solar cells, as pore filling is essential for the operation of this solar cell structure. This work presents structural and quantitative proof of complete pore filling into mesoporous perovskite-based solar cells, substantiating their high power conversion efficiency.

  1. Manganites in Perovskite Superlattices: Structural and Electronic Properties

    KAUST Repository

    Jilili, Jiwuer

    2016-07-13

    Perovskite oxides have the general chemical formula ABO3, where A is a rare-earth or alkali-metal cation and B is a transition metal cation. Perovskite oxides can be formed with a variety of constituent elements and exhibit a wide range of properties ranging from insulators, metals to even superconductors. With the development of growth and characterization techniques, more information on their physical and chemical properties has been revealed, which diversified their technological applications. Perovskite manganites are widely investigated compounds due to the discovery of the colossal magnetoresistance effect in 1994. They have a broad range of structural, electronic, magnetic properties and potential device applications in sensors and spintronics. There is not only the technological importance but also the need to understand the fundamental mechanisms of the unusual magnetic and transport properties that drive enormous attention. Manganites combined with other perovskite oxides are gaining interest due to novel properties especially at the interface, such as interfacial ferromagnetism, exchange bias, interfacial conductivity. Doped manganites exhibit diverse electrical properties as compared to the parent compounds. For instance, hole doped La0.7Sr0.3MnO3 is a ferromagnetic metal, whereas LaMnO3 is an antiferromagnetic insulator. Since manganites are strongly correlated systems, heterojunctions composed of manganites and other perovskite oxides are sunject to complex coupling of the spin, orbit, charge, and lattice degrees of freedom and exhibit unique electronic, magnetic, and transport properties. Electronic reconstructions, O defects, doping, intersite disorder, magnetic proximity, magnetic exchange, and polar catastrophe are some effects to explain these interfacial phenomena. In our work we use first-principles calculations to study the structural, electronic, and magnetic properties of manganite based superlattices. Firstly, we investigate the electronic

  2. A first principles study of Nd doped cubic LaAlO3 perovskite: mBJ+U study

    Science.gov (United States)

    Sandeep; Rai, D. P.; Shankar, A.; Ghimire, M. P.; Khenata, R.; Thapa, R. K.

    2016-11-01

    The structural, electronic and magnetic properties of Nd-doped Rare earth aluminate, La1-xNdxAlO3 (x=0-100%) are studied using the full potential linearized augmented plane-wave (FP-LAPW) method within the density functional theory. The effects of Nd substitution in LaAlO3 are studied using super-cell calculations. The electronic structures were computed using modified Beck Johnson (mBJ) potential based approximation with the inclusion of Coulomb energy (U) for Nd-4f state electrons. The La1-xNdxAlO3 may possess half metallic behavior on Nd doping with finite density of states at EF. The direct and indirect band gaps were studied as a function of Nd concentration in LaAlO3. The calculated magnetic moments in La1-xNdxAlO3 were found to arise mainly from the Nd-4f state electrons. A probable half-metallic nature is suggested for these systems with supportive integral magnetic moments and high spin polarized electronic structures in these doped cases at EF. The controlled decrease in band gap with increase in concentration of Nd doping is a suitable technique for harnessing useful spintronic and magnetic devices.

  3. On structural transitions in a discontinuous micellar cubic phase loaded with sodium diclofenac.

    Science.gov (United States)

    Efrat, R; Aserin, A; Garti, N

    2008-05-01

    An intermediate mesophase of lyotropic liquid crystalline structure from the ternary mixtures of glycerol monooleate, water, and ethanol was recently characterized in our lab. This mesophase, termed Q(L), consists of discrete discontinuous micelles arranged in a cubic array. The Q(L) phase can solubilize very significant loads of water-insoluble anti-inflamatory drug sodium diclofenac (Na-DFC). Close examination of the internal structures of the lyotropic liquid structure upon increasing the solubilization loads reveals the existence of three structural transitions controlled by the Na-DFC levels. Up to 0.4 wt% Na-DFC, the Q(L) structure remains intact with some influence on the hydration of the headgroups and on the intermicellar forces. However, at 0.8 to 1.2 wt% Na-DFC, the discontinuous micellar cubic phase is transformed into a more condensed mesophase of a bicontinuous cubic phase. At > or =1.2 wt% Na-DFC, the cubic phase is converted into a lamellar phase (L(alpha)). Within 5.5 to 7.3 wt% Na-DFC the mesophase is progressively transformed into a less ordered lamellar structure. At 12 wt% Na-DFC crystals tend to precipitate out. At low Na-DFC concentrations the drug behaves like a lyotropic or kosmotropic salt and can salt-out the surfactant from its water layer, but at higher levels it behaves like a hydrotropic, chaotropic salt and can salt-in the surfactant. The Na-DFC location and position within the interface as well as its polarization and partial ionization are strongly affected by its solubilization contents and the structure that it is inducing. In the cubic phase the drug is located less close to the hydration layer while once transition occurs it is exposed more to the water layer and the surfactant headgroups.

  4. Efficiency Enhancement of Inverted Structure Perovskite Solar Cells via Oleamide Doping of PCBM Electron Transport Layer.

    Science.gov (United States)

    Xia, Fei; Wu, Qiliang; Zhou, Pengcheng; Li, Yi; Chen, Xiang; Liu, Qing; Zhu, Jun; Dai, Songyuan; Lu, Yalin; Yang, Shangfeng

    2015-06-24

    An amphiphilic surfactant, oleamide, was applied to dope the PCBM electron transport layer (ETL) of inverted structure perovskite solar cells (ISPSCs), resulting in a dramatic efficiency enhancement. Under the optimized oleamide doping ratio of 5.0 wt %, the power conversion efficiency of the CH3NH3PbIxCl(3-x) perovskite-based ISPSC device is enhanced from 10.05% to 12.69%, and this is primarily due to the increases of both fill factor and short-circuit current. According to the surface morphology study of the perovskite/PCBM bilayer film, oleamide doping improves the coverage of PCBM ETL onto the perovskite layer, and this is beneficial for the interfacial contact between the perovskite layer and the Ag cathode and consequently the electron transport from perovskite to the Ag cathode. Such an improved electron transport induced by oleamide doping is further evidenced by the impedance spectroscopic study, revealing the prohibited electron-hole recombination at the interface between the perovskite layer and the Ag cathode.

  5. Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

    Science.gov (United States)

    Olthof, Selina; Meerholz, Klaus

    2017-01-01

    We present investigations on the interface formation between the hybrid perovskite MAPbI3 and various substrates, covering a wide range of work functions. The perovskite films are incrementally evaporated in situ while the electronic structure is evaluated using photoelectron spectroscopy. Our results show that there is an induction period in the growth of the perovskite during which volatile compounds are formed, catalyzed by the substrate. The duration of the induction period depends strongly on the nature of the substrate material, and it can take up to 20–30 nm of formal precursor deposition before the surface is passivated and the perovskite film starts forming. The stoichiometry of the 2–3 nm thin passivation layer deviates from the expected perovskite stoichiometry, being rich in decomposition products of the organic cation. During the regular growth of the perovskite, our measurements show a deviation from the commonly assumed flat band condition, i.e., dipole formation and band bending dominate the interface. Overall, the nature of the substrate not only changes the energetic alignment of the perovskite, it can introduce gap states and influence the film formation and morphology. The possible impact on device performance is discussed.

  6. Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

    Science.gov (United States)

    Olthof, Selina; Meerholz, Klaus

    2017-01-01

    We present investigations on the interface formation between the hybrid perovskite MAPbI3 and various substrates, covering a wide range of work functions. The perovskite films are incrementally evaporated in situ while the electronic structure is evaluated using photoelectron spectroscopy. Our results show that there is an induction period in the growth of the perovskite during which volatile compounds are formed, catalyzed by the substrate. The duration of the induction period depends strongly on the nature of the substrate material, and it can take up to 20–30 nm of formal precursor deposition before the surface is passivated and the perovskite film starts forming. The stoichiometry of the 2–3 nm thin passivation layer deviates from the expected perovskite stoichiometry, being rich in decomposition products of the organic cation. During the regular growth of the perovskite, our measurements show a deviation from the commonly assumed flat band condition, i.e., dipole formation and band bending dominate the interface. Overall, the nature of the substrate not only changes the energetic alignment of the perovskite, it can introduce gap states and influence the film formation and morphology. The possible impact on device performance is discussed. PMID:28084313

  7. A note on the prolongation structure of the cubically nonlinear integrable Camassa-Holm type equation

    Energy Technology Data Exchange (ETDEWEB)

    Stalin, S. [Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu (India); Senthilvelan, M., E-mail: velan@cnld.bdu.ac.in [Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu (India)

    2011-10-17

    In this Letter, we formulate an exterior differential system for the newly discovered cubically nonlinear integrable Camassa-Holm type equation. From the exterior differential system we establish the integrability of this equation. We then study Cartan prolongation structure of this equation. We also discuss the method of identifying conservation laws and Baecklund transformation for this equation from the identified exterior differential system. -- Highlights: → An exterior differential system for a cubic nonlinear integrable equation is given. → The conservation laws from the exterior differential system is derived. → The Baecklund transformation from the Cartan-Ehresmann connection is obtained.

  8. The structure model of a cubic aperiodic phase ('quasicrystal without forbidden symmetry axes').

    Science.gov (United States)

    Kraposhin, V S; Talis, A L; Thanh Lam, Ha

    2008-03-19

    A model structure of the aperiodic cubic phase (a cubic quasicrystal) has been constructed as a periodical packing of hierarchical octahedral clusters which were composed of truncated tetrahedra (Friauf-Laves polyhedra) and chains of Frank-Kasper polyhedra with 14 vertices. The construction of the hierarchical model for the cubic aperiodic phase became possible due to the discovery of a new space subdivision with equal edges and with vertices belonging to two orbits of the space group Fm3m. The subdivision is characterized by unique values and unique relations between the coordinates of the starting points of two orbits. Calculated x-ray diffraction patterns for the proposed hierarchical model are in qualitative agreement with published experimental x-ray patterns for aperiodical phases observed in melt-quenched Mg-Al and Fe-Nb-B-Si alloys.

  9. A first principles study of Nd doped cubic LaAlO{sub 3} perovskite: mBJ+U study

    Energy Technology Data Exchange (ETDEWEB)

    Sandeep, E-mail: sndp.chettri@gmail.com [Dept. of Physics, Mizoram University, Aizawl 796004 (India); Rai, D.P. [Dept. of Physics, Pachhunga University College, Aizawl, Mizoram 796001 (India); Shankar, A. [Department of Physics, University of North Bengal, Darjeeling 734013 (India); Ghimire, M.P. [Condensed Matter Physics Research Center, Butwal-13, Rupandehi, Lumbini (Nepal); Khenata, R. [Laboratoire de Physique Quantique et de Modlisation Mathmatique (LPQ3M), Dpartement de Technologie, Universit de Mascara, 29000 Mascara (Algeria); Thapa, R.K. [Dept. of Physics, Mizoram University, Aizawl 796004 (India)

    2016-11-01

    The structural, electronic and magnetic properties of Nd-doped Rare earth aluminate, La{sub 1−x}Nd{sub x}AlO{sub 3} (x=0–100%) are studied using the full potential linearized augmented plane-wave (FP-LAPW) method within the density functional theory. The effects of Nd substitution in LaAlO{sub 3} are studied using super-cell calculations. The electronic structures were computed using modified Beck Johnson (mBJ) potential based approximation with the inclusion of Coulomb energy (U) for Nd-4f state electrons. The La{sub 1−x}Nd{sub x}AlO{sub 3} may possess half metallic behavior on Nd doping with finite density of states at E{sub F}. The direct and indirect band gaps were studied as a function of Nd concentration in LaAlO{sub 3}. The calculated magnetic moments in La{sub 1−x}Nd{sub x}AlO{sub 3} were found to arise mainly from the Nd-4f state electrons. A probable half-metallic nature is suggested for these systems with supportive integral magnetic moments and high spin polarized electronic structures in these doped cases at E{sub F}. The controlled decrease in band gap with increase in concentration of Nd doping is a suitable technique for harnessing useful spintronic and magnetic devices. - Highlights: • Electronic and magnetic properties of La{sub 1−x}Nd{sub x}AlO{sub 3} to study the effect of doping (x=0%, 25%, 50%, 75% and 100%) is carried out using DFT. • Theoretically calculated U was used in the mBJ+U approximation in order to stress accuracy in band-gap determination along with electron correlation effects in rare earth ions. • A high DOS at E{sub F} for certain doping concentrations in one spin channel with insulting DOS in the other channel supported their probable use as spintronic devices. • The change in doping concentration was found suitable for rare earth aluminates for desirable properties through band-gap tuning.

  10. Crystallographic and Electronic Structure of the Sr3Sb2CoO9 Triple Perovskite

    Science.gov (United States)

    González, W.; Cardona, R.; Landínez Téllez, D. A.; Roa-Rojas, J.

    2014-04-01

    Compounds The perovskites are materials with physical and chemical characteristics that make them optimal for application in the technological and scientist. When the ideal formula of perovskite ABO3 is modified by introducing a special structural arrangement can get to get triple perovskites, which correspond to the formula A3B2B'O9. In this work we report the synthesis process and the study of electronic structure and crystal Sr3Sb2CoO9 new triple perovskite. From the experiments of X-ray Diffraction and the application of the Rietveld refinement method was revealed that the system crystallizes in a perovskite structure with a characteristic triple given by the space group Immm (#71) and lattice parameters a=9.791(9) Å, b=5.656(7) Å and c=16.957(8) Å. Ab initio calculations of density of states (DOS) and electronic structure were carried out for this perovskite-like system by using the Quantum EXPRESSO code. The exchange-correlation potential was treated using the Generalized Gradient Approximation (GGA). All calculations were carried-out using spin polarization. ©2013 Elsevier Science. All rights reserved.

  11. Coordination Chemistry Dictates the Structural Defects in Lead Halide Perovskites.

    Science.gov (United States)

    Rahimnejad, Sara; Kovalenko, Alexander; Forés, Sergio Martí; Aranda, Clara; Guerrero, Antonio

    2016-09-19

    We show the influence of species present in precursor solution during formation of lead halide perovskite materials on the structural defects of the films. The coordination of lead by competing solvent molecules and iodide ions dictate the type of complexes present in the films. Depending on the processing conditions all PbIS5 (+) , PbI2 S4, PbI3 S3 (-) , PbI4 S2 (2-) , PbI5 S2 (3-) , PbI6 (4-) and 1D (Pb2 I4 )n chains are observed by absorption measurements. Different parameters are studied such as polarity of the solvent, concentration of iodide ions, concentration of solvent molecules and temperature. It is concluded that strongly coordinating solvents will preferentially form species with a low number of iodide ions and less coordinative solvents generate high concentration of PbI6 (-) . We furthermore propose that all these plumbate ions may act as structural defects determining electronic properties of the photovoltaic films.

  12. Applications of Cubic MgZnO Thin Films in Metal-Insulator-Silicon Structures

    Institute of Scientific and Technical Information of China (English)

    LIANG Jun; WU Hui-Zhen; LAO Yan-Feng; QIU Dong-Jiang; CHEN Nai-Bo; XU Tian-Ning

    2004-01-01

    @@ Cubic Mgo.55Zno.45O thin film alloys have been deposited on Si substrates at low growth temperature. The topography of the cross section of the epitaxial film by scanning electronic microscope demonstrates good mor phology and high interfacial quality. The high (001) orientation and wide band-gap (Eg > 5.5 eV) of the cubic Mgo.55Zno.45 O thin films accord with the guidelines for metal-insulator-silicon (MIS) device applications. Using the cubic ternary thin films as insulators, MIS structures have been fabricated. The capacitance-voltage measurements show the flat band voltage shift VFB of11.8 V and mobile ion density Dmc of 5.57 × 1010 cm-2 for the MIS structure. Leakage current density as low as ~ 10-7 A/cm2 is obtained at E = 700 kV/cm by the currentvoltage measurements. These unique structural and electrical properties of the fabricated MIS devices indicate that cubic MgZnO materials could become a new candidate for high-κ dielectrics used in silicon integrated circuit technologies.

  13. Crystal structure, electronic and magnetic properties of double perovskite Ba2FeWO6: A combined experimental-theoretical study

    Science.gov (United States)

    Saad, H.-E, M. Musa; Rammeh, N.

    2016-01-01

    Double perovskite oxide Ba2FeWO6 has been synthesized in polycrystalline form by the solid-state ceramic method at 950 °C. Structural characterization was performed by using the X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) followed by Rietveld analysis of these patterns. The crystal structure of Ba2FeWO6 is cubic; space group Fm-3m with lattice parameter of a=8.1351 Å. Also, a density functional theory (DFT) study of the crystal structure, electronic and magnetic properties of Ba2FeWO6 has been carried out using full potential linear muffin-tin orbital (FP-LMTO). We showed that the obtained symmetry lattice parameter agree well with the experimental results. The influence of Fe element on the magnetic and electronic properties of double perovskite oxide Ba2FeWO6 is analyzed. Band structure calculations for cubic Ba2FeWO6 predict an energy-gap in both spin-up and spin-down. The semiconductor antiferromagnetic (AFM) phase is stabilized by the hybridization of nonmagnetic W6+ (5d°) site positioned in between the magnetic Fe2+ (3d6) sites through the O2- anions in a long range O-Fe-O-W-O arrangement. 57Fe Mössbaur spectrum and DFT calculations suggest that the AFM behavior arises since the mixed valence Fe2+-Fe3+ effect introduces in Fe2+-O2--W6+ anticoupling.

  14. Structure constraints and instability leading to the post-perovskite phase transition of MgSiO 3

    Science.gov (United States)

    Martin, C. David; Parise, John B.

    2008-01-01

    Recent experience with Rietveld refinement of structural analogues and literature surveys, suggests anion-anion repulsion limits the stability of the perovskite phase, including in the MgSiO 3 perovskite to post-perovskite transition. Assuming rigid octahedral coordination, still to be tested experimentally, the critical point where intra- and inter-octahedral anion-anion distances are equal provides a useful metric for predicting the pressure of the perovskite/post-perovskite transition and the Clapeyron slope of the phase boundary, once pressure and temperature derivatives of relevant structure parameters are known. The inter-octahedral anion-anion distances and the polyhedral volume ratio are rigorously formulated as a function of octahedral rotation in this work, assuming the orthorhombic ( Pbnm) perovskite structure, where regular octahedra share each corner and conform to the in- and anti-phase rotation schemes designated by space group symmetry. These mathematical expressions are consistent with structure data from 70 perovskite-structured materials surveyed in the literature at ambient as well as extreme conditions and define structure constraints, such as the minimum polyhedral volume ratio, which must be reached before the phase transition to the post-perovskite structure-type can proceed. The formalism we present is general for perovskite ( Pbnm) and dependent on the accuracy with which structures can be determined from, sometimes compromised, high pressure diffraction data.

  15. Structure and antibacterial activity of new layered perovskite compounds

    Institute of Scientific and Technical Information of China (English)

    TAN Shao-zao; ZHANG Li-ling; XIA Liao-yuan; LIU Ying-liang; LI Du-xin

    2007-01-01

    New layered perovskite compounds, AgxNa2-xLa2Ti3O10 (x=0.2, 0.3 and 0.5) were synthesized by an ion-exchange reaction of Na2La2Ti3O10 with AgNO3 solution and characterized by energy dispersive X-ray analysis(EDX), X-ray diffractometry(XRD), scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). The ion-exchange processes were optimized, and the antibacterial activity, light permanency and water-resistance were evaluated. Surprisedly, no significant changes in crystal structure of Na2La2Ti3O10 are found by the exchange of silver ions. The Ag0.3Na1.7La2Ti3O10 particles conglomerate obviously with irregular shape and size. Ag0.3Na1.7La2Ti3O10, possessing the minimum inhibitory concentrations(MICs) against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) of 180 mg/L and 240 mg/L, has high antibacterial activity, good light permanency and water-resistance. The ionic state silver in AgxNa2-xLa2Ti3O10 is the antibacterial active component.

  16. Electronic Structure of New Superconducting Perovskite MgCNi3

    Institute of Scientific and Technical Information of China (English)

    Li CHEN; Hua LI; Liangmo MEI

    2004-01-01

    The electronic structures of new superconducting perovskite MgCNis and related compounds MgCNi2T (T=Co, Fe,and Cu) have been studied using MS-Xα method. In MgCNi3, the main peak of density of states is located below the Fermi level and dominated by Ni d. From the results of total energy calculations, it was found that the number of Ni valence electron decreases faster for the Fe-doped case than that for the Co-doped case. The valence state of Ni changes from +1.43 in MgCNi2Co to +3.02 in MgCNi2Fe. It was confirmed that Co and Fe dopants in MgCNi3 behave as a source of d-band holes and the suppression of superconductivity occurs faster for the Fe-doped case than that for the Co-doped case. In order to explain the fact that Co and Fe dopants in MgCNi3 behave as a source of d-band holes rather than magnetic scattering centers that quench superconductivity, we have also investigated the effects of electron (Cu) doping on the superconductivity and found that both electron (Cu) doping and hole (Co, Fe)doping quench superconductivity exist. Comparing with the hole (Co) doping, there was no much difference between Cu and Co doping. This suggests that Co and Fe doping do not actas magnetic impurity.

  17. Perovskite-supported palladium for methane oxidation - structure-activity relationships.

    Science.gov (United States)

    Eyssler, Arnim; Lu, Ye; Matam, Santhosh Kumar; Weidenkaff, Anke; Ferri, Davide

    2012-01-01

    Palladium is the precious metal of choice for methane oxidation and perovskite-type oxides offer the possibility to stabilize it as PdO, considered crucial for catalytic activity. Pd can adopt different oxidation and coordination states when associated with perovskite-type oxides. Here, we review our work on the effect of perovskite composition on the oxidation and coordination states of Pd and its influence on catalytic activity for methane oxidation in the case of typical Mn, Fe and Co perovskite-based oxidation catalysts. Especially X-ray absorption near edge structure (XANES) spectroscopy is shown to be crucial to fingerprint the different coordination states of Pd. Pd substitutes Fe and Co in the octahedral sites but without modifying catalytic activity with respect to the Pd-free perovskite. On LaMnO(3) palladium is predominantly exposed at the surface thus bestowing catalytic activity for methane oxidation. However, the occupancy of B-cation sites of the perovskite structure by Pd can be exploited to cyclically activate Pd and to protect it from particle growth. This is explicitly demonstrated for La(Fe, Pd)O(3), where catalytic activity for methane oxidation is enhanced under oscillating redox conditions at 500 °C, therefore paving the way to the practical application in three-way catalysts for stoichiometric natural gas engines.

  18. Structural and electronic properties of cubic KNbO{sub 3} (0 0 1) surfaces: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Bingcheng [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Wang, Xiaohui, E-mail: wxh@mail.tsinghua.edu.cn [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Tian, Enke [School of Science, China University of Geosciences, Beijing 100083 (China); Li, Guowu [Crystal Structure Laboratory, National Laboratory of Mineral Materials, China University of Geosciences, Beijing 100083 (China); Li, Longtu [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)

    2015-10-01

    Highlights: • To the best of our knowledge, the (0 0 1) surfaces of SrTiO{sub 3}, BaTiO{sub 3}, CaTiO{sub 3} and PbTiO{sub 3} have been extensively investigated, but few ab initio calculations of structural and electronic properties of cubic KNbO{sub 3} (0 0 1) surface are reported. • The surface energy for the KO terminated was 1.21 eV, higher than the calculated surface energy of 0.75 eV for NbO{sub 2} termination, revealing that it take much less energy to cleave on the NbO{sub 2} plane than on the KO plane. • Mulliken population showed a strong increase in the K−O chemical bonding on the top surface of the KO-terminated slab, while the Nb−O chemical bonding on the top surface of the NbO{sub 2}-terminated slab decreased by 50 me. • The bond populations for K−O were much smaller than that for Nb−O, indicating significant covalency for Nb−O bonding. - Abstract: We present the calculations of the cubic perovskite KNbO{sub 3} (0 0 1) surface with NbO{sub 2} and KO terminations within the first-principles density functional theory. The electronic structure, surface energy, and charge distribution for both termination are calculated. For the case of NbO{sub 2}-terminated surfaces, the largest atomic relaxation is in the first-layer atoms, while for KO terminations in the second-layer atoms. The surface energy for the KO terminated was 1.21 eV, higher than the calculated surface energy of 0.75 eV for NbO{sub 2} termination, revealing that it takes much less energy to cleave on NbO{sub 2} plane than on a KO plane. The band gaps for KO-terminated and NbO{sub 2}-terminated surface are 1.70 and 1.30 eV, respectively. Mulliken population analysis shows the strong increase in the K−O chemical bonding on the top surface of the KO-terminated slab and significant covalency for Nb−O bonding.

  19. Factors controlling the oxide ion conductivity of fluorite and perovskite structured oxides

    DEFF Research Database (Denmark)

    Mogensen, Mogens Bjerg; Lybye, D.; Bonanos, N.

    2004-01-01

    for the oxide ion movement, (2) free lattice volume, and (3) average metal-oxide bond energy have been proposed as predictors of high oxide ion conductivity. We discuss how these parameters all depend on ionic radii, and therefore, some of these may be redundant. Furthermore, we explore the interrelations among...... such parameters for fluorite and perovskite oxides by considering their sensitivities to the individual ionic radii. Based on experimental data available in the literature, it is argued that lattice distortion (lattice stress and deviation from cubic symmetry) due to ion radii mismatch determines the ionic...

  20. Observation of Nanoscale Morphological and Structural Degradation in Perovskite Solar Cells by in Situ TEM.

    Science.gov (United States)

    Yang, Bin; Dyck, Ondrej; Ming, Wenmei; Du, Mao-Hua; Das, Sanjib; Rouleau, Christopher M; Duscher, Gerd; Geohegan, David B; Xiao, Kai

    2016-11-30

    High-resolution in situ transmission electron microscopy (TEM) and electron energy loss spectroscopy were applied to systematically investigate morphological and structural degradation behaviors in perovskite films during different environmental exposure treatments. In situ TEM experiment indicates that vacuum itself is not likely to cause degradation in perovskites. In addition, these materials were found to degrade significantly when they were heated to ∼50-60 °C (i.e., a solar cell's field operating temperature) under illumination. This observation thus conveys a critically important message that the instability of perovskite solar cells at such a low temperature may limit their real field commercial applications. It was further unveiled that oxygen most likely attacks the CH3NH3(+) organic moiety rather than the PbI6 component of perovskites during ambient air exposure at room temperature. This finding grants a deeper understanding of the perovskite degradation mechanism and suggests a way to prevent degradation of perovskites by tailoring the organic moiety component.

  1. Crystal Structure of Calcium Silicate Perovskite Synthesized under Water Saturated Conditions at Mantle Related Pressure-Temperature

    Science.gov (United States)

    Chen, H.; Shim, S. H. D.; Leinenweber, K. D.; Meng, Y.; Prakapenka, V.

    2014-12-01

    Perovskite-structured CaSiO3 (Ca-Pv) is the third most abundant mineral in the lower mantle. However, its crystal structure is still under debate and the solubility of H2O in Ca-Pv is not well constrained. We have conducted in situ X-ray diffraction measurements on Ca-Pv under H2O saturated conditions in the laser-heated diamond-anvil cell at the GSECARS and HPCAT sectors of the Advanced Photon Source. Glass starting materials were mixed with platinum powder (10 wt%) for laser coupling and internal pressure scale. Cold compressed foils of the mixtures were loaded in the diamond-anvil cell together with Ne or water. The X-ray diffraction patterns of the Ca-Pv sample synthesized in a Ne medium are consistent with a cubic perovskite structure at both 300 K and high temperatures up to 2,400 K at 50 GPa. No clear peak splittings were observed within the resolution of the angle-dispersive powder diffraction technique. However, in the experiments with water, clear splitting of the 200 diffraction line appears during heating to temperatures over 2000 K and remain after temperature quench at 32 GPa. The peak splittings were clearly observed at high temperatures to 2400 K, which is close to the melting point of water at the pressure. The different structural behaviors of Ca-Pv depending on media (Ne and water) may suggest that OH might enter into the crystal structure of nominally anhydrous Ca-Pv phase at high pressure and high temperature.

  2. Recent Advances in the Inverted Planar Structure of Perovskite Solar Cells.

    Science.gov (United States)

    Meng, Lei; You, Jingbi; Guo, Tzung-Fang; Yang, Yang

    2016-01-19

    Inorganic-organic hybrid perovskite solar cells research could be traced back to 2009, and initially showed 3.8% efficiency. After 6 years of efforts, the efficiency has been pushed to 20.1%. The pace of development was much faster than that of any type of solar cell technology. In addition to high efficiency, the device fabrication is a low-cost solution process. Due to these advantages, a large number of scientists have been immersed into this promising area. In the past 6 years, much of the research on perovskite solar cells has been focused on planar and mesoporous device structures employing an n-type TiO2 layer as the bottom electron transport layer. These architectures have achieved champion device efficiencies. However, they still possess unwanted features. Mesoporous structures require a high temperature (>450 °C) sintering process for the TiO2 scaffold, which will increase the cost and also not be compatible with flexible substrates. While the planar structures based on TiO2 (regular structure) usually suffer from a large degree of J-V hysteresis. Recently, another emerging structure, referred to as an "inverted" planar device structure (i.e., p-i-n), uses p-type and n-type materials as bottom and top charge transport layers, respectively. This structure derived from organic solar cells, and the charge transport layers used in organic photovoltaics were successfully transferred into perovskite solar cells. The p-i-n structure of perovskite solar cells has shown efficiencies as high as 18%, lower temperature processing, flexibility, and, furthermore, negligible J-V hysteresis effects. In this Account, we will provide a comprehensive comparison of the mesoporous and planar structures, and also the regular and inverted of planar structures. Later, we will focus the discussion on the development of the inverted planar structure of perovskite solar cells, including film growth, band alignment, stability, and hysteresis. In the film growth part, several

  3. Structure and Luminescence Properties of Eu3+-Doped Cubic Mesoporous Silica Thin Films

    Directory of Open Access Journals (Sweden)

    Lu Qingshan

    2010-01-01

    Full Text Available Abstract Eu3+ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol–gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu3+ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of5D0-7F1 and 5D0-7F2 of Eu3+ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu3+ ions-doped mesoporous silica thin films increases linearly with increasing Eu3+ concentration.

  4. Structure and luminescence properties of eu3+-doped cubic mesoporous silica thin films.

    Science.gov (United States)

    Lu, Qingshan; Wang, Zhongying; Wang, Peiyu; Li, Jiangong

    2010-02-11

    Eu3+ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol-gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu3+ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of5D0-7F1 and 5D0-7F2 of Eu3+ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu3+ ions-doped mesoporous silica thin films increases linearly with increasing Eu3+ concentration.

  5. Mixed structural face-centered cubic and body-centered cubic orders in near stoichiometric Fe2MnGa alloys

    Science.gov (United States)

    Kudryavtsev, Y. V.; Perekos, A. E.; Uvarov, N. V.; Kolchiba, M. R.; Synoradzki, K.; Dubowik, J.

    2016-05-01

    Magnetic and transport properties of near stoichiometric metastable FexMnyGaz alloys (46 ≤ x ≤ 52, 17 ≤ y ≤ 25, 26 ≤ z ≤ 30) with face-centered cubic (FCC), body-centered cubic (BCC), and two-phase (FCC + BCC) structures are investigated. The experimental results are analyzed in terms of first-principles calculations of stoichiometric Fe2MnGa alloy with the L21, L12, and the tetragonally distorted L21 structural orderings. It is shown that the pure BCC and FCC phases have distinct magnetic and transport properties. Two-phase Fe2MnGa alloys have magnetic and transport properties typical of the mixed BCC and FCC phases. Among the investigated alloys, Fe46Mn24Ga30 has a martensitic transformation accompanied with significant changes of its magnetic and transport properties.

  6. A Monolithic Perovskite Structure for Use as a Magnetic Regenerator

    DEFF Research Database (Denmark)

    Pryds, Nini; Clemens, Frank; Menon, Mohan

    2011-01-01

    A La0.67Ca0.26Sr0.07Mn1.05O3 (LCSM) perovskite was prepared for the first time as a ceramic monolithic regenerator used in a regenerative magnetic refrigeration device. The parameters influencing the extrusion process and the performance of the regenerator, such as the nature of the monolith paste...

  7. Perovskite solid electrolytes: Structure, transport properties and fuel cell applications

    DEFF Research Database (Denmark)

    Bonanos, N.; Knight, K.S.; Ellis, B.

    1995-01-01

    Doped barium cerate perovskites, first investigated by Iwahara and co-workers, have ionic conductivities of the order of 20 mS/cm at 800 degrees C making them attractive as fuel cell electrolytes for this temperature region. They have been used to construct laboratory scale fuel cells, which...

  8. Oxidation of Membrane Curvature-Regulating Phosphatidylethanolamine Lipid Results in Formation of Bilayer and Cubic Structures.

    Science.gov (United States)

    Sankhagowit, Shalene; Lee, Ernest Y; Wong, Gerard C L; Malmstadt, Noah

    2016-03-15

    Oxidation is associated with conditions related to chronic inflammations and aging. Cubic structures have been observed in the smooth endoplasmic reticulum and mitochondrial membranes of cells under oxidative stress (e.g., tumor cells and virus-infected cells). It has been previously suspected that oxidation can result in the rearrangement of lipids from a fluid lamellar phase to a cubic structure in organelles containing membranes enriched with amphiphiles that have nonzero intrinsic curvature, such as phosphatidylethanolamine (PE) and cardiolipin. This study focuses on the oxidation of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), a lipid that natively forms an inverted hexagonal phase at physiological conditions. The oxidized samples contain an approximately 3:2 molar ratio of nonoxidized to oxidized DOPE. Optical microscopy images collected during the hydration of this mixture from a dried film suggest that the system evolves into a coexistence of a stable fluid lamellar phase and transient square lattice structures with unit cell sizes of 500-600 nm. Small-angle X-ray scattering of the same lipid mixture yielded a body-centered Im3m cubic phase with the lattice parameter of 14.04 nm. On average, the effective packing parameter of the oxidized DOPE species was estimated to be 0.657 ± 0.069 (standard deviation). This suggests that the oxidation of PE leads to a group of species with inverted molecular intrinsic curvature. Oxidation can create amphiphilic subpopulations that potently impact the integrity of the membrane, since negative Gaussian curvature intrinsic to cubic phases can enable membrane destabilization processes.

  9. Ab-Initio Calculation of Electronic Structure of Lead Halide Perovskites with Formamidinium Cation as an Active Material for Perovskite Solar Cells

    Science.gov (United States)

    Indari, E. D.; Wungu, T. D. K.; Hidayat, R.

    2017-07-01

    Organic lead halide perovskite material based solar cells show impressive power conversion efficiencies, which can reach above 19 percent for perovskite solar cell with methyl-ammonium cations. These efficiencies are originated from efficient photoexcitation and charge carrier transport and not observed in conventional perovskite crystals. In this preliminary research work, we therefore performed Density Functional Theory (DFT) calculation of formamidinium lead iodide (FAPI), an alternative to methyl-ammonium lead iodide (MAPI), to predict their electronic structure and density of state (DOS). The calculation result at the most stable lattice parameters show a good agreement with the experiment results. The obtained band gap energy is 1.307 eV. The valence band is dominantly formed by the 5p orbitals of I- anions, while the conduction band is dominantly formed by the 6p orbitals of Pb2+ cations. The DOS of valence band of this perovskite seems smaller compared to the case of methyl-ammonium lead iodide perovskite, which then may explain the observation of smaller power conversion efficiencies in perovskite solar cells with this formamidinium cations.

  10. Magnetic properties of cubic FeCo nanoparticles with anisotropic long chain structure

    Science.gov (United States)

    Liu, Jinming; Wu, Kai; Wang, Jian-Ping

    2016-05-01

    Cubic FeCo alloy nanoparticles (NPs) with body-centered cubic (bcc) phase were prepared using sputter based gas-condensation method. When the NPs formed long chain assemblies, the magnetic properties were quite different from that of well-dispersed NPs. Most of the well-dispersed NPs were superparamagnetic at room temperature while the long chain NP assemblies were ferromagnetic with coercivities around 765 Oe, which displayed quite different magnetic properties. The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM) to superferromagetism (SFM). Zero-field-cooled (ZFC) and field-cooled (FC) curves were obtained and long chain NP assemblies displayed ferromagnetism at the temperature ranging from 10 K to 400 K. Time-dependent remanent magnetic moment curves also indicated that the long chain structure had better thermal stability due to the strong exchange coupling.

  11. Magnetic properties of cubic FeCo nanoparticles with anisotropic long chain structure

    Directory of Open Access Journals (Sweden)

    Jinming Liu

    2016-05-01

    Full Text Available Cubic FeCo alloy nanoparticles (NPs with body-centered cubic (bcc phase were prepared using sputter based gas-condensation method. When the NPs formed long chain assemblies, the magnetic properties were quite different from that of well-dispersed NPs. Most of the well-dispersed NPs were superparamagnetic at room temperature while the long chain NP assemblies were ferromagnetic with coercivities around 765 Oe, which displayed quite different magnetic properties. The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM to superferromagetism (SFM. Zero-field-cooled (ZFC and field-cooled (FC curves were obtained and long chain NP assemblies displayed ferromagnetism at the temperature ranging from 10 K to 400 K. Time-dependent remanent magnetic moment curves also indicated that the long chain structure had better thermal stability due to the strong exchange coupling.

  12. Main-Group Halide Semiconductors Derived from Perovskite: Distinguishing Chemical, Structural, and Electronic Aspects.

    Science.gov (United States)

    Fabini, Douglas H; Labram, John G; Lehner, Anna J; Bechtel, Jonathon S; Evans, Hayden A; Van der Ven, Anton; Wudl, Fred; Chabinyc, Michael L; Seshadri, Ram

    2017-01-03

    Main-group halide perovskites have generated much excitement of late because of their remarkable optoelectronic properties, ease of preparation, and abundant constituent elements, but these curious and promising materials differ in important respects from traditional semiconductors. The distinguishing chemical, structural, and electronic features of these materials present the key to understanding the origins of the optoelectronic performance of the well-studied hybrid organic-inorganic lead halides and provide a starting point for the design and preparation of new functional materials. Here we review and discuss these distinguishing features, among them a defect-tolerant electronic structure, proximal lattice instabilities, labile defect migration, and, in the case of hybrid perovskites, disordered molecular cations. Additionally, we discuss the preparation and characterization of some alternatives to the lead halide perovskites, including lead-free bismuth halides and hybrid materials with optically and electronically active organic constituents.

  13. Cubic AlGaN/GaN structures for device application

    Energy Technology Data Exchange (ETDEWEB)

    Schoermann, Joerg

    2007-05-15

    The aim of this work was the growth and the characterization of cubic GaN, cubic AlGaN/GaN heterostructures and cubic AlN/GaN superlattice structures. Reduction of the surface and interface roughness was the key issue to show the potential for the use of cubic nitrides in futur devices. All structures were grown by plasma assisted molecular beam epitaxy on free standing 3C-SiC (001) substrates. In situ reflection high energy electron diffraction was first investigated to determine the Ga coverage of c-GaN during growth. Using the intensity of the electron beam as a probe, optimum growth conditions were found when a 1 monolayer coverage is formed at the surface. GaN samples grown under these conditions reveal excellent structural properties. On top of the c-GaN buffer c-AlGaN/GaN single and multiple quantum wells were deposited. The well widths ranged from 2.5 to 7.5 nm. During growth of Al{sub 0.15}Ga{sub 0.85}N/GaN quantum wells clear reflection high energy electron diffraction oscillations were observed indicating a two dimensional growth mode. We observed strong room-temperature, ultraviolet photoluminescence at about 3.3 eV with a minimum linewidth of 90 meV. The peak energy of the emission versus well width is reproduced by a square-well Poisson- Schroedinger model calculation. We found that piezoelectric effects are absent in c-III nitrides with a (001) growth direction. Intersubband transition in the wavelength range from 1.6 {mu}m to 2.1 {mu}m was systematically investigated in AlN/GaN superlattices (SL), grown on 100 nm thick c-GaN buffer layers. The SLs consisted of 20 periods of GaN wells with a thickness between 1.5 nm and 2.1 nm and AlN barriers with a thickness of 1.35 nm. The first intersubband transitions were observed in metastable cubic III nitride structures in the range between 1.6 {mu}m and 2.1 {mu}m. (orig.)

  14. Oxidation Potential, Not Crystal Structure, Controls the Oxidation State of Iron in Perovskite

    Science.gov (United States)

    Panero, W. R.; Pigott, J. S.; Watson, H. C.; Scharenberg, M.; Green, H. W.; McComb, D. W.; Williams, R. E.

    2013-12-01

    The mantle's oxidation state has broad implications on the state and evolution of the earth's interior. The relatively high oxidation potential of the upper mantle is such that iron is predominantly Fe2+ with small amounts of Fe3+ . Fe3+ is more stable than Fe2+ in the dominant lower mantle mineral, perovskite, despite the fact that the effect of pressure is to reduce the oxidizing potential of a system. It is therefore suggested that iron undergoes a disproportionation reaction of 3Fe2+ =2Fe3+ +Fe0 , controlled by the crystallography instead of oxidation potential. We crystallized synthetic enstatite glass with 5% Al2O3, 14% FeO, and 3% Fe2O3 in the laser-heated diamond anvil cell at 25-63 GPa and 1700-2800 K. We find that for temperatures nm iron precipitates on grain boundaries. The precipitates have small amounts of dissolved oxygen, but are Mg- and Al- free. We interpret that the stishovite is forming due to the oxidation of the ferric iron to ferrous iron according to (Mg2+,Al3+)(Fe3+,Si4+)O3 +SiO2 + Fe0 while the lower-temperature samples crystallizing as approximately (Mg2+ Fe2+ Al3+ )(Fe3+ Al3+ Si4+ )O3. We observe 2.8(2) Å3 volume expansion of the perovskite and a 28(2) GPa decrease in compressibility of the perovskite relative to the perovskite forming at lower temperature, consistent with the proposed compositions of the perovskites. As the increased temperature increases the oxidation potential of the system, we suggest that the oxidation state of iron in perovskite is dependent on oxidation potential as opposed to perovskite's crystal structure. Transmission Electron Microscopy (TEM) coupled with Electron Energy Loss Spectroscopy (EELS) show iron precipitation on grain boundaries supporting the conclusion. We present a discussion of the results and implications for core formation and lower mantle dynamics.

  15. Crystal Structure Formation of CH3NH3PbI3-xClx Perovskite

    Directory of Open Access Journals (Sweden)

    Shiqiang Luo

    2016-02-01

    Full Text Available Inorganic-organic hydride perovskites bring the hope for fabricating low-cost and large-scale solar cells. At the beginning of the research, two open questions were raised: the hysteresis effect and the role of chloride. The presence of chloride significantly improves the crystallization and charge transfer property of the perovskite. However, though the long held debate over of the existence of chloride in the perovskite seems to have now come to a conclusion, no prior work has been carried out focusing on the role of chloride on the electronic performance and the crystallization of the perovskite. Furthermore, current reports on the crystal structure of the perovskite are rather confusing. This article analyzes the role of chloride in CH3NH3PbI3-xClx on the crystal orientation and provides a new explanation about the (110-oriented growth of CH3NH3PbI3 and CH3NH3PbI3-xClx.

  16. Luminescence of lead-containing tungstates with perovskite structure

    NARCIS (Netherlands)

    Bleijenberg, K.C.; Blasse, G.

    1975-01-01

    The luminescence of perovskites with formula Sr1-xPbxLaLiWO6 and Ba2-xPbxMgWO6 is reported. The lower-energy emission in the lead-containing compounds is ascribed to a transition within a centre consisting of a tungstate octahedron with lead-ion neighbours. The presence of Bi3+ is SrLaLiWO6 causes a

  17. Luminescence of lead-containing tungstates with perovskite structure

    NARCIS (Netherlands)

    Bleijenberg, K.C.; Blasse, G.

    1975-01-01

    The luminescence of perovskites with formula Sr1-xPbxLaLiWO6 and Ba2-xPbxMgWO6 is reported. The lower-energy emission in the lead-containing compounds is ascribed to a transition within a centre consisting of a tungstate octahedron with lead-ion neighbours. The presence of Bi3+ is SrLaLiWO6 causes a

  18. Strain engineering on structures and properties in ferroelectric thin films with perovskite structures

    Directory of Open Access Journals (Sweden)

    TANG Yanxue

    2015-08-01

    Full Text Available Ferroelectric thin films possess ferroelectric,piezoelectric,pyroelectric and photovoltaic properties,which have bright prospect for transducers,actuators,sensors,energy harvesting and solar cells.The properties of ferroelectric films are closely related to their strain due to films constrained by substrates.Therefore,the key to improve the properties of ferroelectric films is how to use substrates to regulate and control their strain,and then regulate their polarized state.This paper review the research progress of regulating the properties of ferroelectric films with perovskite structure by strain engineering and the problems needed to be resolved.

  19. Structural, optical, and electronic studies of wide-bandgap lead halide perovskites

    KAUST Repository

    Comin, Riccardo

    2015-01-01

    © The Royal Society of Chemistry 2015. We investigate the family of mixed Br/Cl organolead halide perovskites which enable light emission in the blue-violet region of the visible spectrum. We report the structural, optical and electronic properties of this air-stable family of perovskites, demonstrating full bandgap tunability in the 400-550 nm range and enhanced exciton strength upon Cl substitution. We complement this study by tracking the evolution of the band levels across the gap, thereby providing a foundational framework for future optoelectronic applications of these materials.

  20. Lanthanum Influence on EuAlO3 Perovskite Structural Properties: Experimental and Molecular Dynamics Studies

    Directory of Open Access Journals (Sweden)

    Enrique Lima

    2012-01-01

    Full Text Available X-ray diffraction, 27Al MAS NMR, and FTIR spectra along with results of molecular dynamics simulations were used to characterise LaxEu1−xAlO3 perovskites for x=0.3,  0.1. Experimental and simulation results show that local changes in the perovskite-like structure can be achieved as lanthanum ions substitute europium ones. The introduction of La3+ ions in the EuAlO3 parent causes an increase in the mobility of oxygen network.

  1. Significant light absorption improvement in perovskite/CIGS tandem solar cells with dielectric nanocone structures

    Science.gov (United States)

    Wang, Huahua; Cai, Boyuan; Yuan, Xiaocong

    2017-06-01

    Here, we propose a novel perovskite/CIGS tandem solar cell geometry with tailored dielectric nanocone structure incorporated on the top surface for light manipulation. Absorption enhancement as high as 15.39% has been achieved both in the top and bottom subcells, leading to a 14.29% thickness reduction of the bottom subcell.

  2. Domain-dependent electronic structure and optical absorption property in hybrid organic-inorganic perovskite.

    Science.gov (United States)

    Meng, Xiang; Zhang, Ruifeng; Fu, Zhongheng; Zhang, Qianfan

    2016-10-05

    Hybrid organic-inorganic perovskites, represented by materials in the CH3NH3PbI3 series, have become one of the most promising materials for solar cells with a high power conversion efficiency and low cost. The ordered Pb-I cage in such hybrid perovskites can induce the polarized cations to form a variety of polarization domains with long-range order, which will lead to the formation of specific atomic conformations or metastable crystalline phases, unique electronic band structures and optical absorption properties. Such domain-dependent characteristics play a critical role in the phase transition and service stability of such solar cells, and also open up the opportunity of tuning their electronic structure. In the present study, we systematically investigate the band structures and optical absorption properties of different electronically ordered domains in CH3NH3PbI3. By comparing different perovskites containing various cations, we have clarified the important influence of cation polarization on domain-dependent properties. Our results provide not only a possible pathway for the manipulation of band structure by applying an external field, but also a novel scheme for improving the performance and stability of hybrid perovskites.

  3. Energy transfer between octahedral tungstate and uranate groups in oxides with perovskite structure

    NARCIS (Netherlands)

    Steen, A.C. van der; Hair, J.Th.W. de; Blasse, G.

    1975-01-01

    Energy transfer between tungstate and uranate groups in oxides with perovskite structure is reported. The critical distance for this process is about 25 Å. Evidence is given for energy transfer between tungstate groups. In this case the critical distance is estimated to be about 8 Å.

  4. Reduced thermal conductivity by nanoscale intergrowths in perovskite like layered structure La2Ti2O

    NARCIS (Netherlands)

    Khaliq, J.; Li, C.; Chen, K.; Shi, B.; Ye, H.; Grande, A.M.; Yan, H.; Reece, M.J.

    2015-01-01

    The effect of substitution and oxidation-reduction on the thermal conductivity of perovskite-like layered structure (PLS) ceramics was investigated in relation to mass contrast and non-stoichiometry. Sr (acceptor) was substituted on the A site, while Ta (donor) was substituted on the B site of La2Ti

  5. Energy transfer between octahedral tungstate and uranate groups in oxides with perovskite structure

    NARCIS (Netherlands)

    Steen, A.C. van der; Hair, J.Th.W. de; Blasse, G.

    1975-01-01

    Energy transfer between tungstate and uranate groups in oxides with perovskite structure is reported. The critical distance for this process is about 25 Å. Evidence is given for energy transfer between tungstate groups. In this case the critical distance is estimated to be about 8 Å.

  6. Impedance spectroscopy and structural properties of the perovskite-like Sn(Ba,Sr)O{sub 3} stagnate

    Energy Technology Data Exchange (ETDEWEB)

    Cuervo Farfan, J. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 5997, Bogota DC (Colombia); Ciencias Basicas, Universidad Manuela Beltran, Bogota DC (Colombia); Olaya, J.J. [Departamento de Ingenieria Mecanica y Mecatronica, Universidad Nacional de Colombia, Bogota DC (Colombia); Vera Lopez, E. [Grupo de Superficies, Electroquimica y Corrosion, Universidad Pedagogica y Tecnologica de Colombia, Tunja (Colombia); Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 5997, Bogota DC (Colombia); Roa-Rojas, J., E-mail: jroar@unal.edu.co [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 5997, Bogota DC (Colombia)

    2012-08-15

    An exhaustive study of structural, electrical and transport properties on the perovskite stagnate Sn(Ba,Sr)O{sub 3} was performed. Samples of SnBa{sub 1-x}Sr{sub x}O{sub 3} with 0{<=}x{<=}1.00 were prepared by the solid state reaction method. The crystallographic structure was studied by X-ray diffraction experiments and Rietveld refinement using the GSAS code. Results reveal the material synthesized in a cubic structure (space group Pm3-bar m, no. 221) for 0{<=}x{<=}0.50 and in an orthorhombic (space group Pnma, no. 62) for x>0.50. The approximate grain size was found from experiments' Scanning Electron Microscopy. The electric response was studied by the Impedance Spectroscopy technique from 10.0 mHz up to 0,10 MHz. Electric polarization measurements for SnSrO{sub 3} and SnBaO{sub 3} were determined through curves of polarization as a function of applied electric field, which reveal the ferroelectric character of the material. From the saturation polarization the dielectric constants of materials were calculated.

  7. Phase stability, electronic structure and equation of state of cubic TcN from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Song, T., E-mail: songting_lzjtu@yeah.net [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Ma, Q. [School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Sun, X.W., E-mail: xsun@carnegiescience.edu [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Liu, Z.J., E-mail: liuzj_lzcu@163.com [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Department of Physics, Lanzhou City University, Lanzhou 730070 (China); Fu, Z.J. [School of Electrical and Electronic Engineering, Chongqing University of Arts and Sciences, Chongqing 402160 (China); Wei, X.P.; Wang, T.; Tian, J.H. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China)

    2016-09-07

    The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.

  8. Size dependence of cubic to trigonal structural distortion in silver micro- and nanocrystals under high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Qixum [Los Alamos National Laboratory; Zhao, Yusheng [Los Alamos National Laboratory; Zin, Zhijun [Los Alamos National Laboratory; Wang, Zhongwu [CORNELL UNIV; Skrabalak, Sara E [INDIANA UNIV; Xia, Younan [WASHINGTON UNIV

    2008-01-01

    Silver micro- and nanocrystals with sizes of {approx}2--3.5 {mu}m and {approx}50--100 nm were uniaxially compressed under nonhydrostatic pressures (strong deviatoric stress) up to {approx}30 GPa at room temperature in a symmetric diamond-anvil cell and studied in situ using angle-dispersive synchrotron X-ray diffraction. A cubic to trigonal structural distortion along a 3-fold rotational axis was discovered by careful and comprehensive analysis of the apparent lattice parameter and full width at half-maximum, which are strongly dependent upon the Miller index and crystal size.

  9. Structural characterization of a new vacancy ordered perovskite modification found for Ba{sub 3}Fe{sub 3}O{sub 7}F (BaFeO{sub 2.333}F{sub 0.333}): Towards understanding of vacancy ordering for different perovskite-type ferrites

    Energy Technology Data Exchange (ETDEWEB)

    Clemens, Oliver, E-mail: oliver.clemens@kit.edu [Technische Universität Darmstadt, Joint Research Laboratory Nanomaterials, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2015-05-15

    The new vacancy ordered perovskite-type compound Ba{sub 3}Fe{sub 3}O{sub 7}F (BaFeO{sub 2.33}F{sub 0.33}) was prepared by topochemical low-temperature fluorination of Ba{sub 2}Fe{sub 2}O{sub 5} (BaFeO{sub 2.5}) using stoichiometric amounts of polyvinylidene difluoride (PVDF). The vacancy order was found to be unique so far for perovskite compounds, and the connectivity pattern can be explained by the formula Ba{sub 3}(FeX{sub 6/2}) (FeX{sub 5/2}) (FeX{sub 3/2}X{sub 1/1}), with X=O/F. Mössbauer measurements were used to confirm the structural analysis and agree with the presence of Fe{sup 3+} in the above mentioned coordination environments. Group–subgroup relationships were used to build a starting model for the structure solution and to understand the relationship to the cubic perovskite structure. Furthermore, a comparison of a variety of vacancy-ordered iron-containing perovskite-type structures is given, highlighting the factors which favour one structure type over the other depending on the composition. - Graphical abstract: The crystal structure of Ba{sub 3}Fe{sub 3}O{sub 7}F in comparison to other perovskite type ferrites. - Highlights: • The crystal structure of Ba{sub 3}Fe{sub 3}O{sub 7}F in comparison to other perovskite type ferrites. • Ba{sub 3}Fe{sub 3}O{sub 7}F was synthesized by low temperature fluorination of Ba{sub 2}Fe{sub 2}O{sub 5}. • Ba{sub 3}Fe{sub 3}O{sub 7}F shows a unique vacancy order not found for other perovskite type compounds. • The structure of Ba{sub 3}Fe{sub 3}O{sub 7}F was solved using group–subgroup relationships. • A systematic comparison to other ferrite type compounds reveals structural similarities and differences. • The A-site coordination of the cation is shown to play an important role for the type of vacancy order found.

  10. Superior solid solubility of MnSiO3 in CaSiO3 perovskite

    Science.gov (United States)

    Li, Lin; Nagai, Takaya; Seto, Yusuke; Fujino, Kiyoshi; Kawano, Jun; Itoh, Shoich

    2015-02-01

    The silicate perovskite phase relation between CaSiO3 and MnSiO3 was investigated at 35-52 GPa and at 1,800 K using laser-heated diamond anvil cells combined with angle-dispersive synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopic chemical analyses with scanning or transmission electron microscopy. We found that MnSiO3 can be incorporated into CaSiO3 perovskite up to 55, and 20 mol % of CaSiO3 is soluble in MnSiO3 perovskite. The range of 55-80 mol % of MnSiO3 in the CaSiO3-MnSiO3 perovskite system could be immiscible. We also observed that the two perovskite structured phases of the Mn-bearing CaSiO3 and the Ca-bearing MnSiO3 coexisted at these conditions. The Mn-bearing CaSiO3 perovskite has non-cubic symmetry and the Ca-bearing MnSiO3 perovskite has an orthorhombic structure with space group Pbnm. All the perovskite structured phases in the CaSiO3-MnSiO3 system convert to the amorphous phase during pressure release. MnSiO3 is the first chemical component confirmed to show such a superior solid solubility in CaSiO3 perovskite.

