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Sample records for ferrimagnetic double perovskites

  1. Magnetism in Re-based ferrimagnetic double perovskites

    Science.gov (United States)

    Winkler, A.; Narayanan, N.; Mikhailova, D.; Bramnik, K. G.; Ehrenberg, H.; Fuess, H.; Vaitheeswaran, G.; Kanchana, V.; Wilhelm, F.; Rogalev, A.; Kolchinskaya, A.; Alff, L.

    2009-07-01

    We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A2FeReO6 (A=Ba, Sr, Ca) by x-ray magnetic circular dichroism (XMCD) at the Re L2, 3 edges. In these ferrimagnetic compounds, an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr2ScReO6 proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.

  2. Magnetism in Re-based ferrimagnetic double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Winkler, A; Narayanan, N; Mikhailova, D; Bramnik, K G; Ehrenberg, H; Fuess, H; Kolchinskaya, A; Alff, L [Technische Universitaet Darmstadt, Petersenstrasse 23, 64287 Darmstadt (Germany); Vaitheeswaran, G; Kanchana, V [Royal Institute of Technology (KTH), Brinellvaegen 23, 10044 Stockholm (Sweden); Wilhelm, F; Rogalev, A [European Synchrotron Radiation Facility (ESRF), 6 Rue Jules Horowitz, BP 220, 38043 Grenoble Cedex 9 (France)], E-mail: alff@oxide.tu-darmstadt.de

    2009-07-15

    We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A{sub 2}FeReO{sub 6} (A=Ba, Sr, Ca) by x-ray magnetic circular dichroism (XMCD) at the Re L{sub 2,3} edges. In these ferrimagnetic compounds, an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr{sub 2}ScReO{sub 6} proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.

  3. Promising ferrimagnetic double perovskite oxides towards high spin polarization at high temperature

    Directory of Open Access Journals (Sweden)

    Si-Da Li

    2013-01-01

    Full Text Available We predict through our first-principles calculations that four double perovskite oxides of Bi2ABO6 (AB = FeMo, MnMo, MnOs, CrOs are half-metallic ferrimagnets. Our calculated results shows that the four optimized structures have negative formation energy, from -0.42 to -0.26 eV per formula unit, which implies that they could probably be realized. In the case of Bi2FeMoO6, the half-metallic gap and Curie temperature are predicted to reach to 0.71 eV and 650 K, respectively, which indicates that high spin polarization could be kept at high temperatures far beyond room temperature. It is believed that some of them could be synthesized soon and would prove useful for spintronic applications.

  4. Ferrimagnetic order in the insulating Sr{sub 3}Fe{sub 2}ReO{sub 9} double perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Pannunzio Miner, E.V. [INFIQC, CONICET-Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Cuidad Universitaria, 5000, Cordoba (Argentina); De Paoli, J.M. [Centro Atomico Bariloche, CNEA, Av. E. Bustillo 9500, 8400, San Carlos de Bariloche, Rio Negro (Argentina); Alonso, J.A. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain); Garcia-Hernandez, M. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain); Sanchez, R.D. [Centro Atomico Bariloche, CNEA, Av. E. Bustillo 9500, 8400, San Carlos de Bariloche, Rio Negro (Argentina)]. E-mail: rodo@cab.cnea.gov.ar; Carbonio, R.E. [INFIQC, CONICET-Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Cuidad Universitaria, 5000, Cordoba (Argentina)

    2007-09-01

    A new iron(III)/rhenium(VI) double perovskite oxide, Sr{sub 3}Fe{sub 2}ReO{sub 9}, has been synthesized in polycrystalline form at 1200 C by solid-state reaction from citrate precursors. The Rietveld analysis of the synchrotron X-ray powder diffraction pattern shows that this compound, at 300 K, has orthorhombic symmetry (S.G.: Immm), with a=5.56733(1) A, b=5.56796(1) A and c=7.90224(2) A. The refinement of the relative Fe/Re occupancies of each B site reveals the presence of a partial cationic order. At high temperatures, the magnetic susceptibility of the Sr{sub 3}Fe{sub 2}ReO{sub 9} is well described as a paramagnet with ferrimagnetic correlations. Below 450 K, the system displays a spontaneous magnetization, and hysteresis loops are observed.

  5. The effect of chemical pressure on the structure and properties of A2CrOsO6 (A=Sr, Ca) ferrimagnetic double perovskite

    Science.gov (United States)

    Morrow, Ryan; Soliz, Jennifer R.; Hauser, Adam J.; Gallagher, James C.; Susner, Michael A.; Sumption, Michael D.; Aczel, Adam A.; Yan, Jiaqiang; Yang, Fengyuan; Woodward, Patrick M.

    2016-06-01

    The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously Sr2CrOsO6 crystallizes with R 3 bar symmetry due to a-a-a- octahedral tilting. A decrease in the tolerance factor leads to a-a-b+ octahedral tilting and P21/n space group symmetry for Ca2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. Sr2CrOsO6 orders at 660 K while Ca2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in Sr2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in Ca2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for Sr2CrOsO6 and η=76.2(5)% for Ca2CrOsO6, where η=2θ-1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.

  6. Spin-Orbital Superstructure in Strained Ferrimagnetic Perovskite Cobalt Oxide

    Science.gov (United States)

    Fujioka, J.; Yamasaki, Y.; Nakao, H.; Kumai, R.; Murakami, Y.; Nakamura, M.; Kawasaki, M.; Tokura, Y.

    2013-07-01

    We have investigated the Co-3d spin-orbital state in a thin film of perovskite LaCoO3 to clarify the origin of strain induced spontaneous magnetization (TC=94K) by means of x-ray diffraction, optical spectroscopy, and magnetization measurements. A lattice distortion with the propagation vector (1/4 -​​1/4 1/4) and an anomalous activation of optical phonons coupled to Co-3d orbital are observed below 126 K. Combined with the azimuthal angle analysis of superlattice reflection, we propose that the ordering of Co-3d orbital promoted by an epitaxial strain produces a unique ferrimagnetic structure.

  7. Double Double Cation Order in the High-Pressure Perovskites MnRMnSbO6.

    Science.gov (United States)

    Solana-Madruga, Elena; Arévalo-López, Ángel M; Dos Santos-García, Antonio J; Urones-Garrote, Esteban; Ávila-Brande, David; Sáez-Puche, Regino; Attfield, J Paul

    2016-08-01

    Cation ordering in ABO3 perovskites adds to their chemical variety and can lead to properties such as ferrimagnetism and magnetoresistance in Sr2 FeMoO6 . Through high-pressure and high-temperature synthesis, a new type of "double double perovskite" structure has been discovered in the family MnRMnSbO6 (R=La, Pr, Nd, Sm). This tetragonal structure has a 1:1 order of cations on both A and B sites, with A-site Mn(2+) and R(3+) cations ordered in columns and Mn(2+) and Sb(5+) having rock salt order on the B sites. The MnRMnSbO6 double double perovskites are ferrimagnetic at low temperatures with additional spin-reorientation transitions. The ordering direction of ferrimagnetic Mn spins in MnNdMnSbO6 changes from parallel to [001] below TC =76 K to perpendicular below the reorientation transition at 42 K at which Nd moments also order. Smaller rare earths lead to conventional monoclinic double perovskites (MnR)MnSbO6 for Eu and Gd.

  8. Magnetoresistance stories of double perovskites

    Indian Academy of Sciences (India)

    Abhishek Nag; Sugata Ray

    2015-06-01

    Tunnelling magnetoresistance (TMR) in polycrystalline double perovskites has been an important research topic for more than a decade now, where the nature of the insulating tunnel barrier is the core issue of debate. Other than the nonmagnetic grain boundaries as conventional tunnel barriers, intragrain magnetic antiphase boundaries (APB) as well as magnetically frustrated grain surfaces have also been proposed to act as tunnel barriers in Sr2FeMoO6. In this review, the present state of the debate has been discussed briefly and how the physical state of the material can affect the magnetoresistance signal of double perovskites in many different ways has been pointed out.

  9. Epitaxial Halide Perovskite Lateral Double Heterostructure.

    Science.gov (United States)

    Wang, Yiping; Chen, Zhizhong; Deschler, Felix; Sun, Xin; Lu, Toh-Ming; Wertz, Esther A; Hu, Jia-Mian; Shi, Jian

    2017-03-28

    Epitaxial III-V semiconductor heterostructures are key components in modern microelectronics, electro-optics, and optoelectronics. With superior semiconducting properties, halide perovskite materials are rising as promising candidates for coherent heterostructure devices. In this report, spinodal decomposition is proposed and experimentally implemented to produce epitaxial double heterostructures in halide perovskite system. Pristine epitaxial mixed halide perovskites rods and films were synthesized via van der Waals epitaxy by chemical vapor deposition method. At room temperature, photon was applied as a knob to regulate the kinetics of spinodal decomposition and classic coarsening. By this approach, halide perovskite double heterostructures were created carrying epitaxial interfaces and outstanding optical properties. Reduced Fröhlich electron-phonon coupling was discovered in coherent halide double heterostructure, which is hypothetically attributed to the classic phonon confinement effect widely existing in III-V double heterostructures. As a proof-of-concept, our results suggest that halide perovskite-based epitaxial heterostructures may be promising for high-performance and low-cost optoelectronics, electro-optics, and microelectronics. Thus, ultimately, for practical device applications, it may be worthy to pursue these heterostructures via conventional vapor phase epitaxy approaches widely practised in III-V field.

  10. Magnetic Properties of Ferromagnetic Double Layers with Ferrimagnetic Interlayer Coupling at Zero Temperature

    Institute of Scientific and Technical Information of China (English)

    JIANG Wei; ZHU Cheng-Bo; WANG Wei; ZHANG Fan

    2009-01-01

    Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature.The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique.The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.

  11. 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)

  12. 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.