  11. Crystal structures, thermal expansion and phase transitions of mixed Pr{sub 1-x}La{sub x}AlO{sub 3} perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Basyuk, Tetyana; Vasylechko, Leonid [Lviv Polytechnic National University (Ukraine); Syvorotka, Igor [SRC, Carat, Lviv (Ukraine); Schmidt, Ulrike [Max-Planck-Institut fuer Chemische Physik Fester Stoffe, Dresden (Germany); Trots, Dmytro [HASYLAB, DESY, Hamburg (Germany); Niewa, Rainer [Technische Universitaet Muenchen, Garching (Germany)

    2009-05-15

    The crystal structures, thermal expansion and phase transitions of mixed Pr{sub 1-x}La{sub x}AlO{sub 3} perovskites have been examined by using an in situ high resolution X-ray powder diffraction technique applying synchrotron radiation in a wide temperature range of 12-1173 K. At room temperature all samples in the PrAlO{sub 3}-LaAlO{sub 3} pseudo-binary system adopt the rhombohedral perovskite-like structure. At elevated temperatures, all Pr{sub 1-x}La{sub x}AlO{sub 3}compositions undergo continuous phase transitions from rhombohedral to cubic structures. The sequence of the low-temperature (LT) phase transformations R anti 3 c<->Imma<->C2/m has been observed in Pr{sub 1-x}La{sub x}AlO{sub 3} samples. Temperatures of HT and LT phase transitions in Pr{sub 1-x}La{sub x}AlO{sub 3}decrease with decreasing Pr content. Crystal structure parameters for all compositions Pr{sub 1-x}La{sub x}AlO{sub 3} have been determined. Based on in situ powder diffraction and DTA/DSC data, the phase diagram of the PrAlO{sub 3}-LaAlO{sub 3}pseudo-binary system has been constructed. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Structural and optoelectronic properties of the zinc titanate perovskite and spinel by modified Becke–Johnson potential

    Energy Technology Data Exchange (ETDEWEB)

    Ali, Zahid, E-mail: zahidf82@gmail.com [Materials Modeling Center, Department of Physics, University of Malakand, Chakdara (Pakistan); Ali, Sajad [Materials Modeling Center, Department of Physics, University of Malakand, Chakdara (Pakistan); Department of Physics, Abdul Wali Khan University, Mardan (Pakistan); Ahmad, Iftikhar; Khan, Imad [Materials Modeling Center, Department of Physics, University of Malakand, Chakdara (Pakistan); Rahnamaye Aliabad, H.A. [Department of Physics, Hakim Savzevari University, Sabzevar (Iran, Islamic Republic of)

    2013-07-01

    Structural and electronic properties of the cubic perovskite ZnTiO{sub 3} and spinel Zn{sub 2}TiO{sub 4} are theoretically studied by the modified Becke–Johnson (mBJ) potential within the framework of density functional theory (DFT). The calculated lattice constants are found to be consistent with the experimental results. The electronic band structures of both the materials reveal that ZnTiO{sub 3} is an indirect band gap while Zn{sub 2}TiO{sub 4} is a direct band gap semiconductor. The calculated fundamental band gaps of these compounds are 2.7 eV and 3.18 eV, which are consistent with the experimental band gaps of 2.9 eV and 3.1 eV, respectively. Zn{sub 2}TiO{sub 4} is a wide and direct band gap compound and hence is an attractive material for optoelectronic applications, especially in near ultraviolet (UV) optoelectronics. Keeping in view the importance of Zn{sub 2}TiO{sub 4} in low frequency UV devices its optical properties like dielectric functions, refractive index, reflectivity and energy loss function are also evaluated and discussed in detail.

  13. Effects of Bi doping on structural and magnetic properties of double perovskite oxides Sr2FeMoO6

    Science.gov (United States)

    Lan, Yaohai; Feng, Xiaomei; Zhang, Xin; Shen, Yifu; Wang, Ding

    2016-08-01

    A new series of double perovskite compounds Sr2 - δBixFeMoO6 have been synthesized by solid-state reaction. δ refers to the nominal doping content of Bi (δ = 0, 0.1, 0.2, 0.3, 0.4, 0.5), while the Bi content obtained by the Rietveld refinement is x = 0, 0.01, 0.05, 0.08, 0.10 and 0.12. Their crystal structure and magnetic properties are investigated. Rietveld analysis of the room temperature XRD data shows all the samples crystallize in the cubic crystal structure with the space group Fm 3 ‾ m and have no phase transition. SEM images show that substituted samples present a denser microstructure and bigger grains than Sr2FeMoO6, which is caused by a liquid sintering process due to the effumability of Bi. The unit cell volume increases with augment of Bi3+ concentration despite the smaller ionic radius Bi3+ compared with the Sr2+, which is attributed to the electronic effect. The degree of Fe/Mo order (η) increases first and then decreases to almost disappearance with augment of Bi doping, which is the result of contribution from electronic effect. Calculated saturation magnetization Ms(3) according to our phase separation likeness model matches well with the experimental ones. The observed variations of magnetoresistance (MR) are consistent with the Fe/Mo order (η) due to the internal connection with anti-site defect (ASD).

  14. Effect of Structure, Temperature, and Metal Work Function on Performance of Organometallic Perovskite Solar Cells

    Science.gov (United States)

    Hossain, M. I.; Aïssa, B.

    2017-01-01

    The impact of hole transport materials (HTMs) on the performance of methylammonium lead halide (CH3NH3PbI3)-based perovskite solar cells has been investigated using computational analysis. The main objective is to replace the HTM with the aim of enhancing the lifetime and decreasing the overall cost of the device. As the CH3NH3PbI3 absorber layer shows an absorption coefficient as high as 105/cm, all photons with incident energy larger the material bandgap are absorbed within only a 400-nm-thick layer. Also, all the electronic and optical properties of such an absorber layer are suitable for use in photovoltaic (PV) devices. Hence, the effects of the HTM thickness, operating temperature, incident light spectrum, and metal electrode work function on the charge collection were studied numerically. For a cell with Cu2O as HTM, efficiency exceeding 25% is predicted for a 350-nm-thick absorber layer. Also, a fully optimized device architecture without HTM shows the possibility of fabricating a perovskite solar cell with PV efficiency exceeding 15%. We expect considerable minimization of the energy loss in this structure due to charge transfer across the heterojunction. Moreover, the effect of temperature on perovskite solar cells and potential electrodes with different work functions has been investigated. Our results are believed to help open an experimental avenue to achieve optimum results for perovskite solar cells with various structures.

  15. Effect of Structure, Temperature, and Metal Work Function on Performance of Organometallic Perovskite Solar Cells

    Science.gov (United States)

    Hossain, M. I.; Aïssa, B.

    2017-03-01

    The impact of hole transport materials (HTMs) on the performance of methylammonium lead halide (CH3NH3PbI3)-based perovskite solar cells has been investigated using computational analysis. The main objective is to replace the HTM with the aim of enhancing the lifetime and decreasing the overall cost of the device. As the CH3NH3PbI3 absorber layer shows an absorption coefficient as high as 105/cm, all photons with incident energy larger the material bandgap are absorbed within only a 400-nm-thick layer. Also, all the electronic and optical properties of such an absorber layer are suitable for use in photovoltaic (PV) devices. Hence, the effects of the HTM thickness, operating temperature, incident light spectrum, and metal electrode work function on the charge collection were studied numerically. For a cell with Cu2O as HTM, efficiency exceeding 25% is predicted for a 350-nm-thick absorber layer. Also, a fully optimized device architecture without HTM shows the possibility of fabricating a perovskite solar cell with PV efficiency exceeding 15%. We expect considerable minimization of the energy loss in this structure due to charge transfer across the heterojunction. Moreover, the effect of temperature on perovskite solar cells and potential electrodes with different work functions has been investigated. Our results are believed to help open an experimental avenue to achieve optimum results for perovskite solar cells with various structures.

  16. Structural and chemical reactivity modifications of a cobalt perovskite induced by Sr-substitution. An in situ XAS study

    Energy Technology Data Exchange (ETDEWEB)

    Hueso, Jose L.; Holgado, Juan P.; Pereñíguez, Rosa; Gonzalez-DelaCruz, V.M.; Caballero, Alfonso, E-mail: caballero@us.es

    2015-02-01

    LaCoO{sub 3} and La{sub 0.5}Sr{sub 0.5}CoO{sub 3−δ} perovskites have been studied by in situ Co K-edge XAS. Although the partial substitution of La(III) by Sr(II) species induces an important increase in the catalytic oxidation activity and modifies the electronic state of the perovskite, no changes could be detected in the oxidation state of cobalt atoms. So, maintaining the electroneutrality of the perovskite requires the generation of oxygen vacancies in the network. The presence of these vacancies explains that the substituted perovskite is now much more reducible than the original LaCoO{sub 3} perovskite. As detected by in situ XAS, after a consecutive reduction and oxidation treatment, the original crystalline structure of the LaCoO{sub 3} perovskite is maintained, although in a more disordered state, which is not the case for the Sr doped perovskite. So, the La{sub 0.5}Sr{sub 0.5}CoO{sub 3−δ} perovskite submitted to the same hydrogen reduction treatment produces metallic cobalt, while as determined by in situ XAS spectroscopy the subsequent oxidation treatment yields a Co(III) oxide phase with spinel structure. Surprisingly, no Co(II) species are detected in this new spinel phase. - Highlights: • A Sr-substituted lanthanum cobalt perovskite has been prepared by spray pyrolysis. • It has been established that Co(III) cations are present in both perovskites. • LaCoO{sub 3} is a less reducible phase than the substituted La{sub 0.5}Sr{sub 0.5}CoO{sub 3−δ}. • After reoxidation of reduced La{sub 0.5}Sr{sub 0.5}CoO{sub 3−δ}, a 100% Co(III) spinel is obtained.

  17. Crystal structure, electronic and magnetic properties of double perovskite Ba{sub 2}FeWO{sub 6}: A combined experimental–theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Musa Saad, H.-E., E-mail: musa.1964@gmail.com [Department of Physics, College of Science, Qassim University, P.O. 4466, Buraidah 51452 (Saudi Arabia); Rammeh, N. [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B. P. 95, Hammam-Lif 2050 (Tunisia)

    2016-01-15

    Double perovskite oxide Ba{sub 2}FeWO{sub 6} has been synthesized in polycrystalline form by the solid-state ceramic method at 950 °C. Structural characterization was performed by using the X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) followed by Rietveld analysis of these patterns. The crystal structure of Ba{sub 2}FeWO{sub 6} is cubic; space group Fm-3m with lattice parameter of a=8.1351 Å. Also, a density functional theory (DFT) study of the crystal structure, electronic and magnetic properties of Ba{sub 2}FeWO{sub 6} has been carried out using full potential linear muffin-tin orbital (FP-LMTO). We showed that the obtained symmetry lattice parameter agree well with the experimental results. The influence of Fe element on the magnetic and electronic properties of double perovskite oxide Ba{sub 2}FeWO{sub 6} is analyzed. Band structure calculations for cubic Ba{sub 2}FeWO{sub 6} predict an energy-gap in both spin-up and spin-down. The semiconductor antiferromagnetic (AFM) phase is stabilized by the hybridization of nonmagnetic W{sup 6+} (5d°) site positioned in between the magnetic Fe{sup 2+} (3d{sup 6}) sites through the O{sup 2−} anions in a long range O–Fe–O–W–O arrangement. {sup 57}Fe Mössbaur spectrum and DFT calculations suggest that the AFM behavior arises since the mixed valence Fe{sup 2+}–Fe{sup 3+} effect introduces in Fe{sup 2+}–O{sup 2–}–W{sup 6+} anticoupling.

  18. Crystal structure of new Li + ion conducting perovskites: Li 2 xCa 0.5- xTaO 3 and Li 0.2[Ca 1- ySr y] 0.4TaO 3

    Science.gov (United States)

    Pham, Quoc Nghi; Crosnier-Lopez, Marie-Pierre; Le Berre, Françoise; Fauth, François; Fourquet, Jean-Louis

    2004-09-01

    Two new solid solutions—Li 2 xCa 0.5- xTaO 3 (0.05⩽ x⩽0.25) and Li 0.2[Ca 1- ySr y] 0.4TaO 3 (0ABO 3 perovskite structural type, are synthesized. The crystal structures of these Li + ion conducting compounds are solved from synchrotron radiation and conventional X-ray powder diffraction data. The unit cells exhibit a classical orthorhombic distortion of the cubic perovskite model (space group Pnma No. 62) with parameters close to 2a p, 2 ap, 2a p ( ap, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a+b-b- of the TaO 6 octahedra. For the same lithium content ( x=0.10), the Sr 2+ substitution to Ca 2+ is found to enhance the electrical conductivity by quasi-one order of magnitude (at 200 °C, bulk dc conductivity values are close to 2.3×10 -6 and 1.1×10 -5 S cm -1 for Li 0.2Ca 0.4TaO 3 and Li 0.2[Ca 0.9Sr 0.1] 0.4TaO 3, respectively).

  19. Potassium doped methylammonium lead iodide (MAPbI3) thin films as a potential absorber for perovskite solar cells; structural, morphological, electronic and optoelectric properties

    Science.gov (United States)

    Muzammal uz Zaman, Muhammad; Imran, Muhammad; Saleem, Abida; Kamboh, Afzal Hussain; Arshad, Muhammad; Khan, Nawazish Ali; Akhter, Parvez

    2017-10-01

    In this article, we have demonstrated the doping of K in the light absorbing CH3NH3PbI3 perovskite i.e. (M = CH3, A = NH3; x = 0-1). One of the major merits of methylammonium lead iodide (CH3NH3PbI3) perovskites is that they act as efficient absorbing material of light in photovoltaic cell imparting long carrier lifetime and optimum band gap. The structural, morphological, electronic and optoelectric properties of potassium (K) doped light absorber methylammonium lead iodide (CH3NH3PbI3) perovskites are reported here i.e. Kx(MA)1-xPbI3 (M = CH3, A =NH3; x = 0-1). The thin films of perovskites (x = 0-1) were deposited by spin coating on cleaned FTO substrates and characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), current-voltage (IV), X-ray photoelectron spectroscopy (XPS) and Diffused reflectance spectroscopy (DRS) analysis. The organic constituents i.e. MA = CH3NH3, in perovskites solar cells induce instability even at the room temperature. To overcome such instabilities we have replaced the organic constituents by K because both of them have electropositive nature. Potassium successfully replaces the CH3NH3. Initially, this compound grows in a tetragonal crystal structure, however, beyond 30% doping of potassium orthorhombic distortions are induced in the parent tetragonal unit cell. Such phase transformation is microscopically visible in the electron micrographs of doped samples; cubic grains for MAPbI3 begin to transform into strip like structures in K-doped samples. The resistance of the samples is decreased for partial K-doping, which we suggested to be arising due to the electropositive nature of K. It is observed that the binding energy difference between Pb4f and I3d core levels are very similar in all the investigated systems and show formal oxidation states. Also, the partially doped samples showed increased absorption and bandgaps around 1.5 eV which is an optimum value for solar absorption.

  20. Systematic study of grain boundary atomistic structures and related properties in cubic zirconia bicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, N.; Ikuhara, Y. [Inst. of Engineering Innovation, Univ. of Tokyo, Tokyo (Japan); Oba, F. [Dept. of Materials Science and Engineering, Graduate School of Engineering, Kyoto Univ., Kyoto (Japan); Yamamoto, T. [Dept. of Advanced Materials Science, Graduate School of Frontier Science, Univ. of Tokyo, Kashiwa, Chiba (Japan)

    2005-02-01

    Systematic grain boundary study of cubic zirconia has been conducted by using bicrystals. It is clearly demonstrated that grain boundary atomistic structures dramatically change according to the misorientations and plane orientations of the boundaries, resulting in a dramatic change of excess energies and solute segregation behaviors. Combining with theoretical calculations, it is found that grain boundaries possess unique coordination-deficient cation sites at the cores, and their densities have a clear correlation with these properties in high-angle grain boundaries. This result indicates that grain boundary properties in ceramics are possibly determined by the accumulation of coordination-deficient sites. Thus, systematic grain boundary study using bicrystal offers fundamental understandings of the relationship between atomistic structures and properties in ceramic grain boundaries. (orig.)

  1. Flexible perovskite solar cells based on the metal-insulator-semiconductor structure.

    Science.gov (United States)

    Wei, Jing; Li, Heng; Zhao, Yicheng; Zhou, Wenke; Fu, Rui; Pan, Huiyue; Zhao, Qing

    2016-09-14

    The metal-insulator-semiconductor (MIS) structure is applied to perovskite solar cells, in which the traditional compact layer TiO2 is replaced by Al2O3 as the hole blocking material to realize an all-low-temperature process. Flexible devices based on this structure are also realized with excellent flexibility, which hold 85% of their initial efficiency after bending 100 times.

  2. Structural phase transition in perovskite metal-formate frameworks: a Potts-type model with dipolar interactions.

    Science.gov (United States)

    Šimėnas, Mantas; Balčiūnas, Sergejus; Ma Combining Cedilla Czka, Mirosław; Banys, Jūras; Tornau, Evaldas E

    2016-07-21

    We propose a combined experimental and numerical study to describe an order-disorder structural phase transition in perovskite-based [(CH3)2NH2][M(HCOO)3] (M = Zn(2+), Mn(2+), Fe(2+), Co(2+) and Ni(2+)) dense metal-organic frameworks (MOFs). The three-fold degenerate orientation of the molecular (CH3)2NH2(+) (DMA(+)) cation implies a selection of the statistical three-state model of the Potts type. It is constructed on a simple cubic lattice where each lattice point can be occupied by a DMA(+) cation in one of the available states. In our model the main interaction is the nearest-neighbor Potts-type interaction, which effectively accounts for the H-bonding between DMA(+) cations and M(HCOO)3(-) cages. The model is modified by accounting for the dipolar interactions which are evaluated for the real monoclinic lattice using density functional theory. We employ the Monte Carlo method to numerically study the model. The calculations are supplemented with the experimental measurements of electric polarization. The obtained results indicate that the three-state Potts model correctly describes the phase transition order in these MOFs, while dipolar interactions are necessary to obtain better agreement with the experimental polarization. We show that in our model with substantial dipolar interactions the ground state changes from uniform to the layers with alternating polarization directions.

  3. Tuning the band gap in hybrid tin iodide perovskite semiconductors using structural templating.

    Science.gov (United States)

    Knutson, Jeremy L; Martin, James D; Mitzi, David B

    2005-06-27

    Structural distortions within the extensive family of organic/inorganic hybrid tin iodide perovskite semiconductors are correlated with their experimental exciton energies and calculated band gaps. The extent of the in- and out-of-plane angular distortion of the SnI4(2-) perovskite sheets is largely determined by the relative charge density and steric requirements of the organic cations. Variation of the in-plane Sn-I-Sn bond angle was demonstrated to have the greatest impact on the tuning of the band gap, and the equatorial Sn-I bond distances have a significant secondary influence. Extended Hückel tight-binding band calculations are employed to decipher the crystal orbital origins of the structural effects that fine-tune the band structure. The calculations suggest that it may be possible to tune the band gap by as much as 1 eV using the templating influence of the organic cation.

  4. Generalized trends in the formation energies of perovskite oxides.

    Science.gov (United States)

    Zeng, ZhenHua; Calle-Vallejo, Federico; Mogensen, Mogens B; Rossmeisl, Jan

    2013-05-28

    Generalized trends in the formation energies of several families of perovskite oxides (ABO3) and plausible explanations to their existence are provided in this study through a combination of DFT calculations, solid-state physics analyses and simple physical/chemical descriptors. The studied elements at the A site of perovskites comprise rare-earth, alkaline-earth and alkaline metals, whereas 3d and 5d metals were studied at the B site. We also include ReO3-type compounds, which have the same crystal structure of cubic ABO3 perovskites except without A-site elements. From the observations we extract the following four conclusions for the perovskites studied in the present paper: for a given cation at the B site, (I) perovskites with cations of identical oxidation state at the A site possess close formation energies; and (II) perovskites with cations of different oxidation states at the A site usually have quite different but ordered formation energies. On the other hand, for a given A-site cation, (III) the formation energies of perovskites vary linearly with respect to the atomic number of the elements at the B site within the same period of the periodic table, and the slopes depend systematically on the oxidation state of the A-site cation; and (IV) the trends in formation energies of perovskites with elements from different periods at the B site depend on the oxidation state of A-site cations. Since the energetics of perovskites is shown to be the superposition of the individual contributions of their constituent oxides, the trends can be rationalized in terms of A-O and B-O interactions in the ionic crystal. These findings reveal the existence of general systematic trends in the formation energies of perovskites and provide further insight into the role of ion-ion interactions in the properties of ternary compounds.

  5. Structural and magnetic study of the double-perovskites Ba{sub 2}(Fe,B'){sub 2}O{sub 6} (B'=Mo, W and Re)

    Energy Technology Data Exchange (ETDEWEB)

    Rammeh, N.; Bramnik, K.G.; Ehrenberg, H.; Fuess, H. [Institute for Materials Sciences, University of Technology, 64287 Darmstadt (Germany); Ritter, C. [Institute Laue Langevin, BP 156, 38042 Grenoble Cedex 9 (France); Cheikh-Rouhou, A. [Laboratoire de Physique des Materiaux, Faculte des Sciences de Sfax, BP 802, 3018 Sfax (Tunisia)

    2004-05-01

    Ceramics of Ba{sub 2}(Fe,B'){sub 2}O{sub 6} double-perovskites have been prepared and studied for B'=Mo, W and Re. Rietveld analysis confirms that all samples crystallize in a cubic double-perovskite structure with Fm anti 3 m space group. Magnetization measurements performed in the temperature range from 5 K to 350 K show a ferromagnetic behaviour for both materials Ba{sub 2}(Fe,Mo){sub 2}O{sub 6} and Ba{sub 2}(Fe,Re){sub 2}O{sub 6}, with T{sub C}=335 K,318 K respectively, and antiferromagnetic behaviour for Ba{sub 2}(Fe,W){sub 2}O{sub 6} with T{sub N}=20 K. (Abstract Copyright [2004], Wiley Periodicals, Inc.)

  6. MAPbI2.9-xBrxCl0.1 hybrid halide perovskites: Shedding light on the effect of chloride and bromide ions on structural and photoluminescence properties

    Science.gov (United States)

    Atourki, Lahoucine; Vega, Erika; Marí, Bernabé; Mollar, Miguel; Ait Ahsaine, Hassan; Bouabid, Khalid; Ihlal, Ahmed

    2016-12-01

    The optical and structural properties of CH3NH3PbI3 can be adjusted by introducing other extrinsic ions such as chloride and bromide. In this work, mixed bromide iodide lead perovskites with a 10% fraction of chloride were prepared from methylamine, lead nitrate and the corresponding hydro acid (X = I, Br, Cl). The effect of bromide and chloride incorporation on different properties of perovskite thin film was investigated. The Pawley fit method indicates the formation of the iodide halide MAPbI3 Pm-3 m cubic phase for x = 0 and the tetragonal P4/mmm phase for x ≥ 0.3. All deposited films showed a strong absorbance in the UV-vis range. The band gap values were estimated from absorbance measurements. It was found that the onset of the absorption edge for MAPbI2.9-xBrxCl0.1 thin film perovskites ranges between 1.60 and 1.80 eV. Moreover, it was found that both Cl and Br affect the PL emission of the mixed halide lead perovskite, the MAPbI2.9-xBrxCl0.1 films displayed intermediate values from 730 nm (MAPbI2.2Br0.7Cl0.1) to 770 nm (MAPbI2.6Br0.3Cl0.1).

  7. Structural, optical spectroscopy, optical conductivity and dielectric properties of BaTi$_{0.5}$(Fe$_{0.33}$W$_{0.17}$)O$_{3}$ perovskite ceramic

    Indian Academy of Sciences (India)

    FAYÇAL BOURGUIBA; AHMED DHAHRI; TAREK TAHRI; KAMEL TAIBI; JEMAI DHAHRI; E K HLIL

    2016-12-01

    Fe and W co-substituted BaTiO3 perovskite ceramics, compositional formula BaTi$_{0.5}$(Fe$_{0.33}$W$_{0.17}$)O$_3$, were synthesized by the standard solid-state reaction method and studied by X-ray diffraction, scanning electronmicroscopy and spectroscopy ellipsometry. The prepared sample remains as double phases with the perovskite structure. The structure refinement of BaTi$_0.5$(Fe$_{0.33}$W$_{0.17}$)O$_3$ sample was performed in the cubic double and hexagonal setting of the Fm$\\bar{3}$m and P6$_3$/mmc space groups. Spectral dependence of optical parameters; real and imaginaryparts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were carried out in the range between 1.4 and 4.96 eV by using the ellipsometry experiments. Direct bandgap energy of 4.36 eV was found from the analysis of absorption coefficient vs. photon energy. In addition, the oscillator energy, dispersion energy and zero-frequency refractive index values were found from the analysis of the experimental data usingWemple–DiDomenico single-effective-oscillator model.

  8. Electronic structure and magnetic properties of PbMO3 (M = Fe, Co, Ni) magnetic perovskites: An ab initio study

    Science.gov (United States)

    Erkişi, Aytaç; Yıldırım, Erdem Kamil; Gökoğlu, Gökhan

    2014-08-01

    We present the electronic, magnetic and structural properties of the magnetic transition metal oxides PbMO3 (M = Fe, Co, Ni) in cubic perovskite structure. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and local spin density approximation (LSDA) of the exchange-correlation functional. On-site Coulomb interaction is also included in calculations (LSDA+U). The systems are considered in ferromagnetic (FM) and G-type antiferromagnetic (G-AFM) order. FM structures are energetically more favored than G-AFM and than non-magnetic states for all the systems studied. The spin-polarized electronic band structures show that all the structures have metallic property in FM order without Hubbard-U interaction (Ueff = 0). However, the inclusion of on-site Coulomb interaction (Ueff = 7 eV) opens a semiconducting gap for majority spin channel of PbFeO3 and of PbNiO3 resulting in a half-metallic character. PbCoO3 system remains as metallic with LSDA+U scheme. Bonding features of all structures are largely determined by the hybridizations between O-p and d-states of transition metal atoms. The partial magnetic moment of Fe atom in PbFeO3 is enhanced by inclusion of Hubbard-U interaction (2.55 μB ⇒ 3.78 μB). Total magnetic moments of half-metallic PbFeO3 and of PbNiO3 compounds are very close to integer values.

  9. Structural study of nanosized yttrium-doped CaMnO3 perovskites

    Indian Academy of Sciences (India)

    J Zagorac; A Zarubica; A Radosavljevic-Mihajlovic; D Zagorac; B Matovic

    2014-05-01

    Nanostructured compounds with general formula Ca1-YMnO3 (0 ≤ ≤ 1) were synthesized by modified glycine nitrate procedure. In the next step, we have investigated crystal structure and microstructure of the synthesized samples using X-ray methods and Rietveld analysis. Focus of this research was the structural stability of the yttrium-doped CaMnO3 perovskite phases, which crystallize in orthorhombic space group Pnma. We observed that the unit cell volumes of the investigated compounds increase proportionally with yttrium amount. Furthermore, we investigated the influence of yttrium amount on Mn–O bond angles and distances, tilting of MnO6 octahedra and deformation due to the presence of Jahn–Teller distortion around Mn3+ cation. In order to estimate effective coordination of and sites, bond valence calculations (BVC) were performed for and site cations. Finally, the photoelectron spectroscopy (XPS) method was applied in order to follow yttrium concentration in the perovskite phases.

  10. Research Update: The electronic structure of hybrid perovskite layers and their energetic alignment in devices

    Directory of Open Access Journals (Sweden)

    Selina Olthof

    2016-09-01

    Full Text Available In recent years, the interest in hybrid organic–inorganic perovskites has increased at a rapid pace due to their tremendous success in the field of thin film solar cells. This area closely ties together fundamental solid state research and device application, as it is necessary to understand the basic material properties to optimize the performances and open up new areas of application. In this regard, the energy levels and their respective alignment with adjacent charge transport layers play a crucial role. Currently, we are lacking a detailed understanding about the electronic structure and are struggling to understand what influences the alignment, how it varies, or how it can be intentionally modified. This research update aims at giving an overview over recent results regarding measurements of the electronic structure of hybrid perovskites using photoelectron spectroscopy to summarize the present status.

  11. Hydrothermal Synthesis, Structure Characterization and Magnetic Studies of Perovskite-type Fluorides K2NaVF6 and (NH4)aVF6

    Institute of Scientific and Technical Information of China (English)

    HE Li-jie; ZHANG Dong; FENG Shou-hua; CHEN Gang; ZOU Bo

    2012-01-01

    Two perovskite-type fluorides K2NaVF6 and (NH4)3VF6 were synthesized under mild hydrothermal conditions.The structures of the compounds were determined by means of powder X-ray diffraction analysis.The Rietveld refinement indicates that K2NaVF6 has a cubic elpasolite-type structure and crystallizes in space group Fm-3m with lattice constant a=8.3180(2) nm.(NH4)3VF6 has a cubic cryolite-type structure and crystallizes in space group Fm-3m with lattice parameter a=9.090(1) nm.The compounds were further characterized by scanning electron microscopy(SEM),thermogravimetric(TG) and differential thermal analysis(DTA).The variable temperature magnetic susceptibility of these two compounds was characterized for the first time and the result shows that the magnetic ordering is related to the crystallographic features and isolated magnetic unit with the temperature decreasing.

  12. A bifunctional perovskite catalyst for oxygen reduction and evolution.

    Science.gov (United States)

    Jung, Jae-Il; Jeong, Hu Young; Lee, Jang-Soo; Kim, Min Gyu; Cho, Jaephil

    2014-04-25

    La0.3(Ba0.5Sr0.5)0.7Co0.8Fe0.2O3d is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm-scale rhombohedral LaCoO3 cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A-site cations with La3+ and local stress on Cosite sub-lattice with the cubic perovskite structure.

  13. Structure imaging and vanadium substitution in cubic TiCr2 Laves phase

    Science.gov (United States)

    Ghosh, Chanchal; Sharma, Vinit; Basu, Joysurya; Ramachandran, Divakar; Mohandas, E.

    2015-08-01

    Properties of Laves phase compounds can be tailored by alloying and microstructural engineering. V-substituted cubic TiCr2 Laves phase has been studied to understand the location of V atoms in the lattice, by structural imaging and first-principle computations. Even though Ti, V and Cr appear next to each other in the periodic table, V preferentially replaces the Ti lattice producing anti-site defects. The defect formation energy for V substitution in Ti and in Cr lattice is 0.29 and 0.40 eV, respectively. V replacement in the Ti lattice generates atomic scale strain. Atomic numbers of V, Ti and Cr being very close, this phase is not quite suitable for incoherent imaging for understanding the structure and the chemistry. Instead, difference in channelling behaviour of electron waves along the Ti columns and along the Cr columns could be exploited to preferentially image the individual atom columns. Nature of the exit phase wave, phase and amplitude has been used to understand the contrast qualitatively. The intensity distribution of any particular atom column that is disturbed by the presence of foreign atom has been used to detect the position of V atoms. This method could be extended to study other Laves phases and complex intermetallic structures to understand their structure, defects and interfaces.

  14. Engineering Interface Structure to Improve Efficiency and Stability of Organometal Halide Perovskite Solar Cells.

    Science.gov (United States)

    Qiu, Longbin; Ono, Luis K; Jiang, Yan; Leyden, Matthew R; Raga, Sonia R; Wang, Shenghao; Qi, Yabing

    2017-05-25

    The rapid rise of power conversion efficiency (PCE) of low cost organometal halide perovskite solar cells suggests that these cells are a promising alternative to conventional photovoltaic technology. However, anomalous hysteresis and unsatisfactory stability hinder the industrialization of perovskite solar cells. Interface engineering is of importance for the fabrication of highly stable and hysteresis free perovskite solar cells. Here we report that a surface modification of the widely used TiO2 compact layer can give insight into interface interaction in perovskite solar cells. A highest PCE of 18.5% is obtained using anatase TiO2, but the device is not stable and degrades rapidly. With an amorphous TiO2 compact layer, the devices show a prolonged lifetime but a lower PCE and more pronounced hysteresis. To achieve a high PCE and long lifetime simultaneously, an insulating polymer interface layer is deposited on top of TiO2. Three polymers, each with a different functional group (hydroxyl, amino, or aromatic group), are investigated to further understand the relation of interface structure and device PCE as well as stability. We show that it is necessary to consider not only the band alignment at the interface, but also interface chemical interactions between the thin interface layer and the perovskite film. The hydroxyl and amino groups interact with CH3NH3PbI3 leading to poor PCEs. In contrast, deposition of a thin layer of polymer consisting of an aromatic group to prevent the direct contact of TiO2 and CH3NH3PbI3 can significantly enhance the device stability, while the same time maintaining a high PCE. The fact that a polymer interface layer on top of TiO2 can enhance device stability, strongly suggests that the interface interaction between TiO2 and CH3NH3PbI3 plays a crucial role. Our work highlights the importance of interface structure and paves the way for further optimization of PCEs and stability of perovskite solar cells.

  15. Jubilite: A 4-,8-connected Cubic Structural Pattern in Space Group Pm3

    Directory of Open Access Journals (Sweden)

    Eduardo A. Castro

    2005-05-01

    Full Text Available Abstract: In the course of investigating structural modifications of the 3-,4-connected net known as the Pt3O4 structure-type (waserite, a novel 4-,8-connected structure-type was discovered. This lattice is generated by replacing the 3-connected trigonal planar vertices of the Pt3O4 structure-type with 4-connected tetrahedral vertices, to achieve a structure which possesses a generic empirical formula of JK6L8. In such a topological modification, the four 3-fold axes of the parent cubic, Pm3n, Pt3O4 structure-type are retained. Thus the 4-connected tetrahedral vertices are oriented so as to preserve cubic symmetry in the resulting Pm3, JK6L8 (jubilite lattice. The unit cell contains a single 8-connected cubecentered vertex, six 4-connected distorted square planar vertices and eight 4-connected distorted tetrahedral vertices. It is a Wellsean structure with a Wells point symbol given by (4166484(42826(43838 and a Schläfli symbol of (53/4, 4.2667. This latter index reveals a decrease in the lattice’s polygonality and concomitant increase in the connectivity through the transformation from waserite to jubilite. The topology of the parent waserite lattice (Pt3O4 corresponds to that of the Catalan structures with the Wells point symbol (843(834, which has the Schläfli symbol (8, 3.4285. Finally, it can be seen that a sequence of structure-types starting with waserite (Pt3O4 and moving to jubilite (JK6L8 and finally to fluorite (CaF2 represents a continuous crystallographic structural transformation in which the symmetry and topology undergo concomitant changes from one structure-type (waserite to the other structure-types. The topology of the fluorite lattice, represented by the Wells point symbol (424(462, and the Schläfli symbol (4, 51/3, indicates a discontinuous topological transformation from the intermediate jubilite lattice; like the discontinuous topological transformation from Pt3O4 to JK6L8; in which the

  16. High-pressure synthesis, crystal structure, and unusual valence state of novel perovskite oxide CaCu3Rh4O12.

    Science.gov (United States)

    Yamada, Ikuya; Ochi, Mikiko; Mizumaki, Masaichiro; Hariki, Atsushi; Uozumi, Takayuki; Takahashi, Ryoji; Irifune, Tetsuo

    2014-07-21

    A novel perovskite oxide, CaCu3Rh4O12, has been synthesized under high-pressure and high-temperature conditions (15 GPa and 1273 K). Rietveld refinement of synchrotron X-ray powder diffraction data indicates that this compound crystallizes in a cubic AA'3B4O12-type perovskite structure. Synchrotron X-ray absorption and photoemission spectroscopy measurements reveal that the Cu and Rh valences are nearly trivalent. The spectroscopic analysis based on calculations suggests that the appropriate ionic model of this compound is Ca(2+)Cu(∼2.8+)3Rh(∼3.4+)4O12, as opposed to the conventional Ca(2+)Cu(2+)3Rh(4+)4O12. The uncommon valence state of this compound is attributed to the relative energy levels of the Cu 3d and Rh 4d orbitals, in which the large crystal-field splitting energy of the Rh 4d orbitals is substantial.

  17. Simple descriptors for proton-conducting perovskites from density functional theory

    DEFF Research Database (Denmark)

    Bork, Nicolai Christian; Bonanos, Nikolaos; Rossmeisl, Jan

    2010-01-01

    series of (pseudo)cubic perovskites, ABO3, have been investigated using density functional theory calculations. The structures have been optimized and thermodynamic properties and activation energies for the relevant steps of the hydrogen/proton diffusion mechanism have been calculated using...

  18. The Relationship Between Atomic Structure and Strain Distribution of Misfit Dislocation Cores at Cubic Heteroepitaxial Interfaces.

    Science.gov (United States)

    Wen, Cai

    2017-03-09

    The atomic reconstruction of a misfit dislocation (MD) core causes change in the strain distribution around the core. Several MD cores at the AlSb/GaAs (001) cubic zincblende interface, including a symmetrical glide set Lomer dislocation (LD), a left-displaced glide set LD, a glide set LD with an atomic step, a symmetrical shuffle set LD, and a 60° dislocation pair, were studied using simulated projected potential and aberration-corrected transmission electron microscope images. Image deconvolution was also used to restore structure images from nonoptimum-defocus images. The corresponding biaxial strain maps, ε xx (in-plane) and ε yy (out-of-plane), were obtained by geometric phase analysis using the GaAs substrate as the reference lattice. The results show that atomic structure characteristics of MD cores can be revealed by the strain maps. The strain maps should be measured from optimum-defocus images or restored structure images. Furthermore, the ε xx strain map has been found more accurate than the ε yy strain map for MD cores, and the specimen thickness should be below the critical thickness due to the influence of dynamical scattering.

  19. Thickness dependencies of structural and magnetic properties of cubic and tetragonal Heusler alloy bilayer films

    Science.gov (United States)

    Ranjbar, R.; Suzuki, K. Z.; Sugihara, A.; Ando, Y.; Miyazaki, T.; Mizukami, S.

    2017-07-01

    The thickness dependencies of the structural and magnetic properties for bilayers of cubic Co-based Heusler alloys (CCHAs: Co2FeAl (CFA), Co2FeSi (CFS), Co2MnAl (CMA), and Co2MnSi (CMS)) and D022-MnGa were investigated. Epitaxy of the B2 structure of CCHAs on a MnGa film was achieved; the smallest thickness with the B2 structure was found for 3-nm-thick CMS and CFS. The interfacial exchange coupling (Jex) was antiferromagnetic (AFM) for all of the CCHAs/MnGa bilayers except for unannealed CFA/MnGa samples. A critical thickness (tcrit) at which perpendicular magnetization appears of approximately 4-10 nm for the CMA/MnGa and CMS/MnGa bilayers was observed, whereas this thickness was 1-3 nm for the CFA/MnGa and CFS/MnGa films. The critical thickness for different CCHAs materials is discussed in terms of saturation magnetization (Ms) and the Jex .

  20. The structure, thermal properties and phase transformations of the cubic polymorph of magnesium tetrahydroborate.

    Science.gov (United States)

    David, W I F; Callear, S K; Jones, M O; Aeberhard, P C; Culligan, S D; Pohl, A H; Johnson, S R; Ryan, K R; Parker, J E; Edwards, P P; Nuttall, C J; Amieiro-Fonseca, A

    2012-09-07

    The structure of the cubic polymorph of magnesium tetrahydroborate (γ-Mg(BH(4))(2)) has been determined in space group Ia3d from a structural database of the isoelectronic compound SiO(2); this has been corroborated by DFT calculations. The structure is found to concur with that recently determined by Filinchuk et al. (Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov and H. Hagemann, Angew. Chem. Int. Ed., 2011, DOI: 10.1002/anie.201100675). The phase transformations and subsequent decomposition of γ-Mg(BH(4))(2) on heating have been ascertained from variable-temperature synchrotron X-ray diffraction data combined with thermogravimetric and mass spectrometry measurements. At ~160 °C, conversion to a disordered variant of the β-Mg(BH(4))(2) phase (denoted as β') is observed along with a further unidentified polymorph. There is evidence of amorphous phases during decomposition but there is no direct crystallographic indication of the existence of Mg(B(12)H(12)) or other intermediate Mg-B-H compounds. MgH(2) and finally Mg are observed in the X-ray diffraction data after decomposition.

  1. Thermal evolution of the crystal structure of the orthorhombic perovskite LaFeO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Dixon, Charlotte A.L.; Kavanagh, Christopher M. [School of Chemistry and EaStCHEM, University of St Andrews, St Andrews KY16 9ST (United Kingdom); Knight, Kevin S.; Kockelmann, Winfried [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom); Morrison, Finlay D. [School of Chemistry and EaStCHEM, University of St Andrews, St Andrews KY16 9ST (United Kingdom); Lightfoot, Philip, E-mail: pl@st-and.ac.uk [School of Chemistry and EaStCHEM, University of St Andrews, St Andrews KY16 9ST (United Kingdom)

    2015-10-15

    The thermal evolution of the crystal structure of the prototypical orthorhombic perovskite LaFeO{sub 3} has been studied in detail by powder neutron diffraction in the temperature range 25perovskite LaFeO{sub 3} is rationalized from a detailed powder neutron diffraction study. - Highlights: • Crystal structure of the perovskite LaFeO{sub 3} studied in detail by powder neutron diffraction. • Unusual thermal evolution of lattice metrics rationalized. • Contrasting behavior to Bi-doped LaFeO{sub 3}. • Octahedral distortion/tilt parameters explain unusual a and c lattice parameter behavior.

  2. Atomistic Origins of Surface Defects in CH3NH3PbBr3 Perovskite and Their Electronic Structures.

    Science.gov (United States)

    Liu, Yunxia; Palotas, Krisztian; Yuan, Xiao; Hou, Tingjun; Lin, Haiping; Li, Youyong; Lee, Shuit-Tong

    2017-02-28

    The inherent instability of CH3NH3PbX3 remains a major technical barrier for the industrial applications of perovskite materials. Recently, the most stable surface structures of CH3NH3PbX3 have been successfully characterized by using density functional theory (DFT) calculations together with the high-resolution scanning tunneling microscopy (STM) results. The two coexisting phases of the perovskite surfaces have been ascribed to the alternate orientation of the methylammonium (MA) cations. Notably, similar surface defect images (a dark depression at the sites of X atoms) have been observed on surfaces produced with various experimental methods. As such, these defects are expected to be intrinsic to the perovskite crystals and may play an important role in the structural decomposition of perovskite materials. Understanding the nature of such defects should provide some useful information toward understanding the instability of perovskite materials. Thus, we investigate the chemical identity of the surface defects systematically with first-principles density functional theory calculations and STM simulations. The calculated STM images of the Br and Br-MA vacancies are both in good agreement with the experimental measurements. In vacuum conditions, the formation energy of Br-MA is 0.43 eV less than the Br vacancy. In the presence of solvation effects, however, the formation energy of a Br vacancy becomes 0.42 eV lower than the Br-MA vacancy. In addition, at the vacancy sites, the adsorption energies of water, oxygen, and acetonitrile molecules are significantly higher than those on the pristine surfaces. This clearly demonstrated that the structural decomposition of perovskites are much easier to start from these vacancy sites than the pristine surfaces. Combining DFT calculations and STM simulations, this work reveals the chemical identities of the intrinsic defects in the CH3NH3PbX3 perovskite crystals and their effects on the stability of perovskite materials.

  3. Role of structure imperfection in the formation of the magnetotransport properties of rare-earth manganites with a perovskite structure

    Science.gov (United States)

    Pashchenko, A. V.; Pashchenko, V. P.; Prokopenko, V. K.; Turchenko, V. A.; Revenko, Yu. F.; Mazur, A. S.; Sycheva, V. Ya.; Liedienov, N. A.; Pitsyuga, V. G.; Levchenko, G. G.

    2017-01-01

    The structure, the structure imperfection, and the magnetoresistance, magnetotransport, and microstructure properties of rare-earth perovskite La0.3Ln0.3Sr0.3Mn1.1O3-δ manganites are studied by X-ray diffraction, thermogravimetry, electrical resistivity measurement, magnetic, 55Mn NMR, magnetoresistance measurement, and scanning electron microscopy. It is found that the structure imperfection increases, and the symmetry of a rhombohedrally distorted R3̅ c perovskite structure changes into its pseudocubic type during isovalent substitution for Ln = La3+, Pr3+, Nd3+, Sm3+, or Eu3+ when the ionic radius of an A cation decreases. Defect molar formulas are determined for a real perovskite structure, which contains anion and cation vacancies. The decrease in the temperatures of the metal-semiconductor ( T ms) and ferromagnet-paramagnet ( T C) phase transitions and the increase in electrical resistivity ρ and activation energy E a with increasing serial number of Ln are caused by an increase in the concentration of vacancy point defects, which weaken the double exchange 3 d 4(Mn3+)-2 p 6(O2-)-3 d 3(Mn4+)- V ( a)-3 d 4(Mn3+). The crystal structure of the compositions with Ln = La contains nanostructured planar clusters, which induce an anomalous magnetic hysteresis at T = 77 K. Broad and asymmetric 55Mn NMR spectra support the high-frequency electronic double exchange Mn3+(3 d 4) ↔ O2-(2 p 6) ↔ Mn4+(3 d 3) and indicate a heterogeneous surrounding of manganese by other ions and vacancies. A correlation is revealed between the tunneling magnetoresistance effect and the crystallite size. A composition-structure imperfection-property experimental phase diagram is plotted. This diagram supports the conclusion about a strong influence of structure imperfection on the formation of the magnetic, magnetotransport, and magnetoresistance properties of rare-earth perovskite manganites.

  4. Synthesis, structural transformation, thermal stability, valence state, and magnetic and electronic properties of PbNiO3 with perovskite- and LiNbO3-type structures.

    Science.gov (United States)

    Inaguma, Yoshiyuki; Tanaka, Kie; Tsuchiya, Takeshi; Mori, Daisuke; Katsumata, Tetsuhiro; Ohba, Tomonori; Hiraki, Ko-ichi; Takahashi, Toshihiro; Saitoh, Hiroyuki

    2011-10-26

    We synthesized two high-pressure polymorphs PbNiO(3) with different structures, a perovskite-type and a LiNbO(3)-type structure, and investigated their formation behavior, detailed structure, structural transformation, thermal stability, valence state of cations, and magnetic and electronic properties. A perovskite-type PbNiO(3) synthesized at 800 °C under a pressure of 3 GPa crystallizes as an orthorhombic GdFeO(3)-type structure with a space group Pnma. The reaction under high pressure was monitored by an in situ energy dispersive X-ray diffraction experiment, which revealed that a perovskit-type phase was formed even at 400 °C under 3 GPa. The obtained perovskite-type phase irreversibly transforms to a LiNbO(3)-type phase with an acentric space group R3c by heat treatment at ambient pressure. The Rietveld structural refinement using synchrotron X-ray diffraction data and the XPS measurement for both the perovskite- and the LiNbO(3)-type phases reveal that both phases possess the valence state of Pb(4+)Ni(2+)O(3). Perovskite-type PbNiO(3) is the first example of the Pb(4+)M(2+)O(3) series, and the first example of the perovskite containing a tetravalent A-site cation without lone pair electrons. The magnetic susceptibility measurement shows that the perovskite- and LiNbO(3)-type PbNiO(3) undergo antiferromagnetic transition at 225 and 205 K, respectively. Both the perovskite- and LiNbO(3)-type phases exhibit semiconducting behavior.

  5. Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

    Energy Technology Data Exchange (ETDEWEB)

    Peterman, D.J.

    1980-01-01

    Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.

  6. Molecularly Engineered Organic-Inorganic Hybrid Perovskite with Multiple Quantum Well Structure for Multicolored Light-Emitting Diodes.

    Science.gov (United States)

    Hu, Hongwei; Salim, Teddy; Chen, Bingbing; Lam, Yeng Ming

    2016-09-16

    Organic-inorganic hybrid perovskites have the potential to be used as a new class of emitters with tunable emission, high color purity and good ease of fabrication. Recent studies have so far been focused on three-dimensional (3D) perovskites, such as CH3NH3PbBr3 and CH3NH3PbI3 for green and infrared emission. Here, we explore a new series of hybrid perovskite emitters with a general formula of (C4H9NH3)2(CH3NH3)n-1PbnI3n+1 (where n = 1, 2, 3), which possesses a multiple quantum well structure. The quantum well thickness of these materials is adjustable through simple molecular engineering which results in a continuously tunable bandgap and emission spectra. Deep saturated red emission was obtained with a peak external quantum efficiency of 2.29% and a maximum luminance of 214 cd/m(2). Green and blue LEDs were also demonstrated through halogen substitutions in these hybrid perovskites. We expect these results to open up the way towards high performance perovskite LEDs through molecular-structure engineering of these perovskite emitters.

  7. Molecularly Engineered Organic-Inorganic Hybrid Perovskite with Multiple Quantum Well Structure for Multicolored Light-Emitting Diodes

    Science.gov (United States)

    Hu, Hongwei; Salim, Teddy; Chen, Bingbing; Lam, Yeng Ming

    2016-01-01

    Organic-inorganic hybrid perovskites have the potential to be used as a new class of emitters with tunable emission, high color purity and good ease of fabrication. Recent studies have so far been focused on three-dimensional (3D) perovskites, such as CH3NH3PbBr3 and CH3NH3PbI3 for green and infrared emission. Here, we explore a new series of hybrid perovskite emitters with a general formula of (C4H9NH3)2(CH3NH3)n−1PbnI3n+1 (where n = 1, 2, 3), which possesses a multiple quantum well structure. The quantum well thickness of these materials is adjustable through simple molecular engineering which results in a continuously tunable bandgap and emission spectra. Deep saturated red emission was obtained with a peak external quantum efficiency of 2.29% and a maximum luminance of 214 cd/m2. Green and blue LEDs were also demonstrated through halogen substitutions in these hybrid perovskites. We expect these results to open up the way towards high performance perovskite LEDs through molecular-structure engineering of these perovskite emitters. PMID:27633084

  8. Inhibition of a structural phase transition in one-dimensional organometal halide perovskite nanorods grown inside porous silicon nanotube templates

    Science.gov (United States)

    Arad-Vosk, N.; Rozenfeld, N.; Gonzalez-Rodriguez, R.; Coffer, J. L.; Sa'ar, A.

    2017-02-01

    One-dimensional organo-metal halide perovskite (C H3N H3Pb I3 ) nanorods whose diameter and length are dictated by the inner size of porous silicon nanotube templates have been grown, characterized, and compared to bulk perovskites in the form of microwires. We have observed a structural phase transition for bulk perovskites, where the crystal structure changes from tetragonal to orthorhombic at about 160 K, as opposed to small diameter one-dimensional perovskite nanorods, of the order of 30-70 nm in diameter, where the phase transition is inhibited and the dominant phase remains tetragonal. Two major experimental techniques, infrared absorption spectroscopy and photoluminescence, were utilized to probe the temperature dependence of the perovskite phases over the 4-300 K temperature range. Yet, different characteristics of the phase transition were measured by the two spectroscopic methods and explained by the presence of small, tetragonal inclusions embedded in the orthorhombic phase. The inhibition of the phase transition is attributed to the large surface area of these one-dimensional perovskite nanorods, which gives rise to a large stress that, in turn, prevents the formation of the orthorhombic phase. The absence of phase transition enables the measurement of the tetragonal bandgap energy down to low temperatures.

  9. All Inorganic Halide Perovskites Nanosystem: Synthesis, Structural Features, Optical Properties and Optoelectronic Applications.

    Science.gov (United States)

    Li, Xiaoming; Cao, Fei; Yu, Dejian; Chen, Jun; Sun, Zhiguo; Shen, Yalong; Zhu, Ying; Wang, Lin; Wei, Yi; Wu, Ye; Zeng, Haibo

    2017-03-01

    The recent success of organometallic halide perovskites (OHPs) in photovoltaic devices has triggered lots of corresponding research and many perovskite analogues have been developed to look for devices with comparable performance but better stability. Upon the preparation of all inorganic halide perovskite nanocrystals (IHP NCs), research activities have soared due to their better stability, ultrahigh photoluminescence quantum yield (PL QY), and composition dependent luminescence covering the whole visible region with narrow line-width. They are expected to be promising materials for next generation lighting and display, and many other applications. Within two years, a lot of interesting results have been observed. Here, the synthesis of IHPs is reviewed, and their progresses in optoelectronic devices and optical applications, such as light-emitting diodes (LEDs), photodetectors (PDs), solar cells (SCs), and lasing, is presented. Information and recent understanding of their crystal structures and morphology modulations are addressed. Finally, a brief outlook is given, highlighting the presently main problems and their possible solutions and future development directions.

  10. Topotactic synthesis of strontium cobalt oxyhydride thin film with perovskite structure

    Directory of Open Access Journals (Sweden)

    Tsukasa Katayama

    2015-10-01

    Full Text Available The substitution of hydride anions (H− into transition metal oxides has recently become possible through topotactic reactions or high-pressure synthesis methods. However, the fabrication of oxyhydrides is still difficult because of their inherently less-stable frameworks. In this study, we successfully fabricated perovskite SrCoOxHy thin films via the topotactic hydride doping of brownmillerite SrCoO2.5 epitaxial thin films with CaH2. The perovskite-type cation framework was maintained during the topotactic treatment owing to epitaxial stabilization. Structural and chemical analyses accompanied by X-ray absorption spectroscopy measurements revealed that the doped hydride ions form a two-dimensional network of Co-H−-Co bonds, in contrast to other reported perovskite oxyhydrides, SrMO3−xHx (M = Cr, Ti, V. The SrCoOxHy thin film exhibited insulating behavior and had a direct band gap of 2.1 eV. Thus, topotactic hydride doping of transition-metal-oxide thin films on suitable substrates is a promising method for the synthesis of new transition metal oxyhydrides.

  11. Topotactic synthesis of strontium cobalt oxyhydride thin film with perovskite structure

    Energy Technology Data Exchange (ETDEWEB)

    Katayama, Tsukasa [Department of Chemistry, The University of Tokyo, Tokyo 113-0033 (Japan); Chikamatsu, Akira, E-mail: chikamatsu@chem.s.u-tokyo.ac.jp; Kamisaka, Hideyuki [Department of Chemistry, The University of Tokyo, Tokyo 113-0033 (Japan); CREST, Japan Science and Technology Agency (JST), Tokyo 113-0033 (Japan); Yokoyama, Yuichi; Hirata, Yasuyuki; Wadati, Hiroki [Institute for Solid State Physics, The University of Tokyo, Chiba 277-8581 (Japan); Fukumura, Tomoteru [CREST, Japan Science and Technology Agency (JST), Tokyo 113-0033 (Japan); Department of Chemistry, Tohoku University, Miyagi 980-8578 (Japan); Hasegawa, Tetsuya [Department of Chemistry, The University of Tokyo, Tokyo 113-0033 (Japan); CREST, Japan Science and Technology Agency (JST), Tokyo 113-0033 (Japan); Kanagawa Academy of Science and Technology (KAST), Kawasaki 213-0012 (Japan)

    2015-10-15

    The substitution of hydride anions (H{sup −}) into transition metal oxides has recently become possible through topotactic reactions or high-pressure synthesis methods. However, the fabrication of oxyhydrides is still difficult because of their inherently less-stable frameworks. In this study, we successfully fabricated perovskite SrCoO{sub x}H{sub y} thin films via the topotactic hydride doping of brownmillerite SrCoO{sub 2.5} epitaxial thin films with CaH{sub 2}. The perovskite-type cation framework was maintained during the topotactic treatment owing to epitaxial stabilization. Structural and chemical analyses accompanied by X-ray absorption spectroscopy measurements revealed that the doped hydride ions form a two-dimensional network of Co-H{sup −}-Co bonds, in contrast to other reported perovskite oxyhydrides, SrMO{sub 3−x}H{sub x} (M = Cr, Ti, V). The SrCoO{sub x}H{sub y} thin film exhibited insulating behavior and had a direct band gap of 2.1 eV. Thus, topotactic hydride doping of transition-metal-oxide thin films on suitable substrates is a promising method for the synthesis of new transition metal oxyhydrides.

  12. Structural and Optoelectronic Properties of Cubic CsPbF3 for Novel Applications

    Institute of Scientific and Technical Information of China (English)

    G. Murtaza; Iftikhar Ahmad; M. Maqbool; H. A. Rahnamaye Aliabad; A. Afaq

    2011-01-01

    Chemical bonding as well as structural, electronic and optical properties of CsPbF3 are calculated using the highly accurate full potential linearized augmented plane-wave method within the framework of density functional theory (DFT). The calculated lattice constant is found to be in good agreement with the experimental results. The electron density plots reveal strong ionic bonding in Cs-F and strong covalent bonding in Pb-F. The calculations show that the material is a direct and wide bandgap semiconductor with a fundamental gap at the R-symmetry point. Optical properties such as the real and imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, optical conductivity and absorption coefficient are also calculated. Based on the calculated wide and direct bandgap, as well as other optical properties of the compound, it is predicted that CsPbF3 is suitable for optoelectronic devices and anti-reflecting coatings.%Chemical bonding as well as structural,electronic and optical properties of CsPbF3 are calculated using the highly accurate full potential linearized augmented plane-wave method within the framework of density functional theory (DFT).The calculated lattice constant is found to be in good agreement with the experimental results.The electron density plots reveal strong ionic bonding in Cs-F and strong covalent bonding in Pb-F.The calculations show that the material is a direct and wide bandgap semiconductor with a fundamental gap at the R-symmetry point.Optical properties such as the real and imaginary parts of the dielectric function,refractive index,extinction coefficient,reflectivity,optical conductivity and absorption coefficient are also calculated.Based on the calculated wide and direct bandgap,as well as other optical properties of the compound,it is predicted that CsPbF3 is suitable for optoelectronic devices and anti-reflecting coatings.Perovskites have gained high technological and fundamental importance

  13. Incommensurate magnetic structure in the orthorhombic perovskite ErMnO3

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Feng [ORNL; Lorenz, Bernd [ORNL; Huang, Q. [National Institute of Standards and Technology (NIST); Wang, Y. Q. [University of Houston, Houston; Sun, Y. Y. [University of Houston, Houston; Chu, C. W. [University of Houston, Houston; Fernandez-Baca, Jaime A [ORNL; Dai, Pengcheng [ORNL; Mook Jr, Herbert A [ORNL

    2007-01-01

    By combining dielectric, specific heat, and magnetization measurements and high-resolution neutron powder diffraction, we have investigated the thermodynamic and magnetic and structural properties of the metastable orthorhombic perovskite ErMnO3 prepared by high-pressure synthesis. The system becomes antiferromagnetically correlated below 42 K and undergoes a lock-in transition at 28 K with propagation wave vector (0,kb,0), which remains incommensurate at low temperature. The intercorrelation between the magnetic structure and electric properties and the role of the rare earth moment are discussed.

  14. Incommensurate magnetic structure in the orthorhombic perovskite ErMnO3

    Science.gov (United States)

    Ye, F.; Lorenz, B.; Huang, Q.; Wang, Y. Q.; Sun, Y. Y.; Chu, C. W.; Fernandez-Baca, J. A.; Dai, Pengcheng; Mook, H. A.

    2007-08-01

    By combining dielectric, specific heat, and magnetization measurements and high-resolution neutron powder diffraction, we have investigated the thermodynamic and magnetic and structural properties of the metastable orthorhombic perovskite ErMnO3 prepared by high-pressure synthesis. The system becomes antiferromagnetically correlated below 42K and undergoes a lock-in transition at 28K with propagation wave vector (0,kb,0) , which remains incommensurate at low temperature. The intercorrelation between the magnetic structure and electric properties and the role of the rare earth moment are discussed.

  15. Phase transformation of Ca-perovskite in MORB at D" region

    Science.gov (United States)

    Nishitani, N.; Ohtani, E.; Sakai, T.; Kamada, S.; Miyahara, M.; Hirao, N.

    2012-12-01

    Seismological studies indicate the presence of seismic anomalies in the Earth's deep interior. To investigate the anomaly, the physical property of the major minerals in lower mantle such as MgSiO3-perovskite, MgSiO3 post-perovskite and MgO periclase were studied well. Other candidate, CaSiO3 perovskite (Ca-perovskite) exists in peridotitic mantle and basaltic oceanic crust (mid-ocean ridge basalt; MORB). Previous studies indicate the abundance of Ca-perovskite is up to ~9 vol.% in the pyrolite mantle and ~24 vol.% in the MORB oceanic crust. However, the pressure range of previous works are still not enough to understand the D" region. In this study, natural MORB was compressed in double sided laser heated DAC. Au was used as a pressure maker and a laser absorber. NaCl was used as the thermal insulator and pressure medium. The phase relation of Ca-perovskite in MORB was investigated from 36 to 156 GPa and 300 to 2600 K by the in situ X-ray diffraction measurements at SPring-8 (BL10XU). The transition of Ca-perovskite from a tetragonal structure to a cubic structure occurred at about 1800 K up to about 100 GPa and below 1500 K at pressures above 100 GPa. This suggests that the tetragonal-cubic transition of Ca-perovskite could occur in MORB, associating with Al2O3 contents. The present results suggest that the seismic anomaly at D" layer could be caused by the transition in Ca-perovskite.

  16. Role of Dispersive Interactions in Determining Structural Properties of Organic-Inorganic Halide Perovskites: Insights from First-Principles Calculations.

    Science.gov (United States)

    Egger, David A; Kronik, Leeor

    2014-08-07

    A microscopic picture of structure and bonding in organic-inorganic perovskites is imperative to understanding their remarkable semiconducting and photovoltaic properties. On the basis of a density functional theory treatment that includes both spin-orbit coupling and dispersive interactions, we provide detailed insight into the crystal binding of lead-halide perovskites and quantify the effect of different types of interactions on the structural properties. Our analysis reveals that cohesion in these materials is characterized by a variety of interactions that includes important contributions from both van der Waals interactions among the halide atoms and hydrogen bonding. We also assess the role of spin-orbit coupling and show that it causes slight changes in lead-halide bonding that do not significantly affect the lattice parameters. Our results establish that consideration of dispersive effects is essential for understanding the structure and bonding in organic-inorganic perovskites in general and for providing reliable theoretical predictions of structural parameters in particular.

  17. Local structure and electronic properties of BaTaO2N with perovskite-type structure

    NARCIS (Netherlands)

    Fang, C.M.; Wijs, G.A. de; Orhan, E.; With, G. de; de Groot, R.A.; Hintzen, H.T.; Marchand, R.

    2003-01-01

    First-principles calculation based on density-functional theory in the pseudo-potential approach have been performed for the total energy and crystal structure of BaTaO2N. The calculations indicate a random occupation of the anionic positions by O and N in a cubic structure, in agreement with neutro

  18. Effect of Gd3+ doping on structural, optical and frequency-dependent dielectric response properties of pseudo-cubic BaTiO3 nanostructures

    Science.gov (United States)

    Borah, Manjit; Mohanta, Dambarudhar

    2014-06-01

    We report on the structural, optical and dielectric characterization of solid state derived, pseudo-cubic nanoscale barium titanates (BTs) with gadolinium (Gd3+) as substitutional dopant. Referring to X-ray diffractograms, apart from the BT peaks related to perovskite structure, the non-existence of any additional peaks due to byproducts has revealed that Gd3+ has undergone substitutional doping into the BT host lattice. The well-separated BT nanoparticles of typical size ˜10-15 nm were observed through electron microscopy studies. Following a direct, allowed type carrier transition ( n=1/2), a reduction in the optical band gap value (from 3.28 to 3.255 eV) was observed when the Gd-doping level was varied within 0-7 %. Conversely, the Urbach energy followed an increasing trend, from a value of 0.741 to 1.879 eV. Furthermore, the dielectric constant showed a decreasing tendency with doping content and with increasing frequency. However, in the low-frequency region, the loss tangent (tan δ), which is the combined result of orientational polarization and electrical conduction, was found to be quite high in the doped samples as compared to their un-doped counterpart. The frequency-dependent electrical data were also analyzed in the framework of conductivity and impedance formalisms. In particular, the ac conductivity which varies as ˜ ω s approaches ideal Debye behavior ( s→1) for a low Gd level and a higher doping concentration did not show improved dielectric feature of the host. The incorporation of rare-earth (Gd3+) ions into the BT host system could greatly manifest dielectric relaxation and carrier conduction mechanisms, in a given frequency range, and thus can find immense scope in miniaturized nanoelectronic elements including ceramic capacitors and transducers.

  19. Effects of Nonhydrostatic Stress on Structural and Optoelectronic Properties of Methylammonium Lead Bromide Perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Rong; Cai, Weizhao; Bi, Tiange; Zarifi, Niloofar; Terpstra, Tyson; Zhang, Chuang; Verdent, Z. Valy; Zurek, Eva; Deemyad, Shanti (Buffalo); (Utah)

    2017-07-13

    We report synchrotron X-ray diffraction, photoconductivity, and photoluminescence investigations of methylammonium-lead-bromide (MAPbBr3) under various stress conditions, supported by density-functional-theory (DFT) calculations. The properties of MAPbBr3 show substantial dependence on the hydrostatic conditions. While nonhydrostatic compression of MAPbBr3 leads to amorphization above 2.4 GPa, under quasi-hydrostatic (Ar) and hydrostatic (He) pressure, the sample remains in crystalline phases. A sequence of phase transitions between two cubic phases and orthorhombic Pnma phase is observed when using Ar, or no pressure-transmitting-medium (PTM). In helium-PTM only transitions between the two cubic structures and a new isostructural phase transition with a large volume collapse to a third cubic-phase at 2.7 GPa was observed. The photoluminescence measurements indicate a pressure-induced band gap-narrowing in the cubic phase I, and a blue-shift in the orthorhombic structure. DFT calculations illustrate that the dynamics of the organic molecules and the inorganic lattice, coupled via the N–H···Br hydrogen-bonding interactions, affect the Pb–Br distance and the bandgap evolution under pressure.

  20. The electronic structure of metal oxide/organo metal halide perovskite junctions in perovskite based solar cells.

    Science.gov (United States)

    Dymshits, Alex; Henning, Alex; Segev, Gideon; Rosenwaks, Yossi; Etgar, Lioz

    2015-03-03

    Cross-sections of a hole-conductor-free CH3NH3PbI3 perovskite solar cell were characterized with Kelvin probe force microscopy. A depletion region width of about 45 nm was determined from the measured potential profiles at the interface between CH3NH3PbI3 and nanocrystalline TiO2, whereas a negligible depletion was measured at the CH3NH3PbI3/Al2O3 interface. A complete solar cell can be realized with the CH3NH3PbI3 that functions both as light harvester and hole conductor in combination with a metal oxide. The band diagrams were estimated from the measured potential profile at the interfaces, and are critical findings for a better understanding and further improvement of perovskite based solar cells.

  1. New hybrid lead iodides: From one-dimensional chain to two-dimensional layered perovskite structure

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, Kecai; Liu, Wei [Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 (United States); Teat, Simon J. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); An, Litao; Wang, Hao; Emge, Thomas J. [Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 (United States); Li, Jing, E-mail: jingli@rutgers.edu [Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 (United States)

    2015-10-15

    Two new hybrid lead halides (H{sub 2}BDA)[PbI{sub 4}] (1) (H{sub 2}BDA=1,4-butanediammonium dication) and (HNPEIM)[PbI{sub 3}] (2) (HNPEIM=N-​phenyl-ethanimidamidine cation) have been synthesized and structurally characterized. X-ray diffraction analyses reveal that compound 1 features a two-dimensional corner-sharing perovskite layer whereas compound 2 contains one-dimensional edge-sharing double chains. The N-​phenyl-ethanimidamidine cation within compound 2 was generated in-situ under solvothermal conditions. The optical absorption spectra collected at room temperature suggest that both compounds are semiconductors having direct band gaps, with estimated values of 2.64 and 2.73 eV for 1 and 2, respectively. Results from the density functional theory (DFT) calculations are consistent with the experimental data. Density of states (DOS) analysis reveals that in both compounds 1 and 2, the energy states in the valence band maximum region are iodine 5p atomic orbitals with a small contribution from lead 6s, while in the region of conduction band minimum, the major contributions are from the inorganic (Pb 6p atomic orbitals) and organic components (C and N 2p atomic orbitals) in compound 1 and 2, respectively. - Graphical abstract: Two new hybrid lead halides built on one-dimensional edge-sharing double chains and two-dimensional corner-sharing perovskite layers are synthesized and their structural and electronic properties are analyzed. - Highlights: • Two new hybrid lead iodides are designed, synthesized, and characterized. • They are closely related to, but different from, perovskite structures. • The electronic properties of both compounds are analyzed by DFT calculations.

  2. An Ultrahigh-Performance Photodetector based on a Perovskite-Transition-Metal-Dichalcogenide Hybrid Structure.

    Science.gov (United States)

    Kang, Dong-Ho; Pae, Seong Ryul; Shim, Jaewoo; Yoo, Gwangwe; Jeon, Jaeho; Leem, Jung Woo; Yu, Jae Su; Lee, Sungjoo; Shin, Byungha; Park, Jin-Hong

    2016-09-01

    An ultrahigh performance MoS2 photodetector with high photoresponsivity (1.94 × 10(6) A W(-1) ) and detectivity (1.29 × 10(12) Jones) under 520 nm and 4.63 pW laser exposure is demonstrated. This photodetector is based on a methyl-ammonium lead halide perovskite/MoS2 hybrid structure with (3-aminopropyl)triethoxysilane doping. The performance degradation caused by moisture is also minimized down to 20% by adopting a new encapsulation bilayer of octadecyltrichlorosilane/polymethyl methacrylate.

  3. Temperature and Pressure Sensors Based on Spin-Allowed Broadband Luminescence of Doped Orthorhombic Perovskite Structures

    Science.gov (United States)

    Eldridge, Jeffrey I. (Inventor); Chambers, Matthew D. (Inventor)

    2014-01-01

    Systems and methods that are capable of measuring pressure or temperature based on luminescence are discussed herein. These systems and methods are based on spin-allowed broadband luminescence of sensors with orthorhombic perovskite structures of rare earth aluminates doped with chromium or similar transition metals, such as chromium-doped gadolinium aluminate. Luminescence from these sensors can be measured to determine at least one of temperature or pressure, based on either the intense luminescence of these sensors, even at high temperatures, or low temperature techniques discussed herein.

  4. Structural and magnetic properties of the 5$d^2$ double perovskites Sr$_2 B$ReO$_6$ ($B$ $=$ Y, In)

    OpenAIRE

    Aczel, A. A.; Zhao, Z.; Calder, S.; Adroja, D T; Baker, P. J.; Yan, J. -Q.

    2016-01-01

    We have performed magnetic susceptibility, heat capacity, neutron powder diffraction, and muon spin relaxation experiments to investigate the magnetic ground states of the 5$d^2$ double perovskites Sr$_2$YReO$_6$ and Sr$_2$InReO$_6$. We find that Sr$_2$YReO$_6$ is a spin glass, while Sr$_2$InReO$_6$ hosts a non-magnetic singlet state. By making detailed comparisons with other 5$d^2$ double perovskites, we argue that a delicate interplay between spin-orbit coupling, non-cubic crystal fields, a...

  5. Performance of biotrickling filters packed with structured or cubic polyurethane sponges for VOC removal

    Institute of Scientific and Technical Information of China (English)

    Chunping Yang; Guanlong YU; Guangming Zeng; Haining Yang; Fayuan Chen; Congying Jin

    2011-01-01

    Two identical bench-scale biotrickling filters (BTFs),BTF 1 and BTF 2,were evaluated for toluene removal at various gas empty bed contact times (EBCTs) and organic loadings.BTF 1 and BTF 2 were packed with structured and cubic synthetic polyurethane sponges,respectively.At a constant toluene loading of 16 g/(m3.hr),toluene removal efficiencies decreased from 98.8% to 64.3% for BTF 1 and from 98.4% to 74.1% for BTF 2 as gas EBCT decreased from 30 to 5 see.When the toluene loading increased from 35 to 140 g/(m3·hr) at a gas EBCT of 30 see,the removal efficiencies decreased from 99.1% to 77.4% for BTF 1 and from 99.0% to 81.5% for BTF 2.The pressure drop for both BTFs increased with increased air flow rate,and did not significantly vary while the toluene loading was increased under similar operation conditions.BTF 1 and BTF 2 could start up successfully within 19 and 27 days,respectively,when packed with fresh sponge media,and the performances could be restored in 3-7 days after biomass was removed and wasted from the media.BTF 2 displayed higher removal efficiency even under shorter EBCT or higher loading rate than BTF1 when other operation conditions were similar,while it showed lower pressure drop than BTF 1 during the whole period of operation.These results demonstrated that both BTFs could treat waste gas containing toluene effectively.

  6. Effect of cooling rate on the crystallization behavior of perovskite in high titanium-bearing blast furnace slag

    Institute of Scientific and Technical Information of China (English)

    Lu Liu; Mei-long Hu; Chen-guang Bai; Xue-weiLü; Yu-zhou Xu; Qing-yu Deng

    2014-01-01

    The effect of cooling rate on the crystallization of perovskite in high Ti-bearing blast furnace (BF) slag was studied using confocal scanning laser microscopy (CSLM). Results showed that perovskite was the primary phase formed during the cooling of slag. On the slag surface, the growth of perovskite proceeded via the successive production of quasi-particles along straight lines, which further extended in certain directions. The morphology and structure of perovskite was found to vary as a function of cooling rate. At cooling rates of 10 and 30 K/min, the dendritic arms of perovskite crossed obliquely, while they were orthogonal at a cooling rate of 20 K/min and hexagonal at cooling rates of 40 and 50 K/min. These three crystal morphologies thus obtained at different cooling rates respectively corresponded to the ortho-rhombic, cubic and hexagonal crystal structures of perovskite. The observed change in the structure of perovskite could probably be attrib-uted to the deficiency of O2-,when Ti2O3 was involved in the formation of perovskite.

  7. Rotational and translational distortions of the crystal structure of the Sr{sub 2}HrRuO{sub 6} (Hr = Ho, Dy, Gd, Eu) complex perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Triana, C.A., E-mail: ctrianae@unal.edu.co [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, A.A. 5997, Bogotá D.C. (Colombia); Landínez Téllez, D.A. [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, A.A. 5997, Bogotá D.C. (Colombia); Roa-Rojas, J., E-mail: jroar@unal.edu.co [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, A.A. 5997, Bogotá D.C. (Colombia)

    2013-05-15

    Sr{sub 2}HrRuO{sub 6} (Hr = Ho, Dy, Gd, Eu) complex perovskites were synthesized through the high-temperature solid-state reaction method, and their crystal structures were analyzed in detail as a function of the Hr-cation ionic radius. Results of powder XRD pattern measurement and Rietveld analysis of the experimental profiles show that the Sr{sub 2}HrRuO{sub 6} compounds crystallize in a monoclinic distorted perovskite-like structure, P2{sub 1}/n (#14) space group, where the unit cell parameters are related to the primitive unit cell a{sub p} by a≈√(2)a{sub p}, b≈√(2)a{sub p} and c ≈ 2a{sub p}. The structures show an alternate distribution of the Ru{sup 5+} (2d: 0.5, 0, 0) and Hr{sup 3+} (2c: 0, 0.5, 0) making up RuO{sub 6} and HrO{sub 6} octahedra alternatively arranged in two interleaving fcc sublattices, where the O(1), O(2), and O(3) ions are localized at the corner of the octahedral, while the Sr{sup 2+} is located at the A-site, occupying the cavities built by the corner-sharing octahedra with Wyckoff position 4e. Due to the existence of mismatched ionic sizes between the ionic radii of the Sr{sub 2}HrRuO{sub 6} compounds, the HrO{sub 6} and RuO{sub 6} octahedra are constrained to tilting around the [111]{sub c}, [001]{sub c}, and [110]{sub c} cubic directions so as to optimize the Sr–O inter-atomic bond lengths, tending to rotate the structure in order to fix the Ru{sup 5+} and Hr{sup 3+} ions on the M′ and M″ sites of the complex perovskites. The cell parameters a, b, and c, the inter-atomic bond angles, the inter-atomic bond lengths, and the tilting angles increase as the Hr-cation ionic radius increases. The mismatch that exists in the Sr{sub 2}HrRuO{sub 6} ionic radius produces a large distortion from the ideal cubic symmetry. The pure perovskite-like phase of Sr{sub 2}HrRuO{sub 6} is thermodynamically and kinetically stable at high temperatures above 1420 K, where it is entirely governed by the average size of the Hr{sup 3+} and Ru

  8. Solar cells, structures including organometallic halide perovskite monocrystalline films, and methods of preparation thereof

    KAUST Repository

    Bakr, Osman M.

    2017-03-02

    Embodiments of the present disclosure provide for solar cells including an organometallic halide perovskite monocrystalline film (see fig. 1.1B), other devices including the organometallic halide perovskite monocrystalline film, methods of making organometallic halide perovskite monocrystalline film, and the like.

  9. White-Light Emission and Structural Distortion in New Corrugated Two-Dimensional Lead Bromide Perovskites.

    Science.gov (United States)

    Mao, Lingling; Wu, Yilei; Stoumpos, Constantinos C; Wasielewski, Michael R; Kanatzidis, Mercouri G

    2017-03-29

    Hybrid inorganic-organic perovskites are developing rapidly as high performance semiconductors. Recently, two-dimensional (2D) perovskites were found to have white-light, broadband emission in the visible range that was attributed mainly to the role of self-trapped excitons (STEs). Here, we describe three new 2D lead bromide perovskites incorporating a series of bifunctional ammonium dications as templates which also emit white light: (1) α-(DMEN)PbBr4 (DMEN = 2-(dimethylamino)ethylamine), which adopts a unique corrugated layered structure in space group Pbca with unit cell a = 18.901(4) Å, b = 11.782(2) Å, and c = 23.680(5) Å; (2) (DMAPA)PbBr4 (DMAPA = 3-(dimethylamino)-1-propylamine), which crystallizes in P21/c with a = 10.717(2) Å, b = 11.735(2) Å, c = 12.127(2) Å, and β = 111.53(3)°; and (3) (DMABA)PbBr4 (DMABA = 4-dimethylaminobutylamine), which adopts Aba2 with a = 41.685(8) Å, b = 23.962(5) Å, and c = 12.000(2) Å. Photoluminescence (PL) studies show a correlation between the distortion of the "PbBr6" octahedron in the 2D layer and the broadening of PL emission, with the most distorted structure having the broadest emission (183 nm full width at half-maximum) and longest lifetime (τavg = 1.39 ns). The most distorted member α-(DMEN)PbBr4 exhibits white-light emission with a color rendering index (CRI) of 73 which is similar to a fluorescent light source and correlated color temperature (CCT) of 7863 K, producing "cold" white light.

  10. Structure-property relationships: Synthesis and characterization of Perovskite-related transition metal oxides

    Science.gov (United States)

    Whaley, Louis

    The fundamental structural component of perovskite-related phases is the octahedrally coordinated transition metal ion, symbolized as BO6 . Corner-sharing networks of BO6 octahedra are present in perovskites and related Ruddlesden-Popper Phases, ABO3 and AO(ABO 3)n, respectively. Face-sharing octahedra arranged into columns are characteristic of hexagonal, perovskite-related phases, and the relationship will be described in detail in Chapter 1. Edge sharing octahedra are characteristic of Keggin- and Lindquist-type polyoxometallates, which at first glance, seem unconnected from perovskites. However, Chapter 1 will show the deep connections among all of the phases mentioned above, by starting with perovskite phases. Temperature- and field-dependent, magnetic and electronic transitions are linked to the structure by overlap of metal d-orbitals with oxygen 2p orbitals, and (in special cases) direct d-d overlap. A mixed-transition metal oxide with two or more type of B ions provides an environment in which dissimilar B-ion orbitals can interact via exchange of charge carriers (hole or electron transport). The general goal in choosing two B ions is to provide an opportunity for the large combined magnetic moment and a low barrier to hopping of charge carriers, achieved by pairing a 3d-ion having 3 to 5 unpaired d-electrons, with a 4d or 5d transition metal ion, having 1 or 2 unpaired electrons, such as Fe(III) and Mo(V), which have compatible reduction potentials (i.e., they can co-exist in the same oxide, and exchange takes place with a low barrier). This research includes the following systems: an n = 2 Ruddlesden-Popper (RP) phase, Sr3Fe5/4Mo3/4O6.9, containing 3-7% Sr2FeMoO6, as intergrowths (not separate crystal grains, by high-resolution transmission electron microscopy), and G-type antiferromagnetism below 150°K and a "partial spin-reorientation transition" by powder neutron diffraction (PND), not previously reported for n = 2 RP phases in the Sr-Fe-Mo-O system

  11. Real-time probing of structural dynamics in perovskite materials

    Energy Technology Data Exchange (ETDEWEB)

    Elsaesser, Thomas [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin (Germany)

    2009-07-01

    Femtosecond x-ray diffraction probes structural dynamics of solids in real-time and gives insight into reversible geometry changes on atomic length and time scales. After a brief introduction into this field, recent results on the lattice dynamics of ferroelectric SrRuO{sub 3}/PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} superlattice structures and their interplay with the electric polarization of the material are presented. Ultrafast optical generation of mechanical stress allows for switching-off the polarization on a time scale of a few picoseconds. As a second example, magnetostriction in a ferromagnetic SrRuO{sub 3}/SrTiO{sub 3} superlattice structure is analyzed in real time.

  12. A two-layer structured PbI2 thin film for efficient planar perovskite solar cells

    Science.gov (United States)

    Ying, Chao; Shi, Chengwu; Wu, Ni; Zhang, Jincheng; Wang, Mao

    2015-07-01

    In this paper, a two-layer structured PbI2 thin film was constructed by the spin-coating procedure using a 0.80 M PbI2 solution in DMF and subsequent close-spaced vacuum thermal evaporation using PbI2 powder as a source. The bottom PbI2 thin film was compact with a sheet-like appearance, parallel to the FTO substrate, and can be easily converted to a compact perovskite thin film to suppress the charge recombination of the electrons of the TiO2 conduction band and the holes of the spiro-OMeTAD valence band. The top PbI2 thin film was porous with nano-sheet arrays, perpendicular to the FTO substrate, and can be easily converted to a porous perovskite thin film to improve the hole migration from the perovskite to spiro-OMeTAD and the charge separation at the perovskite/spiro-OMeTAD interface. The planar perovskite solar cells based on the two-layer structured PbI2 thin film exhibited a photoelectric conversion efficiency of 11.64%, along with an open-circuit voltage of 0.90 V, a short-circuit photocurrent density of 19.29 mA cm-2 and a fill factor of 0.67.

  13. Fluence dependence of the ultrafast transition from the A7 to the simple cubic structure in arsenic

    Energy Technology Data Exchange (ETDEWEB)

    Huntemann, Nils; Zijlstra, Eeuwe S.; Garcia, Martin E. [Universitaet Kassel, Theoretische Physik, Kassel (Germany)

    2009-07-15

    We extend a previous theoretical study, in which we have predicted that a solid-solid phase transition can be induced by a laser in arsenic under pressure, to higher fluences. In particular, we compute the fluence that is needed to induce an ultrafast structural transition from the A7 to the simple cubic phase as a function of the applied pressure. We further discuss the possibility of ultrafast, laser-induced melting. (orig.)

  14. Effect of γ-irradiation on structure and properties of Nd3+ doped Perovskite

    Science.gov (United States)

    Mahadik, P.; Sengupta, Pranesh; Vishwanadh, B.; Mishra, S. K.; Sudarsan, V.; Dey, G. K.

    2017-10-01

    Perovskite is one of the potential host matrices for immobilization of high level nuclear waste. In the present investigation Nd3+ doped BaZrO3 materials were synthesized by conventional solid state route and their phase structure was evaluated by X-ray diffraction technique. Phase pure Nd3+ doped BaZrO3 materials were exposed to gamma radiation and their defects in structure as well as strain produced was measured. Structural defects and morphology before and after gamma irradiation were investigated using photoluminescence (PL) spectroscopy, Raman spectroscopy and Transmission electron microscopic (TEM) analysis. Both undoped and Nd3+ doped BaZrO3 compositions showed excellent resistant to gamma irradiation with no change in structure, morphology and optical properties.

  15. Crystal structure and electrical transport properties of single layered perovskite LaSrCoO4

    Science.gov (United States)

    Ahad, Abdul; Shukla, D. K.; Rahman, F.; Majid, S.; Tarachand; Okram, G. S.; Phase, D. M.

    2016-10-01

    We present here investigations on the influence of structure on electrical transport properties of polycrystalline LaSrCoO4 that is single layered perovskite with K2NiF4 type structure synthesized using solid state reaction route. Using Reitveld refinement of X-ray diffraction (XRD) data, it is found that the sample is in single phase with tetragonal structure (space group I4/mmm). Electrical resistivity performed in the temperature range 140-300K shows semiconducting character of the sample. Considerable contrasts in the Co-O bond length is associated with the intermediate spin (IS) state of Co ion that correlates the structural and transport properties. Detailed analysis indicates that the temperature dependent electrical resistivity follows the three-dimensional variable range hopping (VRH) model in low temperature region below 225K. The high temperature (225-300K) resistivity data has been found to follow the thermally activated behaviour.

  16. Strontium superstoichiometry and defect structure of SrCeO3 perovskite.

    Science.gov (United States)

    Mather, Glenn C; Figueiredo, Filipe M; Paz, Julio Romero de; García-Martín, Susana

    2008-02-04

    Strontium cerate (SrCeO(3)) is the parent phase of a family of prototype proton-conducting perovskites with important potential applications as electrolytes in protonic ceramic fuel cells, hydrogen-separation membranes, and sensors for hydrogen and humidity. Apparent nonstoichiometric behavior and the microstructure of SrCeO(3) have been investigated. Phase analysis by X-ray diffraction indicates that single-phase material in the system Sr(1+x)CeO(3+)delta is obtained for compositions x = 0.02-0.03 and that nominally stoichiometric SrCeO(3) (x = 0) synthesized by either solid-state reaction or the citrate method is Sr-rich. Selected area electron diffraction confirms that the system crystallizes with the GdFeO(3)-type orthorhombic perovskite structure (space group Pnma). Structural defects characterized by high-resolution transmission electron microscopy include twin domain boundaries and SrO-rich, Ruddlesden-Popper-type planar defects. Magnetic susceptibility measurements down to 2 K indicate that the Ce(3+) content is minor ( approximately 0.01 mol per formula unit for slow-cooled material) and does not influence the observed nonstoichiometry.

  17. Real-Space Imaging of the Atomic Structure of Organic-Inorganic Perovskite.

    Science.gov (United States)

    Ohmann, Robin; Ono, Luis K; Kim, Hui-Seon; Lin, Haiping; Lee, Michael V; Li, Youyong; Park, Nam-Gyu; Qi, Yabing

    2015-12-30

    Organic-inorganic perovskite is a promising class of materials for photovoltaic applications and light emitting diodes. However, so far commercialization is still impeded by several drawbacks. Atomic-scale effects have been suggested to be possible causes, but an unequivocal experimental view at the atomic level is missing. Here, we present a low-temperature scanning tunneling microscopy study of single crystal methylammonium lead bromide CH3NH3PbBr3. Topographic images of the in situ cleaved perovskite surface reveal the real-space atomic structure. Compared to the bulk we observe modified arrangements of atoms and molecules on the surface. With the support of density functional theory we explain these by surface reconstruction and a substantial interplay of the orientation of the polar organic cations (CH3NH3)(+) with the position of the hosting anions. This leads to structurally and electronically distinct domains with ferroelectric and antiferroelectric character. We further demonstrate local probing of defects, which may also impact device performance.

  18. Nanoscale structural oscillations in perovskite oxides induced by oxygen evolution

    Science.gov (United States)

    Han, Binghong; Stoerzinger, Kelsey A.; Tileli, Vasiliki; Gamalski, Andrew D.; Stach, Eric A.; Shao-Horn, Yang

    2017-01-01

    Understanding the interaction between water and oxides is critical for many technological applications, including energy storage, surface wetting/self-cleaning, photocatalysis and sensors. Here, we report observations of strong structural oscillations of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) in the presence of both H2O vapour and electron irradiation using environmental transmission electron microscopy. These oscillations are related to the formation and collapse of gaseous bubbles. Electron energy-loss spectroscopy provides direct evidence of O2 formation in these bubbles due to the incorporation of H2O into BSCF. SrCoO3-δ was found to exhibit small oscillations, while none were observed for La0.5Sr0.5CoO3-δ and LaCoO3. The structural oscillations of BSCF can be attributed to the fact that its oxygen 2p-band centre is close to the Fermi level, which leads to a low energy penalty for oxygen vacancy formation, high ion mobility, and high water uptake. This work provides surprising insights into the interaction between water and oxides under electron-beam irradiation.

  19. Ab initio study of the structural phase transitions of the double perovskites Sr2MWO6 (M=Zn, Ca, Mg)

    Science.gov (United States)

    Petralanda, U.; Etxebarria, I.

    2014-02-01

    We study the interplay of structural distortions in double perovskites Sr2MWO6 (M = Zn, Ca, Mg) by means of first-principles calculations and group theoretical analysis. Structure relaxations of the cubic, tetragonal, and monoclinic phases show that the ground states of the three compounds are monoclinic, although the energy difference between the monoclinic and tetragonal structures is very small in the case of Sr2MgWO6. The symmetry analysis of the distortions involved in the experimental and calculated low-temperature structures shows that the amplitude of two primary distortions associated to rigid rotations of the MX6 and WO6 octahedra are dominant, although the amplitude of a third mode related to deformations of the MX6 groups can not be neglected. The energy maps of the space spanned by the three relevant modes are calculated, and the couplings among the modes are evaluated, showing that the role of a hard secondary mode (in the Landau sense) coupled trilinearly to the two primary instabilities is crucial to stabilize the monoclinic ground state. Results suggest that the key role of the trilinear coupling among three modes could be rather common. A phenomenological theory including the effects of the chemical pressure is also developed. We find that the evolution of the stiffness constants in terms of the atomic substitution follows an accurate linear dependence and that the influence of quantum saturation of the order parameters could stabilize the tetragonal phase of Sr2MgWO6.

  20. Three-Dimensional Structure of a Simple Liquid at a Face-Centered-Cubic (001) Solid Surface Interface.

    Science.gov (United States)

    Bao, Luyao; Hu, Haibao; Wen, Jun; Sepri, Paavo; Luo, Kai

    2016-07-19

    A liquid in the vicinity of a solid-liquid interface (SLI) may exhibit complex structures. In this study, we used molecular dynamics simulations demonstrating for the first time that the liquid adjacent to the SLI can have a two-level structure in some cases: a major structure and a minor structure. Through a time-averaging process of molecular motions, we identified the type of the liquid structure by calculating positions of the maximum liquid density in three spatial dimensions, and these positions were found to distribute in many dispersed zones (called high-density zones (HDZs)). The major structure appears throughout the SLI, while the minor structure only occurs significantly within the third layer. Instead of the previously reported body-centered cubic (BCC) or face-centered-cubic (FCC) types, the major structure was found to show a body-centered tetragonal (BCT) type. The adjacent HDZs are connected by specific junctions, demonstrating that atoms diffuse along some particular high probability paths from one HDZ to another. By considering the three-dimensional liquid density distribution from the continuum point of view, more complete details of the structure and diffusive behavior of liquids in the SLI are also possible to be revealed.

  1. Three-Dimensional Structure of a Simple Liquid at a Face-Centered-Cubic (001) Solid Surface Interface

    Science.gov (United States)

    Bao, Luyao; Hu, Haibao; Wen, Jun; Sepri, Paavo; Luo, Kai

    2016-07-01

    A liquid in the vicinity of a solid-liquid interface (SLI) may exhibit complex structures. In this study, we used molecular dynamics simulations demonstrating for the first time that the liquid adjacent to the SLI can have a two-level structure in some cases: a major structure and a minor structure. Through a time-averaging process of molecular motions, we identified the type of the liquid structure by calculating positions of the maximum liquid density in three spatial dimensions, and these positions were found to distribute in many dispersed zones (called high-density zones (HDZs)). The major structure appears throughout the SLI, while the minor structure only occurs significantly within the third layer. Instead of the previously reported body-centered cubic (BCC) or face-centered-cubic (FCC) types, the major structure was found to show a body-centered tetragonal (BCT) type. The adjacent HDZs are connected by specific junctions, demonstrating that atoms diffuse along some particular high probability paths from one HDZ to another. By considering the three-dimensional liquid density distribution from the continuum point of view, more complete details of the structure and diffusive behavior of liquids in the SLI are also possible to be revealed.

  2. Temperature-dependent EXAFS study of the local structure and lattice dynamics in cubic Y₂O₃.

    Science.gov (United States)

    Jonane, Inga; Lazdins, Karlis; Timoshenko, Janis; Kuzmin, Alexei; Purans, Juris; Vladimirov, Pavel; Gräning, Tim; Hoffmann, Jan

    2016-03-01

    The local structure and lattice dynamics in cubic Y2O3 were studied at the Y K-edge by X-ray absorption spectroscopy in the temperature range from 300 to 1273 K. The temperature dependence of the extended X-ray absorption fine structure was successfully interpreted using classical molecular dynamics and a novel reverse Monte Carlo method, coupled with the evolutionary algorithm. The obtained results allowed the temperature dependence of the yttria atomic structure to be followed up to ∼6 Å and to validate two force-field models.

  3. High-efficiency perovskite solar cells prepared by using a sandwich structure MAI-PbI2-MAI precursor film.

    Science.gov (United States)

    Zhang, Xuhui; Ye, Jiajiu; Zhu, Liangzheng; Zheng, Haiying; Liu, Guozhen; Liu, Xuepeng; Duan, Bin; Pan, Xu; Dai, Songyuan

    2017-01-11

    Two-step deposition has been widely used in the perovskite layer preparation for perovskite solar cells due to its attractive morphology controllability. However, the limited diffusivity of CH3NH3I (MAI) might cause some PbI2 to remain in the perovskite film. The residual PbI2 in the perovskite film would lead to inferior performance of devices, such as, low power conversion efficiency (PCE), poor reproducibility and weak air stability. In this work, we developed a sandwich structure MAI-PbI2-MAI precursor film to prepare a PbI2-free CH3NH3PbI3 perovskite film. In comparison to the two-step approach, the MAI-PbI2-MAI precursor film with a typical sandwich structure formed a uniform and pinhole-free perovskite film without any PbI2 residue, which could significantly improve the performance of the devices. Moreover, the bottom MAI layer of the MAI-PbI2-MAI precursor film could improve the interfacial contact of the porous TiO2 layer, leading to the promotion of the charge transfer and reduction of the recombination rate. Therefore, the devices fabricated from the sandwich structure MAI-PbI2-MAI precursor films showed dramatic improvements of open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF) and PCE. As a result, a promising PCE of 17.8% with good long-term air stability was achieved for the MAI-PbI2-MAI precursor film based PSC, which is better than that prepared by a two-step approach.

  4. Photo-induced effect in the layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Ruili; DAI; Jianming; SONG; Wenhai; MA; Yongqing; Y

    2004-01-01

    It is helpful to study the photo-induced effect in the perovskite manganites not only for elucidating the mechanism of colossal magnetoresistance (CMR) effect but also for potential applications in technology. The laser-induced effect in the Co doping layered perovskite manganites La1.2Sr1.8Mn1.8Co0.2O7 is studied in this paper and the obtained results are also compared with that gained in the Nd-doping manganites with cubic perovskite structure.

  5. Charge/orbital ordering structure in ordered perovskite Sm sub 1 sub / sub 2 Ba sub 1 sub / sub 2 MnO sub 3

    CERN Document Server

    Uchida, M; Akahoshi, D; Kumai, R; Tomioka, Y; Tokura, Y; Arima, T H

    2002-01-01

    In an A-site ordered perovskite manganite Sm sub 1 sub / sub 2 Ba sub 1 sub / sub 2 MnO sub 3 , a new charge/orbital ordering pattern was found at room temperature. Electron diffraction studies revealed a series of superlattice reflections with modulation vectors at q sub 2 =(1/2, 1/2, 1/2) as well as at q sub 1 =(1/4, 1/4, 0) in the tetragonal setting (a sub p x a sub p x 2a sub p , a sub p being the cubic perovskite lattice parameter). Together with the results of the resonant X-ray scattering and the charge-transport and magnetization measurements, a new model for the three-dimensional charge/orbital ordering in the ordered perovskite is proposed. (author)

  6. Specific heat and phonon density of state of cubic phase of protonic conductor LaAlO3

    Science.gov (United States)

    Sharma, Anupam Deep; Sinha, M. M.

    2016-05-01

    Perovskite oxides find wide range of applications like oxygen sensors, catalyst support, high frequency capacitors, high temperature superconducting microwave devices, solid state oxide fuel cell (SOFC) etc. LaAlO3 is one of such type of prominent perovskite oxides and very prominent material for protonic conductions. Therefore knowledge of the thermal properties of LaAlO3 is most significant. Hence in the present study we have studied phonon density of states and specific heat of LaAlO3 in cubic structure by applying lattice dynamical theoretical model. The calculated results are interpreted with existing experimental or theoretical results.

  7. Hybrid Perovskite/Perovskite Heterojunction Solar Cells.

    Science.gov (United States)

    Hu, Yinghong; Schlipf, Johannes; Wussler, Michael; Petrus, Michiel L; Jaegermann, Wolfram; Bein, Thomas; Müller-Buschbaum, Peter; Docampo, Pablo

    2016-06-28

    Recently developed organic-inorganic hybrid perovskite solar cells combine low-cost fabrication and high power conversion efficiency. Advances in perovskite film optimization have led to an outstanding power conversion efficiency of more than 20%. Looking forward, shifting the focus toward new device architectures holds great potential to induce the next leap in device performance. Here, we demonstrate a perovskite/perovskite heterojunction solar cell. We developed a facile solution-based cation infiltration process to deposit layered perovskite (LPK) structures onto methylammonium lead iodide (MAPI) films. Grazing-incidence wide-angle X-ray scattering experiments were performed to gain insights into the crystallite orientation and the formation process of the perovskite bilayer. Our results show that the self-assembly of the LPK layer on top of an intact MAPI layer is accompanied by a reorganization of the perovskite interface. This leads to an enhancement of the open-circuit voltage and power conversion efficiency due to reduced recombination losses, as well as improved moisture stability in the resulting photovoltaic devices.

  8. Ionic Transport and Structural Characterization of the Lithium-Rich Anti-Perovskite Li3OCl

    Science.gov (United States)

    Howard, John; Daemen, Luke; Hartl, Monika; Chlistunoff, Jerzy; Zhao, Yusheng

    2013-03-01

    We will discuss the structural and electrochemical characterization of the newly synthesized lithium-rich anti-perovskite, Li3OCl. The crystal structure of this compound was solved using x-ray diffraction techniques, and the electronic and ionic conductivities were measured using electrochemical impedance spectroscopy. This material has an ionic conductivity ranging approximately from 10-4 S/cm to 10-1 S/cm over the temperature range 25°C to 270°C (room temperature to just below the melting point). The high ionic conductivity of this lithium-rich electrolyte demonstates strong promise that this material is an ideal candidate for solid state battery applications.

  9. A combined DFT and post-DFT investigation on cubic XMoO3 (X  =  Sr, Ba) perovskite oxides

    Science.gov (United States)

    Dar, Sajad Ahmad; Srivastava, Vipul; Sakalle, Umesh Kumar

    2017-08-01

    Highly precise and accurate density functional theory has been used to check the structural, elasto-mechanical thermo-electronic and thermodynamic properties of XMoO3 (X  =  Sr, Ba). The study was accomplished within different exchange correlation potentials like (GGA, GGA  +  U, mBJ, and GGA  +  U  +  SOC). The optimization for both the compounds was achieved for paramagnetic, ferromagnetic and anti-ferromagnetic phases and the compounds were found to have paramagnetic stable phase. The spin polarized band structure and density of states present metallic nature for both the compounds. The symmetric spin polarized band for both (up, down) states and negligible spin magnetic moment also confirm the paramagnetic nature of these compounds. The post DFT treatment through Boltztrap code was used to check the temperature dependence of electrical conductivity. The elastic constants and mechanical properties like Young modulus, shear modulus, Poisson ratio and anisotropic factor have also been calculated. The calculated value of B/G ratio and Cauchy pressure show that both compounds establish ductile nature. Debye temperature along with melting temperature for both the compounds was predicted. Further the nature of thermodynamic parameters like heat capacity and Debye temperature were also checked under pressure and temperature variation using quasi-harmonic Debye approximation.

  10. Preparation and Luminescence Properties of MZrO3:Eu3+, A (M=Ca2+, Ba2+; A=Li+, Na+, K+) Phosphors with Perovskite Structure

    Institute of Scientific and Technical Information of China (English)

    MAR B; CEMBRERO-COCA P; SINGH K C; KAUSHIK R D; OM Hari

    2013-01-01

    Calcium and barium zirconate powders based upon CaZrO3:Eu3+, A and BaZrO3:Eu3+, A (A=Li+, Na+, K+) were prepared by combustion synthesis method and heating to ~1000 °C to improve crystal inity. The structure and morphology of materials were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results showed that CaZrO3:Eu3 +, A and BaZrO3:Eu3 +, A (A=Li +, Na +, K +) perovskites possessed orthorhombic and cubic structures, respectively. The morphologies of al powders were very similar consisting of smal , coagulated, cubical particles with narrow size distributions and smooth and regular surfaces. The characteristic luminescences of Eu3+ ions in CaZrO3:Eu3+, A (A=Li+, Na+, K+) lattices were present with strong emissions at 614 and 625 nm for 5D0→7F2 transitions with other weaker emissions observed at 575, 592, 655, and 701 nm corresponding to 5D0→7Fn transitions (where n=0, 1, 3, 4, respectively). In BaZrO3:Eu3 + both the 5D0→7F1 and 5D0→7F2 transitions at 595 and 613 nm were strong. Photoluminescence intensities of CaZrO3:Eu3+ samples were higher than those of BaZrO3:Eu3+ lattices. This remarkable increase of photoluminescence intensity (corresponding to 5D0→7Fn transitions) was observed in CaZrO3:Eu3 + and BaZrO3:Eu3 + if co-doped with Li + ions. An additional broad band composed of many peaks between 440 to 575 nm was observed in BaZrO3:Eu3 +, A samples. The intensity of this band was greatest in Li+ co-doped samples and lowest for K+ doped samples.

  11. Synthesis, crystal structure, and properties of a perovskite-related bismuth phase, (NH43Bi2I9

    Directory of Open Access Journals (Sweden)

    Shijing Sun

    2016-03-01

    Full Text Available Organic-inorganic halide perovskites, especially methylammonium lead halide, have recently led to remarkable advances in photovoltaic devices. However, due to environmental and stability concerns around the use of lead, research into lead-free perovskite structures has been attracting increasing attention. In this study, a layered perovskite-like architecture, (NH43Bi2I9, is prepared from solution and the structure solved by single crystal X-ray diffraction. The band gap, which is estimated to be 2.04 eV using UV-visible spectroscopy, is lower than that of CH3NH3PbBr3. The energy-minimized structure obtained from first principles calculations is in excellent agreement with the X-ray results and establishes the locations of the hydrogen atoms. The calculations also point to a significant lone pair effect on the bismuth ion. Single crystal and powder conductivity measurements are performed to examine the potential application of (NH43Bi2I9 as an alternative to the lead containing perovskites.

  12. Coherent Fe-rich nano-scale perovskite oxide phase in epitaxial Sr2FeMoO6 films grown on cubic and scandate substrates

    Science.gov (United States)

    Deniz, Hakan; Preziosi, Daniele; Alexe, Marin; Hesse, Dietrich

    2017-01-01

    We report the growth of high-quality epitaxial Sr2FeMoO6 (SFMO) thin films on various unconventional oxide substrates, such as TbScO3, DyScO3, and Sr2Al0.3Ga0.7TaO6 (SAGT) as well as on the most commonly used one, SrTiO3 (STO), by pulsed laser deposition. The films were found to contain a foreign nano-scale phase coherently embedded inside the SFMO film matrix. Through energy dispersive X-ray spectroscopy and scanning transmission electron microscopy, we identified the foreign phase to be Sr2-xFe1+yMo1-yO6, an off-stoichiometric derivative of the SFMO compound with Fe rich content (y ≈ 0.6) and a fairly identical crystal structure to SFMO. The films on STO and SAGT exhibited very good magnetic properties with high Curie temperature values. All the samples have fairly good conducting behavior albeit the presence of a foreign phase. Despite the relatively large number of items of the foreign phase, there is no significant deterioration in the properties of the SFMO films. We discuss in detail how magneto-transport properties are affected by the foreign phase.

  13. Structural and Quantitative Investigation of Perovskite Pore Filling in Mesoporous Metal Oxides

    OpenAIRE

    Shany Gamliel; Inna Popov; Bat-El Cohen; Vladimir Uvarov; Lioz Etgar

    2016-01-01

    In recent years, hybrid organic–inorganic perovskite light absorbers have attracted much attention in the field of solar cells due to their optoelectronic characteristics that enable high power conversion efficiencies. Perovskite-based solar cells’ efficiency has increased dramatically from 3.8% to more than 20% in just a few years, making them a promising low-cost alternative for photovoltaic applications. The deposition of perovskite into a mesoporous metal oxide is an influential factor af...

  14. Crystalline, Magnetic and Electronic Structure of the Ba2DySbO6 Complex Perovskite

    Science.gov (United States)

    Cardona, R.; Moreno Mendoza, R.; Carrero Bermúdez, L. A.; Landínez Téllez, D. A.; Roa-Rojas, J.

    2016-01-01

    In this work, we report the synthesis of the Ba2DySbO6 new double perovskite by means of the solid-state reaction recipe from high-purity oxide powders of BaCO3, Dy2O3, and Sb2O5. The analysis of the crystal structure was carried out through the X-ray diffraction technique with posterior Rietveld refinement of the experimental diffraction data by the GSAS code. Results reveal that the Ba2DySbO6 material crystallizes in a rhombohedral perovskite structure, belonging to the R-3 (#148) space group with lattice parameter a = 5.96260(5) Å, and angle α = 60.008°. The magnetic characterization was performed by measurements of magnetic susceptibility as a function of temperature. The behavior observed in the temperature regime from 4 K up to 300 K was paramagnetic. The characteristic magnetic parameters were obtained from the fitting with the Curie equation, obtaining the values of susceptibility independent of temperature 0.00633 emu/mol and effective magnetic moment 8.9 \\upmu B, which is 84 % in agreement with the expected value predicted by the Hund's rules. The electronic structure was calculated by means of linearized augmented plane waves in the framework of the density functional theory (DFT). This study considers the cohesion energies as a function of the lattice parameter, with a lattice constant a, whose value is 98 % in agreement with the experimental result. Curves of density of states as a function of the wave number reveal that this material behaves as an insulator with energy gap 3.65 eV. This result was corroborated by diffuse reflectance experiments adjusted to the Kubelka-Munk equation. The effective magnetic moment obtained from the DFT calculations was 7.7 \\upmu B.

  15. Structural properties of undoped and doped cubic GaN grown on SiC(001)

    OpenAIRE

    Martínez-Guerrero, Esteban; Bellet-Amalric, E.; Martinet, L.; Feuillet, G.; Daudin, B.

    2002-01-01

    Transmission electron microscopy and x-ray diffraction measurements reveal the presence of stacking faults ~SFs! in undoped cubic GaN thin layers. We demonstrate the importance of the defects in the interfacial region of the films by showing that the SFs act as nucleation sites for precipitates of residual impurities such as C and Si present in the GaN layers grown on SiC~001! substrates. We used the imaging secondary ion mass spectroscopy technique to locate these impurities. The systemat...

  16. Structural and surface analysis of unsupported and alumina-supported La(Mn,Fe,Mo)O{sub 3} perovskite oxides

    Energy Technology Data Exchange (ETDEWEB)

    Rosmaninho, M.G.; Tristao, J.C.; Moura, F.C.C.; Lago, R.M.; Araujo, M.H. [Universidade Federal de Minas Gerais (UFMG), Departamento de Quimica, ICEx, Minas Gerais (Brazil); Fierro, J.L.G. [Instituto de Catalisis y Petroleoquimica (ICP), Madrid (Spain)

    2010-04-15

    A series of bulk and Al{sub 2}O{sub 3}-supported perovskite oxides of the type LaMn{sub 1-x-y} Fe{sub x} Mo{sub y} O{sub 3} (x=0.00-0.90 and y=0.00-0.09) were synthesized by the citric acid complexation-gelation method followed by annealing in air at 800 C. For all samples, the local environment and the chemical state and concentration of surface species were determined. Moessbauer spectra revealed the only presence of octahedral Fe {sup 3+} ions dispersed in the perovskite structure, however well-crystallized together with a poorly crystalline LaFeO{sub 3} phases were detected for larger substitutions (x=0.90). A similar picture was obtained for Mo-loaded (y=0.02 and 0.05) samples but a new phase most likely related to Fe {sup 3+} ions dispersed aside from the perovskite structure was found for larger substitutions (y=0.09). Together with these structures, supported samples showed the presence of LaFeO{sub 3} nanoparticles. Finally, photoelectron spectroscopy indicated that the chemical state and composition of the samples in the surface region (2-3 nm) approaches that of the bulk. For the unsupported substituted samples, iron (and molybdenum) enters into the perovskite structure while manganese tends to be slightly segregated. Moreover, in supported perovskites, a fraction of Mo and La atoms interact with the alumina surface. All these oxides were active in methane combustion and best performance was recorded for the Fe-rich composition (x=0.9) in which both Mn {sup 3+} and Mo {sup 3+} ions were in the same proportion (y=0.05). (orig.)

  17. Crystal structure and magnetic properties of Mo-substituted 'Ba{sub 2}(Fe,W){sub 2}O{sub 6}' double-perovskites: a synchrotron diffraction, magnetization and Moessbauer study

    Energy Technology Data Exchange (ETDEWEB)

    Rammeh, N.; Bramnik, K.G.; Ehrenberg, H.; Stahl, B.; Fuess, H.; Cheikh-Rouhou, A

    2004-01-28

    Synchrotron diffraction and Moessbauer spectroscopy on Ba{sub 2}(Fe,W){sub 2}O{sub 6} confirmed an Fe excess in this double-perovskite, better described as Ba{sub 2}Fe(Fe{sub x}W{sub 1-x})O{sub 6-{delta}} with x=0.2. The crystal structure is cubic (Fm3-bar m) down to 10 K, and a recently reported tetragonal structure of Ba{sub 2}FeWO{sub 6} is critically reviewed. Magnetic properties of Ba{sub 2}(Fe,W{sub 1-x}Mo{sub x}){sub 2}O{sub 6} compounds were studied by SQUID measurements and revealed weak ferromagnetism at low temperatures, and T{sub C} increases with more substitution of Mo for W.