  13. Electron paramagnetic resonance of double perovskite Ba{sub 2}FeMoO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Gomez, Pablo [Dept. Electricidad y Electronica, Universidad de Valladolid, Valladolid (Spain); Almanza, Ovidio [Dept. Fisica, Universidad Nacional de Colombia, Ciudad Universitaria, Bogota D.C. (Colombia)

    2007-07-01

    In this work we present electron paramagnetic resonance (EPR) measurement of double perovskite Ba{sub 2}FeMoO{sub 6}. This type of materials are of great interest due to their simultaneous conducting and ferrimagnetic properties, being them able to use in practical devices for their giant magnetoresistance effect at room temperature The samples have been synthesized with standard ceramic route, with sintering temperature of 1200 C in a reducing He/H{sub 2} atmosphere. EPR measurements have been carried out in a Bruker spectrometer operating in X band, in the temperature range 80 to 400 K. Below Curie temperature the single line becomes asymmetric, broadens and shifts to lower fields with decreasing temperature. In the paramagnetic region the peak-to-peak intensity decreases sharply and the line broadens up to 340 K. The experimental data are compared with similar results of other double perovskites analyzed previously by other authors. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Magnetic domain wall induced ferroelectricity in double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Hai Yang; Zhao, Hong Jian, E-mail: dielectric-hjzhao@126.com, E-mail: xmchen59@zju.edu.cn; Chen, Xiang Ming, E-mail: dielectric-hjzhao@126.com, E-mail: xmchen59@zju.edu.cn [Laboratory of Dielectric Materials, Department of Materials Science and Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027 (China); Zhang, Wen Qing [Department of Physics, Shanghai University, 99 Shangda Road, Shanghai 200444 (China)

    2015-04-13

    Recently, a magnetically induced ferroelectricity occurring at magnetic domain wall of double perovskite Lu{sub 2}CoMnO{sub 6} has been reported experimentally. However, there exists a conflict whether the electric polarization is along b or c direction. Here, by first-principles calculations, we show that the magnetic domain wall (with ↑↑↓↓ spin configuration) can lead to the ferroelectric displacements of R{sup 3+}, Ni{sup 2+}, Mn{sup 4+}, and O{sup 2−} ions in double perovskites R{sub 2}NiMnO{sub 6} (R = rare earth ion) via exchange striction. The resulted electric polarization is along b direction with the P2{sub 1} symmetry. We further reveal the origin of the ferroelectric displacements as that: (1) on a structural point of view, such displacements make the two out-of-plane Ni-O-Mn bond angles as well as Ni-Mn distance unequal, and (2) on an energy point of view, such displacements weaken the out-of-plane Ni-Mn super-exchange interaction obviously. Finally, our calculations show that such a kind of ferroelectric order is general in ferromagnetic double perovskites.

  15. 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.

  16. Competition between Band Filling and Steric Effect in Ordered Double Perovskites Sr2-xLaxMnMoO6

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2-xLaxMnMoO6 (0≤x≤1). The compounds have a monoclinic structure (space group P21/n) and the cell volume expands monotonically with La doping. The TC and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-xLaxMnMoO6 decreases only at low doping levels (x≤0.2); while at high doping levels (0.8≤x≤1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.

  17. Raman studies of A2MWO6 tungstate double perovskites.

    Science.gov (United States)

    Andrews, R L; Heyns, A M; Woodward, P M

    2015-06-21

    The Raman spectra of seven A(2)MWO(6) tungstate double perovskites are analysed. Ba(2)MgWO(6) is a cubic double perovskite with Fm3[combining macron]m symmetry and its Raman spectrum contain three modes that can be assigned in a straightforward manner. A fourth mode, the asymmetric stretch of the [WO(6)](6-) octahedron, is too weak to be observed. The symmetry of Ba(2)CaWO(6) is lowered to tetragonal I4/m due to octahedral tilting, but the distortion is sufficiently subtle that the extra bands predicted to appear in the Raman spectrum are not observed. The remaining five compounds have additional octahedral tilts that lower the symmetry to monoclinic P2(1)/n. The further reduction of symmetry leads to the appearance of additional lattice modes involving translations of the A-site cations and librations of the octahedra. Comparing the Raman spectra of fourteen different A(2)MWO(6) tungstate double perovskites shows that the frequency of the symmetric stretch (ν(1)) of the [WO(6)](6-) octahedron is relatively low for cubic perovskites with tolerance factors greater than one due to underbonding of the tungsten and/or M cation. The frequency of this mode increases rapidly as the tolerance factor drops below one, before decreasing gradually as the octahedral tilting gets larger. The frequency of the oxygen bending mode (ν(5)) is shown to be dependent on the mass of the A-site cation due to coupling of the internal bending mode with external A-site cation translation modes.

  18. Magnetic transition in double perovskite systems

    Energy Technology Data Exchange (ETDEWEB)

    Navarro, O., E-mail: navarro@servidor.unam.m [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apdo. Postal 70-360, 04510 Mexico DF (Mexico); Aguilar, B. [Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Geofisica, Sede Michoacan, Universidad Nacional Autonoma de Mexico, Morelia (Mexico); Avignon, M. [Institut Neel, CNRS and Universite Joseph Fourier, BP 166, 38042 Grenoble Cedex 9 (France)

    2010-05-15

    The search for materials having complete spin polarization and high Curie temperature have received a lot of attention in view of spintronics applications, especially the ferromagnetic (F) Sr{sub 2}FeMoO{sub 6}, because of its fairly high Curie temperature (T{sub C}= 450 K), half-metallic character, large magnetoresistance and potential applications. On the other hand, Sr{sub 2}FeWO{sub 6} is insulating and antiferromagnetic (AF) with T{sub N}=37K. With a double exchange type model it has been shown that F-AF transition can be driven by super-exchange interactions with increasing Fe-M (M=Mo, W) charge transfer energy. So, the charge transfer energy is expected to be larger in FeW than in FeMo compounds. Using a tight-binding model with the renormalized perturbation expansion technique, we determine the density of states for the AF phase and the electronic energy difference for the F- and AF-phases as a function of the Fe-M charge transfer energy. The F-AF transition in the ordered system Sr{sub 2}FeMo{sub x}W{sub 1-x}O{sub 6} occurs for xapprox0.3, in good agreement with the experimental value. We also studied the effect of the diagonal disorder in the variation of the number of conduction electrons on Fe and M sites. Finally, the behavior of the Curie temperature as a function of the Mo/W concentration is determined.

  19. On the search for magnetic correlations in double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Hammerath, Franziska [Institute for Solid State Physics, Dresden Technical University (Germany); IFW Dresden, Institute for Solid State Research (Germany); Sarkar, Rajib; Kamusella, Sirko; Klauss, H.H. [Institute for Solid State Physics, Dresden Technical University (Germany); Baines, C. [Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, Villigen (Switzerland); Dey, T.; Aslan Cansever, Gizem; Manna, Kaustuv; Zimmermann, Andreas; Maljuk, Andrey; Sturza, Mihai; Efremov, Dmitriy; Wurmehl, Sabine; Buechner, Bernd [IFW Dresden, Institute for Solid State Research (Germany)

    2016-07-01

    The cubic double perovskite Ba{sub 2}YIrO{sub 6} has been investigated by the local probe techniques NMR and μSR. Both methods confirm the absence of long range order in this compound, but observe signatures of magnetic correlations: The NMR spin-lattice relaxation rate suggests the presence of growing magnetic correlations at low temperatures. An increase of the μSR spin-lattice relaxation rate confirms the presence of weak magnetism. These findings cannot be explained by the recently suggested excitonic type of magnetism, but also go beyond a simple nonmagnetic ground state picture of the 5d{sup 4} (J{sub eff}=0) electronic configuration of Ir{sup 5+}. In the monoclinic analog Sr{sub 2}YIrO{sub 6}, the NMR line width and spin-lattice relaxation rates reveal a nonmagnetic behavior, in contrast to a first report, but in line with a recent study.

  20. Ab Initio Research on a New Type of Half-Metallic Double Perovskites, A2CrMO6 (A = IVA Group Elements; M = Mo, Re and W

    Directory of Open Access Journals (Sweden)

    Yun-Ping Liu

    2014-03-01

    Full Text Available The research based on density functional theory was carried out using generalized gradient approximation (GGA for full-structural optimization and the addition of the correlation effect (GGA + U (Coulomb parameter in a double perovskite structure, A2BB’O6. According to the similar valance electrons between IIA(s2 and IVA(p2, IVA group elements instead of alkaline-earth elements settled on the A-site ion position with fixed BB' combinations as CrM (M = Mo, Re and W. The ferrimagnetic half-metallic (HM-FiM properties can be attributed to the p-d hybridization between the Crd-Mp and the double exchange. All the compounds can be half-metallic (HM materials, except Si2CrMoO6, Ge2CrMo and Ge2CrReO6, because the strong-correlation correction should be considered. For M = W, only A = Sn and Pb are possible candidates as HM materials. Nevertheless, an examination of the structural stability is needed, because Si, Ge, Sn and Pb are quite different from Sr. All compounds are stable, except for the Si-based double perovskite structure.

  1. First principles calculations of magnetism, dielectric properties and spin-phonon coupling in double perovskite Bi(2)CoMnO(6).

    Science.gov (United States)

    Bhattacharjee, Satadeep; Eriksson, Olle; Sanyal, Biplab

    2012-07-25

    First principles electronic structure calculations have been performed for the double perovskite Bi(2)CoMnO(6) in its non-centrosymmetric polar state using the generalized gradient approximation plus the Hubbard U approach. We find that the ferromagnetic state is more favored compared to the ferrimagnetic state with both Co and Mn in high spin states. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. The magnetic structure dependent phonon frequencies indicate the presence of a weak spin-phonon coupling. Using the Berry phase method, we obtain a spontaneous ferroelectric polarization of 5.88 μC cm(-2), which is close to the experimental value observed for a similar compound, Bi(2)NiMnO(6).

  2. Spinodal Decomposition-Enabled Halide Perovskite Double Heterostructure with Reduced Fr\\"ohlich Electron-Phonon Coupling

    OpenAIRE

    Wang, Yiping; Chen, Zhizhong; Deschler, Felix; Sun, Xin; Lu, Toh-Ming; Wertz, Esther; Hu, Jia-Mian; Shi, Jian

    2016-01-01

    Epitaxial III-V semiconductor heterostructures are key components in modern microelectronics, electro-optics and optoelectronics. With superior semiconducting properties, halide perovskite materials are rising as promising candidates for coherent heterostructure devices. In this report, spinodal decomposition is proposed and experimentally implemented to produce epitaxial double heterostructures in halide perovskite system. Pristine epitaxial mixed halide perovskites rods and films were synth...

  3. A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution

    Science.gov (United States)

    Zhao, Bote; Zhang, Lei; Zhen, Dongxing; Yoo, Seonyoung; Ding, Yong; Chen, Dongchang; Chen, Yu; Zhang, Qiaobao; Doyle, Brian; Xiong, Xunhui; Liu, Meilin

    2017-01-01

    Rechargeable metal–air batteries and water splitting are highly competitive options for a sustainable energy future, but their commercialization is hindered by the absence of cost-effective, highly efficient and stable catalysts for the oxygen evolution reaction. Here we report the rational design and synthesis of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofiber as a highly efficient and robust catalyst for the oxygen evolution reaction. Co-doping of strontium and iron into PrBaCo2O5+δ is found to be very effective in enhancing intrinsic activity (normalized by the geometrical surface area, ∼4.7 times), as validated by electrochemical measurements and first-principles calculations. Further, the nanofiber morphology enhances its mass activity remarkably (by ∼20 times) as the diameter is reduced to ∼20 nm, attributed to the increased surface area and an unexpected intrinsic activity enhancement due possibly to a favourable eg electron filling associated with partial surface reduction, as unravelled from chemical titration and electron energy-loss spectroscopy. PMID:28240282

  4. 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...