  18. Exploring a Lead-free Semiconducting Hybrid Ferroelectric with a Zero-Dimensional Perovskite-like Structure.

    Science.gov (United States)

    Sun, Zhihua; Zeb, Aurang; Liu, Sijie; Ji, Chengmin; Khan, Tariq; Li, Lina; Hong, Maochun; Luo, Junhua

    2016-09-19

    Perovskite lead halides (CH3 NH3 PbI3 ) have recently taken a promising position in photovoltaics and optoelectronics because of remarkable semiconducting properties and possible ferroelectricity. However, the potential toxicity of lead arouses great environmental concern for widespread application. A new chemically tailored lead-free semiconducting hybrid ferroelectric is reported, N-methylpyrrolidinium)3 Sb2 Br9 (1), which consists of a zero-dimensional (0-D) perovskite-like anionic framework connected by corner- sharing SbBr6 coordinated octahedra. It presents a large ferroelectric spontaneous polarization of approximately 7.6 μC cm(-2) , as well as notable semiconducting properties, including positive temperature-dependent conductivity and ultraviolet-sensitive photoconductivity. Theoretical analysis of electronic structure and energy gap discloses a dominant contribution of the 0-D perovskite-like structure to the semiconducting properties of the material. This finding throws light on the rational design of new perovskite-like hybrids, especially lead-free semiconducting ferroelectrics.

  19. Structural, electronic and optical properties of ilmenite and perovskite CdSnO3 from DFT calculations.

    Science.gov (United States)

    Sesion, P D; Henriques, J M; Barboza, C A; Albuquerque, E L; Freire, V N; Caetano, E W S

    2010-11-03

    CdSnO(3) ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at ω = 0 and ∞ were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn-Sham band structures obtained for the CdSnO(3) polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO(3) does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO(3) with ferroelectric properties.

  20. Structural, electronic and optical properties of ilmenite and perovskite CdSnO{sub 3} from DFT calculations

    Energy Technology Data Exchange (ETDEWEB)

    Sesion Jr, P D [Escola de Ciencias e Tecnologia, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte (Brazil); Henriques, J M [Departamento de Fisica Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte (Brazil); Barboza, C A; Albuquerque, E L [Departamento de Biofisica e Farmacologia, Universidade Federal do Rio Grande do Norte, 59072-900 Natal, Rio Grande do Norte (Brazil); Freire, V N [Departamento de Fisica, Universidade Federal do Ceara, 60455-970 Fortaleza, Ceara (Brazil); Caetano, E W S, E-mail: ewcaetano@gmail.co [Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara, Avenida 13 de Maio, 2081, Benfica, 60040-531 Fortaleza, Ceara (Brazil)

    2010-11-03

    CdSnO{sub 3} ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at {omega} = 0 and {infinity} were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn-Sham band structures obtained for the CdSnO{sub 3} polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO{sub 3} does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO{sub 3} with ferroelectric properties.

  1. Chalcogenide perovskites for photovoltaics.

    Science.gov (United States)

    Sun, Yi-Yang; Agiorgousis, Michael L; Zhang, Peihong; Zhang, Shengbai

    2015-01-14

    Chalcogenide perovskites are proposed for photovoltaic applications. The predicted band gaps of CaTiS3, BaZrS3, CaZrSe3, and CaHfSe3 with the distorted perovskite structure are within the optimal range for making single-junction solar cells. The predicted optical absorption properties of these materials are superior compared with other high-efficiency solar-cell materials. Possible replacement of the alkaline-earth cations by molecular cations, e.g., (NH3NH3)(2+), as in the organic-inorganic halide perovskites (e.g., CH3NH3PbI3), are also proposed and found to be stable. The chalcogenide perovskites provide promising candidates for addressing the challenging issues regarding halide perovskites such as instability in the presence of moisture and containing the toxic element Pb.

  2. Magnetic and structural properties of the double-perovskite Ca 2FeReO 6

    Science.gov (United States)

    Westerburg, W.; Lang, O.; Ritter, C.; Felser, C.; Tremel, W.; Jakob, G.

    2002-04-01

    We suceeded in the preparation of polycrystalline Ca 2FeReO 6 which has a Curie temperature TC of 540 K, the highest value of all magnetic perovskites investigated till now. This material has been characterised by X-ray and neutron powder diffraction. We found at 548 K, a monoclinic unit cell (space group P2 1/ n) with a=5.4366(5) Å, b=5.5393(5) Å, c=7.7344(5) Å, and β=90.044(4)°. For temperatures below 400 K, a phase separation in two monoclinic phases with identical cell volume is observed in neutron scattering. The two phases possess different magnetic structure and coercivity. The conductivity is thermally activated for all temperatures and no significant magnetoresistivity is observed.

  3. Effective field study of ising model on a double perovskite structure

    Science.gov (United States)

    Ngantso, G. Dimitri; El Amraoui, Y.; Benyoussef, A.; El Kenz, A.

    2017-02-01

    By using the effective field theory (EFT), the mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model adapted to a double perovskite structure has been studied. The EFT calculations have been carried out from Ising Hamiltonian by taking into account first and second nearest-neighbors interactions and the crystal and external magnetic fields. Both first- and second-order phase transitions have been found in phase diagrams of interest. Depending on crystal-field values, the thermodynamic behavior of total magnetization indicated the compensation phenomenon existence. The hysteresis behaviors are studied by investigating the reduced magnetic field dependence of total magnetization and a series of hysteresis loops are shown for different reduced temperatures around the critical one.

  4. Peculiarities of Crystal Structure of the Cubic System Compounds with T 4 and T 5 Space Groups

    Science.gov (United States)

    Zolotarev, M. L.; Poplavnoi, A. S.

    2016-09-01

    We study symmetry peculiarities of crystalline compounds of a cubic system with the space groups T 4 and T 5 caused by the absence of point Wyckoff-sets in the unit cells of these groups. Due to the high multiplicity of the available Wyckoff positions, such compounds possess unit cells of complex composition. In these compounds, pseudosymmetry is realized with high probability when some group of atoms is located in positions close to the positions of higher-symmetry groups. We provide examples of crystalline compounds showing predicted specific structural features.

  5. Structural, elastic and electronic Properties of isotropic cubic crystals of carbon and silicon nanotubes : Density functional based tight binding calculations.

    Directory of Open Access Journals (Sweden)

    Alexander L. Ivanovskii

    2008-01-01

    Full Text Available Atomic models of cubic crystals (CC of carbon and graphene-like Si nanotubes are offered and their structural, cohesive, elastic and electronic properties are predicted by means of the DFTB method. Our main findings are that the isotropic crystals of carbon nanotubes adopt a very high elastic modulus B and low compressibility β, namely B = 650 GPa, β = 0.0015 1/GPa. In addition, these crystals preserve the initial conductivity type of their “building blocks”, i.e. isolated carbon and Si nanotubes. This feature may be important for design of materials with the selected conductivity type.

  6. Degradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion Migration.

    Science.gov (United States)

    Yuan, Haifeng; Debroye, Elke; Janssen, Kris; Naiki, Hiroyuki; Steuwe, Christian; Lu, Gang; Moris, Michèle; Orgiu, Emanuele; Uji-I, Hiroshi; De Schryver, Frans; Samorì, Paolo; Hofkens, Johan; Roeffaers, Maarten

    2016-02-04

    Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degradation pathways. Here, we apply simultaneous luminescence and electron microscopy on perovskites for the first time, allowing us to monitor in situ morphology evolution and optical properties upon perovskite degradation. Interestingly, morphology, photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degradation driven by electron beam (e-beam) or by light. A transversal electric current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degradation results in material decomposition to scattered particles and shows little PL spectral shifts. The differences in degradation can be ascribed to different electric currents that drive ion migration. Moreover, solution-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphology. Our results reveal the essential role of ion migration in perovskite degradation and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphology and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degradation and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using scanning electron microscopy or transmission electron microscopy techniques.

  7. Synthesis, structure and total conductivity of A-site doped LaTiO{sub 3−δ} perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Bradha, M. [Nanotech Research Facility, PSG Institute of Advanced Studies, Coimbatore 641 004, TN (India); Hussain, S.; Chakravarty, Sujay [UGC-DAE CSR, Kalpakkam Node, Kokilamedu 603 104, TN (India); Amarendra, G. [UGC-DAE CSR, Kalpakkam Node, Kokilamedu 603 104, TN (India); Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, TN (India); Ashok, Anuradha, E-mail: anu.machina@gmail.com [Nanotech Research Facility, PSG Institute of Advanced Studies, Coimbatore 641 004, TN (India)

    2015-03-25

    Highlights: • A-site divalent alkaline earth metal doped LaTiO{sub 3−δ} perovskites were synthesised by sol–gel method. • Structural studies revealed no change in crystal symmetry but change in cell dimensions after doping. • After doping divalent cations in A-site, an enhancement in total conductivity was observed in LaTiO{sub 3−δ}. • Temperature dependent electrical property was observed in all synthesised perovskites. - Abstract: Oxygen deficient perovskites LaTiO{sub 3−δ} and La{sub 0.8}A{sub 0.2}TiO{sub 3−δ} (A = Ba, Sr, Ca) were synthesized by sol–gel method. The effect of divalent dopants on microstructure is investigated in detail using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The oxidation states of La{sup 3+} and Ti{sup 3+} ions have been deduced using X-ray Photoelectron Spectroscopy (XPS). Impedance spectroscopy was used to analyze the total conductivity, an increase in conductivity was observed after doping in the A-site with divalent cations Ba, Ca and Sr. Among the investigated perovskites La{sub 0.8}Ca{sub 0.2}TiO{sub 3−δ} exhibited the maximum conductivity of 1.22 × 10{sup −2} S/cm in air atmosphere at 650 °C.

  8. Direct synthesis of diphenyl carbonate over heterogeneous catalyst:effects of structure of substituted perovskite carrier on the catalyst activities

    Institute of Scientific and Technical Information of China (English)

    WU Guangwen; WU Yuxin; MA Peisheng; JIN Fang; ZHANG Guangxu; LI Dinghuo; WANG Cunwen

    2007-01-01

    The perovskite-type compound LaMnO3 was substituted for the part of La in position A and for the part of Mn in position B by citrate method.The phases were detected by X-ray diffraction.Powder morphologies were scanned by scanning electron microscopy.The valence of atoms was determined by X-ray photoelectron spectroscopy.It was found that the perovskite can form crystal defect and increase the proportion of high valence B element by doping.Active component Pd was loaded on various perovskite supports for synthesis of diphenyl carbonate.The results showed that the activities of catalysts in which supports have crystal defect by substitution were higher.It can be concluded that perovskite with defect structure by doping could lead to the formation of oxygen vacancy where the lattice oxygen became exchangeable with the oxygen gas.Also,this improved the redox process of the carrier by transferring electrons and activities of catalysts.

  9. Perfect cubic texture, structure, and mechanical properties of nonmagnetic copper-based alloy ribbon substrates

    Science.gov (United States)

    Khlebnikova, Yu. V.; Rodionov, D. P.; Gervas'eva, I. V.; Egorova, L. Yu.; Suaridze, T. R.

    2015-03-01

    A sharp cubic texture is formed in a number of copper alloys subjected to cold deformation by rolling by 98.6-99% followed by recrystallization annealing, which opens up fresh opportunities for long thin ribbons made of these alloys to be used as substrates in the production of second-generation high- T c superconductor (2G HTSC) cables. The possibility of creating ternary alloys based on a binary Cu-30 at % Ni alloy with additional elements that harden its fcc matrix (iron, chromium) is shown. The measurements of the mechanical properties of textured ribbons made of these alloys demonstrate that their yield strength is higher than that of a textured ribbon made of pure copper by a factor of 2.5-4.5.

  10. Hydrogen absorption in uranium-based alloys with cubic γ -U structure

    Science.gov (United States)

    Havela, L.; Kim-Ngan, N.-T. H.

    2017-03-01

    UH3-type hydrides were formed by hydrogenation of splat-cooled U-based alloys upon applying high H2 pressures (>2.5 bar). Hydrogenation of U1‑x Mo x alloys (with x  ⩾  0.12 (12 at.% Mo) containing the cubic γ-U phase leads to a formation of nanocrystalline β-UH3, why those of U1‑x Zr x alloys (with x  ⩾15 at.% Zr) implies a pure α-UH3. The Curie temperature of hydride (UH3)0.85Mo0.15 reaches 200 K it may be the first U-based ferromagnet with such high T C. The results reflect the dominant U–H interaction. Invited talk at 8th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2016), 8–12 November 2016, Ha Long City, Vietnam.

  11. Perovskites and garnets

    Energy Technology Data Exchange (ETDEWEB)

    Khattak, C.P.; Wang, F.F.Y.

    1976-01-01

    The preparation and properties of perovskites and garnets are reviewed. Data and information are presented on crystal chemistry, crystal structure, phase equilibria, electrical properties, optical properties, and mechanical properties. (JRD)

  12. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AIN and InN

    Science.gov (United States)

    1992-12-01

    AD-A258 804 Final Technical Report Ii Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent...Technical 6/1/86-12/31/92 4. TITLE AND SUBTITLE Growth, Nitrogen Vacancy Reduction and 5. FUNDING NUMBERS Solid Solution Formation in Cubic GaN Thin...According to the structural and chemical analyses, there is no reason to believe that a homogeneous solid solution close to this composition had

  13. Lead-Free Halide Double Perovskites via Heterovalent Substitution of Noble Metals.

    Science.gov (United States)

    Volonakis, George; Filip, Marina R; Haghighirad, Amir Abbas; Sakai, Nobuya; Wenger, Bernard; Snaith, Henry J; Giustino, Feliciano

    2016-04-07

    Lead-based halide perovskites are emerging as the most promising class of materials for next-generation optoelectronics; however, despite the enormous success of lead-halide perovskite solar cells, the issues of stability and toxicity are yet to be resolved. Here we report on the computational design and the experimental synthesis of a new family of Pb-free inorganic halide double perovskites based on bismuth or antimony and noble metals. Using first-principles calculations we show that this hitherto unknown family of perovskites exhibits very promising optoelectronic properties, such as tunable band gaps in the visible range and low carrier effective masses. Furthermore, we successfully synthesize the double perovskite Cs2BiAgCl6, perform structural refinement using single-crystal X-ray diffraction, and characterize its optical properties via optical absorption and photoluminescence measurements. This new perovskite belongs to the Fm3̅m space group and consists of BiCl6 and AgCl6 octahedra alternating in a rock-salt face-centered cubic structure. From UV-vis and photoluminescence measurements we obtain an indirect gap of 2.2 eV.

  14. The crystal structure and twinning of neodymium gallium perovskite single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ubizskii, S.B.; Vasylechko, L.O.; Savytskii, D.I.; Matkovskii, A.O.; Syvorotka, I.M. [Res. Production Amalgamation Carat, L' viv (Ukraine)

    1994-10-01

    By means of X-ray structure analysis, the crystal structure of neodymium gallium perovskite (NGP) single crystals (NdGaO{sub 3}) being used as a substrate for HTSC film epitaxy has been refined and the position of atoms has been determined. The possibility of YBa{sub 2}Cu{sub 3}O{sub 7-x} film epitaxy on the plane (110) of NGP crystal as well as its advantages and pitfalls are analysed from structural data. The twinning types in the NGP crystal were established. The twinning structure of NGP substrates is found to be stable up to a temperature of 1173 K, as differentiated from the LaGaO{sub 3} and LaAlO{sub 3} substrates. It is intimated that the twinning in the NGP substrates oriented as (001) can result in creation of 90 degrees twin bonds in a film, and in the case of (110)-oriented plates it is possible to ignore the twinning presence in substrate completely. (author)

  15. High throughput thermal conductivity of high temperature solid phases: The case of oxide and fluoride perovskites

    CERN Document Server

    van Roekeghem, Ambroise; Oses, Corey; Curtarolo, Stefano; Mingo, Natalio

    2016-01-01

    Using finite-temperature phonon calculations and machine-learning methods, we calculate the mechanical stability of about 400 semiconducting oxides and fluorides with cubic perovskite structures at 0 K, 300 K and 1000 K. We find 92 mechanically stable compounds at high temperatures -- including 36 not mentioned in the literature so far -- for which we calculate the thermal conductivity. We demonstrate that the thermal conductivity is generally smaller in fluorides than in oxides, largely due to a lower ionic charge, and describe simple structural descriptors that are correlated with its magnitude. Furthermore, we show that the thermal conductivities of most cubic perovskites decrease more slowly than the usual $T^{-1}$ behavior. Within this set, we also screen for materials exhibiting negative thermal expansion. Finally, we describe a strategy to accelerate the discovery of mechanically stable compounds at high temperatures.

  16. Pressure Effects on Structure and Optical Properties in Cesium Lead Bromide Perovskite Nanocrystals.

    Science.gov (United States)

    Xiao, Guanjun; Cao, Ye; Qi, Guangyu; Wang, Lingrui; Liu, Chuang; Ma, Zhiwei; Yang, Xinyi; Sui, Yongming; Zheng, Weitao; Zou, Bo

    2017-07-26

    Metal halide perovskites (MHPs) are gaining increasing interest because of their extraordinary performance in optoelectronic devices and solar cells. However, developing an effective strategy for achieving the band-gap engineering of MHPs that will satisfy the practical applications remains a great challenge. In this study, high pressure is introduced to tailor the optical and structural properties of MHP-based cesium lead bromide nanocrystals (CsPbBr3 NCs), which exhibit excellent thermodynamic stability. Both the pressure-dependent steady-state photoluminescence and absorption spectra experience a stark discontinuity at ∼1.2 GPa, where an isostructural phase transformation regarding the Pbnm space group occurs. The physical origin points to the repulsive force impact due to the overlap between the valence electron charge clouds of neighboring layers. Simultaneous band-gap narrowing and carrier-lifetime prolongation of CsPbBr3 trihalide perovskite NCs were also achieved as expected, which facilitates the broader solar spectrum absorption for photovoltaic applications. Note that the values of the phase change interval and band-gap red-shift of CsPbBr3 nanowires are between those for CsPbBr3 nanocubes and the corresponding bulk counterparts, which results from the unique geometrical morphology effect. First-principles calculations unravel that the band-gap engineering is governed by orbital interactions within the inorganic Pb-Br frame through structural modification. Changes of band structures are attributed to the synergistic effect of pressure-induced modulations of the Br-Pb bond length and Pb-Br-Pb bond angle for the PbBr6 octahedral framework. Furthermore, the significant distortion of the lead-bromide octahedron to accommodate the Jahn-Teller effect at much higher pressure would eventually lead to a direct to indirect band-gap electronic transition. This study enables high pressure as a robust tool to control the structure and band gap of CsPbBr3 NCs, thus

  17. Crystallography and Chemistry of Perovskites

    OpenAIRE

    Johnsson, Mats; Lemmens, Peter

    2005-01-01

    Despite the simplicity of the original perovskite crystal structure, this family of compounds shows an enormous variety of structural modifications and variants. In the following, we will describe several examples of perovskites, their structural variants and discuss the implications of distortions and non-stoichiometry on their electronic and magnetic properties.

  18. Multiple-stage structure transformation of organic-inorganic hybrid perovskite CH3NH3PbI3

    CERN Document Server

    Chen, Qiong; Kim, Hui-Seon; Liu, Yucheng; Yang, Mengjin; Yue, Naili; Ren, Gang; Zhu, Kai; Liu, Shengzhong; Park, Nam-Gyu; Zhang, Yong

    2016-01-01

    By performing spatially resolved Raman and photoluminescence spectroscopy with varying excitation wavelength, density, and data acquisition parameters, we have achieved a unified understanding towards the spectroscopy signatures of the organic-inorganic hybrid perovskite, transforming from the pristine state (CH3NH3PbI3) to fully degraded state (i.e., PbI2) for samples with varying crystalline domain size from mesoscopic scale (approximately 100 nm) to macroscopic size (cm), synthesized by three different techniques. We show that the hybrid perovskite exhibits multiple stages of structure transformation occurring either spontaneously or under light illumination, with exceptionally high sensitivity to the illumination conditions (e.g., power, illumination time and interruption pattern). We highlight four transformation stages (Stage 1 - 4, with Stage 1 being the pristine state) along a primary structure degradation path exhibiting distinctly different Raman spectroscopy features at each stage, and point out th...

  19. Redetermination of Nd2Ti2O7: a non-centrosymmetric structure with perovskite-type slabs.

    Science.gov (United States)

    Ishizawa, Nobuo; Ninomiya, Keisuke; Sakakura, Terutoshi; Wang, Jun

    2013-04-01

    Single crystals of dineodymium(III) dititanium(IV) hepta-oxide, Nd2Ti2O7, were synthesized by the flux method and found to belong to the family of compounds with perovskite-type structural motifs. The asymmetric unit contains four Nd, four Ti and 14 O-atom sites. The perovskite-type slabs are stacked parallel to (010) with a thickness corresponding to four corner-sharing TiO6 octa-hedra. The Nd and Ti ions are displaced from the geometrical centres of respective coordin-ation polyhedra so that the net polarization occurs along the c axis. The investigated crystals were all twinned and have a halved monoclinic unit cell in comparison with the first structure determination of this compound [Scheunemann & Müller-Buschbaum (1975 ▶). J. Inorg. Nucl. Chem. 37, 2261-2263].

  20. First principal studya of structural, electronic and thermodynamic properties of KTaO3-perovskite.

    Directory of Open Access Journals (Sweden)

    Hiadsi S.

    2013-03-01

    Full Text Available The results of first-principles theoretical study of structural, elastic, electronic and thermodynamic properties of KTaO3 compound, have been performed using the full-potential linear augmented plane-wave method plus local orbitals (FP-APW+lo as implemented in the Wien2k code. The exchange-correlation energy, is treated in generalized gradient approximation (GGA using the Perdew–Burke–Ernzerhof (PBE96 and PBEsol, Perdew 2008 parameterization. Also we have used the Engel-Vosko GGA optimizes the corresponding potential for band structure calculations. The calculated equilibrium parameter is in good agreement with other works. The elastic constants were calculated by using the Mehl method. The electronic band structure of this compound has been calculated using the Angel-Vosko (EV generalized gradient approximation (GGA for the exchange correlation potential. We deduced that KTaO3-perovskite exhibit an indirect from R to Γ point. To complete the fundamental characterization of KTaO3 material we have analyzed the thermodynamic properties using the quasi-harmonic Debye model.

  1. Pressure dependent structural changes and predicted electrical polarization in perovskite RMnO₃.

    Science.gov (United States)

    Wu, T; Chen, H; Gao, P; Yu, T; Chen, Z; Liu, Z; Ahn, K H; Wang, X; Cheong, S-W; Tyson, T A

    2016-02-10

    High pressure x-ray diffraction measurements on perovskite RMnO3 (R  =  Dy, Ho and Lu) reveal that varying structural changes occur for different R ions. Large lattice changes (orthorhombic strain) occur in DyMnO3 and HoMnO3 while the Jahn-Teller (JT) distortion remains stable. Conversely, in the small R-ion system LuMnO3, Mn-O bond distortions are observed between 4 and 8 GPa with a broad minimum in the JT distortion. High pressure infrared measurements indicate that a phonon near 390 cm(-1) corresponding to the complex motion of the Mn and O ions changes anomalously for LuMnO3. It softens in the 4-8 GPa region, which is consistent with the structural change in Mn-O bonds and then hardens at higher pressures. By contrast, the phonons continuously harden with increasing pressure for DyMnO3 and HoMnO3. Density functional theory methods show that E-phase LuMnO3 is the most stable phase up to the 10 GPa pressure examined. Simulations indicate that the distinct structural change under pressure in LuMnO3 can possibly be used to optimize the electric polarization by pressure/strain.

  2. Pressure dependent structural changes and predicted electrical polarization in perovskite RMnO3

    Science.gov (United States)

    Wu, T.; Chen, H.; Gao, P.; Yu, T.; Chen, Z.; Liu, Z.; Ahn, K. H.; Wang, X.; Cheong, S.-W.; Tyson, T. A.

    2016-02-01

    High pressure x-ray diffraction measurements on perovskite RMnO3 (R  =  Dy, Ho and Lu) reveal that varying structural changes occur for different R ions. Large lattice changes (orthorhombic strain) occur in DyMnO3 and HoMnO3 while the Jahn-Teller (JT) distortion remains stable. Conversely, in the small R-ion system LuMnO3, Mn-O bond distortions are observed between 4 and 8 GPa with a broad minimum in the JT distortion. High pressure infrared measurements indicate that a phonon near 390 cm-1 corresponding to the complex motion of the Mn and O ions changes anomalously for LuMnO3. It softens in the 4-8 GPa region, which is consistent with the structural change in Mn-O bonds and then hardens at higher pressures. By contrast, the phonons continuously harden with increasing pressure for DyMnO3 and HoMnO3. Density functional theory methods show that E-phase LuMnO3 is the most stable phase up to the 10 GPa pressure examined. Simulations indicate that the distinct structural change under pressure in LuMnO3 can possibly be used to optimize the electric polarization by pressure/strain.

  3. Cation-induced band-gap tuning in organohalide perovskites: interplay of spin-orbit coupling and octahedra tilting.

    Science.gov (United States)

    Amat, Anna; Mosconi, Edoardo; Ronca, Enrico; Quarti, Claudio; Umari, Paolo; Nazeeruddin, Md K; Grätzel, Michael; De Angelis, Filippo

    2014-06-11

    Organohalide lead perovskites have revolutionized the scenario of emerging photovoltaic technologies. The prototype MAPbI3 perovskite (MA = CH3NH3(+)) has dominated the field, despite only harvesting photons above 750 nm (∼1.6 eV). Intensive research efforts are being devoted to find new perovskites with red-shifted absorption onset, along with good charge transport properties. Recently, a new perovskite based on the formamidinium cation ((NH2)2CH(+) = FA) has shown potentially superior properties in terms of band gap and charge transport compared to MAPbI3. The results have been interpreted in terms of the cation size, with the larger FA cation expectedly delivering reduced band-gaps in Pb-based perovskites. To provide a full understanding of the interplay among size, structure, and organic/inorganic interactions in determining the properties of APbI3 perovskites, in view of designing new materials and fully exploiting them for solar cells applications, we report a fully first-principles investigation on APbI3 perovskites with A = Cs(+), MA, and FA. Our results evidence that the tetragonal-to-quasi cubic structural evolution observed when moving from MA to FA is due to the interplay of size effects and enhanced hydrogen bonding between the FA cations and the inorganic matrix altering the covalent/ionic character of Pb-I bonds. Most notably, the observed cation-induced structural variability promotes markedly different electronic and optical properties in the MAPbI3 and FAPbI3 perovskites, mediated by the different spin-orbit coupling, leading to improved charge transport and red-shifted absorption in FAPbI3 and in general in pseudocubic structures. Our theoretical model constitutes the basis for the rationale design of new and more efficient organohalide perovskites for solar cells applications.

  4. Correlation of annealing time with crystal structure, composition, and electronic properties of CH3NH3PbI3-xClx mixed-halide perovskite films.

    Science.gov (United States)

    Ralaiarisoa, Maryline; Busby, Yan; Frisch, Johannes; Salzmann, Ingo; Pireaux, Jean-Jacques; Koch, Norbert

    2016-12-21

    Using 3D imaging with time-of-flight secondary ion mass spectrometry (ToF-SIMS) complemented by grazing-incidence X-ray diffraction (GIXRD), we spatially resolve changes in both the composition and structure of CH3NH3I3-xClx perovskite films on conducting polymer substrates at different annealing stages, in particular, before and after complete perovskite crystallization. The early stage of annealing is characterized by phase separation throughout the entire film into domains with perovskite and domains with a dominating chloride-rich phase. After sufficiently long annealing, one single perovskite phase of homogeneous composition on the (lateral) micrometer scale is observed, along with pronounced film texture. This composition evolution is accompanied by diffusion of chloride from the perovskite layer towards the conducting polymer substrate, and even accumulation there. Photoelectron spectroscopy analysis further shows that perovskite films become increasingly n-type with annealing time and upon full conversion, which correlates with the change of film composition. Our results accentuate the importance of chloride for the formation of crystalline and textured films, which are crucial for enhancing the PV performance of perovskite-based solar cells.

  5. The effect of moisture on the structures and properties of lead halide perovskites: a first-principles theoretical investigation.

    Science.gov (United States)

    Zhang, Lei; Ju, Ming-Gang; Liang, WanZhen

    2016-08-17

    With efficiencies exceeding 20% and low production costs, lead halide perovskite solar cells (PSCs) have become potential candidates for future commercial applications. However, there are serious concerns about their long-term stability and environmental friendliness, heavily related to their commercial viability. Herein, we present a theoretical investigation based on the ab initio molecular dynamics (AIMD) simulations and the first-principles density functional theory (DFT) calculations to investigate the effects of sunlight and moisture on the structures and properties of MAPbI3 perovskites. AIMD simulations have been performed to simulate the impact of a few water molecules on the structures of MAPbI3 surfaces terminated in three different ways. The evolution of geometric and electronic structures as well as the absorption spectra has been shown. It is found that the PbI2-terminated surface is the most stable while both the MAI-terminated and PbI2-defective surfaces undergo structural reconstruction, leading to the formation of hydrated compounds in a humid environment. The moisture-induced weakening of photoabsorption is closely related to the formation of hydrated species, and the hydrated crystals MAPbI3·H2O and MA4PbI6·2H2O scarcely absorb the visible light. The electronic excitation in the bare and water-absorbed MAPbI3 nanoparticles tends to weaken Pb-I bonds, especially those around water molecules, and the maximal decrease of photoexcitation-induced bond order can reach up to 20% in the excited state in which the water molecules are involved in the electronic excitation, indicating the accelerated decomposition of perovskites in the presence of sunlight and moisture. This work is valuable for understanding the mechanism of chemical or photochemical instability of MAPbI3 perovskites in the presence of moisture.

  6. Structural and IR-spectroscopic characterization of some new Sr{sub 2}LnSbO{sub 6} perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Lavat, Araceli E. [Departamento de Ingenieria Quimica, Facultad de Ingenieria, Universidad Nacional del Centro de la Provincia de Buenos Aires, 7400 Olavarria (Argentina); Baran, Enrique J. [Centro de Quimica Inorganica (CEQUINOR/CONICET, UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C. Correo 962, 1900 La Plata (Argentina)], E-mail: baran@quimica.unlp.edu.ar

    2008-07-28

    A series of ternary perovskite-type oxides of composition Sr{sub 2}LnSbO{sub 6} (with Ln = La, Nd, Sm, Gd, Dy, Er, Yb and Y), have been prepared and their unit cell parameters determined by X-ray powder diffractometry. The infrared spectra of these materials were also recorded and briefly discussed on the basis of their structural peculiarities and by comparison with those of related oxides.

  7. Ferromagnetism in manganite s substituted with silver of perovskite structure; Ferromagnetismo en manganitas sustituidas con plata de estructura perovskita

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez, N.; Hernandez, T.; Dzul, I.; Pena, Y., E-mail: thernang@yahoo.co [Universidad Autonoma de Nuevo Leon, Facultad de Ciencias Quimicas, Laboratorio de Materiales I, Ciudad Universitaria, Av. Pedro de Alba s/n, 66450 San Nicolas de los Garza, Nuevo Leon (Mexico)

    2011-07-01

    A series of mixed oxides of general formula Sm{sub 1-x}Ag{sub x}MnO{sub 3} with perovskite structure were prepared by first by conventional solid-state reaction processing. The structure, morphology and magnetism of the samples are investigated. The X-ray diffraction patterns show that the x=0.1 sample is a single perovskite structure, while x{>=} 0.2, samples consist of a ferromagnetic perovskite phase and two nonmagnetic phases, Ag and Ag{sub 1.8}Mn{sub 8}O{sub 16}. The ferromagnetic behavior of Sm{sub 1-x}Ag{sub x}MnO{sub 3} decrease with increase of Ag composition. The Sem analysis when x=0.1 revealed that the random distribution of morphology and size of particles result of preparation method. The samples of Sm{sub 1-x}Ag{sub x}MnO{sub 3} by x between 0.1 and 0.5 show that applying 10 T fields these cannot reach a saturation value. (Author)

  8. Electronic structure and metallization of cubic GdH3 under pressure: Ab initio many-body GW calculations

    Science.gov (United States)

    Kong, Bo; Zhang, Yachao

    2016-07-01

    The electronic structures of the cubic GdH3 are extensively investigated using the ab initio many-body GW calculations treating the Gd 4f electrons either in the core (4f-core) or in the valence states (4f-val). Different degrees of quasiparticle (QP) self-consistent calculations with the different starting points are used to correct the failures of the GGA/GGA + U/HSE03 calculations. In the 4f-core case, GGA + G0W0 calculations give a fundamental band gap of 1.72 eV, while GGA+ GW0 or GGA + GW calculations present a larger band gap. In the 4f-val case, the nonlocal exchange-correlation (xc) functional HSE03 can account much better for the strong localization of the 4f states than the semilocal or Hubbard U corrected xc functional in the Kohn-Sham equation. We show that the fundamental gap of the antiferromagnetic (AFM) or ferromagnetic (FM) GdH3 can be opened up by solving the QP equation with improved starting point of eigenvalues and wave functions given by HSE03. The HSE03 + G0W0 calculations present a fundamental band gap of 2.73 eV in the AFM configuration, and the results of the corresponding GW0 and GW calculations are 2.89 and 3.03 eV, respectively. In general, for the cubic structure, the fundamental gap from G0W0 calculations in the 4f-core case is the closest to the real result. By G0W0 calculations in the 4f-core case, we find that H or Gd defects can strongly affect the band structure, especially the H defects. We explain the mechanism in terms of the possible electron correlation on the hydrogen site. Under compression, the insulator-to-metal transition in the cubic GdH3 occurs around 40 GPa, which might be a satisfied prediction.

  9. Charge Carriers in Planar and Meso-Structured Organic-Inorganic Perovskites: Mobilities, Lifetimes, and Concentrations of Trap States.

    Science.gov (United States)

    Hutter, Eline M; Eperon, Giles E; Stranks, Samuel D; Savenije, Tom J

    2015-08-06

    Efficient solar cells have been obtained using thin films of solution-processed organic-inorganic perovskites. However, there remains limited knowledge about the relationship between preparation route and optoelectronic properties. We use complementary time-resolved microwave conductivity (TRMC) and photoluminescence (PL) measurements to investigate the charge carrier dynamics in thin planar films of CH3NH3PbI(3-x)Cl(x), CH3NH3PbI3, and their meso-structured analogues. High mobilities close to 30 cm(2)/(V s) and microsecond-long lifetimes are found in thin films of CH3NH3PbI(3-x)Cl(x), compared to lifetimes of only a few hundred nanoseconds in CH3NH3PbI3 and meso-structured perovskites. We describe our TRMC and PL experiments with a global kinetic model, using one set of kinetic parameters characteristic for each sample. We find that the trap density is less than 5 × 10(14) cm(-3) in CH3NH3PbI(3-x)Cl(x), 6 × 10(16) cm(-3) in the CH3NH3PbI3 thin film and ca. 10(15) cm(-3) in both meso-structured perovskites. Furthermore, our results imply that band-to-band recombination is enhanced by the presence of dark carriers resulting from unintentional doping of the perovskites. Finally, our general approach to determine concentrations of trap states and dark carriers is also highly relevant to other semiconductor materials.

  10. Pressure-Induced Structural and Optical Properties of Organometal Halide Perovskite-Based Formamidinium Lead Bromide.

    Science.gov (United States)

    Wang, Lingrui; Wang, Kai; Zou, Bo

    2016-07-07

    Organometal halide perovskites (OMHPs) are attracting an ever-growing scientific interest as photovoltaic materials with moderate cost and compelling properties. In this Letter, pressure-induced optical and structural changes of OMHP-based formamidinium lead bromide (FAPbBr3) were systematically investigated. We studied the pressure dependence of optical absorption and photoluminescence, both of which showed piezochromism. Synchrotron X-ray diffraction indicated that FAPbBr3 underwent two phase transitions and subsequent amorphization, leading directly to the bandgap evolution with redshift followed by blueshift during compression. Raman experiments illustrated the high pressure behavior of organic cation and the surrounding inorganic octahedra. Additionally, the effect of cation size and the different intermolecular interactions between organic cation and inorganic octahedra result in the fact that FAPbBr3 is less compressible than the reported methylammonium lead bromide (MAPbBr3). High pressure studies of the structural evolution and optical properties of OMHPs provide important clues in optimizing photovoltaic performance and help to design novel OMHPs with higher stimuli-resistant ability.

  11. Coupling and electrical control of structural, orbital and magnetic orders in perovskites

    OpenAIRE

    Julien Varignon; Bristowe, Nicholas C.; Eric Bousquet; Philippe Ghosez

    2015-01-01

    Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials. The key to the functional electronic properties exhibited by perovskites is often the so-called Jahn-Teller distortion. For applications, an electrical control of the Jahn-Teller distortions, which is so far out of reach, would therefore be highly desirable. Based on universal symmetry arguments, we determin...

  12. Structural and Chemical Evolution of Methylammonium Lead Halide Perovskites during Thermal Processing from Solution

    Energy Technology Data Exchange (ETDEWEB)

    Nenon, David P.; Christians, Jeffrey A.; Wheeler, Lance M.; Blackburn, Jeffrey L.; Sanehira, Erin M.; Dou, Benjia; Olsen, Michele L.; Zhu, Kai; Berry, Joseph J.; Luther, Joseph M.

    2016-06-01

    Following the prominent success of CH3NH3PbI3 in photovoltaics and other optoelectronic applications, focus has been placed on better understanding perovskite crystallization from precursor and intermediate phases in order to facilitate improved crystallinity often desirable for advancing optoelectronic properties. Understanding of stability and degradation is also of critical importance as these materials seek commercial applications. In this study, we investigate the evolution of perovskites formed from targeted precursor chemistries by correlating in situ temperature-dependent X-ray diffraction, thermogravimetric analysis, and mass spectral analysis of the evolved species. This suite of analyses reveals important precursor composition-induced variations in the processes underpinning perovskite formation and degradation. The addition of Cl- leads to widely different precursor evolution and perovskite formation kinetics, and results in significant changes to the degradation mechanism, including suppression of crystalline PbI2 formation and modification of the thermal stability of the perovskite phase. This work highlights the role of perovskite precursor chemistry in both its formation and degradation.

  13. Synthesis of Al3Fe5O12 Cubic Structure by Extremely Low Sintering Temperature of Sol Gel Technique

    Directory of Open Access Journals (Sweden)

    Noorhana Yahya

    2009-01-01

    Full Text Available Problem statement: Fabrication of nano materials particularly nano inductors at low sintering temperature remains a challenge. This study was carried out as our initial response to obtain a nano-size inductors, which is aluminium iron garnet using low sintering temperature. Approach: The aluminum iron garnet (Al3Fe5O12 nano crystals were prepared by sol-gel technique. The starting solution is a mixture of iron nitrate Fe(NO33.9H2O, yttrium nitrate Y(NO33.6H2O and aluminum nitrate Al(NO33.9H2O and were dissolved in 150 mL of citric acid, C6H8O7.H2O. The mixtures were stirred continuously, at about 250 r.p.m, in room temperature until the formation of a gel was observed. The gel was dried at 110°C in an oven to remove the unneeded water. The dried powder was calcined at 600°C, for 3 h in air and was wet crushed using a Fritsch Planetary Micromill for 6 h to obtain fine particles powder. The sample was then characterized by X-Ray Diffraction analysis (XRD to confirm the garnet phase. The sintered powder was characterized at different temperature by X-ray diffraction analysis and Raman Spectroscopy was used to study the vibration of atoms in a materials. Finally, Field Emission Scanning Electron Microscopy (FESEM was used to study the surface morphology of the sample. Results: The XRD results showed that, the best garnet cubic phase giving [1 0 4] plane of the Al3Fe5O12 crystallite appeared at 33.30 of the 2 theta. We report a clear cubic crystal structure of less than 62 nm, which was observed possible for the first time, for this type of garnet, Al3Fe5O12. The much lower sintering temperature 800°C comparing to the conventional method was attributed to the sol gel method. Conclusion: The long stirring time (one month that had allowed self assembly of the anions and cations to form the gelatin. In addition the small radius of aluminium prefers to occupy the tetrahedron and octahedron sites instead of the much larger dodecahedron site resulted to

  14. Instability of Structural, Magnetic, and Magnetoresistive Properties in Ordered Double-perovskite Sr2FeMoO6 Polycrystals

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The problem of instability in polycrystalline ordered double-perovskite Sr2FeMoO6, is presented in this paper. By the X-raydiffraction analysis and the measuring of electrical and magnetic transports, it is indicated that the perovskite structure of thecompound is destroyed, and the Sr2FeMoO6 phase is mainly transformed into SrMoO4 phase when the samples are exposedin damp atmosphere for several weeks or immersed in water for several hours. Simultaneously, their electrical and magneticproperties obviously change, and the value of magnetoresistance remarkably reduces and even vanishes at room temperature.A possible micromechanism of the instability and an effective method to avoid the problem of instability are also discussed.

  15. Structural Stability Driven by the Spin-Orbit Coupling and the Superconductivity in simple-cubic Polonium

    Science.gov (United States)

    Kang, Chang-Jong; Kim, Kyoo; Min, B. I.

    2013-03-01

    Polonium is the only element which has the simple-cubic (SC) structure in the periodic table. We have studied its structural stability based on the phonon dispersion calculations using the first-principles all-electron full-potential band method. We have demonstrated that the strong spin-orbit coupling (SOC) in SC-Po suppresses the Peierls instability and makes the SC structure stable. We have also discussed the structural chirality realized in beta-Po, as a consequence of the phonon instability. Further, we have investigated the possible superconductivity in SC-Po, and predicted that it becomes a superconductor with Tc ~ 4 K at ambient pressure. The transverse soft phonon mode at q ~ 2/3 R, which is greatly affected by the SOC, plays an important role both in the structural stability and the superconductivity in SC-Po. We have explored effects of the SOC and the volume variation on the phonon dispersions and superconducting properties of SC-Po.

  16. Role of the chemical substitution on the structural and luminescence properties of the mixed halide perovskite thin MAPbI3 - xBrx (0 ≤ x ≤ 1) films

    Science.gov (United States)

    Atourki, Lahoucine; Vega, Erika; Marí, Bernabé; Mollar, Miguel; Ait Ahsaine, Hassan; Bouabid, Khalid; Ihlal, Ahmed

    2016-05-01

    Mixed bromide iodide lead perovskites were prepared from methylamine, lead nitrate and the corresponding hydroX acid (X = I, Br), they were then deposited as thin films on ITO substrate by the spin coating process. X-ray diffraction analyses indicated the formation of a tetragonal phase I4/mcm up to x = 0.4 and a cubic perovskite with space group Pm3 m in the composition range of 0.6 ≤ x ≤ 1. Mixed lead perovskites showed a high absorbance in the UV-vis range. The band gap energy of thin films were estimated from absorbance spectral measurements, it was found that the onset of the absorption edge for MAPbI3 - xBrx (x perovskites presented intermediate values from 781 nm (MAPbI3) to 545 nm (MAPbBr3).

  17. Structural and impedance analysis of Co-doped SrTiO3 perovskite

    Science.gov (United States)

    Echeverri, E.; Arnache, O.

    2016-02-01

    SrTi1-xCoxO3 (0.2≥x≥0) polycrystalline samples were prepared by solid-state reaction. X-ray diffraction (XRD) analysis shown the perovskite type structure is conserved for all samples without impurities. A small increase in the lattice parameters were observed for x≥0.05. Morphology and composition were analysed by scanning electron microscopy (SEM- EDX). Impedance spectroscopy measurements form 50Hz to 1MHz were made at different temperatures (25-400°C). The spectra were analysed by Z' vs Z'' plots, which reveal 3 contributions associated to electrodes, grain boundary and grain. From the fits the frequency f) and times relaxation (τ) of the grain were estimated, with values of f∼15KHz and τ∼67µs for 20% Co samples at RT. A dispersion in the permittivity ε* at low frequency (<300Hz) were observed, which increase with the temperature. Each component of ε* converge for frequencies up to ∼300kHz. Finally, a behaviour and activation energy analysis of the electrical conductivity is presented from ln(σ) vs 1/T plots.

  18. Synthesis and characterization of nano-structured perovskite type neodymium orthoferrite NdFeO3

    Directory of Open Access Journals (Sweden)

    Mostafa Yousefi

    2017-01-01

    Full Text Available In this investigation, neodymium orthoferrite (NdFeO3 nanoparticles has been synthesized through ultrasonic method in the presence of octanoic acid as surfactant. This method comparing to the other methods is very fast and it does not need high temperatures during the reaction. The spherical NdFeO3 nanoparticles with an average particles size of about 40 nm can be obtained at a relatively high calcination temperature of 800 °C for 4 h. Also, product obtained by this method are uniform in both morphology and particles size. The phase composition, morphology, lattice parameters and size of particles in these product are characterized by Fourier transform infrared (FT-IR spectroscopy, X-ray diffraction (XRD scanning electron microscopy (SEM and energy dispersive X-ray spectrometer (EDX. The XRD analysis reveals only the pattern corresponding to perovskite type NdFeO3 which crystallizes in the orthorhombic structure. Energy dispersive X-ray analysis confirms the elemental compositions of the synthesized material.

  19. Synthesis of novel perovskite crystal structure phase of strontium doped rare earth manganites using sol gel method

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Latif, I.A. [Physics Department, College of Science, Najran University, P.O. 1988, Najran (Saudi Arabia); Reactor Physics Department, NRC, Atomic Energy Authority, Abou Zabaal, P.O. 13759, Cairo (Egypt); Ismail, Adel A., E-mail: adelali141@yahoo.com [Advanced Materials and Nano-Research Centre, Najran University, P.O. Box 1988, Najran 11001 (Saudi Arabia); Central Metallurgical Research & Development Institute (CMRDI), Helwan 11421, Cairo (Egypt); Bouzid, Houcine [Advanced Materials and Nano-Research Centre, Najran University, P.O. Box 1988, Najran 11001 (Saudi Arabia); Al-Hajry, A. [Physics Department, College of Science, Najran University, P.O. 1988, Najran (Saudi Arabia); Advanced Materials and Nano-Research Centre, Najran University, P.O. Box 1988, Najran 11001 (Saudi Arabia)

    2015-11-01

    In the present work, polycrystalline perovskites of R{sub 0.6}Sr{sub 0.4}MnO{sub 3} nanocomposites (R=La, Nd, or Sm) were synthesized using the sol–gel method in the presence of citric acid and polyethylene glycol as chelating and structure directing agents respectively. The synthesized gel was calcined at 800 °C for 5 h. The XRD revealed that the obtained nanocrystalline R{sub 0.6}Sr{sub 0.4}MnO{sub 3} is monoclinic crystal structure of space group (I2/a). TEM images showed that the prepared perovskites are homogeneous and uniform with particle sizes in a range 20–40 nm and the HR-TEM images and lattice fringes displayed the monoclinic structure. IV measurements showed that Nd{sub 0.6}Sr{sub 0.4}MnO{sub 3} has semiconducting properties at room temperature. With applying low magnetic field, a transition from semiconductor behavior to Ohmic resistivity was observed. The static resistance of Nd{sub 0.6}Sr{sub 0.4}MnO{sub 3} was calculated to be ~2.985 TΩ for semiconductor phase and the resistance increased 1000 times that gives rise to negative magnetoresistance (MR). The value of MR of Nd{sub 0.6}Sr{sub 0.4}MnO{sub 3} equals to 99.84%, which leads to the use of these materials in fabrication of magnetic devices in the industrial scale. - Highlights: • Polycrystalline perovskites of R{sub 0.6}Sr{sub 0.4}MnO{sub 3} were synthesized using the sol–gel method. • The XRD analysis showed the prepared perovskites are monoclinic crystal structure. • The prepared perovskites are homogeneous and uniform with particles size (20–40 nm). • IV measurements displayed that Nd{sub 0.6}Sr{sub 0.4}MnO{sub 3} has semiconducting properties. • The value of MR equals to 99.84% in Nd{sub 0.6}Sr{sub 0.4}MnO{sub 3}.

  20. Krypton irradiation damage in Nd-doped zirconolite and perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Davoisne, C. [Department of Materials, Imperial College London, London (United Kingdom); LRCS, CNRS-UMR 6007, Universite de Picardie Jules Verne, Amiens (France); Stennett, M.C.; Hyatt, N.C. [Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield (United Kingdom); Peng, N.; Jeynes, C. [Ion Beam Centre, University of Surrey, Guildford (United Kingdom); Lee, W.E., E-mail: w.e.lee@imperial.ac.uk [Department of Materials, Imperial College London, London (United Kingdom)

    2011-08-01

    Understanding the effect of radiation damage and noble gas accommodation in potential ceramic hosts for plutonium disposition is necessary to evaluate their long-term behaviour during geological disposal. Polycrystalline samples of Nd-doped zirconolite and Nd-doped perovskite were irradiated ex situ with 2 MeV Kr{sup +} at a dose of 5 x 10{sup 15} ions cm{sup -2} to simulate recoil of Pu nuclei during alpha decay. The feasibility of thin section preparation of both pristine and irradiated samples by Focused Ion Beam sectioning was demonstrated. After irradiation, the Nd-doped zirconolite revealed a well defined amorphous region separated from the pristine material by a thin (40-60 nm) damaged interface. The zirconolite lattice was lost in the damaged interface, but the fluorite sublattice was retained. The Nd-doped perovskite contained a defined irradiated layer composed of an amorphous region surrounded by damaged but still crystalline layers. The structural evolution of the damaged regions is consistent with a change from orthorhombic to cubic symmetry. In addition in Nd-doped perovskite, the amorphisation dose depended on crystallographic orientation and possibly sample configuration (thin section or bulk). Electron Energy Loss Spectroscopy revealed Ti remained in the 4+ oxidation state but there was a change in Ti coordination in both Nd-doped perovskite and Nd-doped zirconolite associated with the crystalline to amorphous transition.

  1. Structured Perovskite-Based Catalysts and Their Application as Three-Way Catalytic Converters—A Review

    Directory of Open Access Journals (Sweden)

    Sylvain Keav

    2014-07-01

    Full Text Available Automotive Three-Way Catalysts (TWC were introduced more than 40 years ago. Despite that, the development of a sustainable TWC still remains a critical research topic owing to the increasingly stringent emission regulations together with the price and scarcity of precious metals. Among other material classes, perovskite-type oxides are known to be valuable alternatives to conventionally used TWC compositions and have demonstrated to be suitable for a wide range of automotive applications, ranging from TWC to Diesel Oxidation Catalysts (DOC, from NOx Storage Reduction catalysts (NSR to soot combustion catalysts. The interest in these catalysts has been revitalized in the past ten years by the introduction of the concept of catalyst regenerability of perovskite-based TWC, which is in principle well applicable to other catalytic processes as well, and by the possibility to reduce the amounts of critical elements, such as precious metals without seriously lowering the catalytic performance. The aim of this review is to show that perovskite-type oxides have the potential to fulfil the requirements (high activity, stability, and possibility to be included into structured catalysts for implementation in TWC.

  2. Structure and electrical properties of Y, Fe-based perovskite mixed conducting composites fabricated by a modified polymer precursor method

    Science.gov (United States)

    Miruszewski, T.; Gdaniec, P.; Rosiński, W.; Karczewski, J.; Bochentyn, B.; Kusz, B.

    2017-08-01

    In this work, samples of Y0.07Sr0.93Ti1-xFexO3-δ with 20, 40, 60 and 80 mol% of iron amount were prepared by a low-temperature polymer precursor method. The SEM-EDS analysis proved that analyzed Y0.07Sr0.93Ti1-xFexO3-δ samples were composites of two Ti- and Fe-rich perovskite samples. This kind of composite consists of two phases in which one has a good ionic and the other electronic conductivity, which makes such a composite a potential mixed ionic and electronic conductors (MIECs) material. The total electrical conductivities of analyzed samples were measured in air atmosphere (cathode conditions in Solid Oxide Fuel Cell). The values changed from ∼10-3 to 10-1 S cm-1 and depended on the ratio between two observed perovskite phases. The 0.12 S cm-1 conductivity value at 800 °C for sample with the highest amount of Fe-rich perovskite in the structure makes this composite material a candidate for air electrode in electrochemical devices.

  3. Simple dopant-free hole-transporting materials with p-π conjugated structure for stable perovskite solar cells

    Science.gov (United States)

    Sun, Mengna; Liu, Xueyuan; Zhang, Fei; Liu, Hongli; Liu, Xicheng; Wang, Shirong; Xiao, Yin; Li, Dongmei; Meng, Qingbo; Li, Xianggao

    2017-09-01

    Two simple hole-transporting materials, Me-QTPA and Me-BPZTPA, which consist of p-π conjugated structure, have been synthesized and studied in solid-state perovskite solar cells. Me-QTPA and Me-BPZTPA show outstanding thermal stabilities and appropriate HOMO levels; in addition, these two materials show wide band gaps, thus they can block the electron transport and hence suppress the carrier recombination. The solution-processed CH3NH3PbI3-based device using dopant-free Me-QTPA and Me-BPZTPA can achieve a power conversion efficiency of 9.07% and 8.16%, respectively. The perovskite solar cells with dopant-free Me-QTPA show better performance than the cells with dopant-free spiro-OMeTAD, especially in long-term stability. The power conversion efficiency for the perovskite solar cells with dopant-free Me-QTPA remains almost constant after 600 h. The dopant-free Me-QTPA layer shows strong hydrophobicity with a contact angle of 101.6° to water, which indicates that Me-QTPA has a promising long-term stability at room temperature.

  4. Device modeling of perovskite solar cells based on structural similarity with thin film inorganic semiconductor solar cells

    Science.gov (United States)

    Minemoto, Takashi; Murata, Masashi

    2014-08-01

    Device modeling of CH3NH3PbI3-xCl3 perovskite-based solar cells was performed. The perovskite solar cells employ a similar structure with inorganic semiconductor solar cells, such as Cu(In,Ga)Se2, and the exciton in the perovskite is Wannier-type. We, therefore, applied one-dimensional device simulator widely used in the Cu(In,Ga)Se2 solar cells. A high open-circuit voltage of 1.0 V reported experimentally was successfully reproduced in the simulation, and also other solar cell parameters well consistent with real devices were obtained. In addition, the effect of carrier diffusion length of the absorber and interface defect densities at front and back sides and the optimum thickness of the absorber were analyzed. The results revealed that the diffusion length experimentally reported is long enough for high efficiency, and the defect density at the front interface is critical for high efficiency. Also, the optimum absorber thickness well consistent with the thickness range of real devices was derived.

  5. Structural and electronic properties of non-magnetic intermetallic YAuX (X = Ge and Si) in hexagonal and cubic phases

    Indian Academy of Sciences (India)

    A Lekhal; F Z Benkhelifa; S Méçabih; B Abbar; B Bouhafs

    2016-02-01

    The structural and electronic properties of non-magnetic intermetallic YAuX (X = Ge and Si) crystallized in hexagonal phase have been investigated using the full potential linearized augmented-plane wave (FPLAPW) method based on the density functional theory (DFT), within the generalized gradient approximation (GGA). The calculated lattice parameters were in good agreement with experiment. Also, the structural and electronic properties of the non-magnetic half-Heusler YAuPb compound including the artificial YAuX (X = Ge and Si) calculated in cubic phase were determined. It was found that the half-Heusler YAuPb compound presented metallic character. The results showed that YAuGe in cubic phase is a semiconductor whereas the cubic YAuSi is an isolator.