  5. Half-metallic antiferromagnetism in double perovskite BiPbCrCuO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Weng, Ke-Chuan [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Wang, Y. K., 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

    The electronic structure and magnetic properties of BiPbCrCuO{sub 6} double perovskite are investigated based on first-principles density functional calculations with generalized gradient approximation (GGA) and GGA incorporated with Coulomb correlation interaction U (GGA + U). The results suggest the half-metallic (HM) and antiferromagnetic (AFM) properties of BiPbCrCuO{sub 6} double perovskite. The HM-AFM property of the double perovskite is caused by the double-exchange mechanism between neighboring Cr{sup 5+}(t{sub 2g}{sup 1}↓) and Cu{sup 2+}(t{sub 2g}{sup 3}↑t{sub 2g}{sup 3}↓e{sub g}{sup 2}↑e{sub g}↓) via the intermediate O{sup 2−}(2s{sup 2}2p{sup 6}) ion.

  6. Double Charged Surface Layers in Lead Halide Perovskite Crystals

    KAUST Repository

    Sarmah, Smritakshi P.

    2017-02-01

    Understanding defect chemistry, particularly ion migration, and its significant effect on the surface’s optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.

  7. 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.

  8. Critical behavior of Y2NiMnO6 double perovskite

    Science.gov (United States)

    Nhalil, Hariharan; Nair, Harikrishnan S.; Elizabeth, Suja

    2016-05-01

    Critical behavior of double perovskite Y2NiMnO6 near the second-order ferromagnetic transition is studied. Scaling exponents calculated frommodified Arrot plots are confirmed by Kouvel-Fisher method and satisfy the Widom's scaling relation. The exponents do not follow any conventional theoretical models.β values areconsistent with 3D-Ising model whileδconformsto TCMF and γ valueclosely relates to the 3D-Heisenberg model. Critical exponents are compared with similar R2NiMnO6 double perovskites which shows that a decrease in size of R ion changes exponents from mean-field to the 3D-Ising model.

  9. Double-layered ZnO nanostructures for efficient perovskite solar cells

    KAUST Repository

    Mahmood, Khalid

    2014-01-01

    To date, a single layer of TiO2 or ZnO has been the most successful implementations of any electron transport layer (ETL) in solution-processed perovskite solar cells. In a quest to improve the ETL, we explore a new nanostructured double-layer ZnO film for mesoscopic perovskite-based thin film photovoltaics. This approach yields a maximum power conversion efficiency of 10.35%, which we attribute to the morphology of oxide layer and to faster electron transport. The successful implementation of the low-temperature hydrothermally processed double-layer ZnO film as ETL in perovskite solar cells highlights the opportunities to further improve the efficiencies by focusing on the ETL in this rapidly developing field. This journal is

  10. On the bonding nature of electron states for the Fe-Mo double perovskite

    Science.gov (United States)

    Carvajal, E.; Oviedo-Roa, R.; Cruz-Irisson, M.; Navarro, O.

    2014-05-01

    The electronic transport as well as the effect of an external magnetic field has been investigated on manganese-based materials, spinels and perovskites. Potential applications of double perovskites go from magnetic sensors to electrodes in solid-oxide fuel cells; besides the practical interests, it is known that small changes in composition modify radically the physical properties of double perovskites. We have studied the Sr2FeMoO6 double perovskite compound (SFMO) using first-principles density functional theory. The calculations were done within the generalized gradient approximation (GGA) scheme with the Perdew-Burke-Ernzerhof (PBE) functional. We have made a detailed analysis of each electronic state and the charge density maps around the Fermi level. For the electronic properties of SFMO it was used a primitive cell, for which we found the characteristic half-metallic behavior density of states composed by eg and t2g electrons from Fe and Mo atoms. Those peaks were tagged as bonding or antibonding around the Fermi level at both, valence and conduction bands.

  11. On the bonding nature of electron states for the Fe-Mo double perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Carvajal, E.; Cruz-Irisson, M. [ESIME-Culhuacán, Instituto Politécnico Nacional, Av. Santa Ana 1000, C.P. 04430, México, D.F. (Mexico); Oviedo-Roa, R. [Programa de Investigación en Ingeniería Molecular, Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas Norte 152, C.P. 07730, México, D.F. (Mexico); Navarro, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, A.P. 70-360, 04510, México, D.F. (Mexico)

    2014-05-15

    The electronic transport as well as the effect of an external magnetic field has been investigated on manganese-based materials, spinels and perovskites. Potential applications of double perovskites go from magnetic sensors to electrodes in solid-oxide fuel cells; besides the practical interests, it is known that small changes in composition modify radically the physical properties of double perovskites. We have studied the Sr{sub 2}FeMoO{sub 6} double perovskite compound (SFMO) using first-principles density functional theory. The calculations were done within the generalized gradient approximation (GGA) scheme with the Perdew-Burke-Ernzerhof (PBE) functional. We have made a detailed analysis of each electronic state and the charge density maps around the Fermi level. For the electronic properties of SFMO it was used a primitive cell, for which we found the characteristic half-metallic behavior density of states composed by e{sub g} and t{sub 2g} electrons from Fe and Mo atoms. Those peaks were tagged as bonding or antibonding around the Fermi level at both, valence and conduction bands.

  12. Anomalous Hall effect in epitaxial ferrimagnetic anti-perovskite Mn{sub 4−x}Dy{sub x}N films

    Energy Technology Data Exchange (ETDEWEB)

    Meng, M.; Wu, S. X., E-mail: wushx3@mail.sysu.edu.cn; Zhou, W. Q.; Ren, L. Z.; Wang, Y. J.; Wang, G. L.; Li, S. W., E-mail: stslsw@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

    2015-08-07

    Anomalous Hall effect (AHE) has been studied for ferrimagnetic antiperovskite Mn{sub 4−x}Dy{sub x}N films grown by molecular-beam epitaxy. The introduction of Dy changes the AHE dramatically, even changes its sign, while the variations in magnetization are negligible. Two sign reversals of the AHE (negative-positive-negative) are ascribed to the variation of charge carriers as a result of Fermi surface reconstruction. We further demonstrate that the AHE current J{sub AH} is dissipationless (independent of the scattering rate), by confirming that anomalous Hall conductivity, σ{sub AH}, is proportional to the carrier density n at 5 K. Our study may provide a route to further utilize antiperovskite manganese nitrides in spintronics.

  13. Disclosing the origin of the reduced magnetoresistance in electron-doped double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Rubi, D; Fontcuberta, J [Institut de Ciencia de Materials de Barcelona, Consejo Superior de Investigaciones CientIficas, Campus UAB, E08198, Bellaterra (Spain)

    2006-08-30

    Electron doping in A{sub 2-x}L{sub x}FeMoO{sub 6} (where L is a trivalent lanthanide and A is a divalent cation) double perovskites has been established as a suitable technique for increasing their Curie temperature. However, it was found that the magnetoresistance gradually decreases with increasing lanthanide substitution. Here we analyse in detail the magnetoresistance as a function of the magnetic field for several series of ceramic A{sub 2-x}L{sub x}FeMoO{sub 6} oxides, showing that the data can be well described by assuming a gradual loss of spin polarization of the conduction band upon electron doping. This observation introduces some constraints to models of ferromagnetic coupling in double perovskites.

  14. Iridium-based double perovskites for efficient water oxidation in acid media

    Science.gov (United States)

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-08-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.

  15. Photovoltaic application of the multiferroic Bi2FeCrO6 double perovskite

    OpenAIRE

    Tablero Crespo, César

    2016-01-01

    Bi2FeCrO6 double-perovskite is a multiferroic semiconductor with ferromagnetic and ferroelectric properties that allows a variety of applications including optoelectronic and photovoltaic applications. An analysis focusing on the potential for solar cells is carried out starting from first-principles. The optoelectronic properties are characterized by two threshold spin gaps. Using the absorption coefficients from first-principles, the efficiencies are evaluated for several sunlight spectra, ...

  16. Ferromagnetic coupling strength and electron-doping effects in double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Fontcuberta, J. [Instiut de Ciencia de Materials de Barcelona, CSIC, Universitat Autonoma de Barcelona, Campus Univ. Autonoma de Barcelona, Belaterra 08193, Catalunya (Spain)]. E-mail: fontcuberta@icmab.es; Rubi, D. [Instiut de Ciencia de Materials de Barcelona, CSIC, Universitat Autonoma de Barcelona, Campus Univ. Autonoma de Barcelona, Belaterra 08193, Catalunya (Spain); Frontera, C. [Instiut de Ciencia de Materials de Barcelona, CSIC, Universitat Autonoma de Barcelona, Campus Univ. Autonoma de Barcelona, Belaterra 08193, Catalunya (Spain); Garcia-Munoz, J.L. [Instiut de Ciencia de Materials de Barcelona, CSIC, Universitat Autonoma de Barcelona, Campus Univ. Autonoma de Barcelona, Belaterra 08193, Catalunya (Spain); Wojcik, M. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw (Poland); Jedryka, E. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw (Poland); Nadolski, S. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw (Poland); Izquierdo, M. [LURE, Centre Universitaire Paris Sud, Bat 209D, 91405 Orsay, France and Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049 Madrid (Spain); Avila, J. [LURE, Centre Universitaire Paris Sud, Bat 209D, 91405 Orsay, France and Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049 Madrid (Spain); Asensio, M.C. [LURE, Centre Universitaire Paris Sud, Bat 209D, 91405 Orsay, France and Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049 Madrid (Spain)

    2005-04-15

    We review experiments and results on ferromagnetic and metallic A{sub 2}FeMoO{sub 6} double perovskites that made it possible to obtain a detailed understanding of the nature of the ferromagnetic coupling and paved the way for further enhancement of the Curie temperature. We show that appropriate chemical substitutions, combined with detailed structural, magnetotransport and spectroscopic data allow us to map quite a complete picture of the properties of these oxides.