  6. First-principles study of electronic structures and stability of body-centered cubic Ti-Mo alloys by special quasirandom structures.

    Science.gov (United States)

    Sahara, Ryoji; Emura, Satoshi; Ii, Seiichiro; Ueda, Shigenori; Tsuchiya, Koichi

    2014-06-01

    The electronic structures and structural properties of body-centered cubic Ti-Mo alloys were studied by first-principles calculations. The special quasirandom structures (SQS) model was adopted to emulate the solid solution state of the alloys. The valence band electronic structures of Ti-Mo and Ti-Mo-Fe alloys were measured by hard x-ray photoelectron spectroscopy. The structural parameters and valence band photoelectron spectra were calculated using first-principles calculations. The results obtained with the SQS models showed better agreement with the experimental results than those obtained using the conventional ordered structure models. This indicates that the SQS model is effective for predicting the various properties of solid solution alloys by means of first-principles calculations.

  7. Advances in Perovskite Solar Cells.

    Science.gov (United States)

    Zuo, Chuantian; Bolink, Henk J; Han, Hongwei; Huang, Jinsong; Cahen, David; Ding, Liming

    2016-07-01

    Organolead halide perovskite materials possess a combination of remarkable optoelectronic properties, such as steep optical absorption edge and high absorption coefficients, long charge carrier diffusion lengths and lifetimes. Taken together with the ability for low temperature preparation, also from solution, perovskite-based devices, especially photovoltaic (PV) cells have been studied intensively, with remarkable progress in performance, over the past few years. The combination of high efficiency, low cost and additional (non-PV) applications provides great potential for commercialization. Performance and applications of perovskite solar cells often correlate with their device structures. Many innovative device structures were developed, aiming at large-scale fabrication, reducing fabrication cost, enhancing the power conversion efficiency and thus broadening potential future applications. This review summarizes typical structures of perovskite solar cells and comments on novel device structures. The applications of perovskite solar cells are discussed.

  8. Effects of Temperature on Structure and Mobility of the <100> Edge Dislocation in Body-Centred Cubic Iron

    Energy Technology Data Exchange (ETDEWEB)

    Terentyev, Dmitry [Belgian Nuclear Research Centre, SCK-CEN; Osetskiy, Yury N [ORNL; Bacon, David J [University of Liverpool

    2010-01-01

    Dislocation segments with Burgers vector b = <1 0 0> are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2<1 1 1>. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight <1 0 0> edge dislocation is investigated here by atomic-scale computer simulation for {alpha}-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2<1 1 1> fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the <1 0 0> dislocation. It is concluded that the response of the <1 0 0> edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2<1 1 1> dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples.

  9. Effects of temperature on structure and mobility of the <1 0 0> edge dislocation in body-centred cubic iron

    Energy Technology Data Exchange (ETDEWEB)

    Terentyev, D.A., E-mail: dterenty@sckcen.be [Nuclear Materials Science Institute, SCK CEN, Boeretang 200, B-2400, Mol (Belgium); Osetsky, Yu. N. [Materials Sciences and Technology, ORNL, Oak Ridge, TN 37831 (United States); Bacon, D.J. [Department of Engineering, University of Liverpool, Brownlow Hill, Liverpool L69 3GH (United Kingdom)

    2010-04-15

    Dislocation segments with Burgers vector b = <1 0 0> are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2<1 1 1>. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight <1 0 0> edge dislocation is investigated here by atomic-scale computer simulation for {alpha}-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2<1 1 1> fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the <1 0 0> dislocation. It is concluded that the response of the <1 0 0> edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2<1 1 1> dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples.

  10. Sintering of Spherical Particles of Equal and Different Size Arranged in a Body Centered Cubic Structure

    DEFF Research Database (Denmark)

    Redanz, Pia; McMeeking, R. M.

    2003-01-01

    Solid-state sintering of a bcc structure of spherical particles has been studied numerically by use of simple shape parameters to describe the state of the unit cell. Both free and pressure-assisted sintering of particles of equal and different sizes for various ratios of boundary and surface...... to interact, or the next-nearest neighbours in the particle structure attain contact. Quantative measures of the density at the transition from open pore space between the particles to closed porosity as well as the density at which the next-nearest neighbours start to touch are derived. Furthermore...

  11. Electronic structure, chemical bonding and elastic properties of the first thorium-containing nitride perovskite TaThN{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Bannikov, V.V.; Shein, I.R.; Ivanovskii, A.L. [Institute of Solid State Chemistry of the Ural Division of the Russian Academy of Sciences, GSP-145, 620041 Ekaterinburg (Russian Federation)

    2007-05-15

    The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange and correlation potential (LAPW-GGA) is used to understand the electronic and elastic properties of the first thorium-containing nitride perovskite TaThN{sub 3}. Total and partial density of states, charge distributions as well as the elastic constants, bulk modulus, compressibility, shear modulus, Young modulus and Poisson ratio are obtained for the first time and analyzed in comparison with cubic ThN. The chemical bonding in TaThN{sub 3} is a combination of ionic Th-N and of mixed covalent-ionic Ta-N bonds. The cubic TaThN{sub 3} is semiconducting with the direct gap at about 0.65 eV. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Self-focusing and solitonlike structures in materials with competing quadratic and cubic nonlinearities

    DEFF Research Database (Denmark)

    Bergé, L.; Bang, O.; Juul Rasmussen, J.;

    1997-01-01

    , mutually trapped waves can self-focus until collapse whenever their respective powers exceed some thresholds. On the contrary, coupled waves diffracting in a one-dimensional plane never collapse and may evolve towards stable solitonlike structures. For higher transverse dimension numbers, we investigate...

  13. Origin of the catalytic activity of face-centered-cubic ruthenium nanoparticles determined from an atomic-scale structure.

    Science.gov (United States)

    Kumara, L S R; Sakata, Osami; Kohara, Shinji; Yang, Anli; Song, Chulho; Kusada, Kohei; Kobayashi, Hirokazu; Kitagawa, Hiroshi

    2016-11-09

    The 3-dimensional (3D) atomic-scale structure of newly discovered face-centered cubic (fcc) and conventional hexagonal close packed (hcp) type ruthenium (Ru) nanoparticles (NPs) of 2.2 to 5.4 nm diameter were studied using X-ray pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) modeling. Atomic PDF based high-energy X-ray diffraction measurements show highly diffuse X-ray diffraction patterns for fcc- and hcp-type Ru NPs. We here report the atomic-scale structure of Ru NPs in terms of the total structure factor and Fourier-transformed PDF. It is found that the respective NPs have substantial structural disorder over short- to medium-range order atomic distances from the PDF analysis. The first-nearest-neighbor peak analyses show a significant size dependence for the fcc-type Ru NPs demonstrating the increase in the peak height due to an increase in the number density as a function of particle size. The bond angle and coordination number (CN) distribution for the RMC-simulated fcc- and hcp-type Ru NP models indicated inherited structural features from their bulk counterparts. The CN analysis of the whole NP and surface of each RMC model of Ru NPs show the low activation energy packing sites on the fcc-type Ru NP surface atoms. Finally, our newly defined order parameters for RMC simulated Ru NP models suggested that the enhancement of the CO oxidation activity of fcc-type NPs was due to a decrease in the close packing ordering that resulted from the increased NP size. These structural findings could be positively supported for synthesized low-cost and high performance nano-sized catalysts and have potential application in fuel-cell systems and organic synthesis.

  14. Electronic Structure Studies and Photocatalytic Properties of Cubic Bi1.5ZnNb1.5O7

    Directory of Open Access Journals (Sweden)

    Ganchimeg Perenlei

    2015-01-01

    Full Text Available The photocatalytic ability of cubic Bi1.5ZnNb1.5O7 (BZN pyrochlore for the decolorization of an acid orange 7 (AO7 azo dye in aqueous solution under ultraviolet (UV irradiation has been investigated for the first time. BZN catalyst powders prepared using low temperature sol-gel and higher temperature solid-state methods have been evaluated and their reaction rates have been compared. The experimental band gap energy has been estimated from the optical absorption edge and has been used as reference for theoretical calculations. The electronic band structure of BZN has been investigated using first-principles density functional theory (DFT calculations for random, completely and partially ordered solid solutions of Zn cations in both the A and B sites of the pyrochlore structure. The nature of the orbitals in the valence band (VB and the conduction band (CB has been identified and the theoretical band gap energy has been discussed in terms of the DFT model approximations.

  15. DFT Study of the Electronic Structure of Cubic-SiC Nanopores with a C-Terminated Surface

    Directory of Open Access Journals (Sweden)

    M. Calvino

    2014-01-01

    Full Text Available A study of the dependence of the electronic structure and energetic stability on the chemical surface passivation of cubic porous silicon carbide (pSiC was performed using density functional theory (DFT and the supercell technique. The pores were modeled by removing atoms in the [001] direction to produce a surface chemistry composed of only carbon atoms (C-phase. Changes in the electronic states of the porous structures were studied by using different passivation schemes: one with hydrogen (H atoms and the others gradually replacing pairs of H atoms with oxygen (O atoms, fluorine (F atoms, and hydroxide (OH radicals. The results indicate that the band gap behavior of the C-phase pSiC depends on the number of passivation agents (other than H per supercell. The band gap decreased with an increasing number of F, O, or OH radical groups. Furthermore, the influence of the passivation of the pSiC on its surface relaxation and the differences in such parameters as bond lengths, bond angles, and cell volume are compared between all surfaces. The results indicate the possibility of nanostructure band gap engineering based on SiC via surface passivation agents.

  16. Synthesis and crystal structure determination of YCo1−FeO3 ( = 0, 0.33, 0.5, 0.67 and 1) perovskites

    Indian Academy of Sciences (India)

    S Dimitrovska-Lazova; S Aleksovska; P Tzvetkov

    2015-07-01

    The results on synthesis, crystal structure determination and calculation of crystallochemical parameters of YCo1−FeO3 ( = 0, 0.33, 0.5, 0.67 and 1) perovskites are presented in this work. The compounds within this series were synthesized by solution combustion method using two different fuels: urea and citric acid. It was found that iron-containing perovskites, obtained by citric acid as a fuel are of better quality and crystallinity. All the compounds crystallize in Pnma space group with = 4. According to the structure and the calculated crystallochemical parameters, the coordination number of Y3+ in these perovskites is 8. The unit cell parameter relationship is of −type suggesting that the main reason for distortion of ideal perovskite structure is the octahedral tilting. The deformation of the octahedrons, as well as the tilting angles, are increasing with the increasing content of Fe3+ but the calculated global instability indices (GII) show that the stability of the perovskite structure is increasing with increasing of the Fe3+ content.

  17. First-principles study of the structural stability of cubic, tetragonal and hexagonal phases in Mn₃Z (Z=Ga, Sn and Ge) Heusler compounds.

    Science.gov (United States)

    Zhang, Delin; Yan, Binghai; Wu, Shu-Chun; Kübler, Jürgen; Kreiner, Guido; Parkin, Stuart S P; Felser, Claudia

    2013-05-22

    We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.

  18. First-principles study of the structural stability of cubic, tetragonal and hexagonal phases in Mn3Z (Z=Ga, Sn and Ge) Heusler compounds

    Science.gov (United States)

    Zhang, Delin; Yan, Binghai; Wu, Shu-Chun; Kübler, Jürgen; Kreiner, Guido; Parkin, Stuart S. P.; Felser, Claudia

    2013-05-01

    We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.

  19. High-Throughput Computation of Thermal Conductivity of High-Temperature Solid Phases: The Case of Oxide and Fluoride Perovskites

    Science.gov (United States)

    van Roekeghem, Ambroise; Carrete, Jesús; Oses, Corey; Curtarolo, Stefano; Mingo, Natalio

    2016-10-01

    Using finite-temperature phonon calculations and machine-learning methods, we assess the mechanical stability of about 400 semiconducting oxides and fluorides with cubic perovskite structures at 0, 300, and 1000 K. We find 92 mechanically stable compounds at high temperatures—including 36 not mentioned in the literature so far—for which we calculate the thermal conductivity. We show that the thermal conductivity is generally smaller in fluorides than in oxides, largely due to a lower ionic charge, and describe simple structural descriptors that are correlated with its magnitude. Furthermore, we show that the thermal conductivities of most cubic perovskites decrease more slowly than the usual T-1 behavior. Within this set, we also screen for materials exhibiting negative thermal expansion. Finally, we describe a strategy to accelerate the discovery of mechanically stable compounds at high temperatures.

  20. Raman Active Phonons in RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) Perovskites

    Institute of Scientific and Technical Information of China (English)

    WANG Wei-Ran; XU Da-Peng; SU Wen-Hui; DING Zhan-Hui; XUE Yan-Feng; SONG Geng-Xin

    2005-01-01

    @@ We examine RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in cubic symmetry for RCoO3 (R=La, Ce, Pr and Nd) and orthorhombic symmetry for RCoO3 (R=Sm, Eu, Gd,and Dy). It is found that the Raman spectra of RCoO3 perovskites are strongly dependent on the ionic radius.of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co-O bond distances, ionic radius of the rare earth elements and Jahn-Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.

  1. On the Sr1−xBaxFeO2F Oxyfluoride Perovskites: Structure and Magnetism from Neutron Diffraction and Mössbauer Spectroscopy

    Directory of Open Access Journals (Sweden)

    Crisanto A. García-Ramos

    2016-11-01

    Full Text Available Four oxyfluorides of the title series (x = 0.00, 0.25, 0.50, 0.75 have been stabilized by topotactic treatment of perovskite precursors Sr1−xBaxFeO3−δ prepared by soft-chemistry procedures, yielding reactive materials that can easily incorporate a substantial amount of F atoms at moderate temperatures, thus avoiding the stabilization of competitive SrF2 and BaF2 parasitic phases. XRD and Neutron Powder Diffraction (NPD measurements assess the phase purity and yield distinct features concerning the unit cell parameters’ variation, the Sr and Ba distribution, the stoichiometry of the anionic sublattice and the anisotropic displacement factors for O and F atoms. The four oxyfluorides are confirmed to be cubic in all of the compositional range, the unit cell parameters displaying Vergard’s law. All of the samples are magnetically ordered above room temperature; the magnetic structure is always G-type antiferromagnetic, as shown from NPD data. The ordered magnetic moments are substantially high, around 3.5 μB, even at room temperature (RT. Temperature-dependent Mössbauer data allow identifying Fe3+ in all of the samples, thus confirming the Sr1−xBaxFeO2F stoichiometry. The fit of the magnetic hyperfine field vs. temperature curve yields magnetic ordering TN temperatures between 740 K (x = 0.00 and 683 K (x = 0.75. These temperatures are substantially higher than those reported before for some of the samples, assessing for stronger Fe-Fe superexchange interactions for these specimens prepared by fluorination of citrate precursors in mild conditions.

  2. Structural and electronic properties of V-doped cubic BN: A density functional theory study

    Science.gov (United States)

    Espitia R, Miguel J.; Díaz F, John H.; Rodríguez Martínez, Jairo Arbey

    2016-10-01

    The structural, electronic, and magnetic properties of c-BN compound doped with V atoms were calculated by means of the pseudopotential method, employed exactly as implemented in computational Quantum ESPRESSO code. For the description of the electron-electron interaction, generalized gradient approximation (GGA) was used. A half-metallic behavior is predicted for the concentrations B0.9375V0.0625N and B0.875V0.125N, because of the fact that the majority spins are metallic and the minority spins are semiconducting. We found magnetic moments of 2.0 and 4.0 μβ per supercell, respectively. The main contribution to the magnetic moment comes from the V atom, with local moments of 1.61 μβ/V-atom. These compounds are good candidates for potential applications in spintronics and as spin injectors.

  3. Electronic structure of ordered double perovskite Ba{sub 2}CoWO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Ray, Rajyavardhan [Department of Physics, Indian Institute of Technology Kanpur, Kanpur-208016, India and Nanostructured and Advanced Material Laboratory, Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Saltlake, Kolkata-700064 (India); Himanshu, A. K., E-mail: himanshu-ak@yahoo.co.in; Bandyopadhyay, S. K.; Sen, Pintu [Nanostructured and Advanced Material Laboratory, Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Saltlake, Kolkata-700064 (India); Brajesh, Kumar [Department of Physics, Veer Kunwar Singh University, Ara-802301, Bihar (India); Choudhary, B. K. [University Department of Physics, Ranchi University, Jharkhand-834001 (India); Kumar, Uday [Department of Physical Sciences, IISER, Mohanpur Campus, Mohanpur-741252, West Bengal (India); Sinha, T. P. [Department of Physics, Bose Institute, Kolkata-700042 (India)

    2014-04-24

    Ba{sub 2}CoWO{sub 6} (BCoW) has been synthesized in polycrystalline form by solid state reaction at 1200 °C. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225) with the lattice parameter, a = 8.210. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy and Kubelka-Munk function, it’s value being 2.45 eV. A detailed study of the electronic properties has also been carried out using the density functional theory (DFT) techniques implemented on WIEN2k. Importance of electron-electron interaction between the Co ions leading to half-metallic behavior, crystal and exchange splitting together with the hybridization between O and Co, W has been investigated using the total and partial density of states.

  4. Structure of the body-centered cubic phase of lipid systems does not consist of indefinitely long straight rods

    OpenAIRE

    Luzzati, Vittorio; Tardieu, Annette; Gulik-Krzywicki, Tadeusz

    1981-01-01

    The observed intensities of the reflections from the body-centered cubic phase of lipid systems are shown to be incompatible with a recently reported model consisting of straight, indefinitely long rods.

  5. Bandgap Control via Structural and Chemical Tuning of Transition Metal Perovskite Chalcogenides.

    Science.gov (United States)

    Niu, Shanyuan; Huyan, Huaixun; Liu, Yang; Yeung, Matthew; Ye, Kevin; Blankemeier, Louis; Orvis, Thomas; Sarkar, Debarghya; Singh, David J; Kapadia, Rehan; Ravichandran, Jayakanth

    2017-03-01

    Transition metal perovskite chalcogenides are a new class of versatile semiconductors with high absorption coefficient and luminescence efficiency. Polycrystalline materials synthesized by an iodine-catalyzed solid-state reaction show distinctive optical colors and tunable bandgaps across the visible range in photoluminescence, with one of the materials' external efficiency approaching the level of single-crystal InP and CdSe.

  6. Structural characterization of the {eta} = 5 layered perovskite neodymium titanate using high-resolution transmission electron microscopy and image reconstruction

    Energy Technology Data Exchange (ETDEWEB)

    Sayagues, M. [Inst. de Ciencia de Materiales de Sevilla, CSIC c/ Americo Vespucio, Sevilla (Spain); Titmuss, K.; Meyer, R.; Kirkland, A.; Hutchison, J. [Dept. of Materials, Univ. of Oxford (United Kingdom); Sloan, J. [Inorganic Chemistry Lab., Univ. of Oxford (United Kingdom); Tilley, R. [Div. of Materials and Minerals, School of Engineering, Univ. of Wales, Cardiff (United Kingdom)

    2003-08-01

    The structure of Nd{sub 5}Ti{sub 5}O{sub 17} has been refined from a reconstruction of the specimen exit-plane wave restored from a series of incrementally defocused high-resolution transmission electron microscope (HRTEM) images. The phase of the exit-plane wave shows contrast attributable to the oxygen anion sublattice and coupled with simulations provides confirmation of the composition of the cation sites as a function of sample thickness. The enhanced resolution in the exit-plane wave additionally allows a direct measurement of the 'skewing' of the perovskite slabs. (orig.)

  7. Photophysical Analysis of the Formation of Organic–Inorganic Trihalide Perovskite Films: Identification and Characterization of Crystal Nucleation and Growth

    OpenAIRE

    Anaya, Miguel; Galisteo-López, Juan F.; Calvo, Mauricio E.; López, Cefe; Míguez, Hernán

    2016-01-01

    In this work we demonstrate that the different processes occurring during hybrid organic–inorganic lead iodide perovskite film formation can be identified and analyzed by a combined in situ analysis of their photophysical and structural properties. Our observations indicate that this approach permits unambiguously identifying the crystal nucleation and growth regimes that lead to the final material having a cubic crystallographic phase, which stabilizes to the well-known tetragonal phase upon...

  8. Bi(3n+1)Ti7Fe(3n-3)O(9n+11) Homologous Series: Slicing Perovskite Structure with Planar Interfaces Containing Anatase-like Chains.

    Science.gov (United States)

    Batuk, Dmitry; Tsirlin, Alexander A; Filimonov, Dmitry S; Zakharov, Konstantin V; Volkova, Olga S; Vasiliev, Alexander; Hadermann, Joke; Abakumov, Artem M

    2016-02-01

    The n = 3-6 members of a new perovskite-based homologous series Bi(3n+1)Ti7Fe(3n-3)O(9n+11) are reported. The crystal structure of the n = 3 Bi10Ti7Fe6O38 member is refined using a combination of X-ray and neutron powder diffraction data (a = 11.8511(2) Å, b = 3.85076(4) Å, c = 33.0722(6) Å, S.G. Immm), unveiling the partially ordered distribution of Ti(4+) and Fe(3+) cations and indicating the presence of static random displacements of the Bi and O atoms. All Bi(3n+1)Ti7Fe(3n-3)O(9n+11) structures are composed of perovskite blocks separated by translational interfaces parallel to the (001)p perovskite planes. The thickness of the perovskite blocks increases with n, while the atomic arrangement at the interfaces remains the same. The interfaces comprise chains of double edge-sharing (Fe,Ti)O6 octahedra connected to the octahedra of the perovskite blocks by sharing edges and corners. This configuration shifts the adjacent perovskite blocks relative to each other over a vector ½[110]p and creates S-shaped tunnels along the [010] direction. The tunnels accommodate double columns of the Bi(3+) cations, which stabilize the interfaces owing to the stereochemical activity of their lone electron pairs. The Bi(3n+1)Ti7Fe(3n-3)O(9n+11) structures can be formally considered either as intergrowths of perovskite modules and polysynthetically twinned modules of the Bi2Ti4O11 structure or as intergrowths of the 2D perovskite and 1D anatase fragments. Transmission electron microscopy (TEM) on Bi10Ti7Fe6O38 reveals that static atomic displacements of Bi and O inside the perovskite blocks are not completely random; they are cooperative, yet only short-range ordered. According to TEM, the interfaces can be laterally shifted with respect to each other over ±1/3a, introducing an additional degree of disorder. Bi10Ti7Fe6O38 is paramagnetic in the 1.5-1000 K temperature range due to dilution of the magnetic Fe(3+) cations with nonmagnetic Ti(4+). The n = 3, 4 compounds demonstrate a

  9. Role of the chemical substitution on the structural and luminescence properties of the mixed halide perovskite thin MAPbI{sub 3−x}Br{sub x} (0 ≤ x ≤ 1) films

    Energy Technology Data Exchange (ETDEWEB)

    Atourki, Lahoucine, E-mail: lahoucine.atourki@edu.uiz.ac.ma [Materials and Renewable Energy Laboratory, Faculty of Science, Ibn Zohr University, Agadir (Morocco); Vega, Erika; Marí, Bernabé; Mollar, Miguel [Instituto de Diseño y Fabricación (IDF), Universitat Politécnica de València, València (Spain); Ait Ahsaine, Hassan [Laboratoire Matériaux et environnement LME, Faculté des Sciences d' Agadir, Université Ibn Zohr, Agadir (Morocco); Bouabid, Khalid; Ihlal, Ahmed [Materials and Renewable Energy Laboratory, Faculty of Science, Ibn Zohr University, Agadir (Morocco)

    2016-05-15

    Highlights: • X-ray diffraction analyses indicate the formation of a tetragonal phase I4/mcm up to x = 0.4 and a cubic perovskite with space group Pm3 m across in the composition range of 0.6 ≤ x ≤ 1. • Perovskite films exhibit a very high absorbance in the visible and short infrared. • As the fraction of bromide change, the adsorption edge of thin film perovskite can be tuned along the visible spectrum from 543 nm to 785 nm. • The incorporating of bromide into MAPbI{sub 3−x}Br{sub x} shifts the PL emission to shorter wavelengths. - Abstract: Mixed bromide iodide lead perovskites were prepared from methylamine, lead nitrate and the corresponding hydroX acid (X = I, Br), they were then deposited as thin films on ITO substrate by the spin coating process. X-ray diffraction analyses indicated the formation of a tetragonal phase I4/mcm up to x = 0.4 and a cubic perovskite with space group Pm3 m in the composition range of 0.6 ≤ x ≤ 1. Mixed lead perovskites showed a high absorbance in the UV–vis range. The band gap energy of thin films were estimated from absorbance spectral measurements, it was found that the onset of the absorption edge for MAPbI{sub 3−x}Br{sub x} (x < 1) thin films is ranging between 1.58 to 1.72 eV. Photoluminescence emission energies for mixed halide perovskites presented intermediate values from 781 nm (MAPbI{sub 3}) to 545 nm (MAPbBr{sub 3}).

  10. Ab initio density functional theory investigation of the structural, electronic and optical properties of Ca{sub 3}Sb{sub 2} in hexagonal and cubic phases

    Energy Technology Data Exchange (ETDEWEB)

    Arghavani Nia, Borhan, E-mail: b.arghavani@gmail.com [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Sedighi, Matin [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Shahrokhi, Masoud [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Moradian, Rostam [Nano-Science and Nano-Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Computational Physics Science Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-1795, Tehran (Iran, Islamic Republic of)

    2013-11-15

    A density functional theory study of structural, electronical and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. In the exchange–correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca{sub 3}Sb{sub 2} has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated. - Graphical abstract: A density functional theory study of structural, electronic and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. Display Omitted - Highlights: • Physical properties of Ca{sub 3}Sb{sub 2} in hexagonal and cubic phases are investigated. • It is found that the hexagonal phase is an indirect gap semiconductor. • Ca{sub 3}Sb{sub 2} is a direct-gap semiconductor at the Γ point in the cubic phase. • By increasing pressure the semiconducting band gap and anti-symmetry gap are decreased.

  11. Investigation of CaIr1-xPtxO3 and CaIr0.5Rh0.5O3 : structural properties, physical properties and stabilising conditions for post-perovskite oxides

    OpenAIRE

    Hirai, Shigeto

    2011-01-01

    Our understanding of the nature of Earth’s D” region was changed significantly by a recent finding by Murakami et al. (2004), who revealed a phase transition from perovskite to post-perovskite structure in MgSiO3 at about 125 GPa and 2500 K, corresponding to conditions of the lowermost mantle. A perovskite to post-perovskite phase transition accounts for many unusual features of the D” region, including its notable seismic anisotropy, and also accounts for the unusual topology of the D” disco...

  12. Ferroelastic Fingerprints in Methylammonium Lead Iodide Perovskite

    KAUST Repository

    Hermes, Ilka M.

    2016-02-12

    Methylammonium lead iodide (MAPbI3) perovskite materials show an outstanding performance in photovoltaic devices. However, certain material properties, especially the possible ferroic behavior, remain unclear. We observed distinct nanoscale periodic domains in the piezoresponse of MAPbI3(Cl) grains. The structure and the orientation of these striped domains indicate ferroelasticity as their origin. By correlating vertical and lateral piezoresponse force microscopy experiments performed at different sample orientations with x-ray diffraction, the preferred domain orientation was suggested to be the a1-a2-phase. The observation of these ferroelastic fingerprints appears to strongly depend on the film texture and thus the preparation route. The formation of the ferroelastic twin domains could be induced by internal strain during the cubic-tetragonal phase transition.

  13. Electronic structure of ferromagnetic semiconductor material on the monoclinic and rhombohedral ordered double perovskites La{sub 2}FeCoO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Fuh, Huei-Ru; Chang, Ching-Ray [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Graduate Institute of Applied Physics, National Taiwan University, Taipei 106, Taiwan (China); Weng, Ke-Chuan [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Wang, Yin-Kuo, E-mail: kant@ntnu.edu.tw [Center for General Education and Department of Physics, National Taiwan Normal University, Taipei 106, Taiwan (China)

    2015-05-07

    Double perovskite La{sub 2}FeCoO{sub 6} with monoclinic structure and rhombohedra structure show as ferromagnetic semiconductor based on density functional theory calculation. The ferromagnetic semiconductor state can be well explained by the superexchange interaction. Moreover, the ferromagnetic semiconductor state remains under the generalized gradient approximation (GGA) and GGA plus onsite Coulomb interaction calculation.

  14. Chalcogenide Perovskites for Solar Energy Harvesting

    Science.gov (United States)

    Perera, Samanthe

    Methylammonium Lead halide perovskites have recently emerged as a promising candidate for realizing high efficient low cost photovoltaic modules. Charge transport properties of the solution processed halide perovskites are comparable to some of the existing absorbers used in the current PV industry which require sophisticated processing techniques. Due to this simple processing required to achieve high efficiencies, halide perovskites have become an active field of research. As a result, perovskite solar cells are rapidly reaching towards theoretical efficiency limit of close to 30%. It's believed that ionicity inherent to perovskite materials is one of the contributing factors for the excellent charge transport properties of perovskites. Despite the growing interest for solar energy harvesting purposes, these halide perovskites have serious limitations such as toxicity and instability that need to be addressed in order to commercialize the solar cells incorporating them. This dissertation focuses on a new class of ionic semiconductors, chalcogenide perovskites for solar energy harvesting purposes. Coming from the family perovskites they are expected to have same excellent charge transport properties inherent to perovskites due to the ionicity. Inspired by few theoretical studies on chalcogenide perovskites, BaZrS3 and its Ti alloys were synthesized by sulfurizing the oxide counterpart. Structural characterizations have confirmed the predicted distorted perovskite phase. Optical characterizations have verified the direct band gap suitable for thin film single junction solar cells. Anion alloying was demonstrated by synthesizing oxysulfides with widely tunable band gap suitable for applications such as solid state lighting and sensing.

  15. Cubical sets and the topological topos

    DEFF Research Database (Denmark)

    Spitters, Bas

    2016-01-01

    Coquand's cubical set model for homotopy type theory provides the basis for a computational interpretation of the univalence axiom and some higher inductive types, as implemented in the cubical proof assistant. This paper contributes to the understanding of this model. We make three contributions...... show that it can also be a target for cubical realization by showing that Coquand's cubical sets classify the geometric theory of flat distributive lattices. As a side result, we obtain a simplicial realization of a cubical set. 2. Using the internal `interval' in the topos of cubical sets, we...... construct a Moore path model of identity types. 3. We construct a premodel structure internally in the cubical type theory and hence on the fibrant objects in cubical sets....

  16. Structural and transport properties of double perovskite Dy{sub 2}NiMnO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Chanda, Sadhan, E-mail: sadhan.physics@gmail.com; Saha, Sujoy; Dutta, Alo; Sinha, T.P.

    2015-02-15

    Highlights: • Sol–gel citrate method is used to prepare the double perovskite Dy{sub 2}NiMnO{sub 6}. • Structure and dielectric relaxation of the sample are studied for nano and bulk phases. • The relaxation mechanism of the sample is modeled by Cole–Cole equation. • With increasing sintering temperature conductivity increases. • Electronic structures and magnetic properties have been studied by DFT calculations. - Abstract: The double perovskite oxide Dy{sub 2}NiMnO{sub 6} (DNMO) is synthesized in nano and bulk phase by the sol–gel citrate method. The Rietveld refinement of X-ray diffraction pattern of the sample at room temperature shows the monoclinic P2{sub 1}/n phase. Dielectric relaxation of the sample is investigated in the impedance and electric modulus formalisms in the frequency range from 50 Hz to 1 MHz and in the temperature range from 253 to 415 K. The Cole–Cole model is used to explain the relaxation mechanism in DNMO. The frequency-dependent maxima in the imaginary part of impedance are found to obey an Arrhenius law with activation energy of 0.346 and 0.344 eV for nano and bulk DNMO, respectively. A significant increase in conductivity of bulk DNMO has been observed than that of the nanoceramic. Electronic structures and magnetic properties of DNMO have been studied by performing first principles calculation based on density functional theory.

  17. Structure Peculiarities of Micro- and Nanocrystalline Perovskite Ferrites La1- x Sm x FeO3

    Science.gov (United States)

    Pavlovska, O. B.; Vasylechko, L. O.; Lutsyuk, I. V.; Koval, N. M.; Zhydachevskii, Ya A.; Pieniążek, A.

    2017-02-01

    Micro- and nanocrystalline lanthanum-samarium ferrites La1- x Sm x FeO3 with orthorhombic perovskite structure were obtained by using both solid state reactions ( x = 0.2, 0.4, 0.6 and 0.8) and sol-gel synthesis ( x = 0.5) techniques. Obtained structural parameters of both series of La1- x Sm x FeO3 are in excellent agreement with the "pure" LaFeO3 and SmFeO3 compounds, thus proving formation of continuous solid solution in the LaFeO3-SmFeO3 system. Peculiarity of La1- x Sm x FeO3 solid solution is divergence behaviour of unit cell dimensions with increasing x: systematic decrease of the a and c lattice parameters is accompanied with increasing b parameter. Such behaviour of the unit cell dimensions in La1- x Sm x FeO3 series led to crossover of the a and c perovskite lattice parameters and formation of dimensionally tetragonal structure near x = 0.04. Linear decrease of the unit cell volume of La1- x Sm x FeO3 with decreasing x according with the Vegard's rule indicate absence of short-range ordering of R-cations in the LaFeO3-SmFeO3 system.

  18. Multiple-Stage Structure Transformation of Organic-Inorganic Hybrid Perovskite CH3NH3PbI3

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Qiong; Liu, Henan; Kim, Hui-Seon; Liu, Yucheng; Yang, Mengjin; Yue, Naili; Ren, Gang; Zhu, Kai; Liu, Shengzhong; Park, Nam-Gyu; Zhang, Yong

    2016-09-15

    By performing spatially resolved Raman and photoluminescence spectroscopy with varying excitation wavelength, density, and data acquisition parameters, we achieve a unified understanding towards the spectroscopy signatures of the organic-inorganic hybrid perovskite, transforming from the pristine state (CH3NH3PbI3) to the fully degraded state (i.e., PbI2) for samples with varying crystalline domain size from mesoscopic scale (approximately 100 nm) to macroscopic size (centimeters), synthesized by three different techniques. We show that the hybrid perovskite exhibits multiple stages of structure transformation occurring either spontaneously or under light illumination, with exceptionally high sensitivity to the illumination conditions (e.g., power, illumination time, and interruption pattern). We highlight four transformation stages (stages I-IV, with stage I being the pristine state) along either the spontaneous or photoinduced degradation path exhibiting distinctly different Raman spectroscopy features at each stage, and point out that previously reported Raman spectra in the literature reflect highly degraded structures of either stage III or stage IV. Additional characteristic optical features of partially degraded materials under the joint action of spontaneous and photodegradation are also given. This study offers reliable benchmark results for understanding the intrinsic material properties and structure transformation of this unique category of hybrid materials, and the findings are pertinently important to a wide range of potential applications where the hybrid material is expected to function in greatly different environment and light-matter interaction conditions.

  19. Nanocube Superlattices of Cesium Lead Bromide Perovskites and Pressure-Induced Phase Transformations at Atomic and Mesoscale Levels.

    Science.gov (United States)

    Nagaoka, Yasutaka; Hills-Kimball, Katie; Tan, Rui; Li, Ruipeng; Wang, Zhongwu; Chen, Ou

    2017-03-10

    Lead halide perovskites are promising materials for a range of applications owing to their unique crystal structure and optoelectronic properties. Understanding the relationship between the atomic/mesostructures and the associated properties of perovskite materials is crucial to their application performances. Herein, the detailed pressure processing of CsPbBr3 perovskite nanocube superlattices (NC-SLs) is reported for the first time. By using in situ synchrotron-based small/wide angle X-ray scattering and photoluminescence (PL) probes, the NC-SL structural transformations are correlated at both atomic and mesoscale levels with the band-gap evolution through a pressure cycle of 0 ↔ 17.5 GPa. After the pressurization, the individual CsPbBr3 NCs fuse into 2D nanoplatelets (NPLs) with a uniform thickness. The pressure-synthesized perovskite NPLs exhibit a single cubic crystal structure, a 1.6-fold enhanced photoluminescence quantum yield, and a longer emission lifetime than the starting NCs. This study demonstrates that pressure processing can serve as a novel approach for the rapid conversion of lead halide perovskites into structures with enhanced properties.

  20. Temperature-Induced Phase Transition of In2O3 from a Rhombohedral Structure to a Body-Centered Cubic Structure

    Institute of Scientific and Technical Information of China (English)

    YANG Lin-Hong; DONG Hong-Xing; SUN Zheng; SUN Liao-Xin; SHEN Xue-Chu; CHEN Zhang-Hai

    2011-01-01

    @@ We report an experimental study on the temperature-induced phase transition of three-dimensional nanosheetbased flower-like microspheres(NBFMs)of In2O3.Using InOOH as precursor, rhombohedral-In2O3 NBFMs are fabricated.Temperature-induced phase transition of In2O3 NBFMs from a rhombohedral(rh) structure to a body-centered cubic(bcc) structure is examined by Raman spectroscopy and x-ray diffraction.The critical phase transition temperature is found to be about 500℃.Photoluminescence(PL)spectra of In2O3 are measured before annealing and after annealing at different temperatures.The PL spectral results provide further evidence for the phase transition, confirming the fabrication of bcc-In2O3 NBFMs via a simple annealing method.

  1. Molecular dynamics of MgSiO3 perovskite melting

    Institute of Scientific and Technical Information of China (English)

    Liu Zi-Jiang; Cheng Xin-Lu; Yang Xiang-Dong; Zhang Hong; Cai Ling-Cang

    2006-01-01

    The melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 13OGPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments.

  2. Mechanism of charge recombination in meso-structured organic-inorganic hybrid perovskite solar cells: A macroscopic perspective

    Science.gov (United States)

    Yang, Wenchao; Yao, Yao; Wu, Chang-Qin

    2015-04-01

    In the currently popular organic-inorganic hybrid perovskite solar cells, the slowness of the charge recombination processes is found to be a key factor for contributing to their high efficiencies and high open circuit voltages, but the underlying recombination mechanism remains unclear. In this work, we investigate the bimolecular recombination (BR) and the trap-assisted monomolecular recombination (MR) in meso-structured perovskite solar cells under steady state working condition, and try to reveal their roles on determining the device performance. Some interfacial effects such as the injection barriers at the selective contacts are examined as well. Based on the macroscopic device modeling, the recombination resistance-voltage (Rrec-V) and the current density-voltage (J-V) curves are calculated to characterize the recombination mechanism and describe the device performance, respectively. Through comparison with the impedance spectroscopy extracted Rrec data, it is found that under the typical BR reduction factor and deep trap densities observed in experiments, the MR dominates the charge recombination in the low voltage regime, while the BR dominates in the high voltage regime. The short circuit current and the fill factor could be reduced by the significant MR but the open circuit voltage is generally determined by the BR. The different electron injection barriers at the contact can change the BR rate and induce different patterns for the Rrec-V characteristics. For the perovskites of increased band gaps, the Rrec's are significantly enhanced, corresponding to the high open circuit voltages. Finally, it is revealed that the reduced effective charge mobility due to the transport in electron and hole transporting material makes the Rrec decrease slowly with the increasing voltage, which leads to increased open circuit voltage.

  3. Mechanism of charge recombination in meso-structured organic-inorganic hybrid perovskite solar cells: A macroscopic perspective

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Wenchao; Yao, Yao, E-mail: yaoyao@fudan.edu.cn; Wu, Chang-Qin, E-mail: cqw@fudan.edu.cn [State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433 (China); Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433 (China)

    2015-04-21

    In the currently popular organic-inorganic hybrid perovskite solar cells, the slowness of the charge recombination processes is found to be a key factor for contributing to their high efficiencies and high open circuit voltages, but the underlying recombination mechanism remains unclear. In this work, we investigate the bimolecular recombination (BR) and the trap-assisted monomolecular recombination (MR) in meso-structured perovskite solar cells under steady state working condition, and try to reveal their roles on determining the device performance. Some interfacial effects such as the injection barriers at the selective contacts are examined as well. Based on the macroscopic device modeling, the recombination resistance-voltage (R{sub rec}−V) and the current density-voltage (J–V) curves are calculated to characterize the recombination mechanism and describe the device performance, respectively. Through comparison with the impedance spectroscopy extracted R{sub rec} data, it is found that under the typical BR reduction factor and deep trap densities observed in experiments, the MR dominates the charge recombination in the low voltage regime, while the BR dominates in the high voltage regime. The short circuit current and the fill factor could be reduced by the significant MR but the open circuit voltage is generally determined by the BR. The different electron injection barriers at the contact can change the BR rate and induce different patterns for the R{sub rec}–V characteristics. For the perovskites of increased band gaps, the R{sub rec}'s are significantly enhanced, corresponding to the high open circuit voltages. Finally, it is revealed that the reduced effective charge mobility due to the transport in electron and hole transporting material makes the R{sub rec} decrease slowly with the increasing voltage, which leads to increased open circuit voltage.

  4. Ab initio density functional theory investigation of the structural, electronic and optical properties of Ca3Sb2 in hexagonal and cubic phases

    Science.gov (United States)

    Arghavani Nia, Borhan; Sedighi, Matin; Shahrokhi, Masoud; Moradian, Rostam

    2013-11-01

    A density functional theory study of structural, electronical and optical properties of Ca3Sb2 compound in hexagonal and cubic phases is presented. In the exchange-correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca3Sb2 has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated.

  5. Full potential calculations and atom in molecule analysis of the bonding properties of perovskites Borides XRh3B (X=Dy, Ho, Er)

    OpenAIRE

    Ouahrani T.; Merad Boudia I.; Lasri B.

    2013-01-01

    ab initio calculations were performed for the cubic perovskites Borides XRh3B, (X=Dy, Ho, Er). In this work, we have used the augmented plane-wave plus local orbital method to compute the equilibrium structural parameters and electronic structure of densities of states, as well as for the first time, prediction of the thermo-elastic properties of these crystals are presented. The chemical bonding of these compounds has been investigated by using of topological analyses grounded in the theory ...

  6. Facile fabrication of three-dimensional TiO2 structures for highly efficient perovskite solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Segeun; Yoon, Jungjin; Ha, Kyungyeon; Kim, Min-cheol; Kim, Dong Hoe; Kim, Sang Moon; Kang, Seong Min; Park, Sei Jin; Jung, Hyun Suk; Choi, Mansoo

    2016-04-01

    The capability of fabricating three dimensional (3-D) nanostructures with desired morphology is a key to realizing effective light-harvesting strategy in optical applications. In this work, we report a novel 3-D nanopatterning technique that combines ion-assisted aerosol lithography (IAAL) and soft lithography that serves as a facile method to fabricate 3-D nanostructures. Aerosol nanoparticles can be assembled into desired 3-D nanostructures via ion-induced electrostatic focusing and antenna effects from charged nanoparticle structures. Replication of the structures with a polymeric mold allows high throughput fabrication of 3-D nanostructures with various liquid-soluble materials. 3-D flower-patterned polydimethylsiloxane (PDMS) stamp was prepared using the reported technique and utilized for fabricating 3-D nanopatterned mesoporous TiO2 layer, which was employed as the electron transport layer in perovskite solar cells. By incorporating the 3-D nanostructures, absorbed photon-to-current efficiency of >95% at 650 nm wavelength and overall power conversion efficiency of 15.96% were achieved. The enhancement can be attributed to an increase in light harvesting efficiency in a broad wavelength range from 400 to 800 nm and more efficient charge collection from enlarged interfacial area between TiO2 and perovskite layers. This hybrid nanopatterning technique has demonstrated to be an effective method to create textures that increase light harvesting and charge collection with 3-D nanostructures in solar cells.

  7. Structural chemistry and magnetic properties of the perovskite Sr3Fe2TeO9

    Science.gov (United States)

    Tang, Yawei; Hunter, Emily C.; Battle, Peter D.; Sena, Robert Paria; Hadermann, Joke; Avdeev, Maxim; Cadogan, J. M.

    2016-10-01

    A polycrystalline sample of perovskite-like Sr3Fe2TeO9 has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. The majority of the reaction product is shown to be a trigonal phase with a 2:1 ordered arrangement of Fe3+ and Te6+ cations. However, the sample is prone to nano-twinning and tetragonal domains with a different pattern of cation ordering exist within many crystallites. Antiferromagnetic ordering exists in the trigonal phase at 300 K and Sr3Fe2TeO9 is thus the first example of a perovskite with 2:1 trigonal cation ordering to show long-range magnetic order. At 300 K the antiferromagnetic phase coexists with two paramagnetic phases which show spin-glass behaviour below ~80 K.

  8. Lithium intercalation in the LiLaNb{sub 2}O{sub 7} perovskite structure; Intercalation du lithium dans la structure perovskite LiLaNb{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Bohnke, C.; Bohnke, O.; Fourquet, J.L. [Universite du Maine, 72 - Le Mans (France). Laboratoire des Fluorures

    1996-12-31

    ABO{sub 3} perovskite-type oxides having vacancies in the A-sites of their structure are interesting candidates for solid electrolytes when their A-sites are occupied by Li{sup +} ions having a high mobility. This is the case with the [Li{sub 3x}La{sub 2/3-x}]TiO{sub 3} solid solution compound which has a 10{sup -3} S cm{sup -1} ionic conductivity at ambient temperature. Electrochemical intercalation in this material is possible thanks to the presence of Ti{sup 4+} but the small amount of vacancies (0.33 maximum) leads to a low intercalation rate. In order to solve this problem, the LiLaNb{sub 2}O{sub 7} material which has a greater amount of vacancies has been studied and the results relative to the electrochemical intercalation of lithium in this perovskite are presented. The thermodynamical and kinetics properties of the lithium intercalation reaction have been studied by intermittent galvano-static discharges and impedance spectroscopy in LiClO{sub 4}-propylene carbonate medium. (J.S.) 7 refs.

  9. Symmetry-Based Tight Binding Modeling of Halide Perovskite Semiconductors.

    Science.gov (United States)

    Boyer-Richard, Soline; Katan, Claudine; Traoré, Boubacar; Scholz, Reinhard; Jancu, Jean-Marc; Even, Jacky

    2016-10-06

    On the basis of a general symmetry analysis, this paper presents an empirical tight-binding (TB) model for the reference Pm-3m perovskite cubic phase of halide perovskites of general formula ABX3. The TB electronic band diagram, with and without spin orbit coupling effect of MAPbI3 has been determined based on state of the art density functional theory results including many body corrections (DFT+GW). It affords access to various properties, including distorted structures, at a significantly reduced computational cost. This is illustrated with the calculation of the band-to-band absorption spectrum, the variation of the band gap under volumetric strain, as well as the Rashba effect for a uniaxial symmetry breaking. Compared to DFT approaches, this empirical model will help to tackle larger issues, such as the electronic band structure of large nanostructures, including many-body effects, or heterostructures relevant to perovskite device modeling suited to the description of atomic-scale features.

  10. Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures

    Science.gov (United States)

    Sadykov, Vladislav; Mezentseva, Natalia; Usoltsev, Vladimir; Sadovskaya, Ekaterina; Ishchenko, Arkady; Pavlova, Svetlana; Bespalko, Yulia; Kharlamova, Tamara; Zevak, Ekaterina; Salanov, Aleksei; Krieger, Tamara; Belyaev, Vladimir; Bobrenok, Oleg; Uvarov, Nikolai; Okhlupin, Yury; Smorygo, Oleg; Smirnova, Alevtina; Singh, Prabhakar; Vlasov, Aleksandr; Korobeynikov, Mikhail; Bryazgin, Aleksandr; Kalinin, Peter; Arzhannikov, Andrei

    This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm -2 at 700 °C in wet H 2/air feeds was demonstrated.

  11. Calculated optical absorption of different perovskite phases

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

    2015-01-01

    We present calculations of the optical properties of a set of around 80 oxides, oxynitrides, and organometal halide cubic and layered perovskites (Ruddlesden-Popper and Dion-Jacobson phases) with a bandgap in the visible part of the solar spectrum. The calculations show that for different classes...

  12. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    Science.gov (United States)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-06-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  13. TEMPERATURE TRENDS OF THE PERMITTIVITY IN COMPLEX OXIDES OF RARE-EARTH ELEMENTS WITH PEROVSKITE-TYPE STRUCTURE

    Directory of Open Access Journals (Sweden)

    A.G.Belous

    2003-01-01

    Full Text Available Ceramic materials based on complex oxides with both the perovskite structure (Ln2/3Nb2O6 and the structure of tetragonal tungsten bronze (Ba6-xLn8+2x/3Ti18O54 have been investigated over a wide frequency and temperature ranges. The results obtained for certain structures denote the presence of the temperature anomalies of dielectric parameters (ε, tanδ. These anomalies occur over the wide frequency range including submilimeter (SMM wavelength range, and are related neither with the processing peculiarities nor with the presence of the phase transitions. Temperature behavior of the permittivity has been considered in terms of the polarization mechanism based on the elastic-strain lattice oscillations. It has been assumed that the observed anomalies could be ascribed to a superposition of harmonic and anharmonic contribution to lattice oscillations that determines τε sign and magnitude.

  14. Perovskite fever

    Science.gov (United States)

    2014-09-01

    Staggering increases in the performance of organic-inorganic perovskite solar cells have renewed the interest in these materials. However, further developments and the support from academic and industrial partners will hinge on the reporting of accurate efficiency values.

  15. A new route of synthesizing perovskite nanotubes by templating approach

    Science.gov (United States)

    Habiballah, Anisah Shafiqah; Osman, Nafisah; Jani, Abdul Mutalib Md

    2017-09-01

    A perovskite oxide for example Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) has attracted growing attention due to its high catalytic activity and mixed ionic/electronic conductivity. Recent research of BSCF is more comprehensively based on a remarkable trajectory of innovation, in particular with regards to the synthesis of perovskite structures in one-dimensional (1-D) nanometric scales as they promote not only to increase an active electrode area for the oxygen reduction reaction, but also allow the tailoring of electrode's architecture. Nevertheless, achieving the desired 1-D structure by a conventional method such as hydrothermal, solvothermal, or sonochemical are far from satisfactory. Herein, the aim of this work is to synthesize the BSCF perovskite nanotubes via soft templating approach, particularly using anodic aluminium oxide (AAO) as a template, focusing on the morphology, composition and structural properties were demonstrated. After the AAO template was anodized at 80 V, the fabricated template was clamped between apair of spectroscopic cells containing BSCF sol and deionized water (with a hole of both sides) for 24 hours. After that, the sample was removed from the cells followed by heat treatment process. The FESEM images showed that BSCF nanotubes were successfully achieved, with the diameter of the nanotubes' approximately 80 nm. The EDX result also confirmed the nominal stoichiometry of Ba0.5Sr0.5Co0.8Fe0.2O3-δ. Meanwhile, the XRD pattern confirmed a single crystalline phase of BSCF nanotubes was successfully obtained and congruent to a cubic perovskite structure of BSCF. Possible formation mechanism,as well as the schematic illustration of BSCF nanotubes inside the template was also discussed in this paper.

  16. Elucidating the band structure and free charge carrier dynamics of pure and impurities doped CH3NH3PbI(3-x)Cl(x) perovskite thin films.

    Science.gov (United States)

    Zhang, Zhen-Yu; Chen, Xin; Wang, Hai-Yu; Xu, Ming; Gao, Bing-Rong; Chen, Qi-Dai; Sun, Hong-Bo

    2015-11-28

    CH3NH3PbI3-xClx perovskite material has been commonly used as the free charge generator and reservoir in highly efficient perovskite-based solid-state solar photovoltaic devices. However, many of the underlying fundamental photophysical mechanisms in this material such as the perovskite transition band structure as well as the dependent relationship between the carrier properties and lattice properties still lack sufficient understanding. Here, we elucidated the fundamental band structure of the pure CH3NH3PbI3-xClx pervoskite lattice, and then reported about the dependent relationship between the free charge carrier characteristic and the different CH3NH3PbI3-xClx pervoskite lattice thin films utilizing femtosecond time-resolved pump-probe technologies. The data demonstrated that the pure perovskite crystal band structure should only have one conduction and one valence band rather than dual valences, and the pure perovskite lattice could trigger more free charge carriers with a slower recombination rate under an identical pump intensity compared with the impurities doped perovskite crystal. We also investigated the perovskite film performance when exposed to moisture and water, the corresponding results gave us a dip in the optimization of the performance of perovskite based devices, and so as a priority this material should be isolated from moisture (water). This work may propose a deeper perspective on the comprehension for this material and it is useful for future optimization of applications in photovoltaic and light emission devices.

  17. Cubic modification crystal structure of cesium neodymium tetrametaphosphates,. beta. -CsNd(POsub(3))sub(4) (CsNdP/sub 4/O/sub 12/)

    Energy Technology Data Exchange (ETDEWEB)

    Palkina, K.K.; Maksimova, S.I.; Chibiskova, N.T. (AN SSSR, Moscow. Inst. Obshchej i Neorganicheskoj Khimii)

    1981-01-01

    A complete X-ray structural investigation into ..beta..-CsNd (PO/sub 3/)/sub 4/ crystallites is presented. ..beta..-CsNd (PO/sub 3/)/sub 4/ is crystallized in the cubic crystal system; space group is 143 d; the parameters of the elementary cell are a=15.233 (3)A; Z=12, V=3535 4A/sup 3/, dsub(roent)=3.34 g/cm/sup 3/. Interatomic distances and valent angles of crystals are presented. It is shown that ..beta..- CsNd(NO/sub 3/)/sub 4/ noncentrosymmetric crystals are isotropic, as they belong to cubic crystal structure and must obviously combine simultaneously luminescent, optic non-linear and piezoelectric properties.

  18. First-principles study of the electronic structure of PbF{sub 2} in the cubic, orthorhombic, and hexagonal phases

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Huitian [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Orlando, Roberto [Dipartimento di Scienze e Tecnologie Avanzate, Universita del Piemonte Orientale, C. so Borsalino 54, I-15100 Alessandria (Italy); Blanco, Miguel A [Departamento de QuImica Fisica y Analitica, Universidad de Oviedo, 33006-Oviedo (Spain); Pandey, Ravindra [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States)

    2004-05-12

    The results of electronic structure calculations for PbF{sub 2} in ambient and high-pressure phases are reported here. We employ the linear combination of atomic orbital-density functional theory approximation using the CRYSTAL program package whose capabilities were expanded to include the so-called soft-core pseudopotentials with higher-order components (e.g. d, f, and g) of the angular momentum terms for heavier atoms in the periodic table. The band structure and density of states of the cubic, orthorhombic, and hexagonal phases were calculated. A direct band gap at X is predicted for the cubic phase, whereas an indirect band gap is predicted for the high-pressure phases. The density of states reveals hybridization features involving Pb s and F p orbitals in the upper valence band of PbF{sub 2}.

  19. Photocatalytic water splitting for hydrogen generation on cubic, orthorhombic, and tetragonal KNbO3 microcubes

    Science.gov (United States)

    Zhang, Tingting; Zhao, Kun; Yu, Jiaguo; Jin, Jian; Qi, Yang; Li, Huiquan; Hou, Xinjuan; Liu, Gang

    2013-08-01

    Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was

  20. The Impact of the Crystallization Processes on the Structural and Optical Properties of Hybrid Perovskite Films for Photovoltaics.