  17. X-ray powder diffraction beamline at D10B of LNLS: application to the Ba2FeReO6 double perovskite.

    Science.gov (United States)

    Ferreira, Fabio Furlan; Granado, Eduardo; Carvalho, Wilson; Kycia, Stefan W; Bruno, Daniele; Droppa, Roosevelt

    2006-01-01

    A new beamline, fully dedicated to X-ray powder diffraction (XPD) measurements, has been installed after the exit port B of the bending magnet D10 at the Brazilian Synchrotron Light Laboratory (LNLS) and commissioned. The technical characteristics of the beamline are described and some performance indicators are listed, such as the incoming photon flux and the angular/energy resolutions obtainable under typical experimental conditions. The results of a Rietveld refinement for a standard sample of Y2O3 using high-resolution data are shown. The refined parameters match those found in the literature, within experimental error. High-resolution XPD measurements on Ba2FeReO6 demonstrate a slight departure from the ideal cubic double-perovskite structure at low temperatures, not detected by previous powder diffraction experiments. The onset of the structural transition coincides with the ferrimagnetic ordering temperature, Tc approximately equal to 315 K. Subtle structural features, such as those reported here for Ba2FeReO6, as well as the determination and/or refinement of complex crystal structures in polycrystalline samples are ideal candidate problems to be investigated on this beamline.

  18. The role of cationic disorder on the magnetic properties of double perovskites (Ca,Sr){sub 2-x}La{sub x}FeIrO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Bufaical, L., E-mail: efelix@ifi.unicamp.b [Instituto de Fisica ' Gleb Wataghin' , UNICAMP, C.P. 6165 13083-970 Campinas-SP (Brazil); Mendonca Ferreira, L.; Lora-Serrano, R.; Pagliuso, P.G. [Instituto de Fisica ' Gleb Wataghin' , UNICAMP, C.P. 6165 13083-970 Campinas-SP (Brazil); Caytuero, A.; Baggio-Saitovich, E. [Centro Brasileiro de Pesquisas Fisicas - CBPF, 22290-180 Rio de Janeiro-RJ (Brazil)

    2009-10-15

    We have synthesized polycrystalline samples of the series of double-perovskite (DP) type structure (Ca,Sr){sub 2-x}La{sub x}FeIrO{sub 6}. Their structural and magnetic properties were investigated by experiments of X-ray powder diffraction, magnetic susceptibility and electrical resistivity. Both series crystallize in a monoclinic structure, space group P2{sub 1}/n (rather than in the triclinic I1-bar), with a significant degree of Fe/Ir cationic disorder. Interestingly, our results indicate a change in the nature of the microscopic magnetic interaction induced by La doping, where the system seems to evolve from antiferromagnetic in the extremities of the series, x=0.0 and 2.0, to ferrimagnetic for intermediate regions of the series. In this work we focus on the comparison of the physical properties of two representative compounds of these families, Ca{sub 1.2}La{sub 0.8}FeIrO{sub 6} and Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6}, which exhibit the higher magnetization within their series. For the Ca-based sample the disorder is around approx 34% while was found to be roughly approx22% for the Sr{sub 2-x}La{sub x}FeIrO{sub 6} compound.

  19. Site-Mixing Effect on the XMCD Spectrum in Double Perovskite Bi{sub 2}FeMnO{sub 6}.

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Towfiq; Chen, Aiping; McFarland, Brian; Wang, Qiang; Ohldag, Hendrik; Sandberg, Richard; Jia, Quanxi; Yarotski, Dmitry A.; Zhu, Jian-Xin

    2016-06-13

    We investigate magnetization in double perovskite multiferroic Bi2FeMnO6 (BFMO) thin film using density functional theory (DFT) simulations, and X-ray magnetic circular dichroism (XMCD) measurements. The exchange interaction between Fe and Mn sites gives rise to a ferrimagnetic ordering in BFMO. When grown without structural defects, distinct XMCD signal is expected from this system. The site resolved magnetization, thus, can be extracted using XMCD sum rules. Although our theoretical calculations are consistent with this expectation for the ideal BFMO system, experimental measurements find evidence of anomalous peak for the L-2 and L-3 edges of XMCD signals, and thus, the XMCD sum rules are no longer valid. We theoretically explain this phenomenon by considering both tetragonal (near interface), and monoclinic (bulk) phases of BFMO system, with Fe and Mn ions interchanged between their respective sites. Such site-mixing between magnetic cations are commonly found during the synthesis process. Our DFT calculations of XMCD for site interchanged Fe and Mn ions in the bulk phase (monoclinic) of BFMO are in good agreement with experimental XMCD signal and reproduce the anomalous peak features at L-2/L-3 edges.

  20. B-site Cation Ordered Double Perovskites as Efficient and Stable Electrocatalysts for Oxygen Evolution Reaction.

    Science.gov (United States)

    Sun, Hainan; Chen, Gao; Zhu, Yinlong; Liu, Bo; Zhou, Wei; Shao, Zongping

    2017-03-02

    Simple disordered perovskite oxides have been intensively exploited as promising electrocatalysts for catalysing the oxygen evolution reaction (OER) towards its application in water splitting, reversible fuel cells, and rechargeable metal-air batteries. Here, we demonstrated that B-site cation-ordered double perovskite Ba2BixSc0.2Co1.8-xO6-δ with two types of cobalt local environments are superior electrocatalysts for OER in alkaline solutions, demonstrating ultrahigh catalytic activity. In addition, no obvious performance degradation was observed for the Ba2Bi0.1Sc0.2Co1.7O6-δ sample after a continuous chronopotentiometry test. The critical role of the ordered [Co2+] and [Sc3+, Bi5+, Co3+] dual environments in improving OER activity was exhibited. The aforementioned results indicate that B-site cation-ordered double perovskite oxides may represent a new class of promising electrocatalysts for the OER in sustainable energy storage and conversion systems.

  1. Vacancy-induced insulator – direct spin gapless semiconductor – half-metal transition in double perovskite La{sub 2}CrFeO{sub 6}: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Haiping, E-mail: mrhpwu@njust.edu.cn [Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, and Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094 (China); State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Qian, Yan, E-mail: qianyan@njust.edu.cn [Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, and Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094 (China); Tan, Weishi; Kan, Erjun; Lu, Ruifeng; Deng, Kaiming [Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, and Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094 (China)

    2015-11-06

    Double perovskite oxide La{sub 2}CrFeO{sub 6} with the characteristic of ferrimagnetic insulator has been reported by Chakraverty and Lee et al. Engineering the physical properties of materials, including obtaining unusual properties, can be achieved by some measures, and defect-tuning has been one of the most efficient measures. Here, by using density-functional calculations, La vacancy is introduced in La{sub 2}CrFeO{sub 6} and special properties are obtained successfully. The results show that the magnetic phase of La{sub 2}CrFeO{sub 6} would transfer from ferrimagnetic to ferromagnetic ordering as long as La vacancy is introduced. Furthermore, La{sub 1.75}CrFeO{sub 6} shows direct spin gapless semiconductor, and La{sub 1.5}CrFeO{sub 6} behaves as half-metal with the half-metallic gap of 0.42 eV. In the whole range of La vacancy, the electronic configurations of both Cr and Fe ions exhibit high-spin states, the magnetic moment of Fe remains 4.20 μ{sub B}, while that of Cr ions decreases from 2.66 to 1.97 μ{sub B} with increasing the amount of La vacancy. This work opens an alternative way to design spintronic materials, especially for direct spin gapless semiconductors which have never been reported in perovskite oxides. - Highlights: • La vacancy is introduced in La{sub 2}CrFeO{sub 6}. • La{sub 1.75}CrFeO{sub 6} shows the direct spin gapless semiconductor. • La{sub 1.5}CrFeO{sub 6} behaves as half-metal with the half-metallic gap of 0.42 eV.

  2. Tungsten and molybdenum double perovskites as pinning centers in melt-textured Y123

    Energy Technology Data Exchange (ETDEWEB)

    Sawh, Ravi-Persad; Weinstein, Roy; Parks, Drew; Gandini, Alberto; Ren, Yanru; Rusakova, Irene

    2003-01-01

    Y123+30 mol% Y211 powders were doped with tungsten and platinum, and textured. Microstructure studies show the presence of profuse spherical deposits, 200-300 nm in diameter. These deposits were identified as (W{sub 0.5}Pt{sub 0.5})YBa{sub 2}O{sub 6}, a double perovskite. The size of the W-rich deposits is independent of the W doping level. There is no substitution of W into the Y123 matrix. For Pt doping >0.5 wt.%, trapped field is observed to increase monotonically up to 40% for W doping of up to 0.48 wt.%. We conservatively estimate that this corresponds to a 60% increase in J{sub c} at constant field. Thus (W{sub 0.5}Pt{sub 0.5})YBa{sub 2}O{sub 6} double perovskites deposits act as pinning centers. Similar studies of molybdenum doping indicate deposits 200-300 nm, of (Mo{sub 0.5}Pt{sub 0.5})YBa{sub 2}O{sub 6}, also a double perovskite. The (W{sub 0.5}Pt{sub 0.5})YBa{sub 2}O{sub 6} and (Mo{sub 0.5}Pt{sub 0.5})YBa{sub 2}O{sub 6} deposits are remarkably similar to the (U{sub 0.6}Pt{sub 0.4})YBa{sub 2}O{sub 6} deposits found earlier in U-doped Y123. Therefore, W and Mo are suitable non-radioactive substitutes for U.

  3. 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.

  4. 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.

  5. A new approach to increase the Curie temperature of Fe-Mo double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Rubi, D. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain); Frontera, C. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain); Roig, A. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain); Nogues, J. [Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Catalunya (Spain); Institut Catala de Recerca i Estudis Avancats (ICREA), 08193 Bellaterra, Catalunya (Spain); Munoz, J.S. [Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Catalunya (Spain); Fontcuberta, J. [Institut de Ciencia de Materials de Barcelona, Campus UAB, E-08193, Bellaterra (Spain)]. E-mail: fontcuberta@icmab.es

    2006-01-25

    Sr{sub 2}FeMoO{sub 6} and related double perovskites are nowadays intensely investigated due to their potential in the field of spintronics. It has been previously shown that the Curie temperature (T {sub C}) of double perovskites can be increased by injecting carriers in the conduction band. We report here on an alternative approach to reinforce the magnetic interaction, and thus raise T {sub C}. It can be suspected that the introduction of Fe excess in the Fe-Mo sub-lattice, which would lead into the appearance of nearest neighbour Fe-O-Fe antiferromagnetic spin coupling, could reinforce the next-near neighbour Fe-O-Fe-O-Fe ferromagnetic ordering and thus raise the Curie temperature. The plausibility of this mechanism was checked, in the first place, by means of Monte Carlo simulations. Afterwards, Nd{sub 2x}Ca{sub 2-2x}Fe{sub 1+x}Mo{sub 1-x}O{sub 6} series was prepared and fully characterized, being found that the Curie temperature rises as much as {delta}T {sub C} {approx} 75 K when the Fe content is increased. We argue that this is a genuine magnetic exchange effect, not related neither to steric distortions nor band filling.

  6. Magnetic glass state and magnetoresistance in SrLaFeCoO6 double perovskite

    Science.gov (United States)

    Pradheesh, R.; Nair, Harikrishnan S.; Haripriya, G. R.; Senyshyn, Anatoliy; Chatterji, Tapan; Sankaranarayanan, V.; Sethupathi, K.

    2017-03-01

    Unusual features in magnetization resembling the kinetic arrest of a magnetic glass state are observed in the La-doped double perovskite, SrLaFeCoO6. Neutron powder diffraction experiments confirm the presence of antisite disorder as well as a lack of long-range magnetic order down to 4 K in this double perovskite which displays spin glass-like features in dc and ac susceptibilities. Magnetic relaxation observed through cooling and heating under unequal fields (CHUF) point towards unusual domain dynamics which is supported by a broad memory effect. Among the two anomalies that are observed at {{T}\\text{a1}}≈ 75 K and at {{T}\\text{a2}}≈ 250 K in the magnetic measurements, the former is associated with a spin-freezing temperature below which the magnetic glass state is experimentally verified. The magnetometric experiments detailed in the paper bring out the non-equilibrium metastable magnetic states in this disordered magnetic system. The magnetic glass state described above manifests in the electrical resistivity ρ (T) through the formation of a ‘hard gap’ because of the spin-exchange energy following the formation of magnetic glass. It is observed that the combination of disorder and magnetic glass state leads to a large, negative magnetoresistance (MR) of  ≈47 % at 5 K in 8 T.

  7. Breathers in ferrimagnetic systems

    Indian Academy of Sciences (India)

    Tarashankar Nag; Swapan Kumar Das; Ajoy Chowdhury

    2006-09-01

    Breathers in discrete nonlinear ferrimagnetic spin lattices are investigated for both easy-axis and easy-plane configurations. The region in frequency space of the formation of breathers is determined and the anticontinuum limit discussed. The mono-chromatic and the coloured breathers are found out numerically for different parameters and different conditions of excitations.

  8. Can Pb-Free Halide Double Perovskites Support High-Efficiency Solar Cells?

    Science.gov (United States)

    Savory, Christopher N; Walsh, Aron; Scanlon, David O

    2016-11-11

    The methylammonium lead halides have become champion photoactive semiconductors for solar cell applications; however, issues still remain with respect to chemical instability and potential toxicity. Recently, the Cs2AgBiX6 (X = Cl, Br) double perovskite family has been synthesized and investigated as stable nontoxic replacements. We probe the chemical bonding, physical properties, and cation anti-site disorder of Cs2AgBiX6 and related compounds from first-principles. We demonstrate that the combination of Ag(I) and Bi(III) leads to the wide indirect band gaps with large carrier effective masses owing to a mismatch in angular momentum of the frontier atomic orbitals. The spectroscopically limited photovoltaic conversion efficiency is less than 10% for X = Cl or Br. This limitation can be overcome by replacing Ag with In or Tl; however, the resulting compounds are predicted to be unstable thermodynamically. The search for nontoxic bismuth perovskites must expand beyond the Cs2AgBiX6 motif.

  9. High-temperature large-gap quantum anomalous Hall insulating state in ultrathin double perovskite films

    Science.gov (United States)

    Baidya, Santu; Waghmare, Umesh V.; Paramekanti, Arun; Saha-Dasgupta, Tanusri

    2016-10-01

    Towards the goal of realizing topological phases in thin films of correlated oxide and heterostructures, we propose here a quantum anomalous Hall insulator (QAHI) in ultrathin films of double perovskites based on mixed 3 d -5 d or 3 d -4 d transition-metal ions, grown along the [111] direction. Considering the specific case of ultrathin Ba2FeReO6 , we present a theoretical analysis of an effective Hamiltonian derived from first principles. We establish that a strong spin-orbit coupling at the Re site, t2 g symmetry of the low-energy d bands, polarity of its [111] orientation of perovskite structure, and mixed 3 d -5 d chemistry results in room temperature magnetism with a robust QAHI state of Chern number C =1 and a large band gap. We uncover and highlight a nonrelativistic orbital Rashba-type effect in addition to the spin-orbit coupling, that governs this QAHI state. With a band gap of ˜100 meV in electronic structure and magnetic transition temperature Tc˜300 K estimated by Monte Carlo simulations, our finding of the QAHI state in ultrathin Ba2FeReO6 is expected to stimulate experimental verification along with possible practical applications of its dissipationless edge currents.

  10. Dielectric response of double layered perovskite Sr3MnTiO7

    Science.gov (United States)

    Chowki, S.; Sahu, B.; Singh, A. K.; Mohapatra, N.

    2016-05-01

    The results of dielectric and resistivity measurements on the Ruddlesden-Popper (RP) type compound Sr3MnTiO7 (SMTO) is presented here. The dielectric response of the compound was recorded in the temperature range 10-300 K with the probing frequency from 500 Hz-5 MHz. We observe a broad anomaly at ~ 200 K in the temperature dependence of dissipation factor (tanδ) and corresponding change in slope in the dielectric constant ɛr'(T) which may be attributed to a difference in the conduction mechanism below and above 200 K. The overall dielectric dispersion of SMTO resembles to that of the double perovskites Sr2MnTiO6 and La2NiMnO6 which follows the modified Debye relaxation equation. This indicates a relaxor type dielectric behavior of SMTO may be due to the contribution of grain boundary effects.

  11. Magnetocaloric and magnetic properties of La2NiMnO6 double perovskite

    Science.gov (United States)

    Masrour, R.; Jabar, A.

    2016-08-01

    The magnetic effect and the magnetocaloric effect in La2NiMnO6(LNMO) double perovskite are studied using the Monte Carlo simulations. The magnetizations, specific heat values, and magnetic entropies are obtained for different exchange interactions and external magnetic fields. The adiabatic temperature is obtained. The transition temperature is deduced. The relative cooling power is established with a fixed value of exchange interaction. According to the master curve behaviors for the temperature dependence of predicted for different maximum fields, in this work it is confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of a second order. The near room-temperature interaction and the superexchange interaction between Ni and Mn are shown to be due to the ferromagnetism of LNMO.

  12. Nature of ``Disorder'' in the Ordered Double Perovskite Sr2FeMoO6

    Science.gov (United States)

    Meneghini, C.; Ray, Sugata; Liscio, F.; Bardelli, F.; Mobilio, S.; Sarma, D. D.

    2009-07-01

    The degree of B/B' alternate cation order is known to heavily influence the magnetic properties of A2BB'O6 double perovskites although the nature of such disorder has never been critically studied. Our detailed x-ray absorption fine structure studies in conjunction with synchrotron radiation x-ray diffraction experiments on polycrystalline Sr2FeMoO6 samples with various degrees of disorder reveal that a very high degree of short range order is preserved even in samples with highly reduced long range chemical order. Based on these experimental results and with the help of detailed structural simulations, we are able to model the nature of the disorder in this important class of materials and discuss the consequent implications on its physical properties.

  13. Nature of "disorder" in the ordered double perovskite Sr2FeMoO6.

    Science.gov (United States)

    Meneghini, C; Ray, Sugata; Liscio, F; Bardelli, F; Mobilio, S; Sarma, D D

    2009-07-24

    The degree of B/B;{'} alternate cation order is known to heavily influence the magnetic properties of A_{2}BB;{'}O_{6} double perovskites although the nature of such disorder has never been critically studied. Our detailed x-ray absorption fine structure studies in conjunction with synchrotron radiation x-ray diffraction experiments on polycrystalline Sr_{2}FeMoO_{6} samples with various degrees of disorder reveal that a very high degree of short range order is preserved even in samples with highly reduced long range chemical order. Based on these experimental results and with the help of detailed structural simulations, we are able to model the nature of the disorder in this important class of materials and discuss the consequent implications on its physical properties.

  14. Magnetic properties of double perovskite Sr2RuHoO6: Monte Carlo Simulation

    Science.gov (United States)

    Nid-bahami, A.; El Kenz, A.; Benyoussef, A.; Bahmad, L.; Hamedoun, M.; El Moussaoui, H.

    2016-11-01

    In this paper, we have studied the double perovskite complex Sr2RuHoO6 (SRHO) using the Mean-Field Approximation (MFA) and Monte Carlo Simulation (MCS). Firstly, we study the ground state of the phase diagrams depending on the exchange couplings and the crystal fields, on the other hand the magnetic properties has been studied. The obtained results by MFA were compared with those obtained using a MCS. Secondly, we have presented the results for finite sizes analysis, of the magnetization and the susceptibility as a function of reduced temperature. Finally, we obtain the critical reduced temperature and critical values of the exponents υ = 0 . 602 ± 0 . 011 , γ = 1 . 179 ± 0 . 022 and β = 0 . 296 ± 0 . 018 which these values are nearest to that of 3D Ising model (υ = 0 ṡ 632 , γ = 1 ṡ 23 and β = 0 ṡ 325).

  15. Optical and electronic properties of double perovskite Ba2ScSbO6

    Science.gov (United States)

    Ray, Rajyavardhan; Himanshu, A. K.; Lahiri, J.; Kumar, Uday; Sen, Pintu; Bandyopadhyay, S. K.; Sinha, T. P.

    2016-05-01

    The ordered double perovskite Ba2ScSbO6 (BSS) has been synthesized in polycrystalline form by solid state reaction at 1400 C for 72 Hrs. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis. The crystal structure is cubic, with space group Fm-3m (No. 225) and lattice parameter, a = 8.20 Ǻ. Optical band-gap has been calculated using UV-Vis Spectroscopy and Kubelka-Munk (KM) function, yielding 4.23 eV. A detailed Ab-initio Density Functional Theory (DFT) study of the electronic properties has been carried out using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) as implemented in WIEN2k. BSS is found to be a large band-gap insulator with potential technological applications.

  16. Magnetic, electronic, and optical properties of double perovskite Bi2FeMnO6

    Science.gov (United States)

    Ahmed, Towfiq; Chen, Aiping; Yarotski, Dmitry A.; Trugman, Stuart A.; Jia, Quanxi; Zhu, Jian-Xin

    2017-03-01

    Double perovskite Bi2FeMnO6 is a potential candidate for the single-phase multiferroic system. In this work, we study the magnetic, electronic, and optical properties in BFMO by performing the density functional theory calculations and experimental measurements of magnetic moment. We also demonstrate the strain dependence of magnetization. More importantly, our calculations of electronic and optical properties reveal that the onsite local correlation on Mn and Fe sites is critical to the gap opening in BFMO, which is a prerequisite condition for the ferroelectric ordering. Finally, we calculate the x-ray magnetic circular dichroism spectra of Fe and Mn ions (L2 and L3 edges) in BFMO.