    Science.gov (United States)

    Grancini, Giulia; Marras, Sergio; Prato, Mirko; Giannini, Cinzia; Quarti, Claudio; De Angelis, Filippo; De Bastiani, Michele; Eperon, Giles E; Snaith, Henry J; Manna, Liberato; Petrozza, Annamaria

    2014-11-06

    We investigate the relationship between structural and optical properties of organo-lead mixed halide perovskite films as a function of the crystallization mechanism. For methylammonium lead tri-iodide, the organic cations rearrange within the inorganic cage, moving from crystals grown in a mesoporous scaffold to larger, oriented crystals grown on a flat substrate. This reduces the strain felt by the bonds forming the cage and affects the motion of the organic cation in it, influencing the electronic transition at the onset of the optical absorption spectrum of the semiconductor. Moreover, we demonstrate that in mixed-halide perovskite, though Cl(-) ions are not present in a detectable concentration in the unit cell, they drive the crystallization dynamics. This induces a preferential order during crystallization, from a molecular, i.e., organic-inorganic moieties arrangement, to a nano-mesoscopic level, i.e., larger crystals with anisotropic shape. Finally, we show that while Cl is mainly expelled from flat films made of large crystals, in the presence of an oxide mesoporous scaffold they are partially retained in the composite.

  1. Advances in Perovskite Solar Cells

    Science.gov (United States)

    Zuo, Chuantian; Bolink, Henk J.; Han, Hongwei; Huang, Jinsong

    2016-01-01

    Organolead halide perovskite materials possess a combination of remarkable optoelectronic properties, such as steep optical absorption edge and high absorption coefficients, long charge carrier diffusion lengths and lifetimes. Taken together with the ability for low temperature preparation, also from solution, perovskite‐based devices, especially photovoltaic (PV) cells have been studied intensively, with remarkable progress in performance, over the past few years. The combination of high efficiency, low cost and additional (non‐PV) applications provides great potential for commercialization. Performance and applications of perovskite solar cells often correlate with their device structures. Many innovative device structures were developed, aiming at large‐scale fabrication, reducing fabrication cost, enhancing the power conversion efficiency and thus broadening potential future applications. This review summarizes typical structures of perovskite solar cells and comments on novel device structures. The applications of perovskite solar cells are discussed.

  2. Thermoelastic and structural properties of ionically conducting cerate perovskites: (I) BaCeO3 at low temperature in the Pbnm phase

    DEFF Research Database (Denmark)

    Knight, Kevin S.; Bonanos, Nikolaos

    2013-01-01

    The thermoelastic and structural properties of BaCeO3 perovskite in the Pbnm phase field have been studied using high resolution neutron diffractometry at 37 temperatures between 2 K and 350 K. From a simultaneous fit of the isochoric heat capacity and unit cell volume, the vibrational density of...

  3. Perovskite solar cells: an emerging photovoltaic technology

    Directory of Open Access Journals (Sweden)

    Nam-Gyu Park

    2015-03-01

    Full Text Available Perovskite solar cells based on organometal halides represent an emerging photovoltaic technology. Perovskite solar cells stem from dye-sensitized solar cells. In a liquid-based dye-sensitized solar cell structure, the adsorption of methylammonium lead halide perovskite on a nanocrystalline TiO2 surface produces a photocurrent with a power conversion efficiency (PCE of around 3–4%, as first discovered in 2009. The PCE was doubled after 2 years by optimizing the perovskite coating conditions. However, the liquid-based perovskite solar cell receives little attention because of its stability issues, including instant dissolution of the perovskite in a liquid electrolyte. A long-term, stable, and high efficiency (∼10% perovskite solar cell was developed in 2012 by substituting the solid hole conductor with a liquid electrolyte. Efficiencies have quickly risen to 18% in just 2 years. Since PCE values over 20% are realistically anticipated with the use of cheap organometal halide perovskite materials, perovskite solar cells are a promising photovoltaic technology. In this review, the opto-electronic properties of perovskite materials and recent progresses in perovskite solar cells are described. In addition, comments on the issues to current and future challenges are mentioned.

  4. Reply to “Structural and magnetic behavior of the cubic oxyfluoride SrFeO{sub 2}F studied by neutron diffraction”

    Energy Technology Data Exchange (ETDEWEB)

    Clemens, Oliver, E-mail: oliver.clemens@kit.edu [Technische Universität Darmstadt, Joint Research Laboratory Nanomaterials, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Berry, Frank J.; Wright, Adrian J. [School of Chemistry, The University of Birmingham, Birmingham B15 2TT (United Kingdom); Knight, Kevin S. [ISIS Facility, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX (United Kingdom); Perez-Mato, J.M.; Igartua, J.M. [Departamentos de Física de la Materia Condensada y Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao (Spain); Slater, Peter R. [School of Chemistry, The University of Birmingham, Birmingham B15 2TT (United Kingdom)

    2015-03-15

    In this article we comment on the results published by Thompson et al. (, J. Solid State Chem. 219 (2014) 173–178) on the crystal structure of SrFeO{sub 2}F, who claim the compound to crystallize in the cubic space group Pm-3m. We give a more detailed explanation of the determination of our previously reported structural model with Imma symmetry (Clemens et al., J. Solid State Chem. 206 (2013) 158–169), with addition of variable temperature XRD measurements with high counting time to provide unambiguous evidence for the Imma model being correct for our sample. - Graphical abstract: The crystal structure of SrFeO{sub 2}F is discussed with regards to previous reports. - Highlights: • SrFeO{sub 2}F was synthesized by polymer based fluorination of SrFeO{sub 3}. • Evaluation of the diffraction data shows a pseudocubic cell metric. • Superstructure reflections at low d-spacings indicate deviation from cubic symmetry. • The phase transition temperature from orthorhombic to cubic was determined using variable temperature X-ray diffraction. • Results published by Thompson et al. are critically discussed with respect to those observations.

  5. Structural distortion on metal-insulator transition in ordered double perovskite Ca sub 2 FeReO sub 6

    CERN Document Server

    Oikawa, K; Kato, H; Tokura, Y

    2003-01-01

    The crystal and magnetic structures of an ordered double perovskite, Ca sub 2 FeReO sub 6 , were studied by high-resolution neutron powder diffraction as a function of the temperature from 7 K to 550 K. All of the diffraction data were precisely refined by the Rietveld method, and we confirmed a structural phase transition at around 140 K where the metal-insulator transition occurs from ferrimagnetic metal (FM) to ferrimagnetic insulator (FI) phases. At this temperature, there exists a change in the distortion direction of [ReO sub 6] octahedra together with a spin reorientation, which strongly supports the occurrence of orbital ordering of the t sub 2 sub g electrons. FM and FI phases coexist in a narrow temperature range at around 140 K, which is typically seen in the first-order phase transition. A phase separation was not detected in our well-characterized sample. (author)

  6. Simulation of current-voltage curves for inverted planar structure perovskite solar cells using equivalent circuit model with inductance

    Science.gov (United States)

    Cojocaru, Ludmila; Uchida, Satoshi; Jayaweera, Piyankarage V. V.; Kaneko, Shoji; Toyoshima, Yasutake; Nakazaki, Jotaro; Kubo, Takaya; Segawa, Hiroshi

    2017-02-01

    Physical modeling of hysteretic behavior in current-voltage (I-V) curves of perovskite solar cells (PSCs) is necessary for further improving their power conversion efficiencies (PCEs). The reduction of hysteresis in inverted planar structure PSCs (p-PSCs) has been achieved by using a [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) layer. In the cases, the opposite trend of the I-V hysteresis has been observed where the forward scan shows slightly higher efficiency than the reverse scan. In this paper, an equivalent circuit model with inductance is proposed. This model consists of a Schottky diode involving a parasitic inductance focusing PCBM/Al(Ca) interface and accurately represents the opposite trend of the I-V hysteresis of the p-PSC with an inverted structure.

  7. Structural and electrical transport properties of a rare earth double perovskite oxide:Ba2ErNbO6

    Institute of Scientific and Technical Information of China (English)

    Rajesh Mukherjee; Binita Ghosh; Sujoy Saha; Chandrahas Bharti; T. P. Sinha

    2014-01-01

    The double perovskite oxide barium erbium niobate, Ba2ErNbO6 (BEN) was synthesized by solid state reaction technique. Rietveld refinement of the X-ray diffraction pattern of the sample showed cubic (Fm3m) phase at room temperature. Fourier trans-form infrared spectrum showed two primary phonon modes of the sample at around 387 and 600 cm-1. Raman spectrum of the sam-ple taken at 488 nm excitation wavelength showed four primary strong peaks at 106, 382, 747 and 814 cm-1. Lorentzian lines with 10 bands were used to fit the Raman spectrum. A group theoretical study was performed to assign all the Raman modes. Impedance spectroscopy was applied to investigate the ac electrical conductivity of BEN in a temperature range from 303 to 673 K and in a fre-quency range from 100 Hz-1 MHz. The dielectric relaxation mechanism was discussed in the frame work of permittivity, conduc-tivity, modulus and impedance formalisms. The complex plane plot of the impedance data was modeled by an equivalent circuit con-sisting of two serially connected R-CPE units, (one for the grain and the other for the grain boundary), each containing a resistor (R) and a constant phase element (CPE). The R-CPE units were used to incorporate the non-ideal character of the polarization phenome-non instead of an ideal capacitive behaviour. The relaxation time corresponding to dielectric loss was found to obey the Arrhenius law with activation energy of 0.85 eV. The frequency dependent conductivity spectra followed the Jonscher power law. The Cole-Cole model was used to investigate the dielectric relaxation mechanism in the sample.

  8. Effect of sintering time on structural, microstructural and chemical composition of Ni-doped lanthanum gallate perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Colomer, M.T., E-mail: tcolomer@icv.csic.es [Instituto de Cerámica y Vidrio, CSIC, C/ Kelsen no. 5, 28049 Madrid (Spain); Kilner, J.A. [Department of Materials, Imperial College, Prince Consort Road, London SW7 2BP (United Kingdom)

    2015-08-15

    This work reports the effect of two different sintering times, 6 and 48 h on the structural, microstructural, and chemical features of Ni-doped La{sub 0.90}Sr{sub 0.10}GaO{sub 3.00−δ}. Independently of the sintering time, La{sub 0.90}Sr{sub 0.10}Ga{sub 1−x}Ni{sub x}O{sub 3.00−δ} (where x=0.10, and 0.20 (mol)) presents a rhombohedral symmetry with a lattice volume that decreases when NiO dopant increases. Besides the perovskite, LaSrGa{sub 3.00}O{sub 7.00} (nominal composition) is present as second phase in all cases. When the samples are doped with NiO, the peaks of this second phase are shifted with respect to the peaks of the pure phase. These shifts suggest that this second phase could admit some Ni ions in its structure. According to the XRD patterns, the amount of the latter phase is larger when sintering time is increased. Electron probe microanalysis (EPMA) indicated that the matrix of the samples sintered for 6 h is constituted by a perovskite with an experimental composition very close to the nominal one. However, when the samples are sintered for 48 h the matrix of each sample is constituted by two perovskites; both with compositional deviations with respect to their nominal one. In particular, a significant Sr depletion compensated by a La increment in the A site is observed. Those compositional deviations could be mainly due to the diffusion of the cations in the bulk and/or from the bulk to the surface of the samples. That diffusion can favour the formation, not only, of a second perovskite with a different composition in relation with the first one formed, but also, the formation of second phases. In addition, a very slight broadening of Bragg peaks of the perovskites sintered for 48 h is observed by XRD and can be related to the presence of two different perovskites in each sample according to EPMA results. By BSEM and EPMA analyses La{sub 4.00}Ga{sub 2.00}O{sub 9.00} (nominal composition) is also observed as second phase when samples are

  9. Structure degradation and conducting properties of the perovskite phase of yttrium ceramics

    CERN Document Server

    Kalanov, M U

    2002-01-01

    It is shown, that under normal conditions the perovskite phase of the yttrium ceramics of the [(Y,Ba)CuO sub 3 sub - subDELTA sub / sub 3] sub 3 is metastable and degrades in time. The degradation results in the YBa sub 2 Cu sub 3 O sub 7 sub - subdelta orthorhombic phase with transition into the superconducting state at T sub c = 91 K. The conductivity type changes thereby from the mixed metal-semiconductor character to the metallic one within the temperature interval of 100-300 K

  10. Synthesis, structural and dielectric properties of double perovskite Ho2FeMnO6

    Science.gov (United States)

    Chakraborty, Tirthankar; Elizabeth, Suja

    2016-05-01

    A new double perovskite Ho2FeMnO6 was grown by nitrate route. Temperature dependent dielectric response was recorded at different frequencies. Relaxor-like-behavior is observed whose activation energy was calculated using Arrhenius equation. The dispersion is very small at room temperature. The Nyquist plot over a broad frequency range at room temperature provides evidence for the presence of three relaxations from sample electrode interface, grain boundary and grain. The corresponding values of resistance and capacitance were calculated from the equivalent circuit model analysis of the Nyquist plot.

  11. Unusual Evolution of the Magnetic Interactions versus Structural Distortions in RMnO3 Perovskites

    Science.gov (United States)

    Zhou, J.-S.; Goodenough, J. B.

    2006-06-01

    We report the refinement of x-ray powder diffraction together with magnetic and thermal conductivity measurements made on the entire family of RMnO3 perovskites prepared by melt growth or under high pressure. Analysis of the data has identified the origin of the transition from type-A to type-E magnetic order as a competition between t-orbital and e-orbital spin-spin interactions within each Mn-O-Mn bond in the (001) planes, the e-orbital interactions decreasing with decreasing R3+-ion size.

  12. Structural and magnetic properties of layered perovskite manganite LaCaBiMn2O7

    Directory of Open Access Journals (Sweden)

    Oubla M.

    2013-09-01

    Full Text Available The layered perovskite oxide, LaCaBiMn2O7, has been prepared by the conventional aqueous solution precipitation method. The powder X-ray diffraction studies suggest that the phase crystallizes with tetragonal unit cell in the space group I4/mmm. The magnetic properties suggest that the ferromagnetic interactions are dominant and manganese ion in the phase is present in mixed valence states Mn3+and Mn4+. The thermomagnetization curve is found to obey the Bloch law. Spin wave stiffness constant D and the approximate value for JMnMnexchange interaction were estimated from the experimental results.

  13. High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites and Pressure Effects on their Electronic and Optical Properties.

    Science.gov (United States)

    Jaffe, Adam; Lin, Yu; Beavers, Christine M; Voss, Johannes; Mao, Wendy L; Karunadasa, Hemamala I

    2016-04-27

    We report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX3 (MA = CH3NH3 (+), X = Br(-) or I(-)) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites' precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaque black with compression. Indeed, electronic conductivity measurements of (MA)PbI3 obtained within a diamond-anvil cell show that the material's resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(Br x I1-x )3 (0.2 solar cells employing these absorbers. Our high-pressure PL data indicate that compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors.

  14. Crystal Structure, Defects, Magnetic and Dielectric Properties of the Layered Bi3n+1Ti7Fe3n-3O9n+11 Perovskite-Anatase Intergrowths.

    Science.gov (United States)

    Batuk, Dmitry; Batuk, Maria; Filimonov, Dmitry S; Zakharov, Konstantin V; Volkova, Olga S; Vasiliev, Alexander N; Tyablikov, Oleg A; Hadermann, Joke; Abakumov, Artem M

    2017-01-17

    The Bi3n+1Ti7Fe3n-3O9n+11 materials are built of (001)p plane-parallel perovskite blocks with a thickness of n (Ti,Fe)O6 octahedra, separated by periodic translational interfaces. The interfaces are based on anatase-like chains of edge-sharing (Ti,Fe)O6 octahedra. Together with the octahedra of the perovskite blocks, they create S-shaped tunnels stabilized by lone pair Bi(3+) cations. In this work, the structure of the n = 4-6 Bi3n+1Ti7Fe3n-3O9n+11 homologues is analyzed in detail using advanced transmission electron microscopy, powder X-ray diffraction, and Mössbauer spectroscopy. The connectivity of the anatase-like chains to the perovskite blocks results in a 3ap periodicity along the interfaces, so that they can be located either on top of each other or with shifts of ±ap along [100]p. The ordered arrangement of the interfaces gives rise to orthorhombic Immm and monoclinic A2/m polymorphs with the unit cell parameters a = 3ap, b = bp, c = 2(n + 1)cp and a = 3ap, b = bp, c = 2(n + 1)cp - ap, respectively. While the n = 3 compound is orthorhombic, the monoclinic modification is more favorable in higher homologues. The Bi3n+1Ti7Fe3n-3O9n+11 structures demonstrate intricate patterns of atomic displacements in the perovskite blocks, which are supported by the stereochemical activity of the Bi(3+) cations. These patterns are coupled to the cationic coordination of the oxygen atoms in the (Ti,Fe)O2 layers at the border of the perovskite blocks. The coupling is strong in the n = 3, 4 homologues, but gradually reduces with the increasing thickness of the perovskite blocks, so that, in the n = 6 compound, the dominant mode of atomic displacements is aligned along the interface planes. The displacements in the adjacent perovskite blocks tend to order antiparallel, resulting in an overall antipolar structure. The Bi3n+1Ti7Fe3n-3O9n+11 materials demonstrate an unusual diversity of structure defects. The n = 4-6 homologues are robust antiferromagnets below TN = 135, 220

  15. Effect of Precursor Mechanism on CO-NO Catalytic Reaction on Body-Centred Cubic Structure: Monte Carlo Simulation

    Institute of Scientific and Technical Information of China (English)

    A. U. Qaisrani; M. Khalid; M. K.Khan

    2005-01-01

    @@ The CO-NO catalytic reaction on body-centred cubic (bcc) lattice is studied by Monte Carlo simulation. The simple Langmuir-Hinshelwood (LH) mechanism yields a steady reactive window, which is separated by continuous and discontinuous irreversible phase transitions. The effect of precursor mechanism on the phase diagram of the system is also studied. According to this mechanism, the precursor motion of CO molecules is considered only on the surface of bcc lattice. Some interesting observations are reported.

  16. A Novel Zirconium-Based Perovskite-Type Membrane Material for Oxygen Permeation

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A novel zirconium-based membrane material of BaCo0.4Fe0.4Zr0.2O3-δ with cubic perovskite structure was synthesized for the first time through a method of citric and EDTA acid combined complexes. The structural stability was characterized by XRD, O2-TPD and H2-TPR techniques respectively. The high oxygen permeation flux of 0.873 mL/cm2min at 950℃ was obtained under He/Air gradient. Meanwhile, the single activation energy for oxygen permeation and the long-term steady operation of 200 h at 800℃ were achieved.

  17. Structure and magnetic properties of spinel-perovskite nanocomposite thin films on SrTiO3 (111) substrates

    Science.gov (United States)

    Kim, Dong Hun; Yang, Junho; Kim, Min Seok; Kim, Tae Cheol

    2016-09-01

    Epitaxial CoFe2O4-BiFeO3 nanocomposite thin films were synthesized on perovskite structured SrTiO3 (001) and (111) substrates by combinatorial pulsed laser deposition and characterized using scanning electron microscopy, x-ray diffraction, and vibrating sample magnetometer. Triangular BiFeO3 nanopillars were formed in a CoFe2O4 matrix on (111) oriented SrTiO3 substrates, while CoFe2O4 nanopillars with rectangular or square top surfaces grew in a BiFeO3 matrix on (001) substrates. The magnetic hysteresis loops of nanocomposites on (111) oriented SrTiO3 substrates showed isotropic properties due to the strain relaxation while those of films on SrTiO3 (001) substrates exhibited a strong out-of-plane anisotropy originated from shape and strain effects.

  18. Dominance of interface chemistry over the bulk properties in determining the electronic structure of epitaxial metal/perovskite oxide heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Chambers, Scott A.; Du, Yingge; Gu, Meng; Droubay, Timothy C.; Hepplestone, Steven; Sushko, Petr

    2015-06-09

    We show that despite very similar crystallographic properties and work function values in the bulk, epitaxial Fe and Cr metallizations on Nb:SrTiO3(001) generate completely different heterojunction electronic properties. Cr is Ohmic whereas Fe forms a Schottky barrier with a barrier height of 0.50 eV. This contrast arises because of differences in interface chemistry. In contrast to Cr [Chambers, S. A. et al., Adv. Mater. 2013, 25, 4001.], Fe exhibits a +2 oxidation state and occupies Ti sites in the perovskite lattice, resulting in negligible charge transfer to Ti, upward band bending, and Schottky barrier formation. The differences between Cr and Fe are understood by performing first-principles calculations of the energetics of defect formation which corroborate the observed interface chemistry and structure.

  19. Effect of metal cation replacement on the electronic structure of metalorganic halide perovskites: Replacement of lead with alkaline-earth metals

    Science.gov (United States)

    Pazoki, Meysam; Jacobsson, T. Jesper; Hagfeldt, Anders; Boschloo, Gerrit; Edvinsson, Tomas

    2016-04-01

    Organic and inorganic lead halogen perovskites, and in particular, C H3N H3Pb I3 , have during the last years emerged as a class of highly efficient solar cell materials. Herein we introduce metalorganic halogen perovskite materials for energy-relevant applications based on alkaline-earth metals. Based on the classical notion of Goldschmidt's rules and quantum mechanical considerations, the three alkaline-earth metals, Ca, Sr, and Ba, are shown to be able to exchange lead in the perovskite structure. The three alkaline-earth perovskites, C H3N H3Ca I3,C H3N H3Sr I3 , and C H3N H3Ba I3 , as well as the reference compound, C H3N H3Pb I3 , are in this paper investigated with density functional theory (DFT) calculations, which predict these compounds to exist as stable perovskite materials, and their electronic properties are explored. A detailed analysis of the projected molecular orbital density of states and electronic band structure from DFT calculations were used for interpretation of the band-gap variations in these materials and for estimation of the effective masses of the electrons and holes. Neglecting spin-orbit effects, the band gap of MACa I3,MASr I3 , and MABa I3 were estimated to be 2.95, 3.6, and 3.3 eV, respectively, showing the relative change expected for metal cation exchange. The shifts in the conduction band (CB) edges for the alkaline-earth perovskites were quantified using scalar relativistic DFT calculations and tight-binding analysis, and were compared to the situation in the more extensively studied lead halide perovskite, C H3N H3Pb I3 , where the change in the work function of the metal is the single most important factor in tuning the CB edge and band gap. The results show that alkaline-earth-based organometallic perovskites will not work as an efficient light absorber in photovoltaic applications but instead could be applicable as charge-selective contact materials. The rather high CB edge and the wide band gap together with the large

  20. Synthesis, structure, and magnetic properties of novel B-site ordered double perovskites, SrLaMReO6 (M = Mg, Mn, Co and Ni).

    Science.gov (United States)

    Thompson, Corey M; Chi, Lisheng; Hayes, John R; Hallas, Alannah M; Wilson, Murray N; Munsie, Timothy J S; Swainson, Ian P; Grosvenor, Andrew P; Luke, Graeme M; Greedan, John E

    2015-06-21

    Four new double perovskites, SrLaMReO(6) (M = Mg, Mn, Co, Ni) in which Re(5+) (5d(2)) is present, were prepared via conventional solid state reactions and characterized by X-ray and neutron powder diffraction, XANES, SQUID magnetometry, and muon spin relaxation (μSR). Synchrotron X-ray and neutron diffraction experiments confirmed that all compounds crystallize in the monoclinic P2(1)/n structure type, which consists of alternately corner-shared octahedra of MO(6) and ReO(6). Rietveld refinement results indicated anti-site mixing of less than 7% on the M/Re sites. Bond valence sum calculations (BVS) suggest all M and Re ions are 2+ and 5+, respectively, and for the Mn-containing phase this is also supported by XANES measurements. All of the materials are paramagnetic at room-temperature and their Curie-Weiss temperatures are positive (except for Mg) indicating net ferromagnetic interactions. No evidence for long-range magnetic order is evident in the dc magnetic susceptibility and μSR measurements for SrLaMgReO(6) to 2 K. The Mn-phase shows long-range order at T(C) = 190 K and neutron diffraction revealed a ferromagnetic structure with a refined net moment of ∼3.7μ(B). Both Co- and Ni-containing phases exhibit spin glass behavior at T(G) = 23 and 30 K, respectively, which is supported by neutron diffraction and a.c. susceptibility data. The structure and physical properties of these four new rhenium based ordered double perovskites are compared to the closely related "pillared perovskites", La(5)Re(3)MO(16), the isoelectronic Os(6+) (5d(2)) double perovskite Sr(2)CoOsO(6), and the Re(6+) (5d(1)) double perovskites, Sr(2)MReO(6), (M = Mg, Ca, Mn, Co, Ni).

  1. Inorganic perovskite photocatalysts for solar energy utilization.

    Science.gov (United States)

    Zhang, Guan; Liu, Gang; Wang, Lianzhou; Irvine, John T S

    2016-10-24

    The development and utilization of solar energy in environmental remediation and water splitting is being intensively studied worldwide. During the past few decades, tremendous efforts have been devoted to developing non-toxic, low-cost, efficient and stable photocatalysts for water splitting and environmental remediation. To date, several hundreds of photocatalysts mainly based on metal oxides, sulfides and (oxy)nitrides with different structures and compositions have been reported. Among them, perovskite oxides and their derivatives (layered perovskite oxides) comprise a large family of semiconductor photocatalysts because of their structural simplicity and flexibility. This review specifically focuses on the general background of perovskite and its related materials, summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation, discusses the theoretical modelling and calculation of perovskite photocatalysts and presents the key challenges and perspectives on the research of perovskite photocatalysts.

  2. A-site ordered quadruple perovskite oxides AA03B4O12

    Institute of Scientific and Technical Information of China (English)

    龙有文

    2016-01-01

    The A-site ordered perovskite oxides with chemical formula AA03B4O12 display many intriguing physical properties due to the introduction of transition metals at both A0 and B sites. Here, research on the recently discovered intermetallic charge transfer occurring between A0-site Cu and B-site Fe ions in LaCu3Fe4O12 and its analogues is reviewed, along with work on the magnetoelectric multiferroicity observed in LaMn3Cr4O12 with cubic perovskite structure. The Cu–Fe intermetallic charge transfer (LaCu3+3 Fe3+4 O12→LaCu2+3 Fe3.75+4 O12) leads to a first-order isostructural phase transition accompanied by drastic variations in magnetism and electrical transport properties. The LaMn3Cr4O12 is a novel spin-driven multiferroic system with strong magnetoelectric coupling effects. The compound is the first example of cubic perovskite multiferroics to be found. It opens up a new arena for studying unexpected multiferroic mechanisms.

  3. A nano-grid structure made of perovskite SrTiO3 nanowires for efficient electron transport layers in inverted polymer solar cells.

    Science.gov (United States)

    Kim, Jeong Won; Suh, Yo-han; Lee, Chang-Lyoul; Kim, Yong Seok; Kim, Won Bae

    2015-03-14

    A nano-grid structure of perovskite SrTiO3 NWs is developed for a novel electron transport layer in inverted polymer solar cells. Due to the excellent charge transporting properties of the SrTiO3 nano-grid structure, the device employing this nanostructure showed ∼32% enhanced photovoltaic performance, compared to the solar cell using a TiO2 thin film.

  4. On the Role of Interfaces in Planar-Structured HC(NH2 )2 PbI3 Perovskite Solar Cells.

    Science.gov (United States)

    Seol, Dong-Jin; Lee, Jin-Wook; Park, Nam-Gyu

    2015-07-20

    Planar-structured HC(NH2 )2 PbI3 (FAPbI3 ) perovskite solar cells were prepared via a two-step deposition process. To investigate the role of interface, the perovskite morphology was intentionally modified by varying HC(NH2 )2 I concentration. Surface and grain sizes of the deposited FAPbI3 became rougher and larger as the HC(NH2 )2 I concentration decreased from 58.2 to 40.7 mM. Average photocurrent was improved but photovoltage deteriorated slightly with decreasing concentration. Consequently, the average efficiency was improved from 7.82 % to 10.70 % and the best efficiency of 12.17 % was obtained at 40.7 mM. Photoluminescence (PL) at TiO2 /FAPbI3 interface was reduced with decreasing concentration, which was, however, reversed at FAPbI3 /spiro-MeOTAD one. By correlating PL data and the photovoltaic performance, we concluded that the TiO2 /perovskite interface plays a crucial role in determining photocurrent while the perovskite/spiro-MeOTAD interface is important in governing photovoltage.

  5. Crystal structures and high-temperature phase-transitions in SrNdMRuO{sub 6} (M=Zn,Co,Mg,Ni) new double perovskites studied by symmetry-mode analysis

    Energy Technology Data Exchange (ETDEWEB)

    Iturbe-Zabalo, E., E-mail: iturbe@ill.fr [Institut Laue-Langevin (ILL), 6 rue Jules Horowitz, BP156, 38042 Grenoble Cedex 9 (France); Fisika Aplikatua II Saila, Zientzia eta Teknologia Fakultatea, UPV/EHU, P.O. Box 644, 48080 Bilbao (Spain); Igartua, J.M. [Fisika Aplikatua II Saila, Zientzia eta Teknologia Fakultatea, UPV/EHU, P.O. Box 644, 48080 Bilbao (Spain); Faik, A. [CICEnergigune, Parque Tecnologico, Albert Einstein 48, 01510 Minano, Alava (Spain); Larranaga, A. [X-Izpien Zerbitzu Orokorra, SGIKer, UPV/EHU, P.O. Box 644, 48080 Bilbao (Spain); Hoelzel, M. [Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), TUM, 85747 Garching (Germany); Cuello, G.J. [Institut Laue-Langevin (ILL), 6 rue Jules Horowitz, BP156, 38042 Grenoble Cedex 9 (France)

    2013-02-15

    Crystal structures of SrNdZnRuO{sub 6}, SrNdCoRuO{sub 6}, SrNdMgRuO{sub 6} and SrNdNiRuO{sub 6} double perovskites have been studied by X-ray, synchrotron radiation and neutron powder diffraction method, at different temperatures, and using the symmetry-mode analysis. All compounds adopt the monoclinic space group P2{sub 1}/n at room-temperature, and contain a completely ordered array of the tilted MO{sub 6} and RuO{sub 6} octahedra, whereas Sr/Nd cations are completely disordered. The analysis of the structures in terms of symmetry-adapted modes of the parent phase allows the identification of the modes responsible for the phase-transition. The high-temperature study (300-1250 K) has shown that the compounds present a temperature induced structural phase-transition: P2{sub 1}/n{yields}P4{sub 2}/n{yields}Fm3{sup Macron }m. - Graphical abstract: Representation of the dominant distortion modes of the symmetry mode decomposition of the room-temperature (P2{sub 1}/n), intermediate (P4{sub 2}/n) and cubic (Fm-3m) phase SrNdMRuO{sub 6} (M=Zn,Co,Mg,Ni), with respect to the parent phase Fm-3m. The dominant distortion modes are: in the monoclinic phase-GM{sub 4}{sup +} (blue arrow), X{sub 3}{sup +} (green arrow) and X{sub 5}{sup +} acting on A-site cations (red arrow); in the tetragonal phase-GM{sub 4}{sup +} (pink arrow), X{sub 3}{sup +} (light blue arrow) and X{sub 5}{sup +} acting on A-site cations (brown arrow). Highlights: Black-Right-Pointing-Pointer Structural study of four ruthenate double perovskites. Black-Right-Pointing-Pointer Room-temperature structural determination using symmetry-mode procedure. Black-Right-Pointing-Pointer Determination of temperature induced structural phase-transitions. Black-Right-Pointing-Pointer Symmetry adapted-mode analysis.

  6. Determination of the structure of the cubic phase in high-ZrO{sub 2}Y{sub 2}O{sub 2}-ZrO{sub 2} alloys by CBED

    Energy Technology Data Exchange (ETDEWEB)

    McClellan, K.J.; Xiao, S.Q.; Lagerlof, K.P.D.; Heuer, A.H. [Case Western Reserve Univ., Cleveland, OH (United States)

    1993-06-20

    Convergent beam electron diffraction (CBED) was used to determine the space group of 9.9 and 18 mol% Y{sub 2}O{sub 3}-stabilized cubic ZrO{sub 2} (Y-CSZ) single crystals. The result (P43m space group) is different from the known tetragonal structure (P4{sub 2}/nmc space group) present in lower solute (3.2 mol% Y{sub 2}O{sub 3}) alloys, and the cubic structure (space group Fm3m) traditionally assumed for cubic ZrO{sub 2}. The oxygen sublattice of the cubic structure is distorted from Fm3m, relative to the cation sublattice, by displacements along the <111> directions. Computer simulations of the CBED patterns agree with experiment and suggest an anion displacement of {approximately}0.3 {Angstrom} from the (1/4,1/4,1/4) positions of the ideal fluorite structure.

  7. The competitive growth of cubic domains in Ti(1-x)AlxN films studied by diffraction anomalous near-edge structure spectroscopy.

    Science.gov (United States)

    Pinot, Y; Tuilier, M-H; Pac, M-J; Rousselot, C; Thiaudière, D

    2015-11-01

    Titanium and aluminium nitride films deposited by magnetron sputtering generally grow as columnar domains made of oriented nanocrystallites with cubic or hexagonal symmetry depending on Al content, which are embedded in more disordered grain boundaries. The substitution of Al atoms for Ti in the cubic lattice of the films improves their resistance to wear and oxidation, allowing their use as protective coatings. Ti K-edge X-ray absorption spectroscopy, which probes both crystallized and more disordered grain boundaries, and X-ray diffraction anomalous fine structure, which is sensitive to short- and long-range order within a given crystallized domain, are carried out on a set of Ti(1-x)AlxN films deposited by magnetron sputtering on Si substrates. Attention is paid to the shape of the pre-edge region, which is sensitive to the symmetry of the site occupied by Ti atoms, either octahedral in face-centred-cubic Ti-rich (TiN, Ti0.54Al0.46N) samples or tetrahedral in hexagonal-close-packed Al-rich (Ti0.32Al0.68N) films. In order to obain information on the titanium environment in the well crystallized areas, subtraction of the smooth part of the energy-dependent structure factor for the Bragg reflections is applied to the pre-edge region of the diffraction anomalous data in order to restore their spectroscopic appearance. A flat pre-edge is related to the typical octahedral environment of Ti atoms for cubic reflections. The difference observed between pre-edge spectra associated with face-centred-cubic 200 and 111 Bragg reflections of Ti0.54Al0.46N is assigned to Ti enrichment of 111 large well ordered domains compared with the more disordered 200 ones. The sharp peak observed in the spectrum recorded from the hexagonal 002 peak of Ti0.32Al0.68N can be regarded as a standard for the pure tetrahedral Ti environment in hexagonal-close-packed nitride.

  8. Perovskite oxides MRuO3 (M = Sr, Ca and Ba: Structural distortion, electronic and magnetic properties with GGA and GGA-modified Becke–Johnson approaches

    Directory of Open Access Journals (Sweden)

    Labdelli Abbes

    2015-01-01

    Full Text Available Electronic and magnetic properties of transition-metal oxides are a continuing research theme due to the variety of ground states and their technological applications. In the present paper, we present first-principles calculations using the full-potential linear augmented plane-wave methods (FP-LAPW on the structural, electronic and magnetic properties of tree cubic (Pm–3m space group perovskite oxides SrRuO3, BaRuO3, and CaRuO3 in comparison with other phases ((4H four-layered hexagonal (P63/mmc space group, (2H two-layered hexagonal (P63/mmc space group and orthorhombic (Pnma space group. The current study is given within the density-functional theory basis DFT. The exchange-correlation potential is introduced by different approaches. We computed the equilibrium lattices, bulk modulus and its pressure derivatives and equilibrium volume. Our obtained results agree successfully with the theoretical and experimental data. The spin magnetic moments of these oxides have been obtained to investigate the magnetic properties. We report a detailed analysis of the different ground states properties for considerable oxides using GGA and GGA-modified Becke–Johnson computational approaches.

  9. Structural and magnetic characterization of the new GdMn1-xFexO3 perovskite material

    Science.gov (United States)

    Cardona Vasquez, J. A.; Landínez Téllez, D. A.; Collazos, C. A.; Roa Rojas, J.

    2016-02-01

    In this paper we presents the synthesis process of the GdMn1-xFexO3 perovskite material by conventional solid state reaction method. Crystalline phase evolution during the synthesis was studied by X-ray Diffraction (XRD) in powder of the materials, observing that the chemical reaction of the precursor oxides was significant above 1000°C. Rietveld refinement of DRX patterns shows a perovskite structure with octahedral distortions (space group Pbnm, # 62) for studied values of x (0, 0.1 and 0.2). The degree of substitution generates an increasing tendency on lattice parameters a and c, while for b is decreasing just as for the volume of the unit cell. The effect of the change in the lattice parameters directly affects the octahedral distortions, ie, with increasing degree of substitution (increased parameter c) octahedra tend to arrange one above the other aligned with the c axis. Magnetization measurements as a function of temperature were performed above room temperature between 300K and 860K with an applied field of 20Oe and below room temperature in Field Cooling (FC) and Zero Field Cooling modes (ZFC) between 4.2K and 300K with an applied field of 200Oe. Magnetic behavior above room temperature is paramagnetic for used values of x, on the other hand at low temperatures (Tx=0.1 the derivative of magnetization shows a peak around 31K, associated to the ferrimagnetic transition for this material. Curie-Weiss fit reveals the antiferromagnetic (ferrimagnetic) behavior of the materials, also shows that the configurations with x=0 and x=0.2 have an effective magnetic moment very similar to the reported value of undoped material, while for x=0.1 a higher value is observed confirming the ferrimagnetic behavior of this configuration.

  10. Solid State Structure-Reactivity Studies on Bixbyites, Fluorites and Perovskites Belonging to the Vanadate, Titanate and Cerate Families

    Science.gov (United States)

    Shafi, Shahid P.

    This thesis primarily focuses on the systematic understanding of structure-reactivity relationships in two representative systems: bixbyite and related structures as well as indium doped CeO2. Topotactic reaction routes have gained significant attention over the past two decades due to their potential to access kinetically controlled metastable materials. This has contributed substantially to the understanding of solid state reaction pathways and provided first insights into mechanisms. Contrary to the widely used ex-situ methods, in-situ techniques including powder x-ray diffraction and thermogravimetric-differential thermal analysis have been employed extensively throughout this work in order to follow the reaction pathways in real time. Detailed analysis of the AVO3 (A = In, Sc) bixbyite reactivity under oxidative conditions has been carried out and a variety of novel metastable oxygen defect phases have been identified and characterized. The novel metastable materials have oxygen deficient fluorite structures and consequently are potential ion conductors. Structural aspects of the topotactic vs. reconstructive transformations are illustrated with this model system. The structure-reactivity study of AVO3 phases was extended to AVO3 perovskite family. Based on the research methodologies and results from AVO3 bixbyite reactivity studies a generalized mechanistic oxidation pathway has been established with a non-vanadium phase, ScTiO3 bixbyite. However, there is stark contrast in terms of structural stability and features beyond this stability limit during AVO3 and ScTiO3 bixbyite reaction pathways. A series of complex reaction sequences including phase separation and phase transitions were identified during the investigation of ScTiO3 reactivity. The two-step formation pathway for the fluorite-type oxide ion conductor Ce1-xInxO2-delta (0 ≤ x ≤ 0.3) is being reported. The formation of the BaCe1-xInxO 3-delta perovskites and the subsequent CO2-capture reaction

  11. New lithium-ion conducting perovskite oxides related to (Li, La)TiO3

    Indian Academy of Sciences (India)

    Litty Sebastian; A K Shukla; J Gopalakrishnan

    2001-10-01

    We describe the synthesis and lithium-ion conductivity of new perovskite-related oxides of the formulas, LiCa1.65 0.35Ti1.3B1.7O9 (B=Nb, Ta) (I, II), LiSr2Ti2.5 W0.5O9 (III) and LiSr1.65 0.35Ti2.15W0.85O9 (IV). Oxides I and II crystallize in orthorhombic (GdFeO3-type) structure, while oxides III and IV possess cubic symmetry. All of them exhibit significant lithium-ion conduction at high temperatures, the highest conductivity of ∼ 10-2S/cm at 800°C among the oxides is exhibited by the composition IV. The results are discussed in the light of previous work on lithium-ion conducting perovskite oxides containing 0 cations.

  12. Ionic transport and structural investigations on MSn(OH){sub 6} (M = Ba, Ca, Mg, Co, Zn, Fe, Mn) hydroxide perovskites synthesized by wet sonochemical methods

    Energy Technology Data Exchange (ETDEWEB)

    Jena, Hrudananda [Materials Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)]. E-mail: hnje@igcar.ernet.in; Kutty, K.V. Govindan [Materials Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Kutty, T.R.N. [Materials Research Centre, Indian Institute of Science, Bangalore 560012 (India)

    2004-11-15

    Hydroxide perovskites of MSn(OH){sub 6} (M = Ba, Ca, Mg, Co, Zn, Fe or Mn) were synthesized by co-precipitation and sonochemical reaction routes. Some of the compounds were also prepared by the hydrothermal method. These were characterized by XRD, TGA/DTA, TEM and IR studies. The hydroxide perovskites are stable up to {approx}523 K and all the compounds stabilize in cubic crystal system (SG = Pn3m) at 298-523 K except BaSn(OH){sub 6}. The as-prepared powders of the above compositions show cubic square net in the reciprocal lattice of their electron diffraction patterns. Among these perovskites; MgSn(OH){sub 6} and CoSn(OH){sub 6} exhibit proton conduction at 298-500 K. Above {approx}523 K, solid solutions of SnO{sub 2} and the corresponding MO components were observed. On heat-treatment at 850-950 K, M{sub 2-x}(V{sub M}){sub x}SnO{sub 4} (M-deficient spinel, x {<=} 1) along with SnO{sub 2} are observed. On further sintering to 1773 K for a duration of 6-7 h, M{sub 2-x}(V{sub M}){sub x}SnO{sub 4} phase is stabilized. The electrical properties of these compounds were measured by four-probe dc method. Co{sub 2-x}(V{sub Co}){sub x}SnO{sub 4} + SnO{sub 2} mixed phase showed oxide ion conductivity at 500-1273 K. The activation energy of oxide ion conduction is 0.93 eV. CaSn(OH){sub 6}does not show any type of electrical conduction at 298-850 K. The loss of proton conduction above 523 K may be ascribed to dehydroxylation and subsequent decomposition to SnO{sub 2} + M{sub 2-x}SnO{sub 4} (defect spinel, M = Mg, Zn, Co) or MSnO{sub 3} (M = Ba, Ca000.

  13. Fluctuations and Anharmonicity in Lead Iodide Perovskites from Molecular Dynamics Supercell Simulationss

    KAUST Repository

    Carignano, Marcelo Andrés

    2017-09-05

    We present a systematic study based on first principles molecular dynamics simulations of lead iodide perovskites with three different cations, including methylammonium (MA), formamidinium (FA) and cesium. Using the high temperature perovskite structure as a reference, we investigate the instabilities that develop as the material is cooled down to 370 K. All three perovskites display anharmonicity in the motion of the iodine atoms, with the stronger effect observed for the MAPbI$_3$ and CsPbI$_3$. At high temperature, this behavior can be traced back to the reduced effective size of the Cs$^+$ and MA$^+$ cations. MAPbI$_3$ undergoes a spontaneous phase transition within our simulation model driven by the dipolar interaction between neighboring MA cations as the temperature is decreased from 450 K. The reverse transformation from tetragonal to cubic is also monitored through the large distribution of the octahedral tilting angles accompanied by an increase in the anharmonicity of the iodine atoms motion. Both MA and FA hybrid perovskites show a strong coupling between the molecular orientations and the local lattice deformations, suggesting mixed order-disorder/displacive characters of the high temperature phase transitions.

  14. Crystal structure and phase transitions in perovskite-like C(NH2)(3)SnCl3

    DEFF Research Database (Denmark)

    Szafranski, M.; Ståhl, Kenny

    2007-01-01

    X-ray single-crystal diffraction, high-temperature powder diffraction and differential thermal analysis at ambient and high pressure have been employed to study the crystal structure and phase transitions of guanidinium trichlorostannate, C(NH2)(3)SnCl3. At 295 K the crystal structure is orthorho......X-ray single-crystal diffraction, high-temperature powder diffraction and differential thermal analysis at ambient and high pressure have been employed to study the crystal structure and phase transitions of guanidinium trichlorostannate, C(NH2)(3)SnCl3. At 295 K the crystal structure...... is orthorhombic, space group Pbca, Z = 8, a = 7.7506(2) angstrom, b = 12.0958(4) angstrom and e = 17.8049(6) angstrom, solved from single-crystal data. It is perovskite-like with distorted corner-linked SnCl6 octahedra and with ordered guanidinium cations in the distorted cuboctahedral voids. At 400 K...

  15. Electronic structure of perovskite LaMnO{sub 3} and CaMnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Chen, B.; Zhao, Y. [University of NSW, Sydney (Australia). School of Materials Science and Engineering; Zheng, X. [University of Sydney, NSW (Australia). School of Chemistry

    1996-12-31

    Perovskite structured lanthanum manganite (LaMnO{sub 3}) can be made to exhibit both strong ferromagnetism and metallic conductivity by partial substitution of La ions (3+ valence) with 2+ valence ions such as Ca. The electronic structures of LaMnO{sub 3} and CaMnO{sub 3} were calculated using Hartree Fock-linear combination of atomic orbitals (LCAO) and Local Density-Molecular Dynamics programs. The band structure show that both are isolators. The valence energy bands are highly degenerated at {Gamma} point in reciprocal space for LaMnO{sub 3}. The conduction bands are partly degenerated in both structures. The dispersion of valence band of LaMnO{sub 3} is about 1.7 eV and the dispersion of conduction band is about 2.0 eV from {Gamma} point to M point. The top two valence bonds of CaMnO{sub 3} are quite flat. The conduction band disperse down significantly, this behaviour could give some reasons why Ca doped LaMnO{sub 3} is metallic conductor. The energy gap was obtained but overestimated as expected. The total density of states was found and compared with experimental results. The electronic images show that the interactions between Mn, Ca and three O are stronger than that between La and O. The bonding of Mn-O is pd{sigma} bond

  16. Symmetry-Based Tight Binding Modeling of Halide Perovskite Semiconductors

    OpenAIRE

    Boyer-Richard, Soline; Katan, Claudine; Traoré, Boubacar; Scholz, Reinhard; Jancu, Jean-Marc; Even, Jacky

    2016-01-01

    International audience; On the basis of a general symmetry analysis, this paper presents an empirical tight-binding (TB) model for the reference Pm-3m perovskite cubic phase of halide perovskites of general formula ABX3. The TB electronic band diagram, with and without spin orbit coupling effect of MAPbI3 has been determined based on state of the art density functional theory results including many body corrections (DFT+GW). It affords access to various properties, including distorted structu...

  17. Anisotropic cubic curvature couplings

    CERN Document Server

    Bailey, Quentin G

    2016-01-01

    To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass dimension 8 coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the Weak Equivalence Principle for self-gravitating bodies. These coefficients can be measured in solar-system tests, while binary-pulsar systems and short-range gravity tests are particularly sensitive.

  18. High temperature studies of Perovskite oxides: x-ray diffraction and PAC spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cuffini, Silvia; Guevara, J.A.; Mascarenhas, Y.P. [Sao Paulo Univ., Sao Carlos, SP (Brazil). Inst. de Fisica; Presa, P. de la; Ayala, A.; Lopez Garcia, A. [La Plata Univ. Nacional (Argentina). Dept. de Fisica

    1997-04-01

    Although the Sr Ru O{sub 3} (SR) and Sr HfO{sub 3} (SH) as other perovskite oxides, have been known for well over 30 years, their crystal are still not well established neither at room temperature nor at higher temperatures. We report the structure analysis by X-Ray Diffraction and Perturbed Angular Correlation (PAC) measurements of SH and SR from room temperature 100 deg C. Both compounds, SH and SR showed an orthorhombic Pnma symmetry at room temperature. At higher temperatures, the compounds undergo a phase transition from orthorhombic to cubic (Pm 3-bar m) symmetry around 700 deg C. (author)

  19. The Synthesis and Characterization of Some Fluoride Perovskites: An Undergraduate Experiment in Solid State Chemistry.

    Science.gov (United States)

    Langley, Richard H.; And Others

    1984-01-01

    Describes a senior-level experiment dealing with the synthesis and characterization of a perovskite. Since most perovskites are cubic, their characterization by x-ray diffraction is simplified. In addition, magnetic ordering may be observed and the effects of a Jahn-Teller distortion seen. (JN)

  20. Electronic structure and chemical bonding in La1-x Sr x MnO3 perovskite ceramics

    Science.gov (United States)

    Thenmozhi, N.; Sasikumar, S.; Sonai, S.; Saravanan, R.

    2017-04-01

    This study reports on the synthesis of La1-x Sr x MnO3 (x  =  0.3, 0.4 and 0.5) manganites by high temperature solid state reaction method using lanthanum oxide, strontium carbonate and manganese oxide as starting materials. The synthesized samples were characterized by XRD, UV-vis, SEM/EDS and VSM. Structural characterization shows that all the prepared samples have the perovskite rhombohedral structure. Influence of Sr doping on electron density distributions in the lattice structure of LaMnO3 were analyzed through maximum entropy method (MEM). Cell parameters are found to be decreasing with the addition of Sr content. The qualitative and quantitative analysis by MEM reveals that, incorporation of Sr into LaMnO3 lattice enhances the ionic nature between La and O ions and decreases the covalent nature between Mn and O ions. Optical band gap values are determined from the UV-visible absorption spectra. Particles with polygonal form are observed from the SEM micrographs. The elemental compositions of the synthesized samples are confirmed by EDS. The magnetic properties studied from the M-H plot taken at room temperature indicated that, the prepared samples are exhibited ferromagnetic behavior.

  1. Oxygen nonstoichiometry and defect chemistry of perovskite-structured SrFe1−xMoxO3−δ solid solutions

    NARCIS (Netherlands)

    Merkulov, O.V.; Naumovich, E.N.; Patrakeev, M.V.; Markov, A.A.; Bouwmeester, H.J.M.; Leonidov, I.A.; Kozhevnikov, V.L.

    2016-01-01

    The oxygen nonstoichiometry ofmixed-conducting perovskite-structured SrFe1−xMoxO3−δ (x=0, 0.07, 0.15 and 0.25) was measured by oxygen coulometric titration in the range of oxygen partial pressure 10−20–0.5 atm and temperature 800–950 °C. Based upon a defect chemical analysis of the non-stoichiometry

  2. Nano-structured CuO-Cu2O Complex Thin Film for Application in CH3NH3PbI3 Perovskite Solar Cells

    Science.gov (United States)

    Chen, Lung-Chieh; Chen, Cheng-Chiang; Liang, Kai-Chieh; Chang, Sheng Hsiung; Tseng, Zhong-Liang; Yeh, Shih-Chieh; Chen, Chin-Ti; Wu, Wen-Ti; Wu, Chun-Guey

    2016-09-01

    Nano-structured CuO-Cu2O complex thin film-based perovskite solar cells were fabricated on an indium tin oxide (ITO)-coated glass and studied. Copper (Cu) thin films with a purity of 99.995 % were deposited on an ITO-coated glass by magnetron reactive sputtering. To optimize the properties of the nano-structured CuO-Cu2O complex thin films, the deposited Cu thin films were thermally oxidized at various temperatures from 300 to 400 °C. A CH3NH3PbI3 perovskite absorber was fabricated on top of CuO-Cu2O complex thin film by a one-step spin-coating process with a toluene washing treatment. Following optimization, the maximum power conversion efficiency (PCE) exceeded 8.1 %. Therefore, the low-cost, solution-processed, stable nano-structured CuO-Cu2O complex thin film can be used as an alternative hole transport layer (HTL) in industrially produced perovskite solar cells.

  3. Highly stable solution processed metal-halide perovskite lasers on nanoimprinted distributed feedback structures

    Science.gov (United States)

    Brenner, Philipp; Stulz, Mareike; Kapp, Dorothee; Abzieher, Tobias; Paetzold, Ulrich W.; Quintilla, Aina; Howard, Ian A.; Kalt, Heinz; Lemmer, Uli

    2016-10-01

    We report on the performance and stability of distributed feedback lasers based on the solution-processed methylammonium lead iodide perovskite (CH3NH3PbI3). The CH3NH3PbI3 layers are processed via solution-casting in ambient atmosphere onto nanoimprinted second order Bragg gratings. This way, we achieve highly polarized surface-emitted lasing at room temperature with a linewidth of less than 0.2 nm and a laser threshold of 120 kW/cm2. The lasing is stable; no change in the laser emission within 15 h of pulsed excitation with a repetition rate of 1 kHz (corresponding to >5 × 107 pulses) is observed, exceeding the stability achieved for solution processed organic semiconductor lasers. Furthermore, adjustment of the grating period allowed the lasing wavelength to be varied over the entire bandwidth of the amplified spontaneous emission (between 781 and 794 nm). The fabrication process of nanoimprinting followed by solution-casting of the gain material demonstrates that stable CH3NH3PbI3 lasers are compatible with scalable production technologies and offers a route towards electrically pumped diode architectures.

  4. Average and equilibrium structures of methyl flouride studied by electron diffraction. A joint analysis with rotational constants and cubic force constants

    Science.gov (United States)

    Egawa, Toru; Yamamoto, Satoshi; Nakata, Munetaka; Kuchitsu, Kozo

    1987-02-01

    Electron diffraction intensity of methyl fluoride was measured and analyzed jointly with the rotational constants, Ao and Bo, of the normal species. The following structure was derived: rg(CF) = 1.391(1) Å, rg(CH) = 1.108(1) Å and β z(FCH) = 108.7(2)°, where the numbers in parentheses represent estimated limits of error. The effective anharmonic constants were derived using the rotational constants and the l-type doubling constants; the cubic force constants calculated by Kondo using a 6-311G** (MP2) basis set were also incorporated in the analysis. The following equilibrium structure was derived from the rz structure and the effective anharmonic constants: re(CF) = 1.383(1) Å, re(CH) = 1.086(2) Å and β e(FCH) = 108.8(3)°.

  5. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AlN and InN

    Science.gov (United States)

    1992-06-01

    AD-A253 331 Semiannual Report Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication...Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using...34 substrates, such as using a graded AlxGal-xN solid solution as a buffer layer. E. Conclusion We have shown that in the use of our modified gas source MBE

  6. Fabrication of nanofibrous A- or B-sites substituted LaCoO{sub 3} perovskites with macroscopic structures and their catalytic applications

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qiang, E-mail: qiangwu@shiep.edu.cn [College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090 (China); Zhao, Li [College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090 (China); Wu, Meixia [Department of Chemistry, Shanxi Datong University, Datong 037009 (China); Yao, Weifeng; Qi, Meixue [College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090 (China); Shi, Xiaoyan [State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084 (China); Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China)

    2014-03-01

    Graphical abstract: Fabrication of nanofibrous La{sub 1−x}Ce{sub x}CoO{sub 3} (x = 0.05, 0.1, 0.2) and LaMn{sub x}Co{sub 1−x}O{sub 3} (x = 0.2, 0.5, 0.8) perovskite-type oxides with macroscopic structures can be successfully achieved by using carbon nanofibers (CNFs) as templates. Furthermore, their application for the combustion of carbon black (CB), which is a model of particulate matter exhausted from diesel engines, was demonstrated. - Highlights: • Nanofibrous perovskites with macroscopic shapes were successfully obtained. • CNFs template method used here is facile, effective and reproducible. • This method might be applicable to other novel material fabrication. • The obtained materials show superior catalytic activity in soot combustion. - Abstract: Fabrication of nanofibrous La{sub 1−x}Ce{sub x}CoO{sub 3} (x = 0.05, 0.1, 0.2) and LaMn{sub x}Co{sub 1−x}O{sub 3} (x = 0.2, 0.5, 0.8) perovskite-type oxides with macroscopic structures can be successfully achieved by using carbon nanofibers (CNFs) as templates. Field emission scanning electron microscopy (FE-SEM), coupled with X-ray diffraction (XRD) analysis confirmed the template effect and formation of the perovskite-type oxides on the macroscopic substrate. It turned out that this facile method can ensure the desired single-phase perovskite-type oxides formation by controlling the corresponding metal ratio during the preparation procedure. In addition, the immobilized nanofibrous La{sub 1−x}Ce{sub x}CoO{sub 3} (x = 0.05) and LaMn{sub x}Co{sub 1−x}O{sub 3} (x = 0.5) perovskite-type oxides can greatly decrease the combustion temperature of nanosized carbon black particles, which has the high potential application prospects in the treatment of diesel soot particles.