  17. Hydrothermal Synthesis and Dielectric Characterization of a Double Perovskite Ba2FeSbO6

    Institute of Scientific and Technical Information of China (English)

    LI Min; YUAN Hong-ming; XU Wei; HAN Mei; YAO Lin-ran; YANG Ming; FENG Shou-hua

    2012-01-01

    A double perovskite oxide Ba2FeSbO6 was hydrothermally synthesized and structurally characterized by X-ray diffraction.This solid compound shows a single phase and has a trigonal structure with space group R-3m and cell parameters of a=0.57261 nm and c=1.40244 nm.The dielectric constant and loss tangent of the solid measured in a frequency range from 100 Hz to 1 MHz at temperatures from 313 K to 513 K reveal a relaxation process of frequency dependence of the real part(ε') of dielectric constant and dielectric loss tanδ.The frequency dependence of electrical property led to the framework of conductivity and electric modulus formalisms.The scaling behavior of imaginary part of electric modulus suggests that the relaxation describes the single mechanism at various temperatures.The variation tendency of the alternating current impedance indicates the thermally activated conduction process follows Jonsche's power law.

  18. Characterization and thermal expansion of Sr2Fe Mo2−O6 double perovskites

    Indian Academy of Sciences (India)

    Y Markandeya; Y Suresh Reddy; Shashidhar Bale; C Vishnuvardhan Reddy; G Bhikshamaiah

    2015-10-01

    Double perovskite oxides Sr2FeMo2−O6 ( = 0.8, 1.0, 1.2, 1.3 and 1.4) (SFMO) of different compositions were prepared by sol–gel growth followed by annealing under reducing atmosphere conditions of H2/Ar flow. X-ray powder diffraction studies revealed that the crystal structure of the samples changes from tetragonal to cubic at around = 1.2. Lattice parameters and unit cell volume of these samples found to decrease with the increase in Fe content. The characteristics absorption bands observed in the range 400–1000 cm−1 of Fourier transform infrared spectra indicate the presence of FeO6 and MoO6 octahedra and confirm the formation of double perovskite phase. The value of g ∼ 2.00 obtained from electron spin resonance studies indicates that Fe is in 3+ ionic state in the SFMO samples. Dilatometric studies of these samples reveal that the average value of coefficient of thermal expansion ($\\overline{\\alpha}$) increases with the increase in temperature or Fe content in SFMO samples. The low value of coefficient of thermal expansion 1.31 × 10−6°C−1 obtained for Sr2Fe0.8Mo1.2O6 in the present study in the temperature range of 40–100°C makes it useful as anode material in fuel cells. The coefficient of thermal expansion ($\\overline{\\alpha}$) and the unit cell volume () of SFMO samples vary inversely with composition in agreement with Grüneisen relation.

  19. Fe-Mo double perovskite: From small clusters to bulk material

    Energy Technology Data Exchange (ETDEWEB)

    Carvajal, E., E-mail: ecarvajalq@ipn.mx [Instituto Politecnico Nacional, ESIME-Culhuacan, Av. Santa Ana 1000, C.P. 04430 Mexico, D.F. (Mexico); Oviedo-Roa, R. [Programa de Investigacion en Ingenieria Molecular, Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas Norte 152, 07730 Mexico, D.F. (Mexico); Cruz-Irisson, M. [Instituto Politecnico Nacional, ESIME-Culhuacan, Av. Santa Ana 1000, C.P. 04430 Mexico, D.F. (Mexico); Navarro, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, A.P. 70-360, 04510 Mexico, D.F. (Mexico)

    2012-09-20

    To understand the differences in behaviour between up- and down-spin electrons observed in the half-metallic Sr{sub 2}FeMoO{sub 6} double perovskite, the density of states (DOS) was studied for the (FeO{sub 6}){sup -4} and (MoO{sub 6}){sup -6} octahedral clusters using first-principles density functional theory within the generalised gradient approximation (GGA) scheme and the Perdew-Burke-Ernzerhof (PBE) functional. Our results reveal that half-metallic character is present, even starting from an isolated (FeO{sub 6}){sup -4} cluster, and is a consequence of spin decoupling of antibonding hybridisations between iron t{sub 2g} states and oxygen p states (t{sub 2g}{sup a} states), i.e., t{sub 2g}{sup a} states lie below the Highest Occupied Molecular Orbital (HOMO) in the up-spin channel, whereas they lie above the HOMO level in the down-spin channel. The spin-induced shifting between up-spin and down-spin DOS situates the HOMO in such a way that the molecular orbitals oxygen p states (p bands) are fully spin-paired by octet electrons. Thus, the down-spin channel has metallic character because the HOMO lies just at the p bands, and the up-spin channel is semiconducting because the HOMO falls within the energy gap between the t{sub 2g}{sup a} and e{sub g}{sup a} bands. Finally, the (MoO{sub 6}){sup -6} octahedron does not inhibit the perovskite half-metallic character since this cluster has a zero total spin.

  20. Organometallic halide perovskite/barium di-silicide thin-film double-junction solar cells

    Science.gov (United States)

    Vismara, R.; Isabella, O.; Zeman, M.

    2016-04-01

    Barium di-silicide (BaSi2) is an abundant and inexpensive semiconductor with appealing opto-electrical properties. In this work we show that a 2-μm thick BaSi2-based thin-film solar cell can exhibit an implied photo-current density equal to 41.1 mA/cm2, which is higher than that of a state-of-the-art wafer-based c-Si hetero-junction solar cell. This performance makes BaSi2 an attractive absorber for high-performing thin-film and multi-junction solar cells. In particular, to assess the potential of barium di-silicide, we propose a thin-film double-junction solar cell based on organometallic halide perovskite (CH3NH3PbI3) as top absorber and BaSi2 as bottom absorber. The resulting modelled ultra-thin double-junction CH3NH3PbI3 / BaSi2 (< 2 μm) exhibits an implied total photo-current density equal to 38.65 mA/cm2 (19.84 mA/cm2 top cell, 18.81 mA/cm2 bottom cell) and conversion efficiencies up to 28%.

  1. Electronic, magnetic, and optical characteristics of half-semiconductor double perovskite oxide Sr2CrOsO6 governed by 3d (t2g3)-5d (t2g3) antiferromagnetic coupling

    Science.gov (United States)

    H.-E., M. Musa Saad

    2016-07-01

    In this study, motivated by observations of the remarkable magnetic insulating nature and high Curie temperature (TC=725 K) of double perovskite oxide Sr2CrOsO6, the electronic, magnetic, and optical characteristics of Sr2CrOsO6 were determined using the full potential linear muffin-tin orbital method according to density functional theory. The spin-orbit coupling contribution was included in the local spin density approximation (LSDA) and generalized gradient approximation (GGA). In addition, the Coulomb repulsion (U) and Hund's exchange (J) energies were considered in both methods (LSDA+U and GGA+U). Full structural optimization confirmed that the ground state of Sr2CrOsO6 is face-centered cubic (Fm-3m symmetry). Calculations predicted that Sr2CrOsO6 is ferrimagnetic half-semiconductive (HSC) due to the vertical hopping of t2g electrons via antiferromagnetic coupling [Cr3+ (t2g3↑)-O (2pπ)-Os5+ (t2g3↓)], which agreed with the experimental results. The HSC energy-gaps originate from the splitting of three partially occupied Os5+ (5d) bands into two fully filled bands and one empty spin-down band. The real ε1 (ω) and imaginary ε2 (ω) parts of the dielectric function ε (ω) and energy-loss spectrum L (ω) were calculated, analyzed, and compared with the electronic results.

  2. Dielectric Relaxation of Rare Earth Ordered Double Perovskite Oxide Ba2ErTaO6

    Science.gov (United States)

    Mukherjee, Rajesh; Dutta, Alo; Sinha, T. P.

    2016-01-01

    The electrical properties of rare-earth based ordered double perovskite oxide barium erbium tantalate, Ba2ErTaO6 synthesized by solid-state reaction method are investigated. The x-ray diffraction pattern of the sample shows cubic Fm3m phase at room temperature with ordering of the B cations. Fourier transform infrared spectrum shows two primary phonon modes of the sample at around 350 cm-1 and 600 cm-1. The dielectric relaxation of the sample is investigated in the frequency range from 50 Hz to 1.1 MHz and in the temperature range from 303 K to 673 K. Electric modulus and electrical impedance data are fitted to the Cole-Cole equation. The frequency dependent conductivity spectra follow the power law. Summerfield scaling is used to explain the conduction mechanism. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures. The complex impedance plane plots show that the relaxation (conduction) mechanism in this material is mainly due to grain boundary effect for all temperatures and grain effect for low temperature. The relaxation frequency corresponding to dielectric loss is found to obey Arrhenius law with activation energy of 0.50 eV. The values of activation energy indicate that the dielectric relaxation and the conduction mechanism are due to adiabatic small polaronic hole hopping mechanism.

  3. Magnetic entropy change and critical exponents in double perovskite Y2NiMnO6

    Science.gov (United States)

    Sharma, G.; Tripathi, T. S.; Saha, J.; Patnaik, S.

    2014-11-01

    We report the magnetic entropy change (ΔSM) and the critical exponents in the double perovskite manganite Y2NiMnO6 with a ferromagnetic to paramagnetic transition TC~85 K. For a magnetic field change ΔH=80 kOe, a maximum magnetic entropy change ΔSM=-6.57 J/kg K is recorded around TC. The critical exponents β=0.363±0.05 and γ=1.331±0.09 obtained from power law fitting to spontaneous magnetization MS(T) and the inverse initial susceptibility χ0-1(T) satisfy well to values derived for a 3D-Heisenberg ferromagnet. The critical exponent δ=4.761±0.129 is determined from the isothermal magnetization at TC. The scaling exponents corresponding to second order phase transition are consistent with the exponents from Kouvel-Fisher analysis and satisfy Widom's scaling relation δ=1+(γ/β). Additionally, they also satisfy the single scaling equation M(H,ɛ)=ɛβf±(H/ɛ) according to which the magnetization-field-temperature data around TC should collapse into two curves for temperatures below and above TC.

  4. Electronic State of Fe in Double Perovskite Oxide Sr 2FeWO 6

    Science.gov (United States)

    Kawanaka, Hirofumi; Hase, Izumi; Toyama, Shunichiro; Nishihara, Yoshikazu

    1999-09-01

    The magnetic properties of double perovskite oxide Sr2FeWO6 have been reported. The magnetic susceptibility and Mössbauer effect of 57Fe show that this compound is an antiferromagnet with T N=37 K. The Mössbauer parameters below ˜20 K are the center shift of +1.2 mm/s relative to metallic iron, the quadrupole splitting of 1.9 mm/s and the hyperfine field of ˜110 kOe. The quadrupole splitting has a strong temperature dependence. From these data, we conclude that Fe in Sr2FeWO6 is in the Fe2+ high-spin state, while the hyperfine field seems to be quite small. The cell volume shows a large increase compared to other Sr2FeTO6 ( T= Mo, Re, etc.), which is in the Fe3+ high-spin state. These results suggest that these compounds have a strongly coupled charge and lattice systems.

  5. Optical absorption analysis of quaternary molybdate- and tungstate-ordered double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Tablero, C., E-mail: ctablero@etsit.upm.es

    2015-08-05

    Highlights: • These compounds present a high optical absorption. • The absorption coefficients using different DFT + U alternatives have been compared. • The absorption coefficients have been split into different contributions. • The maximum efficiency is near the maximum efficiency for multiple-gap solar cells. - Abstract: Quaternary-ordered double perovskite A{sub 2}MM′O{sub 6} (M = Mo,W) semiconductors are a group of materials with a variety of photocatalytic and optoelectronic applications. An analysis focused on the optoelectronic properties is carried out using first-principles density-functional theory with several U orbital-dependent one-electron potentials applied to different orbital subspaces. The structural non-equivalence of the atoms resulting from the symmetry has been taken in account. In order to analyze optical absorption in these materials deeply, the absorption coefficients have been split into inter- and intra-non-equivalent species contributions. The results indicate that the effect of the A and M′ atoms on the optical properties are minimal whereas the largest contribution comes from the non-equivalent O atoms to M transitions.

  6. Dielectric relaxation in double perovskite oxide, Ho2CdTiO6

    Indian Academy of Sciences (India)

    Dev K Mahato; A Dutta; T P Sinha

    2011-06-01

    A new double perovskite oxide holmium cadmium titanate, Ho2CdTiO6 (HCT), prepared by solid state reaction technique is investigated by impedance spectroscopy in a temperature range 50–400°C and a frequency range 75 Hz–1 MHz. The crystal structure has been determined by powder X-ray diffraction which shows monoclinic phase at room temperature. An analysis of complex permittivity with frequency was carried out assuming a distribution of relaxation times as confirmed by Cole–Cole plot. The frequency dependent electrical data are analysed in the framework of conductivity and electric modulus formalisms. The frequencies corresponding to themaxima of the imaginary electric modulus at various temperatures are found to obey an Arrhenius law with an activation energy of 0.13 eV. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures. Nyquist plots are drawn to identify an equivalent circuit and to know the bulk and interface contributions.

  7. 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.

  8. Magnetic behavior of Ca{sub 2}NiWO{sub 6} double perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, C.A. [Area de Quimica General e Inorganica ' Dr. G.F.Puelles' , Facultad de Quimica, Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina); Curiale, J. [Centro Atomico Bariloche and Instituto Balseiro (UNCuyo), CNEA, Av. Bustillo 9500 (R8402AGP) S. C. de Bariloche, RN (Argentina); Viola, M. del C. [Area de Quimica General e Inorganica ' Dr. G.F.Puelles' , Facultad de Quimica, Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina); Pedregosa, J.C. [Area de Quimica General e Inorganica ' Dr. G.F.Puelles' , Facultad de Quimica, Bioquimica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina)]. E-mail: jpedreg@unsl.edu.ar; Sanchez, R.D. [Centro Atomico Bariloche and Instituto Balseiro (UNCuyo), CNEA, Av. Bustillo 9500 (R8402AGP) S. C. de Bariloche, RN (Argentina)]. E-mail: rodo@cab.cnea.gov.ar

    2007-09-01

    Polycrystalline Ca{sub 2}NiWO{sub 6} double perovskite has been prepared by solid-state reaction at 1150 C. The crystal structure of this material has been confirmed by X-ray powder diffraction (XRD). At room temperature, the crystal structure is monoclinic, space group P2{sub 1}/n, with a=5.4061(2) A, b=5.5389(2) A, c=7.6895(3) A, {beta}=90.232(2){sup o}. Magnetic susceptibility and electron spin resonance experiments on Ca{sub 2}NiWO{sub 6} show at high temperature a Curie-Weiss behavior with a {theta}=-75 K. From the Curie-Weiss behavior, the effective magnetic moment is 2.85{mu} {sub B}, which is in agreement with the presence of Ni{sup 2+} in the system. At low temperatures, below 52.5(0.2) K, the magnetic susceptibility shows antiferromagnetic behavior. From the experimental data and the mean field theory of antiferromagnetism we estimated the Ni interactions among the nearest Ni neighbors and the second nearest Ni neighbors.

  9. 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.

  10. Structural and electromagnetic properties driven by oxygen vacancy in Sr{sub 2}FeMoO{sub 6−δ} double perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Q., E-mail: zhangqin@sdjtu.edu.cn; Xu, Z.F.; Wang, L.F.; Gao, S.H.; Yuan, S.J.

    2015-11-15

    Nonstoichiometric Sr{sub 2}FeMoO{sub 6−δ} (δ = 0.132 and 0.296) double perovskite compounds have been synthesized by solid-state reaction. Effect of oxygen vacancy on its structural, magnetic and transport properties has been investigated by X-ray diffraction, magnetic and electronic transport measurements. Despite of different oxygen vacancy, both two compounds are of single phase and belong to the same space group, I4/m. Structural refinement shows that oxygen vacancy lowers the degree of ordering on B site and increases the lattice constant. Further structural analysis finds that owing to the oxygen vacancy, Fe atom is compressed, while the Mo atom changes from being compressed to being elongated. As predicted by the theoretical calculation, besides anti-site defects, oxygen vacancy is another important source for the lower Curie temperature of nonstoichiometric Sr{sub 2}FeMoO{sub 6−δ}. Meanwhile, the hopping integration of electron between Fe–O–Mo–O–Fe is reduced by oxygen vacancy, thus the resistivity and the semiconducting-metallic transition temperature of Sr{sub 2}FeMoO{sub 6−δ} are enhanced. However, the saturation magnetization (M{sub S}) of Sr{sub 2}FeMoO{sub 6−δ} at 5 K can be repeated well based on the ferrimagnetization model, suggesting that the anti-site defect is responsible for the reduction of M{sub S}, which is different from the literature results. - Graphical abstract: Magnetization curves of Sr{sub 2}FeMoO{sub 6−δ} compounds at 5 K. - Highlights: • Structural distortion is introduced to Sr{sub 2}FeMoO{sub 6−δ} due to the occurrence of Oxygen vacancy. • Magnetic interaction and electron-transfer ability between Fe–O–Mo–O–Fe are reduced by oxygen vacancy. • Anti-site defect contributes to the reduced saturation magnetization of Sr{sub 2}FeMoO{sub 6−δ}.

  11. 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.

  12. 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.

  13. Disordered ferromagnetism in Ho2NiMnO6 double perovskite

    Science.gov (United States)

    Chakraborty, Tirthankar; Nair, Harikrishnan S.; Nhalil, Hariharan; Kumar, K. Ramesh; Strydom, André M.; Elizabeth, Suja

    2017-01-01

    Magnetic and dielectric properties of the double perovskite Ho2NiMnO6 are reported. The compound is synthesized by nitrate route and is found to crystallize in monoclinic P21/n space group. Lattice parameters obtained by refining powder x-ray diffraction data are; a  =  5.218(2) Å, b  =  5.543(2) Å, c  =  7.480(3) Å and the monoclinic angle is β ={{90.18}\\circ} (4). A phase transition is observed at {{T}\\text{C}}=86 K in the temperature-dependent magnetization curve, M(T). The inverse magnetic susceptibility, (1/χ (T) ) fits reasonably well with modified Curie-Weiss law by incorporating the paramagnetic response of Ho3+. 1/χ (T) manifests as an upward deviation from ideal Curie-Weiss behaviour well above the ferromagnetic transition. Signs of inherent Griffiths phase pertaining to the Ni/Mn subsystem are visible when one subtracts the Ho3+ paramagnetic contribution from total susceptibility and does the power-law analysis. The magnetic hysteresis at 2 K gives the maximum value of magnetization {{M}\\text{max}}≈ 15 {μ\\text{B}} /f.u. at 50 kOe. Field-derivative of magnetization at 2 K shows discontinuities which indicates the existence of metamagnetic transitions in this compound. This needs to be probed further. Out of the two dielectric relaxations observed, the one at low temperature may be attributed to phononic frequencies and that at higher temperature may be due to Maxwell-Wagner relaxation. A correlation between magnetic and lattice degrees of freedom is plausible since the anomaly in dielectric constant coincides with T C.

  14. Magnetic properties of double perovskite SrCrReO: Mean field approximation and Monte Carlo simulation

    Science.gov (United States)

    El Rhazouani, O.; Benyoussef, A.; Naji, S.; El Kenz, A.

    2014-03-01

    The double perovskite (DP) Sr2CrReO6, with its high Curie temperature, is a good candidate for magneto-electric and magneto-optic applications. Thus, a theoretical study by Monte Carlo Simulation (MCS) and Mean Field Approximation (MFA) in the context of the Ising model is important for a better understanding of the magnetic behavior of this material. The critical behavior of the magnetization and the susceptibility of this system have been determined. The phase diagrams depending on the exchange couplings and the crystal fields have been given. The values of critical exponents are also reported.

  15. 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...

  16. 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.

  17. 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.

  18. Magnetocaloric properties of R2NiMnO6 (R=Pr, Nd, Tb, Ho and Y) double perovskite family

    Science.gov (United States)

    Chakraborty, Tirthankar; Nhalil, Hariharan; Yadav, Ruchika; Wagh, Aditya A.; Elizabeth, Suja

    2017-04-01

    Double perovskite R2NiMnO6 (R=Pr, Nd, Tb, Ho and Y) composites are prepared via solid state synthesis or nitrate route. Isothermal magnetic entropy change (ΔSM (T , H)) and relative cooling power (RCP) for all systems are calculated and compared. All of them possess relatively high values of ΔSM (T , H) and RCP as compared to many perovskite and double perovskite systems reported previously. Ho2NiMnO6 has the highest value for | ΔSM (T , H) | and RCP as 8.4 JKg-1K-1 at 70 kOe and 59.18 J Kg-1 at 20 kOe respectively. This study highlights the potential of magnetocaloric refrigerant materials at low temperature.

  19. 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.