  7. Ab initio study of structural, mechanical, thermal and electronic properties of perovskites Sr(Li,Pd)H3

    Science.gov (United States)

    Benlamari, S.; Amara Korba, S.; Lakel, S.; Meradji, H.; Ghemid, S.; El Haj Hassan, F.

    2016-01-01

    The structural, elastic, thermal and electronic properties of perovskite hydrides SrLiH3 and SrPdH3 have been investigated using the all-electron full-potential linear augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The present results are in good agreement with available theoretical and experimental data. The three independent elastic constants (C11, C12 and C44) are also reported. From electronic band structure and density of states (DOSs), it is found that SrLiH3 is an insulator characterized by an indirect gap of 3.48 eV, while SrPdH3 is metallic with a calculated DOSs at Fermi energy of 0.745 states/eV-unit cell. Poisson’s ratio (σ), Young’s modulus (E), shear modulus (G), anisotropy factor (A), average sound velocities (vm) and density (ρ) of these compounds are also estimated for the first time. The Debye temperature is deduced from the average sound velocity. Variation of elastic constants and bulk modulus of these compounds as a function of pressure is also reported. Pressure and thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.

  8. Hybrid germanium iodide perovskite semiconductors: active lone pairs, structural distortions, direct and indirect energy gaps, and strong nonlinear optical properties.

    Science.gov (United States)

    Stoumpos, Constantinos C; Frazer, Laszlo; Clark, Daniel J; Kim, Yong Soo; Rhim, Sonny H; Freeman, Arthur J; Ketterson, John B; Jang, Joon I; Kanatzidis, Mercouri G

    2015-06-03

    The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI3, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the isolation of 6 new hybrid semiconductors. Using CsGeI3 (1) as the prototype compound, we have prepared methylammonium, CH3NH3GeI3 (2), formamidinium, HC(NH2)2GeI3 (3), acetamidinium, CH3C(NH2)2GeI3 (4), guanidinium, C(NH2)3GeI3 (5), trimethylammonium, (CH3)3NHGeI3 (6), and isopropylammonium, (CH3)2C(H)NH3GeI3 (7) analogues. The crystal structures of the compounds are classified based on their dimensionality with 1–4 forming 3D perovskite frameworks and 5–7 1D infinite chains. Compounds 1–7, with the exception of compounds 5 (centrosymmetric) and 7 (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 eV (1), 1.9 eV (2), 2.2 eV (3), and 2.5 eV (4), while the 1D compounds have indirect band gaps of 2.7 eV (5), 2.5 eV (6), and 2.8 eV (7). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to ∼3 GW/cm(2)). The second-order nonlinear susceptibility, χS(2), was determined to be 125.3 ± 10.5 pm/V (1), (161.0 ± 14.5) pm/V (2), 143.0 ± 13.5 pm/V (3), and 57.2 ± 5.5 pm/V (4). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation.

  9. Current state and perspectives for organo-halide perovskite solar cells. Part 1. Crystal structures and thin film formation, morphology, processing, degradation, stability improvement by carbon nanotubes. A review

    Directory of Open Access Journals (Sweden)

    Nigmat Ashurov

    2017-03-01

    Full Text Available The fundamental problems of the modern state of the studies of organic–inorganic organo-halide perovskites (OHP as basis for high efficiency thin film solar cells are discussed. Perovskite varieties and background properties are introduced. The chronology of development of the studies in this direction has been presented – structural aspects of these OHP perovskites, from early 2D to recent 3D MAPbI3 perovskites and important technological aspects of smooth thin film structure creation by various techniques, such as solvent engineering, spin- and dip - coating, vacuum deposition, cation exchange approach, nanoimprinting (particularly, a many-sided role of polymers. The most important theoretical problems such as electronic structure of lattice, impurity and defect states in pure and mixed perovskites, suppressed electron-hole recombination, extra-long lifetimes, and diffusion lengths are analyzed. Degradation effects associated with moisture and photo irradiation, as well as degradation of metallic electrodes to OHP solar cells have been considered. The application of carbon nanostructures: carbon nanotubes (CNT and graphene as stable semitransparent charge collectors to OHP perovskites is demonstrated on the example of original results of authors.

  10. Electroluminescence from perovskite LEDs with the structure of Ag/Spiro-OMeTAD/CH3NH3PbI3/TiO2/FTO

    Science.gov (United States)

    Wang, Minhuan; Shi, Yantao; Bian, Jiming; Dong, Qingshun; Sun, Hongjun; Liu, Hongzhu; Luo, Yingmin; Zhang, Yuzhi

    2016-10-01

    The perovskite light-emitting diodes (Pe-LEDs) with the structure of Ag/Spiro-OMeTAD/CH3NH3PbI3/TiO2/FTO were synthesized, where the CH3NH3PbI3 perovskite layer was deposited by a two-step spin-coating process. A dominant near-infrared electroluminescence (EL) at 773 nm was detected from the Pe-LEDs under forward bias at room temperature. The origin and mechanism of the EL were discussed in comparison with the photoluminescence (PL) spectra, and it was attributed to the radiative recombination of electrons and holes confined in the CH3NH3PbI3 emissive layer. Moreover, the corresponding energy band diagrams was proposed to illustrate the carrier transport mechanism in the Pe-LED device.

  11. Electronic structure and magnetic and optical properties of double perovskite Bi2FeCrO6 from first-principles investigation

    Institute of Scientific and Technical Information of China (English)

    Song Zhe-Wen; Liu Bang-Gui

    2013-01-01

    Double perovskite Bi2FeCrO6,related with multiferroic BiFeO3,is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature.We investigate its electronic structure and magnetic and optical properties by using a full-potential density-functional method.Our optimization shows that it is a robust ferrimagnetic semiconductor.This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting,in contrast to previous studies.Spin exchange constants and optical properties are calculated.Our Monte Carlo magnetic Curie temperature is 450 K,much higher than any previously calculated value and consistent with experimental results.Our study and analysis reveal that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom.These results are useful in understanding such perovskite materials and exploring their potential applications.

  12. New ferromagnetic La{sub 3}Co{sub 2}TaO{sub 9} double perovskite: Structural and magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Fuertes, V.C.; Blanco, M.C.; Franco, D.G.; De Paoli, J.M.; Pannunzio Miner, E.V. [INFIQC, Dpto. de Fisicoquimica, Fac. de Ciencias Quimicas, U.N.C., Cordoba 5000 (Argentina); Sanchez, R.D. [Laboratorio de Resonancias Magneticas. Centro Atomico Bariloche, Bariloche 8400, Rio Negro (Argentina); Fernandez-Diaz, M.T. [Institut Max Von Laue Paul Langevin, F-38042, Grenoble Cedex 9 (France); Carbonio, R.E., E-mail: carbonio@mail.fcq.unc.edu.a [INFIQC, Dpto. de Fisicoquimica, Fac. de Ciencias Quimicas, U.N.C., Cordoba 5000 (Argentina)

    2009-10-01

    The new double perovskite La{sub 3}Co{sub 2}TaO{sub 9} has been prepared by a solid-state procedure. The crystal and magnetic structures have been studied from X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) data. Rietveld refinements were performed in the monoclinic space group P2{sub 1}/n. The structure consists of an ordered array of alternating B'O{sub 6} and B''O{sub 6} octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a{sup -}b{sup -}c{sup +}. Rietveld refinements show that at RT the cell parameters are a=5.6005(7) A, b=5.6931(7) A, c=7.9429(9) A and beta=89.9539(7){sup o}, and the refined crystallographic formula of this 'double perovskite' can be written as La{sub 2}(Co){sub 2d}(Co{sub 1/3}Ta{sub 2/3}){sub 2c}O{sub 6}. Magnetization measurements and low-temperature NPD data show that the perovskite is a ferromagnet with T{sub C}=72 K. At high T it follows the Curie-Weiss law with an effective magnetic moment of 3.82mu{sub B} per Co ion which is very close to spin only Co{sup 2+} (HS).

  13. Role of strontium addition on the phase transition of lanthanum copper oxide from K{sub 2}NiF{sub 4} to perovskite structure

    Energy Technology Data Exchange (ETDEWEB)

    Yu, H.-C. [Department of Materials Science and Engineering, National Cheng Kung University, No. 1, Ta-Hsueh Road, Tainan 70101, Taiwan (China); Fung, K.-Z. [Department of Materials Science and Engineering, National Cheng Kung University, No. 1, Ta-Hsueh Road, Tainan 70101, Taiwan (China)]. E-mail: kzfung@mail.ncku.edu.tw

    2007-08-16

    Without Sr addition, the sintered La{sub 2}O{sub 3} and CuO powder mixture in a mole ratio of 1:2 formed K{sub 2}NiF{sub 4}-structured La{sub 2}CuO{sub 4} with excess CuO. When 15% of strontium was added, La{sub 2}CuO{sub 4} transformed into the single perovskite La{sub 1-x}Sr {sub x}CuO{sub 2.5-{delta}} phase with orthorhombic structure. As the strontium addition increased to 20%, the perovskite lattice changed from orthorhombic to tetragonal. These phase transitions may be attributed to the enhanced oxidation of the divalent cupper ions (Cu{sup 2+}) to trivalent ones (Cu{sup 3+}) by the strontium addition. Based on the electroneutrality in an ABO{sub 3} perovskite lattice, a divalent cation is unstable in the B-site cation sub-lattice when the A-site is occupied by a trivalent cation such as La{sup 3+}. As strontium was added into the A-site cation sub-lattice, the oxidation of Cu{sup 2+} ion into trivalent Cu{sup 3+} ion was enhanced. The increase of Cu{sup 3+} concentration strengthened the electrostatic bonding (ESB) of copper ions with their neighboring anions. Consequently, the symmetrical tetragonal Sr-doped lanthanum copper oxide was obtained.

  14. Compositional and Structural Versatility in an Unusual Family of anti-Perovskite Fluorides: [Cu(H2O)4]3[(MF6)(M'F6)].

    Science.gov (United States)

    Felder, Justin B; Yeon, Jeongho; Smith, Mark D; Zur Loye, Hans-Conrad

    2016-07-18

    A series of six anti-perovskite fluorides of the type [Cu(H2O)4]3(M1-xM'xF6)2 (where M and M' = V, Cr, Mn, Fe as well as M = Fe and M' = V and Cr) was synthesized as high-quality single crystals via a mild hydrothermal route. These materials belong to a class of perovskite-based structures in which the anions and cations of the regular ABX3 perovskite structure have exchanged positions. Two complex anions, MF6(3-) and M'F6(3-), occupy the normal A and B cation positions, while three complex cations, [Cu(H2O)4](2+), occupy the normally anionic X positions. As in the ABX3 compositions, the A and B positions can be occupied by different complex anions, allowing for the preparation of a wide range of compositions. Magnetic property measurements were performed on all six phases, and complex magnetic behavior was observed at low temperatures in the Mn, Fe, and bimetallic Fe/V and Fe/Cr phases.

  15. Examination of Perovskite Structure CaMnO3-δ with MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

    Directory of Open Access Journals (Sweden)

    Dazheng Jing

    2013-01-01

    Full Text Available Perovskite structure oxygen carriers with the general formula CaMnxMg1-xO3-δ were spray-dried and examined in a batch fluidized bed reactor. The CLOU behavior, reactivity towards methane, and syngas were investigated at temperature 900°C to 1050°C. All particles showed CLOU behavior at these temperatures. For experiments with methane, a bed mass corresponding to 57 kg/MW was used in the reactor, and the average CH4 to CO2 conversion was above 97% for most materials. Full syngas conversion was achieved for all materials utilizing a bed mass corresponding to 178 kg/MW. SEM/EDX and XRD confirmed the presence of MgO in the fresh and used samples, indicating that the Mg cation is not incorporated into the perovskite structure and the active compound is likely pure CaMnO3-δ. The very high reactivity with fuel gases, comparable to that of baseline oxygen carriers of NiO, makes these perovskite particles highly interesting for commercial CLC application. Contrary to NiO, oxygen carriers based on CaMnO3-δ have no thermodynamic limitations for methane oxidation to CO2 and H2O, not to mention that the materials are environmentally friendly and can utilize much cheaper raw materials for production. The physical properties, crystalline phases, and morphology information were also determined in this work.

  16. Studies of Fe-Co based perovskite cathodes with different A-site cations

    DEFF Research Database (Denmark)

    Kammer Hansen, K.

    2006-01-01

    Iron-cobalt based perovskite cathodes with different A-site cations ((Ln(0.6)Sr(0.4))(0.99)Fe0.8Co0.2O3-delta, where Ln is La, Pr, Sm or Gd) have been synthesised, characterised by a powder XRD, dilatometry, 4-point DC conductivity measurements, and electrochemical impedance spectroscopy (EIS......) on cone shaped electrodes. In addition to this scanning electron microscopy (SEM) was used to characterise the bars. XRD revealed that only the La-containing perovskite was hexagonal. The Pr and Sm perovskites were orthorhombic. The gadolinium-based perovskite was a two phase system consisting...... of an orthorhombic and a cubic perovskite phase. The thermal expansion coefficient (TEC) increased systematically with a decrease in the size of the A-site cation until the gadoliniurn-containing perovskite where the TEC decreases abruptly. The total electric conductivity was the highest for the La-based perovskite...

  17. Perovskite-Ni composite: a potential route for management of radioactive metallic waste.

    Science.gov (United States)

    Mahadik, Pooja Sawant; Sengupta, Pranesh; Halder, Rumu; Abraham, G; Dey, G K

    2015-04-28

    Management of nickel - based radioactive metallic wastes is a difficult issue. To arrest the release of hazardous material to the environment it is proposed to develop perovskite coating for the metallic wastes. Polycrystalline BaCe0.8Y0.2O3-δ perovskite with orthorhombic structure has been synthesized by sol-gel route. Crystallographic analyses show, the perovskite belong to orthorhombic Pmcn space group at room temperature, and gets converted to orthorhombic Incn space group at 623K, cubic Pm3m space group (with a=4.434Å) at 1173K and again orthorhombic Pmcn space group at room temperature after cooling. Similar observations have been made from micro-Raman study as well. Microstructural studies of BaCe0.8Y0.2O3-δ-NiO/Ni composites showed absence of any reaction product at the interface. This suggests that both the components (i.e. perovskite and NiO/Ni) of the composite are compatible to each other. Interaction of BaCe0.8Y0.2O3-δ-NiO/Ni composites with simulated barium borosilicate waste glass melt also did not reveal any reaction product at the interfaces. Importantly, uranium from the waste glass melt was found to be partitioned within BaCe0.8Y0.2O3-δ perovskite structure. It is therefore concluded that BaCe0.8Y0.2O3-δ can be considered as a good coating material for management of radioactive Ni based metallic wastes. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. Atomic structure of metal-halide perovskites from first principles: The chicken-and-egg paradox of the organic-inorganic interaction

    Science.gov (United States)

    Li, Jingrui; Rinke, Patrick

    2016-07-01

    We have studied the prototype hybrid organic-inorganic perovskite CH3NH3PbI3 and its three close relatives, CH3NH3SnI3 ,CH3NH3PbCl3 , and CsPbI3, using relativistic density function theory. The long-range van der Waals (vdW) interactions were incorporated into the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional using the Tkatchenko-Scheffler pairwise scheme. Our results reveal that hydrogen bonding, which is well described by the PBE functional, plays a decisive role for the structural parameters of these systems, including the position and orientation of the organic cation as well as the deformation of the inorganic framework. The magnitude of the inorganic-framework deformation depends sensitively on the orientation of the organic cation, and directly influences the stability of the hybrid perovskites. Our results suggest that the organic and the inorganic components complement each other; the low symmetry of the organic cation is the origin of the inorganic-framework deformation, which then aids the overall stabilization of the hybrid perovskite structure. This stabilization is indirectly affected by vdW interactions, which lead to smaller unit-cell volumes than in PBE and therefore modulate the interaction between the organic cation and the inorganic framework. The vdW-induced lattice-constant corrections are system dependent and lead to PBE+vdW lattice constants in good agreement with experiment. Further insight is gained by analyzing the vdW contributions. In all iodide-based hybrid perovskites, the interaction between the organic cation and the iodide anions provides the largest lattice-constant change, followed by iodine-iodine and the organic cation—heavy-metal cation interaction. These corrections follow an almost linear dependence on the lattice constant within the range considered in our study and are therefore approximately additive.

  19. A review on visible light active perovskite-based photocatalysts.

    Science.gov (United States)

    Kanhere, Pushkar; Chen, Zhong

    2014-12-01

    Perovskite-based photocatalysts are of significant interest in the field of photocatalysis. To date, several perovskite material systems have been developed and their applications in visible light photocatalysis studied. This article provides a review of the visible light (λ > 400 nm) active perovskite-based photocatalyst systems. The materials systems are classified by the B site cations and their crystal structure, optical properties, electronic structure, and photocatalytic performance are reviewed in detail. Titanates, tantalates, niobates, vanadates, and ferrites form important photocatalysts which show promise in visible light-driven photoreactions. Along with simple perovskite (ABO3) structures, development of double/complex perovskites that are active under visible light is also reviewed. Various strategies employed for enhancing the photocatalytic performance have been discussed, emphasizing the specific advantages and challenges offered by perovskite-based photocatalysts. This review provides a broad overview of the perovskite photocatalysts, summarizing the current state of the work and offering useful insights for their future development.

  20. Optical, structural and fluorescence properties of nanocrystalline cubic or monoclinic Eu:Lu{sub 2}O{sub 3} films prepared by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Martinet, C. [Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS-Universite Lyon1, 10, rue Andre-Marie Ampere, 69622 Villeurbanne Cedex (France)]. E-mail: martinet@pcml.univ-lyon1.fr; Pillonnet, A. [Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS-Universite Lyon1, 10, rue Andre-Marie Ampere, 69622 Villeurbanne Cedex (France); Lancok, J. [Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 18221 Prague (Czech Republic); Garapon, C. [Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS-Universite Lyon1, 10, rue Andre-Marie Ampere, 69622 Villeurbanne Cedex (France)

    2007-10-15

    Eu{sup 3+}-doped lutetium oxide (Eu:Lu{sub 2}O{sub 3}) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 deg. C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu{sup 3+} fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band.

  1. Magnetic behaviors of a transverse spin-1/2 Ising cubic nanowire with core/shell structure

    Science.gov (United States)

    El Hamri, M.; Bouhou, S.; Essaoudi, I.; Ainane, A.; Ahuja, R.; Dujardin, F.

    2017-02-01

    The surface shell exchange coupling effect on the magnetic properties (surface shell, core, total longitudinal and total transverse magnetizations, susceptibility, phase diagram and hysteresis loops) of a transverse spin-1/2 Ising cubic nanowire is investigated, in the present work, by employing the effective-field theory based on the probability distribution technique with correlations, for both ferro- and antiferromagnetic cases. We have found that this parameter has a strong effect on the magnetic properties in both cases. In the ferromagnetic case, the total longitudinal magnetization curves display Q- and S-type behaviors and the hysteresis loop has just one loop, whereas in the antiferromagnetic case, the N-type behavior, in which one compensation temperature appears below the critical temperature, exists in the total longitudinal magnetization curve versus reduced temperature, and triple hysteresis loops are found. The effect of applied field is also investigated on the total longitudinal magnetization for the both cases, and we have found that a large applied field value can overcome the antiferromagnetic coupling leading to a ferromagnetic-like behavior.

  2. Stability of organometal perovskites with organic overlayers

    Directory of Open Access Journals (Sweden)

    Catherine D. T. Tran

    2015-08-01

    Full Text Available The air-stability of vapour-phase-deposited methylammonium lead triiodide (CH3NH3PbI3 perovskite thin films has been studied using X-ray diffraction. It is found that the perovskite structure without organic coating decomposes completely within a short period of time (∼two days upon exposure to ambient environment. The degradation of the perovskite structure is drastically reduced when the perovskite films are capped with thin N,N′-Di(1-naphthyl-N,N′-diphenyl-(1,1′-biphenyl-4,4′-diamine (NPB films. We discovered that the amount of lead iodide (PbI2, a product of the degradation, grows as a function of time in a sigmoidal manner. Further mathematical modeling analysis shows that the perovskite degradation follows the Avrami equation, a kinetics theory developed for quantifying phase transformations in solid-state materials.

  3. Structures, magnetic and dielectric properties of the ordered double perovskites LnPbNiSbO6 (Ln = La, Pr)

    Science.gov (United States)

    Han, Lin; Bai, Yijia; Liu, Xiaojuan; Yao, Chuangang; Meng, Junling; Liang, Qingshuang; Wu, Xiaojie; Meng, Jian

    2014-09-01

    The crystal structures, magnetic and dielectric properties for the ordered double perovskites LnPbNiSbO6 (Ln = La, Pr) have been investigated. Rietveld refinements of x-ray diffraction data have been indexed for the monoclinic symmetry in space group P21/n (No. 14) and a highly rock-salt ordered arrangement of NiO6 and SbO6 octahedra. The B-site lattices are distorted strongly due to the substitution of rare Earth ions at the A-site. The magnetization measurements show an antiferromagnetic ordering. The effective magnetic moments μ eff are larger than the spin-only values, suggesting that the orbital component for Ni2+ is significant. The maximum values of isothermal magnetization increase due to the lattice distortion of BO6 octahedra, which may weaken the antiferromagnetic interaction via Ni2+-O-Sb5+-O-Ni2+ paths. The dielectric constants for LaPbNiSbO6 present frequency dependence and the tan δ curves exhibit relaxor-like dielectric response. The ɛ‧ decreases with the reduction of the magnetic moments of B-site transition metal ions, which reveals a relationship between the dielectric and magnetic properties.

  4. Structural chemistry and magnetic properties of the perovskite SrLa2Ni2TeO9

    Science.gov (United States)

    Paria Sena, Robert; Hadermann, Joke; Chin, Chun-Mann; Hunter, Emily C.; Battle, Peter D.

    2016-11-01

    A polycrystalline sample of SrLa2Ni2TeO9 has been synthesized using a standard ceramic method and characterized by neutron diffraction, magnetometry and electron microscopy. The compound adopts a monoclinic, perovskite-like structure with space group P21/n and unit cell parameters a=5.6008(1), b=5.5872(1), c=7.9018(2) Å, β=90.021(6)° at room temperature. The two crystallographically-distinct B sites are occupied by Ni2+ and Te6+ in ratios of 83:17 and 50:50. Both ac and dc magnetometry suggest that the compound is a spin glass below 35 K but the neutron diffraction data show that some regions of the sample are antiferromagnetic. Electron microscopy revealed twinning on a nanoscale and local variations in composition. These defects are thought to be responsible for the presence of two distinct types of antiferromagnetic ordering. The magnetic properties of SrLa2Ni2TeO9 are discussed in terms of cation ordering in the microstructure.

  5. Magnetic properties and structural characterization of Sr{sub 2}RuHoO{sub 6} complex perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Corredor, L.T.; Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 5997, Bogota DC (Colombia); Martinez Buitrago, D. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 5997, Bogota DC (Colombia); Grupo Fisica de Materiales, Escuela de Fisica, Universidad Pedagogica y Tecnologica de Colombia, Tunja (Colombia); Albino Aguiar, J. [Departamento de Fisica, Universidade Federal de Pernambuco, 50670-901, Recife PE (Brazil); Roa-Rojas, J., E-mail: jroar@unal.edu.co [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, AA 5997, Bogota DC (Colombia)

    2012-08-15

    We report an experimental study of the crystallographic lattice, morphologic characteristics and magnetic feature of Sr{sub 2}RuHoO{sub 6} complex perovskite, which is used as a precursor in the fabrication process of the superconducting ruthenocuprate RuSr{sub 2}HoCu{sub 2}O{sub 8}. The samples were produced through the standard solid state reaction. A Rietveld refinement of experimental X-ray diffraction patterns shows that the material crystallizes in a monoclinic structure, which belongs to the P21/n (no.14) space group, with lattice parameters a=5.7719(6) A, b=5.8784(5) A, c=8.1651(9) A, and tilt angle {beta}=90.200 Degree-Sign . Magnetic susceptibility measurements reveal the occurrence of an antiferromagnetic ordering for a Neel temperature T{sub N}=10.1 K. From the Curie-Weiss fitting of the paramagnetic regime we obtain an effective magnetic moment of 11.31 {mu}{sub B}.

  6. Finding the Stable Structures of WxN1-x with an ab-initio High-Throughput Approach

    Science.gov (United States)

    2014-03-13

    of NaCl) we looked at all 255 combinations. We found 34 unique structures, including NbO itself, CsCl, S3U4, ReO3,[59] cubic perovskite (with formula...simulation of the liquid-metal/amorphous- semiconductor transition in germanium, Phys. Rev. B 49, 14251–14269 (1994). [36] G. Kresse, , Ph.D. thesis

  7. Cubic Subalgebras and Cubic Closed Ideals of B-algebras

    Directory of Open Access Journals (Sweden)

    Tapan Senapati

    2015-06-01

    Full Text Available In this paper, the concept of cubic set to subalgebras, ideals and closed ideals of B-algebras are introduced. Relations among cubic subalgebras with cubic ideals and cubic closed ideals of B-algebras investigated. The homomorphic image and inverse image of cubic subalgebras, ideals are studied and some related properties are investigated. Also, the product of cubic B-algebras are investigated.

  8. β-Mn-type Co(8+x)Zn(12-x) as a defect cubic Laves phase: site preferences, magnetism, and electronic structure.

    Science.gov (United States)

    Xie, Weiwei; Thimmaiah, Srinivasa; Lamsal, Jagat; Liu, Jing; Heitmann, Thomas W; Quirinale, Dante; Goldman, Alan I; Pecharsky, Vitalij; Miller, Gordon J

    2013-08-19

    The results of crystallographic analysis, magnetic characterization, and theoretical assessment of β-Mn-type Co-Zn intermetallics prepared using high-temperature methods are presented. These β-Mn Co-Zn phases crystallize in the space group P4(1)32 [Pearson symbol cP20; a = 6.3555(7)-6.3220(7)], and their stoichiometry may be expressed as Co(8+x)Zn(12-x) [1.7(2) phase with a Curie temperature of ∼420 K. Neutron powder diffraction and electronic structure calculations using the local spin density approximation indicate that the spontaneous magnetization of this phase arises exclusively from local moments at the Co atoms. Inspection of the atomic arrangements of Co(8+x)Zn(12-x) reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna ab initio simulation package (VASP) and starting from the undistorted, defect Laves phase structure achieved energy minimization at the observed β-Mn structure type, a result that offers greater insight into the β-Mn structure type and establishes a closer relationship with the corresponding α-Mn structure (cI58).

  9. Stability and bandgaps of layered perovskites for one- and two-photon water splitting

    Science.gov (United States)

    Castelli, Ivano E.; María García-Lastra, Juan; Hüser, Falco; Thygesen, Kristian S.; Jacobsen, Karsten W.

    2013-10-01

    Direct production of hydrogen from water and sunlight requires stable and abundantly available semiconductors with well positioned band edges relative to the water red-ox potentials. We have used density functional theory (DFT) calculations to investigate 300 oxides and oxynitrides in the Ruddlesden-Popper phase of the layered perovskite structure. Based on screening criteria for the stability, bandgaps and band edge positions, we suggest 20 new materials for the light harvesting photo-electrode of a one-photon water splitting device and 5 anode materials for a two-photon device with silicon as photo-cathode. In addition, we explore a simple rule relating the bandgap of the perovskite to the number of octahedra in the layered structure and the B-metal ion. Finally, the quality of the GLLB-SC potential used to obtain the bandgaps, including the derivative discontinuity, is validated against G0W0@LDA gaps for 20 previously identified oxides and oxynitrides in the cubic perovskite structure.

  10. Effect of calcination temperature on structural properties and catalytic activity in oxidation reactions of LaNiO3 perovskite prepared by Pechini method

    Institute of Scientific and Technical Information of China (English)

    K.Rida; M.A.Pe(n)a; E.Sastre; A.Martínez-Arias

    2012-01-01

    The study presented the preparation of the perovskite oxide LaNiO3 by the complex citrate method,paying particular attention to evolution of its formation from the amorphous precursor with varied calcination temperatures.The products obtained after heat treatment under air between 200 and 800 ℃ were characterized by X-ray diffraction (XRD),thermogravimetric and differential thermal analysis (TG-DTA),Fourier transform infrared spectroscopy (FTIR),SBET measurements and X-ray photoelectron spectroscopy (XPS).The results showed the formation of a single phase with perovskite structure from ca.550 ℃.Tests on the two catalytic oxidation reactions of C3H6 and CO over the system calcined between mentioned temperatures were examined on the basis of characterization results and showed that optimum catalytic properties for such reactions were achieved for the perovskite calcined at 600 ℃.In turn,correlations between redox and catalytic properties were established on the basis of thermogravimetric temperature programmed reduction (TPR) analysis.

  11. Semiconducting and dielectric properties of barium titanates, tantalates and niobates with perovskite structure

    Science.gov (United States)

    Kolodiazhnyi, Taras

    The dielectric and semiconducting properties of two types of ceramics (n-type BaTiO3 and dielectric Ba(B'1/3 B″2/3)O3 where B' = Mg, Zn, Ni, and B″ = Nb, Ta) were characterized. Complex impedance analysis and dc conductivity measurements of samples prepared at various PO2 have ruled out oxygen chemisorption in favor of interfacial segregation of cation vacancies as the cause of the positive temperature coefficient of resistivity (PTCR) effect in n-type BaTiO3. The effect of preparation conditions, sintering atmosphere, stoichiometry, and post-sinter anneal on the defect chemistry of BaTiO3 was studied using the electron paramagnetic resonance (EPR) technique. Several paramagnetic defects such as, Ti3+, VBa, and VTi were detected and identified by EPR. Current-voltage characteristics (I-V) of PTCR BaTiO 3 were analyzed in light of space-charge-limited-current, trap-filled-limited-current, Frenkel-Poole, small polaron, and double-Schottky barrier models. It was shown that for the double-Schottky barrier model, a partial stabilisation of the potential barrier is expected when the Fermi level is pinned at grain boundaries by a high density of the interface states. The deviation of I-V characteristics of BaTiO3 in the region of the PTCR effect can be explained by dependence of the population of the interface electron states on applied voltage. Based on the Seebeck and Hall effect measurements, it was found that in the range of 100--300 K, the drift mobility of electrons in BaTiO 3 is not thermally activated, which supports the concept of conduction band electron transport rather than small radii polaron hopping. However, further study over a wider temperature range and on better quality crystals is required to unequivocally clarify the electron transport mechanism in BaTiO 3. Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' 1/3B″2/3)O3 where B' = Mg, Zn, Ni, and B″ = Nb, Ta were analyzed

  12. Structures and magnetic properties of double perovskites A sub 2 LnMO sub 6 and 6H-perovskites Ba sub 3 LnRu sub 2 O sub 9 (A=Sr, Ba; Ln=Y, lanthanides; M=Nb, Ta, Ru)

    CERN Document Server

    Hinatsu, Y

    2003-01-01

    This account describes the synthesis, crystal structures and magnetic properties of double perovskites A sub 2 LnMO sub 6 and 6H-perovskites Ba sub 3 LnRu sub 2 O sub 9 (A=Sr, Ba; Ln=Y, lanthanides; M=Nb, Ta, Ru). The double perovskites A sub 2 LnMO sub 6 have two kinds of cations, Ln and M, in the B site of the perovskite ABO sub 3. These cations adopt the alternative ordered arrangement. Measurements of the magnetic susceptibility, specific heat, and powder neutron diffraction showed that all of the A sub 2 LnRuO sub 6 compounds exhibited an antiferromagnetic transition at low temperatures and a complex temperature dependence of the magnetic susceptibility below their transition temperatures. In these compounds, the magnetic interaction between the Ln (4f electrons) and Ru (4d electrons) ions via the Ln-O-Ru pathway contributes greatly to their magnetic cooperative phenomena. The structural and magnetic studies for the 6H-perovskites Ba sub 3 LnRu sub 2 O sub 9 show that the Ln cations occupy the corner-sha...

  13. High-pressure structural study of fluoro-perovskite CsCdF3 up to 60 GPa: A combined experimental and theoretical study

    DEFF Research Database (Denmark)

    Vaitheeswaran, G.; Kanchana, V.; Kumar, Ravhi S.;

    2010-01-01

    The structural behavior of CsCdF3 under pressure is investigated by means of theory and experiment. High-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of 60 GPa using synchrotron radiation. The cubic Pm3̅ m crystal symmetry persists throughout this pressure...

  14. First-principles calculations on the structural and electronic properties of cubic KCaF3 and NaCaF3 (001) surfaces

    Science.gov (United States)

    Yang, Kun; He, Yanqing; Cheng, Yi; Che, Li; Yao, Li

    2017-03-01

    First-principles density functional theory (DFT) calculations have been used to investigate the structural and electronic properties of the cubic KCaF3 and NaCaF3 (001) surfaces with MF (M = K or Na) and CaF2 terminations. For both KCaF3 and NaCaF3 (001) surfaces, the MF termination has stronger surface rumpling than the CaF2 termination. All the computed band gaps for the KCaF3 and NaCaF3 (001) surfaces are smaller than those of the bulks. Furthermore, separated bands that originate from surface layer F p states are introduced at the top of the valance band of MF-terminated surfaces, indicating the emergence of the surface states. The calculated surface energies show that the MF-terminated surface is energetically more favorable than the CaF2-terminated surface.

  15. Global Existence and Convergence of Solutions to a Cross-Diffusion Cubic Predator-Prey System with Stage Structure for the Prey

    Directory of Open Access Journals (Sweden)

    Shengmao Fu

    2010-01-01

    Full Text Available We study a cubic predator-prey system with stage structure for the prey. This system is a generalization of the two-species Lotka-Volterra predator-prey model. Firstly, we consider the asymptotical stability of equilibrium points to the system of ordinary differential equations type. Then, the global existence of solutions and the stability of equilibrium points to the system of weakly coupled reaction-diffusion type are discussed. Finally, the existence of nonnegative classical global solutions to the system of strongly coupled reaction-diffusion type is investigated when the space dimension is less than 6, and the global asymptotic stability of unique positive equilibrium point of the system is proved by constructing Lyapunov functions.

  16. Non-collinear magnetism in multiferroic perovskites.

    Science.gov (United States)

    Bousquet, Eric; Cano, Andrés

    2016-03-31

    We present an overview of the current interest in non-collinear magnetism in multiferroic perovskite crystals. We first describe the different microscopic mechanisms giving rise to the non-collinearity of spins in this class of materials. We discuss, in particular, the interplay between non-collinear magnetism and ferroelectric and antiferrodistortive distortions of the perovskite structure, and how this can promote magnetoelectric responses. We then provide a literature survey on non-collinear multiferroic perovskites. We discuss numerous examples of spin cantings driving weak ferromagnetism in transition metal perovskites, and of spin-induced ferroelectricity as observed in the rare-earth based perovskites. These examples are chosen to best illustrate the fundamental role of non-collinear magnetism in the design of multiferroicity.

  17. Oxygen Evolution at Manganite Perovskite Ruddlesden-Popper Type Particles: Trends of Activity on Structure, Valence and Covalence

    Directory of Open Access Journals (Sweden)

    Majid Ebrahimizadeh Abrishami

    2016-11-01

    Full Text Available An improved understanding of the correlation between the electronic properties of Mn-O bonds, activity and stability of electro-catalysts for the oxygen evolution reaction (OER is of great importance for an improved catalyst design. Here, an in-depth study of the relation between lattice structure, electronic properties and catalyst performance of the perovskite Ca1−xPrxMnO3 and the first-order RP-system Ca2−xPrxMnO4 at doping levels of x = 0, 0.25 and 0.5 is presented. Lattice structure is determined by X-ray powder diffraction and Rietveld refinement. X-ray absorption spectroscopy of Mn-L and O-K edges gives access to Mn valence and covalency of the Mn-O bond. Oxygen evolution activity and stability is measured by rotating ring disc electrode studies. We demonstrate that the highest activity and stability coincidences for systems with a Mn-valence state of +3.7, though also requiring that the covalency of the Mn-O bond has a relative minimum. This observation points to an oxygen evolution mechanism with high redox activity of Mn. Covalency should be large enough for facile electron transfer from adsorbed oxygen species to the MnO6 network; however, it should not be hampered by oxidation of the lattice oxygen, which might cause a crossover to material degradation. Since valence and covalency changes are not entirely independent, the introduction of the energy position of the eg↑ pre-edge peak in the O-K spectra as a new descriptor for oxygen evolution is suggested, leading to a volcano-like representation of the OER activity.

  18. Crystal structure and optical properties of the [Ag62S12(SBu(t))32](2+) nanocluster with a complete face-centered cubic kernel.

    Science.gov (United States)

    Jin, Shan; Wang, Shuxin; Song, Yongbo; Zhou, Meng; Zhong, Juan; Zhang, Jun; Xia, Andong; Pei, Yong; Chen, Man; Li, Peng; Zhu, Manzhou

    2014-11-05

    The crystal structure of the [Ag62S12(SBu(t))32](2+) nanocluster (denoted as NC-I) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag14 core structure with a Ag48(SBu(t))32 shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag62S13(SBu(t))32](4+) structure (denoted as NC-II for short) reported by Wang. Interestingly, NC-I exhibits prominent differences in the optical properties in comparison with the case of the NC-II nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in NC-I in comparison to that of NC-II is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of NC-I and NC-II. These findings offer a new insight into the structure and property evolution of silver cluster materials.

  19. CaCu3Pt4O12: the first perovskite with the B site fully occupied by Pt(4+).

    Science.gov (United States)

    Yamada, Ikuya; Takahashi, Yuka; Ohgushi, Kenya; Nishiyama, Norimasa; Takahashi, Ryoji; Wada, Kohei; Kunimoto, Takehiro; Ohfuji, Hiroaki; Kojima, Yohei; Inoue, Toru; Irifune, Tetsuo

    2010-08-02

    A novel A-site ordered perovskite CaCu(3)Pt(4)O(12) was synthesized under high pressure and high temperature of 12 GPa and 1250 degrees C. CaCu(3)Pt(4)O(12) is the first perovskite in which the B site is fully occupied by Pt(4+). The crystal structure refinement based on the synchrotron powder X-ray diffraction data shows that CaCu(3)Pt(4)O(12) crystallizes in the space group Im3 (cubic) with a lattice constant of a = 7.48946(10) A. The magnetic susceptibility data show the antiferromagnetic transition at T(N) = 40 K, which is attributed to the magnetic ordering of Cu(2+) spins with S = 1/2.

  20. LEED STUDY OF NAXWO3 TUNGSTEN BRONZE - STRUCTURAL RELAXATION OF A PEROVSKITE SURFACE

    NARCIS (Netherlands)

    PEACOR, SD; HIBMA, T

    1993-01-01

    We have performed a low energy electron diffraction study of the sodium tungsten bronze, NaxWO3, x = 0.8, surface. Temperature dependent changes of both polished and cleaved surfaces indicate structural phase transitions of the surface structure, and reflect the general trend in structural phase tra

  1. First-principles calculations of typical anisotropic cubic and hexagonal structures and homogenized moduli estimation based on the Y-parameter: Application to CaO, MgO, CH and Calcite CaCO3

    Science.gov (United States)

    Fu, Jia; Bernard, Fabrice; Kamali-Bernard, Siham

    2017-02-01

    X-ray method to test the material properties and to obtain elastic constants is commonly based on the Reuss model and Kroner model. Y parameter has been turned out to be an effective method to estimate elastic properties of polycrystalline material. Since Y-parameters of cubic polycrystalline material based on the certain uniform stress (Reuss model) has not been given, our work aims to complete this part of the theoretical analysis, which can effectively compare elastic constants measured by the X-ray diffraction method. The structural and the elastic properties of cubic structures (CaO and MgO) and hexagonal structures (CH and Calcite CaCO3) are investigated by the density functional theory method. And then the credibility of Y parameters for determing elastic moduli of cubic structures is proved and elastic properties in typical crystallographic planes of [100], [110] and [111] are also calculated. Meanwhile, Young's moduli of CH and Calcite structure are 58.08 GPa and 84.549 GPa, which are all close to references. Elastic properties of cubic and hexagonal structures under various pressures are calculated and the surface constructions of elastic moduli are drawn, showing the anisotropy at various directions. The crystal structure investigated in this work are typical of some primary or secondary components of Hardened Cements Pastes and their homogenized elastic properties are needed in a hierarchical multi-scale modeling, such as the one developed by some of the authors of this paper.

  2. Influence of strontium on the cubic to ordered hexagonal phase transformation in barium magnesium niobate

    Indian Academy of Sciences (India)

    M Thirumal; A K Ganguli

    2000-12-01

    Oxides of the type Ba3–SrMgNb2O9 were synthesized by the solid state route. The = 0 composition (Ba3MgNb2O9) was found to crystallize in a disordered (cubic) perovskite structure when sintered at 1000C. For higher Sr doping ( ≥ 0.5), there was clearly the presence of an ordered hexagonal phase indicated by the growth of superstructure reflections in the powder X-ray diffraction patterns. In all the compositions there was the presence of a minor amount of Ba5–SrNb4O15 phase which increased with Sr substitution up to = 1 and then it remained nearly constant at about 5%. Samples sintered at 1300C showed the hexagonally ordered phase for the entire range of composition (0 ≤ ≤ 3). The degree of ordering being considerably greater than in the 1000C heated samples as evidenced by several superstructure reflections.

  3. Cubic Curves, Finite Geometry and Cryptography

    CERN Document Server

    Bruen, A A; Wehlau, D L

    2011-01-01

    Some geometry on non-singular cubic curves, mainly over finite fields, is surveyed. Such a curve has 9,3,1 or 0 points of inflexion, and cubic curves are classified accordingly. The group structure and the possible numbers of rational points are also surveyed. A possible strengthening of the security of elliptic curve cryptography is proposed using a `shared secret' related to the group law. Cubic curves are also used in a new way to construct sets of points having various combinatorial and geometric properties that are of particular interest in finite Desarguesian planes.

  4. In-depth investigation of EPR spectra of Mn(2+) ions in ZnS single crystals with pure cubic structure.

    Science.gov (United States)

    Nistor, S V; Stefan, M

    2009-04-01

    The X (9.8 GHz)-band electron paramagnetic resonance (EPR) properties of substitutional Mn(2+) ions in high quality cubic ZnS single crystals grown from PbCl(2) flux have been thoroughly investigated. Accurate spin Hamiltonian (SH) parameters: g = 2.002 25 ± 0.000 06; a = (7.987 ± 0.008) × 10(-4) cm(-1) and A = -(63.88 ± 0.02) × 10(-4) cm(-1) were obtained by simulation and fitting to the experimentally allowed transitions recorded for the magnetic field aligned within ± 0.25° along the main crystal axes. The normally forbidden hyperfine [Formula: see text], Δm = ± 1 transitions were also observed. Their position was found to be in agreement, within the experimental accuracy of ΔH = ± 0.01 mT, with calculations using the same SH parameters. The angular variation of the ratios of the intensities of the central forbidden to the allowed transitions could be accounted for only by including an additional constant contribution. The observed line broadening of the [Formula: see text] and [Formula: see text] fine structure transitions and their line width variation in a (110) plane have been quantitatively described by considering a random distribution of lattice strains at the Mn(2+) impurity ions. The influence of the forbidden transitions and line broadening on the EPR spectra line shape of the Mn(2+) ions in cubic ZnS crystalline powders is also examined.

  5. Structural and electronic transformations in quadruple iron perovskite Ca1−xSrxCu3Fe4O12

    Directory of Open Access Journals (Sweden)

    Ikuya Yamada

    2017-06-01

    Full Text Available Crystal structures and electronic transformations of quadruple iron perovskite solid solution Ca1−xSrxCu3Fe4O12 (x = 0.2, 0.4, 0.6, and 0.8 have been investigated by synchrotrons X-ray powder diffraction, Mössbauer spectroscopy, and magnetization measurements. For x = 0.2, a charge disproportionation transition (2Fe4+ → Fe3+ + Fe5+ occur simultaneously with electron charge transfers from Fe to Cu below ∼200 K, as well as CaCu3Fe4O12. In contrast, negative thermal expansions derived from continuous electron charge transfers from Cu and Fe are observed for x = 0.6 and 0.8 at low temperatures below room temperature, as in SrCu3Fe4O12, followed by charge disproportionation transitions. A two-phase coexistence is observed at low temperature below ∼200 K for x = 0.4, indicating that the phase boundary locates in the vicinity of this composition. We have discovered that the FeO bond lengths are closely related to their covalency which were estimated from Mössbauer isomer shift parameters. The FeO bond covalency plays a crucial role in the types of electronic phase transitions for the Ca1−xSrxCu3Fe4O12 and R3+Cu3Fe4O12 (R: trivalent rare earth metal ions, Y, La–Lu systems, where the two different low-temperature electronic phases are separated by a common isomer shift value of ∼0.17 mm s−1.

  6. Synthesis and structure of Ba 6Co 6ClO 16, a new cobalt oxychloride with a layered perovskite-related structure

    Science.gov (United States)

    Tancret, Nathalie; Roussel, Pascal; Abraham, Francis

    2005-10-01

    Well-developed single crystals of the title compound were prepared using a BaCl 2 flux and investigated by X-ray diffraction methods using Mo( Kα) radiation and a Charge Coupled Device (CCD) detector. The crystal structure was solved and refined in the hexagonal symmetry with P6¯m2 space group, a=5.6698(2) Å and c=14.4654(5) Å to a final R1=0.022 for 44 parameters with 1418 individual reflections. The structure of Ba 6Co 6ClO 16, which is related to the 6H-perovkite-type structure of BaMnO 2.88, is formed by the periodic stacking along [001] of five [BaO 3] layers separated by a [BaOCl] with a ( hhhchc) stacking sequence. The [BaO 3] stacking creates tetranuclear face sharing octahedra units Co 4O 15 containing Co(III) connected by dimers of corner-sharing CoO 4 tetrahedra. This new oxychloride belongs to the family of compounds formulated as [BaOCl] M' 2[Ba n+1M nO 3n+3] where n represents the thickness of the octahedral string in hexagonal perovskite slabs.

  7. Enhanced electron extraction using SnO2 for high-efficiency planar-structure HC(NH2)2PbI3-based perovskite solar cells

    Science.gov (United States)

    Jiang, Qi; Zhang, Liuqi; Wang, Haolin; Yang, Xiaolei; Meng, Junhua; Liu, Heng; Yin, Zhigang; Wu, Jinliang; Zhang, Xingwang; You, Jingbi

    2017-01-01

    Planar structures for halide perovskite solar cells have recently garnered attention, due to their simple and low-temperature device fabrication processing. Unfortunately, planar structures typically show I-V hysteresis and lower stable device efficiency compared with mesoporous structures, especially for TiO2-based n-i-p devices. SnO2, which has a deeper conduction band and higher electron mobility compared with traditional TiO2, could enhance charge transfer from perovskite to electron transport layers, and reduce charge accumulation at the interface. Here we report low-temperature solution-processed SnO2 nanoparticles as an efficient electron transport layer for perovskite solar cells. Our SnO2-based devices are almost free of hysteresis, which we propose is due to the enhancement of electron extraction. By introducing a PbI2 passivation phase in the perovskite layer, we obtain a 19.9 ± 0.6% certified efficiency. The devices can be easily processed under low temperature (150 ∘C), offering an efficient method for the large-scale production of perovskite solar cells.

  8. Crystal structure of monoclinic samarium and cubic europium sesquioxides and bound coherent neutron scattering lengths of the isotopes {sup 154}Sm and {sup 153}Eu

    Energy Technology Data Exchange (ETDEWEB)

    Kohlmann, Holger [Leipzig Univ. (Germany). Inst. of Inorganic Chemistry; Hein, Christina; Kautenburger, Ralf [Saarland Univ., Saarbruecken (Germany). Inorganic Solid State Chemistry; Hansen, Thomas C.; Ritter, Clemens [Institut Laue-Langevin, Grenoble (France); Doyle, Stephen [Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen (Germany). Inst. for Synchrotron Radiation (ISS)

    2016-11-01

    The crystal structures of monoclinic samarium and cubic europium sesquioxide, Sm{sub 2}O{sub 3} and Eu{sub 2}O{sub 3}, were reinvestigated by powder diffraction methods (laboratory X-ray, synchrotron, neutron). Rietveld analysis yields more precise structural parameters than previously known, especially for oxygen atoms. Interatomic distances d(Sm-O) in Sm{sub 2}O{sub 3} range from 226.3(4) to 275.9(2) pm [average 241.6(3) pm] for the monoclinic B type Sm{sub 2}O{sub 3} [space group C2/m, a = 1418.04(3) pm, b = 362.660(7) pm, c = 885.48(2) pm, β = 100.028(1) ], d(Eu-O) in Eu{sub 2}O{sub 3} from 229.9(2) to 238.8(2) pm for the cubic bixbyite (C) type [space group Ia anti 3, a = 1086.87(1) pm]. Neutron diffraction at 50 K and 2 K did not show any sign for magnetic ordering in Sm{sub 2}O{sub 3}. Isotopically enriched {sup 154}Sm{sub 2}O{sub 3} and {sup 153}Eu{sub 2}O{sub 3} were used for the neutron diffraction work because of the enormous absorption cross section of the natural isotopic mixtures for thermal neutrons. The isotopic purity was determined by inductively coupled plasma - mass spectrometry to be 98.9% for {sup 154}Sm and 99.8% for {sup 153}Eu. Advanced analysis of the neutron diffraction data suggest that the bound coherent scattering lengths of {sup 154}Sm and {sup 153}Eu need to be revised. We tentatively propose b{sub c}({sup 154}Sm) = 8.97(6) fm and b{sub c}({sup 153}Eu) = 8.85(3) fm for a neutron wavelength of 186.6 pm to be better values for these isotopes, showing up to 8% deviation from accepted literature values. It is shown that inaccurate scattering lengths may result in severe problems in crystal structure refinements causing erroneous structural details such as occupation parameters, which might be critically linked to physical properties like superconductivity in multinary oxides.

  9. Perovskite catalysts for oxidative coupling

    Science.gov (United States)

    Campbell, Kenneth D.

    1991-01-01

    Perovskites of the structure A.sub.2 B.sub.2 C.sub.3 O.sub.10 are useful as catalysts for the oxidative coupling of lower alkane to heavier hydrocarbons. A is alkali metal; B is lanthanide or lanthanum, cerium, neodymium, samarium, praseodymium, gadolinium or dysprosium; and C is titanium.

  10. Common features of gallium perovskites

    NARCIS (Netherlands)

    Aleksiyko, R; Berkowski, M; Byszewski, P; Dabrowski, B; Diduszko, R; Fink-Finowicki, J; Vasylechko, LO

    2001-01-01

    The Czochralski and floating zone methods have been used to grow single crystals of gallium perovskites solid solutions with rare earth elements La, Pr, Nd, Sm and with Sr. The structure of the crystals has been investigated by powder X-ray, synchrotron radiation and neutron diffraction methods over

  11. A nano-grid structure made of perovskite SrTiO3 nanowires for efficient electron transport layers in inverted polymer solar cells

    Science.gov (United States)

    Kim, Jeong Won; Suh, Yo-Han; Lee, Chang-Lyoul; Kim, Yong Seok; Kim, Won Bae

    2015-02-01

    A nano-grid structure of perovskite SrTiO3 NWs is developed for a novel electron transport layer in inverted polymer solar cells. Due to the excellent charge transporting properties of the SrTiO3 nano-grid structure, the device employing this nanostructure showed ~32% enhanced photovoltaic performance, compared to the solar cell using a TiO2 thin film.A nano-grid structure of perovskite SrTiO3 NWs is developed for a novel electron transport layer in inverted polymer solar cells. Due to the excellent charge transporting properties of the SrTiO3 nano-grid structure, the device employing this nanostructure showed ~32% enhanced photovoltaic performance, compared to the solar cell using a TiO2 thin film. Electronic supplementary information (ESI) available: Experimental details, HR-TEM images with EDX atomic ratio analysis, FE-SEM images, transmittance spectra and light absorbance spectra. See DOI: 10.1039/c4nr06720g

  12. Structural dependence of the photocatalytic properties of double perovskite compounds A2InTaO6 (A = Sr or Ba) doped with nickel.

    Science.gov (United States)

    Lv, Meilin; Wang, Yawei; Lu, Lingwei; Wang, Ruinan; Ni, Shuang; Liu, Gang; Xu, Xiaoxiang

    2016-08-03

    The crystal structure of photocatalysts generally plays a pivotal role in controlling their electronic structure as well as catalytic performance. In this work, a series of double perovskite compounds A2InTaO6 (A = Sr or Ba) and their Ni doped counterparts were investigated with the aim of understanding how doping and structural modification will affect their photocatalytic activity. Our results show that Ni doping is effective in improving the optical absorption of these wide band gap semiconductors and accommodating the Sr cation in the A sites leads to severe structural distortion, i.e. the In(Ni)-O-Ta bond angle deviates largely from 180°. A better photocatalytic performance was observed for samples with Ni doping and Ba in the A sites. The best photocatalytic hydrogen production rate recorded was ∼293.6 μmol h(-1) for Ba2In0.9Ni0.1TaO6 under full range irradiation, corresponding to an apparent quantum efficiency of 2.75%. DFT calculations reveal the role of Ni doping by forming additional spin-polarized bands inside the intrinsic band gap of the native perovskite. The better photocatalytic activity of Ba2In0.9Ni0.1TaO6 can then be understood as a result of a reduced band gap as well as a linear In(Ni)-O-Ta bond arrangement that is favorable for the strong metal-oxygen-metal interactions.

  13. The body-centered cubic structure of methyllithium tetramer crystal: staggered methyl conformation by electrostatic stabilization via intratetramer multipolarization.

    Science.gov (United States)

    Ohta, Yusuke; Demura, Akimitsu; Okamoto, Takuya; Hitomi, Haruko; Nagaoka, Masataka

    2006-06-29

    The methyllithium tetramer (CH3Li)4 structure in the bcc crystal has been theoretically optimized with the use of density functional theory calculations under the periodic boundary condition. The X-ray structure shows that the methyl-group conformation in tetramer in crystal takes the staggered form rather than the eclipsed form that is taken in the isolated tetramer, i.e., the crystal packing effect, and this has been reproduced for the first time. It is concluded that the staggered form is advantageous in crystal, as a whole, due to the larger electrostatic stabilization via the induced intratetramer multipolarization, although it should cause, simultaneously, smaller destabilization in intratetramer electronic energy.

  14. Semisymmetric Cubic Graphs of Order 162

    Indian Academy of Sciences (India)

    Mehdi Alaeiyan; Hamid A Tavallaee; B N Onagh

    2010-02-01

    An undirected graph without isolated vertices is said to be semisymmetric if its full automorphism group acts transitively on its edge set but not on its vertex set. In this paper, we inquire the existence of connected semisymmetric cubic graphs of order 162. It is shown that for every odd prime , there exists a semisymmetric cubic graph of order 162 and its structure is explicitly specified by giving the corresponding voltage rules generating the covering projections.

  15. Non-collinear magnetic structure of manganese quadruple perovskite CdMn7O12

    Science.gov (United States)

    Guo, H.; Fernández-Daz, M. T.; Zhou, L.; Yin, Y.; Long, Y.; Komarek, A. C.

    2017-01-01

    We report on the magnetic structure of CdMn7O12 determined by powder neutron diffraction. We were able to measure the magnetic structure of this Cd containing and highly neutron absorbing material by optimizing the sample geometry and by blending the CdMn7O12 with Aluminum powder. Below its Néel temperature TN1 all magnetic reflections can be indexed by a single commensurate propagation vector k = (0, 0, 1). This is different to the case of CaMn7O12 where the propagation vector is incommensurate and where an in-plane helical magnetic structure has been found. We observe a commensurate non-collinear magnetic structure in CdMn7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12. However, the commensurate propagation vector prevents the appearance of a helical magnetic structure in CdMn7O12. Finally, we also observe a third structural phase transition below ~60 K that can be attributed to phase separation. PMID:28378833

  16. Einsteinian cubic gravity

    Science.gov (United States)

    Bueno, Pablo; Cano, Pablo A.

    2016-11-01

    We drastically simplify the problem of linearizing a general higher-order theory of gravity. We reduce it to the evaluation of its Lagrangian on a particular Riemann tensor depending on two parameters, and the computation of two derivatives with respect to one of those parameters. We use our method to construct a D -dimensional cubic theory of gravity which satisfies the following properties: (1) it shares the spectrum of Einstein gravity, i.e., it only propagates a transverse and massless graviton on a maximally symmetric background; (2) it is defined in the same way in general dimensions; (3) it is neither trivial nor topological in four dimensions. Up to cubic order in curvature, the only previously known theories satisfying the first two requirements are the Lovelock ones. We show that, up to cubic order, there exists only one additional theory satisfying requirements (1) and (2). Interestingly, this theory is, along with Einstein gravity, the only one which also satisfies (3).

  17. Synthesis, crystal structure, and bonding analysis of the hypoelectronic cubic phase Ca5Pd6Ge6.

    Science.gov (United States)

    Doverbratt, Isa; Ponou, Siméon; Wang, Fei; Lidin, Sven

    2015-09-21

    The title compound, Ca5Pd6Ge6, was obtained during a systematic investigation of the Ca-Pd-Ge ternary phase diagram. The crystal structure was determined and refined from single-crystal X-ray diffraction data. It crystallizes in a new structure variant of the Y4PdGa12-type structure (Im3̅m, a = 8.7764(4) Å) that features an arrangement of vertex-sharing body-centered cubes of calcium, Ca@Ca8, with a hierarchical bcc network, interpenetrating a second (Pd6Ge6) network consisting of Ge2 dumbbells surrounded by Pd in a strongly flattened octahedron with Pd(μ(2)-η(2),η(4)-Ge2)-like motifs. These octahedra are condensed through the Pd to form a 3D open fcc network. Theoretical band structure calculations suggested that the compound is hypoelectronic with predominantly multicenter-type interatomic interactions involving all three elements and essentially a Hume-Rothery-like regime of electronic stabilization. The similar electronegativity between germanium and palladium atoms has a decisive impact on the bonding picture of the system.

  18. Structure-property relationships in cubic cuprous iodide: A novel view on stability, chemical bonding, and electronic properties

    Science.gov (United States)

    Pishtshev, A.; Karazhanov, S. Zh.

    2017-02-01

    Based on the combination of density functional theory and theory-group methods, we performed systematic modeling of γ-CuI structural design at the atomistic level. Being started from the metallic copper lattice, we treated a crystal assembly as a stepwise iodination process characterized in terms of a sequence of intermediate lattice geometries. These geometries were selected and validated via screening of possible structural transformations. The genesis of chemical bonding was studied for three structural transformations by analyzing the relevant changes in the topology of valence electron densities. We determined structural trends driven by metal-ligand coupling. This allowed us to suggest the improved scenario of chemical bonding in γ-CuI. In particular, the unconventional effect of spatial separation of metallic and covalent interactions was found to be very important with respect to the preferred arrangements of valence electrons in the iodination process. We rigorously showed that useful electronic and optical properties of γ-CuI originate from the combination of two separated bonding patterns—strong covalency established in I-Cu tetrahedral connections and noncovalent interactions of copper cores is caused by the 3d10 closed-shell electron configurations. The other finding of ours is that the self-consistency of the GW calculations is crucial for correctly determining the dynamic electronic correlations in γ-CuI. Detail reinvestigation of the quasi-particle energy structure by means of the self-consistent GW approach allowed us to explain how p-type electrical conductivity can be engineered in the material.

  19. Structure-property relationships in cubic cuprous iodide: A novel view on stability, chemical bonding, and electronic properties.

    Science.gov (United States)

    Pishtshev, A; Karazhanov, S Zh

    2017-02-14

    Based on the combination of density functional theory and theory-group methods, we performed systematic modeling of γ-CuI structural design at the atomistic level. Being started from the metallic copper lattice, we treated a crystal assembly as a stepwise iodination process characterized in terms of a sequence of intermediate lattice geometries. These geometries were selected and validated via screening of possible structural transformations. The genesis of chemical bonding was studied for three structural transformations by analyzing the relevant changes in the topology of valence electron densities. We determined structural trends driven by metal-ligand coupling. This allowed us to suggest the improved scenario of chemical bonding in γ-CuI. In particular, the unconventional effect of spatial separation of metallic and covalent interactions was found to be very important with respect to the preferred arrangements of valence electrons in the iodination process. We rigorously showed that useful electronic and optical properties of γ-CuI originate from the combination of two separated bonding patterns-strong covalency established in I-Cu tetrahedral connections and noncovalent interactions of copper cores is caused by the 3d(10) closed-shell electron configurations. The other finding of ours is that the self-consistency of the GW calculations is crucial for correctly determining the dynamic electronic correlations in γ-CuI. Detail reinvestigation of the quasi-particle energy structure by means of the self-consistent GW approach allowed us to explain how p-type electrical conductivity can be engineered in the material.

  20. Novel Solvent-free Perovskite Deposition in Fabrication of Normal and Inverted Architectures of Perovskite Solar Cells.

    Science.gov (United States)

    Nejand, Bahram Abdollahi; Gharibzadeh, Saba; Ahmadi, Vahid; Shahverdi, H Reza

    2016-09-19

    We introduced a new approach to deposit perovskite layer with no need for dissolving perovskite precursors. Deposition of Solution-free perovskite (SFP) layer is a key method for deposition of perovskite layer on the hole or electron transport layers that are strongly sensitive to perovskite precursors. Using deposition of SFP layer in the perovskite solar cells would extend possibility of using many electron and hole transport materials in both normal and invert architectures of perovskite solar cells. In the present work, we synthesized crystalline perovskite powder followed by successful deposition on TiO2 and cuprous iodide as the non-sensitve and sensitive charge transport layers to PbI2 and CH3NH3I solution in DMF. The post compressing step enhanced the efficiency of the devices by increasing the interface area between perovskite and charge transport layers. The 9.07% and 7.71% cell efficiencies of the device prepared by SFP layer was achieved in respective normal (using TiO2 as a deposition substrate) and inverted structure (using CuI as deposition substrate) of perovskite solar cell. This method can be efficient in large-scale and low cost fabrication of new generation perovskite solar cells.

  1. Novel Solvent-free Perovskite Deposition in Fabrication of Normal and Inverted Architectures of Perovskite Solar Cells

    Science.gov (United States)

    Nejand, Bahram Abdollahi; Gharibzadeh, Saba; Ahmadi, Vahid; Shahverdi, H. Reza

    2016-09-01

    We introduced a new approach to deposit perovskite layer with no need for dissolving perovskite precursors. Deposition of Solution-free perovskite (SFP) layer is a key method for deposition of perovskite layer on the hole or electron transport layers that are strongly sensitive to perovskite precursors. Using deposition of SFP layer in the perovskite solar cells would extend possibility of using many electron and hole transport materials in both normal and invert architectures of perovskite solar cells. In the present work, we synthesized crystalline perovskite powder followed by successful deposition on TiO2 and cuprous iodide as the non-sensitve and sensitive charge transport layers to PbI2 and CH3NH3I solution in DMF. The post compressing step enhanced the efficiency of the devices by increasing the interface area between perovskite and charge transport layers. The 9.07% and 7.71% cell efficiencies of the device prepared by SFP layer was achieved in respective normal (using TiO2 as a deposition substrate) and inverted structure (using CuI as deposition substrate) of perovskite solar cell. This method can be efficient in large-scale and low cost fabrication of new generation perovskite solar cells.

  2. Luminescence Properties of SrZrO3/Tb(3+) Perovskite: Host-Dopant Energy-Transfer Dynamics and Local Structure of Tb(3+).

    Science.gov (United States)

    Gupta, Santosh Kumar; Ghosh, Partha Sarathi; Yadav, Ashok Kumar; Pathak, Nimai; Arya, Ashok; Jha, Shambhu Nath; Bhattacharyya, Dibyendu; Kadam, Ramakant Mahadeo

    2016-02-15

    SrZrO3 perovskite (SZP) was synthesized using gel-combustion route and characterized systematically using X-ray diffraction and time-resolved photoluminescence techniques. A detailed analysis of the optical properties of Tb(3+) ions in SrZrO3 was performed to correlate them with the local environment of the lanthanide ions in this perovskite. Photoluminescence (PL) spectroscopy showed that emission spectrum consists of host as well as Tb(3+) emission indicating the absence of complete host-dopant energy transfer. On the basis of emission spectrum and PL decay study it was also observed that Tb(3+) is not homogeneously distributed in SrZrO3 perovskite; rather, it is occupying two different sites. It is corroborated using extended X-ray absorption fine structure studies that Tb(3+) is stabilized on both six-coordinated Zr(4+) and eight-coordinated Sr(2) site. The energies calculated using density functional theory (DFT) indicates that Tb occupation in Sr site is energetically more favorable than Zr site. The analysis of valence charge distribution also substantiated our structural stability analysis of site-selective Tb doping in SrZrO3. Time-resolved emission spectroscopy is employed to elucidate the difference in the spectral feature of Tb(3+) ion at Sr(2+) and Zr(4+) site. DFT-calculated density of states analysis showed that energy mismatch of Tb-d states with Zr-d and O-p states of SZP makes the energy transfer from host SZP to Tb(3+) ion difficult.

  3. Theoretical prediction of antiferromagnetism in layered perovskite Sr2TcO4

    Science.gov (United States)

    Horvat, Alen; Pourovskii, Leonid; Aichhorn, Markus; Mravlje, Jernej

    2017-05-01

    We theoretically investigate the magnetic properties of Sr2TcO4 , a 4 d transition-metal layered perovskite of the K2NiF4 type with half-filled t2 g states. The effect of local Coulomb repulsion between the t2 g orbitals is included within the density-functional theory (DFT) + U and DFT + dynamical mean-field theory (DMFT) methods. The DFT + DMFT predicts paramagnetic Sr2TcO4 to be close to the Mott insulator-to-metal transition, similarly to the cubic compound SrTcO3. The intersite exchange interactions computed within the DFT + DMFT framework point to a strong antiferromagnetic coupling between the neighboring Tc sites within the layer. We then evaluate the Néel temperature TN within a classical Monte Carlo approach including dipolar interactions, which stabilize the magnetic order in the frustrated K2NiF4 lattice structure. Our approach is validated by applying it to a set of layered and cubic perovskites, for which we obtain TN in fair agreement with experiment. Within the same approach we obtain the TN of Sr2TcO4 to be about 450 K. We explore also the effect of anisotropy in exchange interactions due to spin-orbit coupling. These lead to a somewhat higher transition temperature, 550 K.

  4. Molecular disorder and translation/rotation coupling in the plastic crystal phase of hybrid perovskites.

    Science.gov (United States)

    Even, J; Carignano, M; Katan, C

    2016-03-28

    The complexity of hybrid organic perovskites calls for an innovative theoretical view that combines usually disconnected concepts in order to achieve a comprehensive picture: (i) the intended applications of this class of materials are currently in the realm of conventional semiconductors, which reveal the key desired properties for the design of efficient devices. (ii) The reorientational dynamics of the organic component resembles that observed in plastic crystals, therefore requiring a stochastic treatment that can be done in terms of pseudospins and rotator functions. (iii) The overall structural similarity with all inorganic perovskites suggests the use of the high temperature pseudo cubic phase as the reference platform on which further refinements can be built. In this paper we combine the existing knowledge on these three fields to define a general scenario based on which we can continue the quest towards a fundamental understanding of hybrid organic perovskites. With the introduction of group theory as the main tool to rationalize the different ideas and with the help of molecular dynamics simulations, several experimentally observed properties are naturally explained with possible suggestions for future work.

  5. Thermodynamic Stability and Defect Chemistry of Bismuth-Based Lead-Free Double Perovskites.

    Science.gov (United States)

    Xiao, Zewen; Meng, Weiwei; Wang, Jianbo; Yan, Yanfa

    2016-09-22

    Bismuth- or antimony-based lead-free double perovskites represented by Cs2 AgBiBr6 have recently been considered promising alternatives to the emerging lead-based perovskites for solar cell applications. These new perovskites belong to the Fm3‾ m space group and consist of two types of octahedra alternating in a rock-salt face-centered cubic structure. We show, by density functional theory calculations, that the stable chemical potential region for pure Cs2 AgBiBr6 is narrow. Ag vacancies are a shallow accepters and can easily form, leading to intrinsic p-type conductivity. Bi vacancies and AgBi antisites are deep acceptors and should be the dominant defects under the Br-rich growth conditions. Our results suggest that the growth of Cs2 AgBiBr6 under Br-poor/Bi-rich conditions is preferred for suppressing the formation of the deep defects, which is beneficial for maximizing the photovoltaic performance.

  6. Temperature-Induced Lattice Relaxation of Perovskite Crystal Enhances Optoelectronic Properties and Solar Cell Performance

    KAUST Repository

    Banavoth, Murali

    2016-12-14

    Hybrid organic-inorganic perovskite crystals have recently become one of the most important classes of photoactive materials in the solar cell and optoelectronic communities. Albeit improvements have focused on state-of-the-art technology including various fabrication methods, device architectures, and surface passivation, progress is yet to be made in understanding the actual operational temperature on the electronic properties and the device performances. Therefore, the substantial effect of temperature on the optoelectronic properties, charge separation, charge recombination dynamics, and photoconversion efficiency are explored. The results clearly demonstrated a significant enhancement in the carrier mobility, photocurrent, charge carrier lifetime, and solar cell performance in the 60 ± 5 °C temperature range. In this temperature range, perovskite crystal exhibits a highly symmetrical relaxed cubic structure with well-aligned domains that are perpendicular to a principal axis, thereby remarkably improving the device operation. This finding provides a new key variable component and paves the way toward using perovskite crystals in highly efficient photovoltaic cells.

  7. New-structured solar cells based on organic-inorganic perovskite materials%基于钙钛矿材料的新型结构太阳能电池器件

    Institute of Scientific and Technical Information of China (English)

    陈海军; 王宁; 何泓材

    2014-01-01

    基于钙钛矿材料的太阳能电池是一种受到广泛关注的新型太阳能电池。根据钙钛矿太阳能电池结构的不同将其分为四类,综述了钙钛矿太阳能电池的研究现状和最新进展。详细介绍了各类钙钛矿太阳能电池的结构和性能,分析总结了其优缺点。最后展望了钙钛矿太阳能电池未来的发展趋势。%The solar cell based on organic-inorganic perovskite materials is a new type of solar cells, which attracts extensive attention worldwide. The perovskite solar cells are classfied into four categories according to structural difference, and their research status and latest developments are reviewed. Then the structures and performances of each type of perovskite solar cells are introduced, while the advantages and disadvantages of each type of perovskite solar cells are summarized. Finally, the future development trends of the perovskite solar cells are presented.

  8. Crystallographic and magnetic structure of the perovskite-type compound BaFeO2.5: unrivaled complexity in oxygen vacancy ordering.

    Science.gov (United States)

    Clemens, Oliver; Gröting, Melanie; Witte, Ralf; Perez-Mato, J Manuel; Loho, Christoph; Berry, Frank J; Kruk, Robert; Knight, Kevin S; Wright, Adrian J; Hahn, Horst; Slater, Peter R

    2014-06-16

    We report here on the characterization of the vacancy-ordered perovskite-type structure of BaFeO2.5 by means of combined Rietveld analysis of powder X-ray and neutron diffraction data. The compound crystallizes in the monoclinic space group P2(1)/c [a = 6.9753(1) Å, b = 11.7281(2) Å, c = 23.4507(4) Å, β = 98.813(1)°, and Z = 28] containing seven crystallographically different iron atoms. The coordination scheme is determined to be Ba7(FeO4/2)1(FeO3/2O1/1)3(FeO5/2)2(FeO6/2)1 = Ba7Fe([6])1Fe([5])2Fe([4])4O17.5 and is in agreement with the (57)Fe Mössbauer spectra and density functional theory based calculations. To our knowledge, the structure of BaFeO2.5 is the most complicated perovskite-type superstructure reported so far (largest primitive cell, number of ABX2.5 units per unit cell, and number of different crystallographic sites). The magnetic structure was determined from the powder neutron diffraction data and can be understood in terms of "G-type" antiferromagnetic ordering between connected iron-containing polyhedra, in agreement with field-sweep and zero-field-cooled/field-cooled measurements.

  9. Synthesis, crystal structures, and magnetic properties of double perovskites SrLaNiOsO6 and BaLaNiOsO6

    Science.gov (United States)

    Feng, Hai L.; Schnelle, Walter; Tjeng, Liu Hao; Jansen, Martin

    2016-10-01

    New double perovskite oxides SrLaNiOsO6 and BaLaNiOsO6 were synthesized by solid state reactions from the respective binary metal oxides, and their crystal structures and magnetic properties were characterized. At room temperature SrLaNiOsO6 and BaLaNiOsO6 crystallize in ordered double perovskite structures with space groups of P21/n (monoclinic) and I4/m (tetragonal), respectively. They are electrically semiconducting with an activation energy of ≈0.35 eV. Specific heat and magnetic measurements indicate that SrLaNiOsO6 shows predominantly antiferromagnetic correlations and displays antiferromagnetic transition around 60 K. However, for the isoelectronic BaLaNiOsO6 ferromagnetic correlations are predominant and there is no clear feature of a magnetic transition detectable. The remarkable change in magnetic properties of ALaNiOsO6 (A = Sr and Ba) can be related to the degree of structure distortions, i.e. the bending of the O-B-O (B = Ni,Os) links.

  10. Thermodynamic Phenomenology for Perovskite Structure Ferroelectric Solid Solutions with Morphotropic Phase Boundaries

    Science.gov (United States)

    2005-12-13

    Adaptive Structures and Technologies ICAST 12 University of Maryland, Oct 15-17, 2001 4. L. Eric Cross, "Diverse Behaviors in Relaxor Ferroelectric...Strain Active Actuator Materials", 13th ICAST October 7 h, Potsdam/Berlin Germany, 2002 11. L. E. Cross, "Recent Progress in Ferroic High Strain

  11. Mapping chemical disorder and ferroelectric distortions in the double perovskite compound Sr 2-x Gd x MnTiO6 by atomic resolution electron microscopy and spectroscopy.

    Science.gov (United States)

    Biškup, Neven; Álvarez-Serrano, Inmaculada; Veiga, Maria; Rivera-Calzada, Alberto; Garcia-Hernandez, Mar; Pennycook, Stephen J; Varela, Maria

    2014-06-01

    In this work we report a study of the chemical and structural order of the double perovskite compound Sr 2-x Gd x MnTiO6 for compositions x=0, 0.25, 0.5, 0.75, and 1. A noticeable disorder at the B-site in the Mn and Ti sublattice is detected at the atomic scale by electron energy-loss spectroscopy for all x values, resulting in Mn-rich and Ti-rich regions. For x ≥ 0.75, the cubic unit cell doubles and lowers its symmetry because of structural rearrangements associated with a giant ferroelectric displacement of the perovskite B-site cation. We discuss this finding in the light of the large electroresistance observed in Sr 2-x Gd x MnTiO6, x ≥ 0.75.

  12. Phase Behavior and Crystal Structure of Perovskite-Type Rare Earth Complex Oxides

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Several compounds of rare earth complex oxides containing manganese and titanium were synthesized in Ar, and their crystal structures were analyzed by powder X-ray diffraction data and Rietveld method. Structures of A0.67Ln0.33Mn0.33Ti0.67O3 (A=Ca or Sr and Ln=rare earth) were found to have orthorhombic symmetry with the space group Pnma, and their interatomic distances and bond angles were obtained. This space group was also derived from electron microscopic study. Electrical conductivity of Ca0.67Ln0.33Mn0.33Ti0.67O3 for several rare earth elements showed a semiconducting property with the activation energy of 0.4 eV. Some of these compounds of the strontium system show the antiferromagnetic properties below 10 K.

  13. Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron

    Directory of Open Access Journals (Sweden)

    Hong-Sub Lee

    2015-01-01

    Full Text Available Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a La0.7Sr0.3MnO3 (LSMO oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

  14. Guarded Cubical Type Theory

    DEFF Research Database (Denmark)

    Birkedal, Lars; Bizjak, Aleš; Clouston, Ranald;

    2016-01-01

    This paper improves the treatment of equality in guarded dependent type theory (GDTT), by combining it with cubical type theory (CTT). GDTT is an extensional type theory with guarded recursive types, which are useful for building models of program logics, and for programming and reasoning with co...

  15. A comparative study based on the first principles calculations of ATiO3 ( A = Ba, Ca, Pb and Sr) perovskite structure

    Science.gov (United States)

    Kamruzzaman, M.; Helal, M. A.; Ara, I. E.; Farid Ul Islam, A. K. M.; Rahaman, M. M.

    2016-10-01

    Structural, electronic, elastic, thermodynamic, vibrational and optical properties of the cubic phase of ATiO3 ( A = Ba, Ca, Pb and Sr) crystals have been carried out based on the density functional theory (DFT). The calculated equilibrium lattice parameters, band structures, elastic constants and the elastic moduli of ATiO3 are in good agreement with the theoretical and experimental results. The ferroelectric phenomenon of the crystals has been analyzed based on the nature of their phonon spectra. The phonon frequencies and the Born effective charges have been calculated to elucidate the ferroelectric instability of the cubic phase of ATiO3 by calculating the interatomic forces for several small displacements consistent with the symmetry of modes.

  16. Elastic Properties of CaSiO3 Perovskite from ab initio Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Shigeaki Ono

    2013-10-01

    Full Text Available Ab initio molecular dynamics simulations were performed to investigate the elasticity of cubic CaSiO3 perovskite at high pressure and temperature. All three independent elastic constants for cubic CaSiO3 perovskite, C11, C12, and C44, were calculated from the computation of stress generated by small strains. The elastic constants were used to estimate the moduli and seismic wave velocities at the high pressure and high temperature characteristic of the Earth’s interior. The dependence of temperature for sound wave velocities decreased as the pressure increased. There was little difference between the estimated compressional sound wave velocity (VP in cubic CaSiO3 perovskite and that in the Earth’s mantle, determined by seismological data. By contrast, a significant difference between the estimated shear sound wave velocity (VS and that in the Earth’s mantle was confirmed. The elastic properties of cubic CaSiO3 perovskite cannot explain the properties of the Earth’s lower mantle, indicating that the cubic CaSiO3 perovskite phase is a minor mineral in the Earth’s lower mantle.

  17. Temperature dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-xSrxMnO3

    Energy Technology Data Exchange (ETDEWEB)

    Arenholz, Elke; Mannella, N.; Booth, C.H.; Rosenhahn, A.; Sell, B.C.; Nambu, A.; Marchesini, S.; Mun, B. S.; Yang, S.-H.; Watanabe, M.; Ibrahim, K.; Arenholz, E.; Young, A.; Guo, J.; Tomioka, Y.; Fadley, C.S.

    2007-12-06

    We have studied the temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La{sub 1-x}Sr{sub x}MnO{sub 3} (x= 0.3-0.4) with core and valence level photoemission (PE), x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS), extended x-ray absorption fine structure (EXAFS) spectroscopy and magnetometry. As the temperature is varied across the Curie temperature T{sub c}, our PE experiments reveal a dramatic change of the electronic structure involving an increase in the Mn spin moment from {approx} 3 {micro}B to {approx} 4 {micro}B, and a modification of the local chemical environment of the other constituent atoms indicative of electron localization on the Mn atom. These effects are reversible and exhibit a slow-timescale {approx}200 K-wide hysteresis centered at T{sub c}. Based upon the probing depths accessed in our PE measurements, these effects seem to survive for at least 35-50 {angstrom} inward from the surface, while other consistent signatures for this modification of the electronic structure are revealed by more bulk sensitive spectroscopies like XAS and XES/RIXS. We interpret these effects as spectroscopic fingerprints for polaron formation, consistent with the presence of local Jahn-Teller distortions of the MnO{sub 6} octahedra around the Mn atom, as revealed by the EXAFS data. Magnetic susceptibility measurements in addition show typical signatures of ferro-magnetic clusters formation well above the Curie temperature.

  18. Perovskite Solar Cells: Progress and Advancements

    Directory of Open Access Journals (Sweden)

    Naveen Kumar Elumalai

    2016-10-01

    Full Text Available Organic–inorganic hybrid perovskite solar cells (PSCs have emerged as a new class of optoelectronic semiconductors that revolutionized the photovoltaic research in the recent years. The perovskite solar cells present numerous advantages include unique electronic structure, bandgap tunability, superior charge transport properties, facile processing, and low cost. Perovskite solar cells have demonstrated unprecedented progress in efficiency and its architecture evolved over the period of the last 5–6 years, achieving a high power conversion efficiency of about 22% in 2016, serving as a promising candidate with the potential to replace the existing commercial PV technologies. This review discusses the progress of perovskite solar cells focusing on aspects such as superior electronic properties and unique features of halide perovskite materials compared to that of conventional light absorbing semiconductors. The review also presents a brief overview of device architectures, fabrication methods, and interface engineering of perovskite solar cells. The last part of the review elaborates on the major challenges such as hysteresis and stability issues in perovskite solar cells that serve as a bottleneck for successful commercialization of this promising PV technology.

  19. Structural, elastic and electronic properties of superconducting anti-perovskites MgCNi 3, ZnCNi 3 and CdCNi 3 from first principles

    Science.gov (United States)

    Shein, I. R.; Bannikov, V. V.; Ivanovskii, A. L.

    2008-01-01

    First principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential were performed to investigate the systematic trends for structural, elastic and electronic properties of the family of superconducting anti-perovskites MCNi 3 depending from the type of M cations (M are Mg, Zn and Cd). In result the optimized lattice parameters, independent elastic constants ( C11, C12 and C44), bulk modulus B, compressibility β, shear modulus G and tetragonal shear modulus G‧ are evaluated. Further, for the first time the numerical estimates of a set of elastic parameters (bulk and shear modulus, Young’s modulus Y, Poisson’s ratio ( ν), Lamé’s coefficients ( μ, λ)) of the polycrystalline superconducting MCNi 3 ceramics (in framework of the Voigt-Reuss-Hill approximation) were performed. Besides, the band structures, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, the shapes of the Fermi surfaces, the Sommerfeld’s coefficients and the molar Pauli paramagnetic susceptibility for these anti-perovskites were obtained and analyzed in comparison with the available theoretical and experimental data.

  20. Structural, electronic, optical and thermodynamic properties of cubic REGa{sub 3} (RE = Sc or Lu) compounds: Ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Laboratory, Department of Physics, Islamia College Peshawar (Pakistan); Gupta, S.K. [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Alahmed, Z.A. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Khachai, H. [Physics Department, Djillali Liabes University of Sidi Bel-Abbes (Algeria); Jha, P.K. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)

    2014-06-01

    Highlights: • REGa{sub 3} (RE = Sc or Lu) compounds are mechanical stabile. • Both ScGa{sub 3} and LuGa{sub 3} exhibit metallic behavior just like other REGa{sub 3} compounds. • Melting temperature T{sub m} (K) for ScGa{sub 3} and LuGa{sub 3} are 1244.2 and 1143.8. • High absorption observed in the visible energy region. • The present study would be helpful for future experimental/theoretical explorations. - Abstract: Structural, elastic, optoelectronic and thermodynamic properties of REGa{sub 3} (RE = Sc and Lu) compounds have been studied self consistently by employing state of the art full potential (FP) linearized (L) approach of augmented plane wave (APW) plus local orbitals method. Calculations were executed at the level of Perdew–Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA) for exchange correlation functional in addition to modified Becke–Johnson (mBJ) potential. Our obtained results of lattice parameters show reasonable agreement to the previously reported experimental and other theoretical studies. Analysis of the calculated band structure of ScGa{sub 3} and LuGa{sub 3} compounds demonstrates their metallic character. Moreover, a positive value of calculated Cauchy pressure, in addition to reflecting their ductile nature, endorses their metallic character as well. To understand optical behavior calculations related to the important optical parameters; real and imaginary parts of the dielectric function, reflectivity R(ω), refractive index n(ω) and electron energy-loss function L(ω) have also been performed. In the present work, thermodynamically properties are also investigated by employing lattice vibrations integrated in quasi harmonic Debye model. Obtained results of volume, heat capacity and Debye temperature as a function of temperature for both compounds, at different values of pressure, are found to be consistent. The calculated value of melting temperature for both compounds (ScGa{sub 3} and Lu

  1. Surface Electronic Structure of Hybrid Organo Lead Bromide Perovskite Single Crystals

    KAUST Repository

    Komesu, Takashi

    2016-08-24

    The electronic structure and band dispersion of methylammonium lead bromide, CH3NH3PbBr3, has been investigated through a combination of angle-resolved photoemission spectroscopy (ARPES) and inverse photoemission spectroscopy (IPES), as well as theoretical modeling based on density functional theory. The experimental band structures are consistent with the density functional calculations. The results demonstrate the presence of a dispersive valence band in MAPbBr3 that peaks at the M point of the surface Brillouin zone. The results also indicate that the surface termination of the CH3NH3PbBr3 is the methylammonium bromide (CH3NH3Br) layer. We find our results support models that predict a heavier hole effective mass in the region of -0.23 to -0.26 me, along the Γ (surface Brillouin center) to M point of the surface Brillouin zone. The surface appears to be n-type as a result of an excess of lead in the surface region. © 2016 American Chemical Society.

  2. KBi(2-x)Pbx (0 phase evolving from a distortion of the cubic Laves-phase structure.

    Science.gov (United States)

    Ponou, Siméon; Müller, Noémi; Fässler, Thomas F; Häussermann, Ulrich

    2005-10-17

    The quasibinary system KBi(2-x)Pbx has been investigated, both experimentally and theoretically. Phases with compositions 0 Laves-phase structure MgCu2 (space group Fdm), which contains a rigid framework of corner-condensed symmetry-equivalent tetrahedra formed by randomly distributed Bi and Pb atoms. For compositions x > or = 0.6, these tetrahedra become alternately elongated and contracted. The distortion of the framework lowers the space-group symmetry to F43m (KBi(1.2)Pb(0.8), F43m, Z = 8, a = 9.572(1) A). Magnetometer measurements show that KBi2 (x = 0) is metallic and goes through a superconducting transition below 3.5 K. First principles calculations reveal that the Fd3m --> F43m distortion is largest for KBiPb (x = 1.0), which at the same time turns into a semiconductor. Thus, F43m KBiPb corresponds to a proper charge-balanced Zintl phase, K+[BiPb]-, with separated polyanionic tetrahedra, (Bi2Pb2)2-. However, it was not possible to prepare F43m KBiPb. Syntheses attempting to increase the Pb content in KBi(2-x)Pbx above x = 0.8 yielded additional, not yet characterized, ternary phases.

  3. Strategic improvement of the long-term stability of perovskite materials and perovskite solar cells.

    Science.gov (United States)

    Xu, Tingting; Chen, Lixin; Guo, Zhanhu; Ma, Tingli

    2016-10-05

    Perovskite solar cells (PSCs) have gained tremendous research interest in recent several years. To date the power conversion efficiency (PCE) of PSCs has been increased from 3.8% to over 22.1%, showing that they have a promising future as a renewable energy resource to compete with conventional silicon solar cells. However, a crucial challenge of PSCs currently is that perovskite materials and PSCs have limitations of easy degradation and inferior long-term stabilities, thus hampering their future commercial applications. In this review, the degradation mechanisms for instable perovskite materials and their corresponding solar cells are discussed. The stability study of perovskite materials and PSCs from the aspect of experimental tests and theoretical calculations is reviewed. The strategies for enhancing the stability of perovskite materials and PSCs are summarized from the viewpoints of perovskite material engineering, substituted organic and inorganic materials for hole transportation, alternative electrodes comprising mainly carbon and its relevant composites, interfacial modification, novel device structure construction and encapsulation, etc. Various approaches and outlooks on the future direction of perovskite materials and PSCs are highlighted. This review is expected to provide helpful insights for further enhancing the stability of perovskite materials and PSCs in this exciting field.

  4. Structural and electronic properties of hybrid perovskites for high-efficiency thin-film photovoltaics from first-principles

    Directory of Open Access Journals (Sweden)

    Federico Brivio

    2013-10-01

    Full Text Available The performance of perovskite solar cells recently exceeded 15% solar-to-electricity conversion efficiency for small-area devices. The fundamental properties of the active absorber layers, hybrid organic-inorganic perovskites formed from mixing metal and organic halides [e.g., (NH4PbI3 and (CH3NH3PbI3], are largely unknown. The materials are semiconductors with direct band gaps at the boundary of the first Brillouin zone. The calculated dielectric constants and band gaps show an orientation dependence, with a low barrier for rotation of the organic cations. Due to the electric dipole of the methylammonium cation, a photoferroic effect may be accessible, which could enhance carrier collection.

  5. Synthesis, surface structure and optical properties of double perovskite Sr2NiMoO6 nanoparticles

    Science.gov (United States)

    Xu, Lei; Wan, Yingpeng; Xie, Hongde; Huang, Yanlin; Yang, Li; Qin, Lin; Seo, Hyo Jin

    2016-12-01

    Double perovskite Sr2NiMoO6 nanoparticles were synthesized via the chemical sol-gel route. The phase formation was investigated through X-ray polycrystalline diffraction (XRD) and Rietveld refinements. The perovskite crystallized in worm-like nano-grains with the diameter of 20-50 nm. The optical properties were measured by the optical absorption spectra. The nanoparticles present an indirect allowed transition with a narrow band gap of 2.1 eV. Sr2NiMoO6 nanoparticles have obvious photocatalytic ability on the degradation of Rhodamine B (RhB) solutions under the irradiation of visible light. The transport behaviors of the excitons were investigated from the photoluminescence spectra and the corresponding decay lifetimes. Sr2NiMoO6 nanoparticles present several advantages for photocatalysis such as the appropriate band energy positions, the quenched luminescence, and the coexistence of multivalent ions in the lattices.

  6. Synthesis and structural characterization of some Pb(B$^{'}_{1/3}$Nb2/3)O3 type materials by two-stage solid-state route

    Indian Academy of Sciences (India)

    Mukul Pastor; P K Bajpai; R N P Choudhary

    2005-06-01

    Two-stage columbite solid state reaction route has been used for the preparation of Pb (B$^{'}_{1/3}$Nb2/3)O3 materials (B′ = Mg, Ni and Cd). The columbite precursor phase was structurally characterized using diffraction data. MgNb2O6, NiNb2O6 and CdNb2O6 show orthorhombic structures i.e. pure columbite phase. Final phase materials get stabilized in mixed phase. The diffraction pattern shows that it is a mixture of cubic pyrochlore and perovskite phase. Percentage of perovskite phase was calculated using the band intensities of (110) perovskite and (222) pyrochlore peaks. The calculated percentages show the dominant perovskite phase. Possible reasons for mixed phase are discussed.

  7. Phase stability, elastic anisotropy and electronic structure of cubic MAl2 (M = Mg, Ca, Sr and Ba) Laves phases from first-principles calculations

    Science.gov (United States)

    Kong, Yuanyuan; Duan, Yonghua; Ma, Lishi; Li, Runyue

    2016-10-01

    By performing first-principles calculations within the generalized gradient approximation, the phase stability, elastic constant and anisotropy, and density of states of cubic C15-type MAl2 (M = Mg, Ca, Sr and Ba) Laves phases have been investigated. Optimized equilibrium lattice parameters and formation enthalpies agree well with the available experimental data. Elastic constants C ij have been evaluated, and these C15-type MAl2 Laves phases are mechanically stable due to the meeting of C ij to the mechanical stability criteria. Polycrystalline elastic moduli have been deduced from elastic constants by Voigt-Reuss-Hill approximation. Plastic properties were characterized via values of B/G, Poisson’s ratio ν and Cauchy pressure (C 12-C 44). The elastic anisotropy has been considered by several anisotropy indexes (A U , A Z , A shear and A comp), anisotropy of shear modulus, and 3D surface constructions of bulk and Young’s moduli. Additionally, the sound velocity anisotropy and Debye temperature were predicted. Finally, electronic structures were carried out to reveal the underlying phase stability mechanism of these Laves phases.

  8. Structural, magnetic, and magneto-optical properties of nanocrystalline face centered cubic Co70Cr30/Pt multilayers with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Papaioannou, E Th; Angelakeris, M; Poulopoulos, P; Tsiaoussis, I; Rüdt, C; Fumagalli, P; Flevaris, N K

    2007-12-01

    Co70Cr30 alloyed layers are combined with extremely thin Pt layers in order to produce novel face-centered-cubic multilayered films to be considered as a potential perpendicular magnetic recording medium. The films were grown on Si, glass and polyimide substrates by e-beam evaporation at a temperature slightly higher than room temperature. The multilayered structure of the films was verified by X-ray diffraction experiments. Plane-view transmission electron microscopy images have revealed the formation of very small grains in the range of 7-9 nm. Hysteresis loops as a function of temperature were recorded via the magneto-optic Kerr effect in the polar geometry configuration. The system exhibits perpendicular magnetic anisotropy, which enhances with decreasing temperature. Hysteresis loops with a squareness of 1 and a coercivity of 1.45 kOe were obtained at 10 K. Furthermore, complete magneto-optic spectra of the films are recorded, showing a strong magneto-optic enhancement in the ultraviolet region at around 4.5 eV.

  9. Magnetic properties and electronic structure of the LaGaO3 perovskite doped with nickel

    Science.gov (United States)

    Chezhina, N. V.; Bodritskaya, É. V.; Zhuk, N. A.; Bannikov, V. V.; Shein, I. R.; Ivanovskiĭ, A. L.

    2008-11-01

    Solid solutions of the composition LaGa1 - x Ni x O3 (0.01 ≤ x ≤ 0.10) are synthesized, and their magnetic and electrical properties are investigated. It is established that the ground state of the Ni(III) atoms is the low-spin state 2 E g ; however, in the temperature range under investigation, there occurs the 2 E g ⇆ 4 T 1 g spin equilibrium. An increase in the nickel concentration leads to an increase in the electron conduction of the solid solutions. The band structure of the LaGa0.5Ni0.5O3 model compound is calculated using the ab initio full-potential linearized augmented-plane-wave method within the generalized gradient approximation (FLAPWGGA). It is shown that the dominant role in the variations observed in the magnetic and electrical properties of the nonmagnetic semiconductor LaGaO3 upon doping with nickel is played by the Ni 3 d( e g ↑, ↓) states.

  10. Structural investigations of complex perovskite oxide films with X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Boldyreva, Ksenia; Rata, Diana; Herklotz, Andreas; Bilani-Zeneli, Orkidia; Huehne, Ruben; Schultz, Ludwig; Doerr, Kathrin [IFW Dresden (Germany)

    2009-07-01

    The electronic and magnetic properties of many complex oxides are highly sensitive to external parameters which include mechanical deformation or strain. Thus, X-ray diffraction methods such as reciprocal space mapping are powerful and indispensable for the characterization of thin films, particularly for evaluating the in-plane strain state. The direct influence of strain on the magnetization of epitaxial La{sub 1-x}Sr{sub x}MnO{sub 3} (LSMO) films has been studied utilizing piezoelectric PMN-PT substrates. On the other hand, La{sub 1-x}Sr{sub x}CoO{sub 3} (LSCO) films also reveal large strain-induced changes of the magnetization and the electrical conductivity. Since the in-plane lattice parameter of the piezoelectric substrate, PMN-PT, of {proportional_to}4.02A is larger than that of most correlated oxides, LaSc{sub 1-x}Al{sub x}O{sub 3} (LSAO) has been explored as a buffer layer showing a lattice parameter that is tunable by the composition x. The lattice structure of (i) LSAO buffers depending on the composition and (ii) of magnetic films (LSMO, LSCO) grown in various strain states is discussed.

  11. A variable temperature synchrotron X-ray diffraction study of the ferroelastic double perovskite Ba2GdMoO6.

    Science.gov (United States)

    Wallace, Thomas K; Colman, Ross H; McLaughlin, Abbie C

    2013-06-14

    A study of the magnetic and structural properties of the double perovskite Ba2GdMoO6 has been performed. The crystal structure distorts from the ideal cubic (Fm3m) structure to the tetragonal space group I4/m at 220 K, before undergoing a second distortion to a triclinic system (I1) at 80 K. The phase transition to triclinic symmetry is also evident in magnetic susceptibility measurements. The variable temperature synchrotron powder X-ray diffraction results reveal that Ba2GdMoO6 is ferroelastic, with the onset of ferroelastic domain formation occurring at the cubic-tetragonal phase transition. A number of Rietveld refinement techniques for modelling diffuse scattering from ferroelastic domain boundaries have been explored.

  12. Polymorphism of the hydroxide perovskite Ga(OH)3 and possible proton-driven transformational behaviour

    Science.gov (United States)

    Welch, M. D.; Kleppe, A. K.

    2016-07-01

    The crystal structure of hydroxide perovskite Ga(OH)3, the mineral söhngeite, has been determined for a natural sample by single-crystal XRD in space group P42/ nmc to R 1 = 0.031, wR 2 = 0.071, GoF = 1.208, and for comparison also in space group P42/ n to R 1 = 0.031, wR 2 = 0.073, GoF = 1.076. Unit cell parameters are a = 7.4546(2) Å, c = 7.3915(2) Å, V = 410.75(2) Å3. The two structures are very similar and both have tilt system a + a + c -. The approximate positions of all H atoms in each structure have been refined. In the P42/ nmc structure all five H sites are half-occupied, whereas in the P42/ n structure four sites are half-occupied and one is fully occupied. The presence of five non-equivalent OH groups in söhngeite is confirmed by single-crystal Raman spectroscopy, but does not allow a choice between these two space groups to be made. There is only a single very weak violator of the c-glide of P42/ nmc and the two refined structures are essentially the same, but are significantly different from that of the original description in which orthorhombic space group Pmn21 was reported with corresponding tilt system a 0 a 0 c +. It is argued here that such a structure is very implausible for a hydroxide perovskite. On heating söhngeite to 423 K, transformation to a cubic structure with Imbar{3} symmetry ( a + a + a +) of the aristotype occurs. This cubic phase was recovered on cooling to 293 K without back-transformation to the tetragonal polymorph. As there is no continuous group/subgroup pathway from P42/ nmc (or P42/ n) to Imbar{3}, the transformation must be first-order, which is consistent with the large hysteresis observed. The change from the tetragonal to cubic structures involves a change in tilt system a + a + c - → a + a + a +, with a significant reconfiguration of hydrogen-bonding topology. The very different tilt systems and hydrogen-bonding configurations of the two polymorphs are responsible for hysteresis and metastable preservation of

  13. Synthesis and Characterization of Complex Metal Oxides with Perovskite-Related Structure

    Science.gov (United States)

    Liu, Chia-Jyi

    A series of materials rm La_ {2-x}Sr_ xNiO_{4-delta } were synthesized via a basic carbonates coprecipitation route. They possess the tetragonal rm K _2NiF_4 structure up to x = 1.5, and undergo a composition dependent metal-nonmetal transition. The materials are nonmetals for x =q 1.1. For compositions near the transition the conductivity type is also dependent on delta. The temperature dependence of the electrical conductivity for nonmetallic rm La_{2-x}Sr _ xNiO_{4-delta} shows two conduction mechanisms: a phonon-assisted variable-range hopping as a result of disorder, and an impurity band conduction. The domination of one of these two mechanisms likely depends upon the composition and the temperature range. The sign and magnitude of the thermoelectric power, as a function of temperature, for the rm La_{2-x}Sr_ xNiO_{4 -delta} materials is a sum of the contributions due to holes and electrons. The negative contribution which increases as the temperature increases (due to diffusive electrons) is determined by the variable-range hopping mechanism for nonmetals and by metallic conduction for the metals. For both lightly doped metals and nonmetals the positive contribution to the thermoelectric power increases and then decreases as the temperature increases. This contribution could be due to a phonon drag mechanism where the holes are created by excitation of electrons from the mobility edge of the sigma^ {*1}_{x^2-y^2 } band to impurity states. In the heavily doped metallic material, where S becomes more negative with increasing doping, the thermoelectric power strongly indicates that electrons and not holes are the majority carriers. A series of solid solutions rm La _{2-x}Sr_ xCu_{1-y} Ni_ yO_{4-delta} were synthesized using a basic carbonate coprecipitation technique. All the resulting powders are single phase solids which exhibit I4/mmm symmetry. Disappearance of the superconductivity at higher Ni content usually accompanies the localization of carriers at low

  14. Perovskite type nanopowders and thin films obtained by chemical methods

    Directory of Open Access Journals (Sweden)

    Viktor Fruth

    2010-09-01

    Full Text Available The review presents the contribution of the authors, to the preparation of two types of perovskites, namely BiFeO3 and LaCoO3, by innovative methods. The studied perovskites were obtained as powders, films and sintered bodies. Their complex structural and morphological characterization is also presented. The obtained results have underlined the important influence of the method of preparation on the properties of the synthesized perovskites.

  15. Structural evolution of the double perovskites Sr{sub 2}B'UO{sub 6} (B' = Mn, Fe, Co, Ni, Zn) upon reduction: Magnetic behavior of the uranium cations

    Energy Technology Data Exchange (ETDEWEB)

    Pinacca, R.M., E-mail: rmp@unsl.edu.ar [Area de Quimica General e Inorganica ' Dr. Gabino F. Puelles' , Departamento de Quimica, Facultad de Quimica, Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina); Viola, M.C.; Pedregosa, J.C. [Area de Quimica General e Inorganica ' Dr. Gabino F. Puelles' , Departamento de Quimica, Facultad de Quimica, Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina); Carbonio, R.E. [INFIQC (CONICET), Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA Cordoba (Argentina); Lope, M.J. Martinez; Alonso, J.A. [Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, 28049 Madrid (Spain)

    2011-11-15

    Highlights: {yields} Evolution of the double perovskites Sr{sub 2}B'UO{sub 6} upon reduction were studied by XRPD. {yields} Orthorhombic (Pnma) disordered perovskites SrB'{sub 0.5-x}U{sub 0.5+x}O{sub 3} were obtained at 900 {sup o}C. {yields} U{sup 5+/4+} and Zn{sup 2+} cations are distributed at random over the octahedral positions. {yields} AFM ordering for the perovskite with B' = Zn appears below 30 K. -- Abstract: We describe the preparation of five perovskite oxides obtained upon reduction of Sr{sub 2}B'UO{sub 6} (B' = Mn, Fe, Co, Ni, Zn) with H{sub 2}/N{sub 2} (5%/95%) at 900 {sup o}C during 8 h, and their structural characterization by X-ray powder diffraction (XRPD). During the reduction process there is a partial segregation of the elemental metal when B' = Co, Ni, Fe, and the corresponding B'O oxide when B' = Mn, Zn. Whereas the parent, oxygen stoichiometric double perovskites Sr{sub 2}B'UO{sub 6} are long-range ordered concerning B' and U cations. The crystal structures of the reduced phases, SrB'{sub 0.5-x}U{sub 0.5+x}O{sub 3} with 0.37 < x < 0.27, correspond to simple, disordered perovskites; they are orthorhombic, space group Pnma (No. 62), with a full cationic disorder at the B site. Magnetic measurements performed on the phase with B' = Zn, indicate uncompensated antiferromagnetic ordering of the U{sup 5+}/U{sup 4+} sublattice below 30 K.

  16. Ferroelectric Graphene-Perovskite Interfaces.

    Science.gov (United States)

    Volonakis, George; Giustino, Feliciano

    2015-07-02

    Owing to their record-breaking energy conversion efficiencies, hybrid organometallic perovskites have emerged as the most promising light absorbers and ambipolar carrier transporters for solution-processable solar cells. Simultaneously, due to its exceptional electron mobility, graphene represents a prominent candidate for replacing transparent conducting oxides. Thus, it is possible that combining these wonder materials may propel the efficiency toward the Schokley-Queisser limit. Here, using first-principles calculations on graphene-CH3NH3PbI3 interfaces, we find that graphene suppresses the octahedral tilt in the very first perovskite monolayer, leading to a nanoscale ferroelectric distortion with a permanent polarization of 3 mC/m(2). This interfacial ferroelectricity drives electron extraction from the perovskite and hinders electron-hole recombination by keeping the electrons and holes separated. The interfacial ferroelectricity identified here simply results from the interplay between graphene's planar structure and CH3NH3PbI3's octahedral connectivity; therefore, this mechanism may be effective in a much broader class of perovskites, with potential applications in photovoltaics and photocatalysis.

  17. perovskite up to 55 GPa

    Science.gov (United States)

    Gréaux, Steeve; Andrault, Denis; Gautron, Laurent; Bolfan-Casanova, Nathalie; Mezouar, Mohamed

    2014-06-01

    Compressibility of perovskite-structured Ca3Al2Si3O12 grossular (GrPv) was investigated at high pressure and high temperature by means of angle-dispersive powder X-ray diffraction using a laser-heated diamond anvil cell. We observed the Pbnm orthorhombic distortion for the pure phase above 50 GPa, whereas below this pressure, Al-bearing CaSiO3 perovskite coexists with an excess of corundum. GrPv has a bulk modulus ( K 0 = 229 ± 5 GPa; fixed to 4) almost similar to that reported for pure CaSiO3 perovskite. Its unit-cell volume extrapolated to ambient conditions ( V 0 = 187.1 ± 0.4 Å3) is found to be ~2.5 % larger than for the Al-free phase. We observe an increasing unit-cell anisotropy with increasing pressure, which could have implications for the shear properties of Ca-bearing perovskite in cold slabs subducted into the Earth's mantle.

  18. Core/Shell Structured TiO2/CdS Electrode to Enhance the Light Stability of Perovskite Solar Cells.

    Science.gov (United States)

    Hwang, Insung; Baek, Minki; Yong, Kijung

    2015-12-23

    In this work, enhanced light stability of perovskite solar cell (PSC) achieved by the introduction of a core/shell-structured CdS/TiO2 electrode and the related mechanism are reported. By a simple solution-based process (SILAR), a uniform CdS shell was coated onto the surface of a TiO2 layer, suppressing the activation of intrinsic trap sites originating from the oxygen vacancies of the TiO2 layer. As a result, the proposed CdS-PSC exhibited highly improved light stability, maintaining nearly 80% of the initial efficiency after 12 h of full sunlight illumination. From the X-ray diffraction analyses, it is suggested that the degradation of the efficiency of PSC during illumination occurs regardless of the decomposition of the perovskite absorber. Considering the light-soaking profiles of the encapsulated cells and the OCVD characteristics, it is likely that the CdS shell had efficiently suppressed the undesirable electron kinetics, such as trapping at the surface defects of the TiO2 and preventing the resultant charge losses by recombination. This study suggests that further complementary research on various effective methods for passivation of the TiO2 layer would be highly meaningful, leading to insight into the fabrication of PSCs stable to UV-light for a long time.

  19. Synthesis, structural and optical properties of a novel bilayered organic-inorganic perovskite C{sub 5}Pb{sub 2}I{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Elleuch, S., E-mail: slimlpa@yahoo.f [Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, 3000, BP 1171, Sfax (Tunisia); Dammak, T.; Abid, Y. [Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, 3000, BP 1171, Sfax (Tunisia); Mlayah, A. [Centre d' Elaboration de Materiaux et d' Etudes Structurales, CNRS-Universite Paul Sabatier, 29 Rue Jeanne Marvig, Toulouse 31055 (France); Boughzala, H. [Laboratoire de Materiaux et Cristallochimie, Institut Preparatoire aux etudes Ingenieur de Nabeul, 8000 Mrezga, Nabeul (Tunisia)

    2010-04-15

    Single crystals of [C{sub 5}H{sub 11}NH{sub 3}]Pb{sub 2}I{sub 5}, abbreviated C{sub 5}Pb{sub 2}I{sub 5}, have been prepared. This compound is a new member of the family of the bilayered organic-inorganic lead-iodide based perovskites. Its crystal structure has been determined by X-ray diffraction. The inorganic sub-lattice consists of periodic bilayers of iodoplumbate octahedra. Each PbI{sub 6} octahedra exhibits both edge- and corner-sharing with adjacent octahedra. The vibrational properties of this compound have been studied by Raman scattering spectroscopy. Optical absorption, photoluminescence and diffuse reflectance measurements have been performed. The room-temperature bandgap and free exciton absorption bands are observed at 2.46 and 2.23 eV, respectively. The exciton binding energy is 230 meV which is the largest value ever reported till date for the bilayered PbI based perovskites. Calculations assuming Wannier-type quasi-two-dimensional excitons and taking into account the image potential of the exciton charges showed that nearly 64% of the exciton binding energy is due to the dielectric confinement effect.

  20. Highly Efficient p-i-n Perovskite Solar Cells Utilizing Novel Low-Temperature Solution-Processed Hole Transport Materials with Linear π-Conjugated Structure.

    Science.gov (United States)

    Li, Yang; Xu, Zheng; Zhao, Suling; Qiao, Bo; Huang, Di; Zhao, Ling; Zhao, Jiao; Wang, Peng; Zhu, Youqin; Li, Xianggao; Liu, Xicheng; Xu, Xurong

    2016-09-01

    Alternative low-temperature solution-processed hole-transporting materials (HTMs) without dopant are critical for highly efficient perovskite solar cells (PSCs). Here, two novel small molecule HTMs with linear π-conjugated structure, 4,4'-bis(4-(di-p-toyl)aminostyryl)biphenyl (TPASBP) and 1,4'-bis(4-(di-p-toyl)aminostyryl)benzene (TPASB), are applied as hole-transporting layer (HTL) by low-temperature (sub-100 °C) solution-processed method in p-i-n PSCs. Compared with standard poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) HTL, both TPASBP and TPASB HTLs can promote the growth of perovskite (CH3 NH3 PbI3 ) film consisting of large grains and less grain boundaries. Furthermore, the hole extraction at HTL/CH3 NH3 PbI3 interface and the hole transport in HTL are also more efficient under the conditions of using TPASBP or TPASB as HTL. Hence, the photovoltaic performance of the PSCs is dramatically enhanced, leading to the high efficiencies of 17.4% and 17.6% for the PSCs using TPASBP and TPASB as HTL, respectively, which are ≈40% higher than that of the standard PSC using PEDOT:PSS HTL.