  20. FT-Raman and FT-IR vibrational spectroscopic studies of Sr{sub 2}RESbO{sub 6} (RE = La to Lu and Y) double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez-Martinez, F.; Montero, J.L.; Carrillo, I. [Departamento de Quimica Industrial y Polimeros, EUITI, Universidad Politecnica de Madrid, 28012 Madrid (Spain); Colon, C., E-mail: cristobal.colon@upm.es [Departamento Fisica Aplicada, EUITI, Universidad Politecnica de Madrid, 28012 Madrid (Spain)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer 14 double perovskites Sr{sub 2}RESbO{sub 6} were synthesized. Black-Right-Pointing-Pointer Crystal lattice parameters have been obtained. Black-Right-Pointing-Pointer IR and Raman spectra have been obtained. Black-Right-Pointing-Pointer The crystal structure has been studied. - Abstract: The Sr{sub 2}RESbO{sub 6} double perovskites (RE = La to Lu and Y) were synthesized by ceramic method. The structure and phase purity of the prepared double perovskites were examined by X-ray diffraction pattern and vibrational spectroscopy. A systematic analysis of the compounds structure was carried out for the first time by Raman and IR spectroscopies. A simple inspection of the diffraction patterns shows that these compounds have lower symmetry than the cubic which can be usually found in the Ba{sub 2}RESbO{sub 6} double perovskites. The four active modes (A{sub 1g}, E{sub g}, and two T{sub 2g}) in the Raman spectra and the active mode (T{sub 1u}) in the IR spectra previously described in the spectroscopic data of Ba compounds have changed. In the Sr compounds these modes have been split into its components, in some cases, being active in both types of spectra. According to our data the Sr{sub 2}RESbO{sub 6} double perovskites can be described by a monoclinic symmetry cell, space group P2{sub 1}/n. However, in the cases of Sr{sub 2}LaSbO{sub 6} and Sr{sub 2}PrSbO{sub 6} an alternative structure should be searched by neutron diffraction technique.

  1. Electrical properties Sr2FeTiO6 double perovskite material synthesized by sol-gel method

    Science.gov (United States)

    Masta, N.; Triyono, D.; Laysandra, H.

    2017-07-01

    The structure and electrical properties of double perovskite Sr2FeTiO6 have been studied. Sr2FeTiO6 were prepared by sol-gel method results in powder form. Then, the powder was pressed and sintered at 1100 °C to form pellet. The structural features of the systems have been studied using X-Ray Diffraction (XRD), Scanning Electron Micrograph (SEM) and Energy Dispersive Spectroscopy (EDS). Through XRD characterization, the structure of the compound is single phase cubic Perovskite (space group Pm3m) with lattice parameter a = 3,899 Å and crystallite size is 26 nm. The electrical properties of the material, as functions of temperature (293 K - 523 K) and frequency (100 Hz - 1 MHz), were examined by Impedance Spectroscopy method using RLC meter. The imaginary of impedance (Zim) data shows the peaks which indicates the presence of relaxation process in this sample. Activation energy for relaxation process which is evaluated by Arrhenius Law indicates the type of charge carrier is p-type polaron.

  2. 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.

  3. First principle research of possible HM-AFM in double perovskites A2MoOsO6 and A2TcReO6 (A = Si, Ge, Sn, and Pb) with group IVA elements set on the A-site position

    Science.gov (United States)

    Fuh, Huei-Ru; Liu, Yun-Ping; Wang, Yin-Kuo

    2013-05-01

    We calculated electronic structures of double perovskite structures of A2MoOsO6 and A2TcReO6 (A = Si, Ge, Sn, and Pb) based on the density functional theory which was carried out with a full structural optimization using generalized gradient approximation and taking into account the correlation effect (GGA + U). In GGA calculation, Pb2TcReO6 shows a half-metallic antiferromagnet (HM-AFM) characteristic, whereas Sn2MoOsO6, Pb2MoOsO6, and Sn2TcReO6 are nearly HM-AFMs. With GGA + U calculation, Sn2MoOsO6 and Pb2MoOsO6 become stable HM-AFM, but Sn2TcReO6 and Pb2TcReO6 changes HM-AFM into an antiferromagnetic insulator. The p-d hybridization between B(B')d-Op and double exchange interaction is the mean reason to result in the half-metallic and compensated ferrimagnetic phase.

  4. Spin polarized itinerant electrons in Ca{sub 2}FeMoO{sub 6} double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Rubi, D. [Institut de Ciencia de Materials de Barcelona, CSIC, Campus U.A.B., 08193 Bellaterra, Catalunya (Spain); Nogues, J. [Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Catalunya (Spain); Institut Catala de Recerca i Estudis Avancats (ICREA), 08193 Bellaterra, Catalunya (Spain); Munoz, J.S. [Departament de Fisica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Catalunya (Spain); Fontcuberta, J. [Institut de Ciencia de Materials de Barcelona, CSIC, Campus U.A.B., 08193 Bellaterra, Catalunya (Spain)]. E-mail: fontcuberta@icmab.es

    2006-01-25

    We report on magnetic studies of the double perovskite Ca{sub 2}FeMoO{sub 6} in its paramagnetic state. It is found that the effective magnetic moment, extracted from the Curie constant, is magnetic field dependent and it is smaller than that expected in a simple ionic scenario. These experimental results, which are in agreement with early reports on Sr{sub 2}FeMoO{sub 6}, are interpreted as a direct evidence of the antiferromagnetic coupling and polarization of the conduction band in these oxides. A simple mean field model accounts for these observations and enlightens the relevance of itinerant carriers on the strength of the magnetic coupling in these oxides.

  5. Synthesis and characterization of the new two-dimensional Heisenberg antiferromagnet double perovskite BaLaCuSbO6.

    Science.gov (United States)

    Blanco, M Cecilia; Paz, Sergio Alexis; Nassif, Vivian M; Guimpel, Julio J; Carbonio, Raúl E

    2015-06-21

    The BaLaCuSbO(6) double perovskite has been successfully synthesized by solid state reaction under an air atmosphere. Its structure was refined using powder neutron diffraction in the monoclinic space group I2/m with a 4% antisite disorder on the B cations. Magnetic measurements give signs of 2D-antiferromagnetic behaviour with TN around 64 K. The Jahn-Teller distortion produced by Cu(2+) ions favours a crystallographic tetragonal distortion and consequently the in-plane super-superexchange antiferromagnetic interactions, J(90°), are favoured over the in-plane J(180°) antiferromagnetic exchange interactions. Both, J and J' magnetic interactions have been evaluated according to a Heisenberg antiferromagnetic rectangular model using an approximation to Curie's law in powers of J/T, being |J| around 10 times stronger than |J'|.

  6. Effect of preparation procedure on the magnetic and transport properties of double perovskite Sr2FeMoO6

    Institute of Scientific and Technical Information of China (English)

    Wang Jin-Hui; Yu Zhi; Liu Gong-Qiang; Du You-Wei

    2004-01-01

    @@ Ordered and disordered double perovskite Sr2FeMoO6 ceramics have been investigated by powder x-ray diffraction,magnetic and transport measurements, as well as Mossbauer spectroscopy. The heavily disordered sample can be acquired by annealing the ordered samples in argon. The annealing procedure affects not only the nature of grain boundaries but also the grain itself. The evidence of Mossbauer spectra performed at 77 and 300 K indicates that there exist small oxygen deficient clusters of SrFeO3-y in the disordered sample. The paramagnetic Fe4+ and Fe3+ ions in the compound subsist down to 77 K and the ratio of Fe4+/Fe3+ increases with decreasing temperature.

  7. Insulator-Metal Transition due to La Doping in Double Perovskite Sr2MnMoO6

    Institute of Scientific and Technical Information of China (English)

    刘晓峻; 黄巧建; 徐胜; 张淑仪; 罗爱华

    2004-01-01

    Resistivity, thermal diffusivity, lattice and magnetic properties of double perovskite Sr2-xLaxMnMoO6 are investigated with systematic change of La doping concentration x from 0.0 to 0.4. The insulator to metal phase transition is observed with increasing x above 0.3, suggesting that the extra electrons via substitution of La3+for Sr2+ ions occupy mainly the conduction Mo-4d band. According to the insulator to metal phase transition,the thermal diffusivity of Sr2-xLaxMnMoO6 enhances from 0.33cm2/s at x = 0.0 to 0.49cm2/s at x = 0.4. We further investigate the La doping effects on the lattice and magnetic properties.

  8. 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).

  9. Thermal conductivity of ferrimagnet GdBaMn2O5.0 single crystals

    Directory of Open Access Journals (Sweden)

    J. C. Wu

    2017-05-01

    Full Text Available GdBaMn2O5.0 is a double-perovskite ferrimagnet consisting of pyramidal manganese layers. In this work, we study the in-plane and the c-axis thermal conductivities of GdBaMn2O5.0 single crystals at low temperatures down to 0.3 K and in high magnetic fields up to 14 T. The κc(T curve shows a broad hump below the Néel temperature (TN = 144 K, which indicates the magnon heat transport along the c axis. Whereas, the κa(T shows a kink at TN, caused by a magnon-phonon scattering effect. This anisotropic behavior is caused by the anisotropy of spin interactions along different directions. At very low temperatures, magnetic-field-induced changes of κa and κc, which is likely due to phonon scattering by free Gd3+ spins, is rather weak. This indicates that the spin coupling between Gd3+ and Mn2+/Mn3+ is rather strong at low temperatures.

  10. It Takes Two to Tango-Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis.

    Science.gov (United States)

    Kegelmann, Lukas; Wolff, Christian M; Awino, Celline; Lang, Felix; Unger, Eva L; Korte, Lars; Dittrich, Thomas; Neher, Dieter; Rech, Bernd; Albrecht, Steve

    2017-05-24

    Solar cells made from inorganic-organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 °C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current-voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The

  11. Preparation of double perovskite-type oxide LaSrFeCoO6for chemical looping steam methane reforming to produce syngas and hydrogen

    Institute of Scientific and Technical Information of China (English)

    赵坤; 沈阳; 何方; 黄振; 魏国强; 郑安庆; 李海滨; 赵增立

    2016-01-01

    Double-perovskite type oxide LaSrFeCoO6was used as oxygen carrier for chemical looping steam methane reforming (CL-SMR) due to its unique structure and reactivity. Solid-phase, amorphous alloy, sol-gel and micro-emulsion methods were used to prepare the LaSrFeCoO6samples, and the as-prepared samples were characterized by means of X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area. Results showed that the samples made by the four different methods exhibited pure crystalline perovskite structure. The ordered dou-ble perovskite LaSrFeCoO6was regarded as a regular arrangement of alternating FeO6and CoO6corner-shared octahedra, with La and Sr cations occupying thevoids in between the octahedral. Because the La3+and Sr2+ions in A-site didnot take part in reaction, the TPR patterns showedthe reductive properties of the B-site metals. The reduction peaks at low temperature revealed the reduction of adsorbed oxygenon surface and combined with the reduction of Co3+to Co2+and to Co0, while the reduction of Fe3+to Fe2+and the partial reduction of Fe2+to Fe0occurred at higher temperatures. From the point of view of the oxygen-donation ability, resistance to carbon formation, as well as hydrogen generation capacity, the sample made by micro-emulsion method exhibited the best reactiv-ity. Its redox reactivitywas very stable in ten successive cycles without deactivation. Compared to the single perovskite-type oxides LaFeO3and LaCoO3, the double perovskite LaSrFeCoO6exhibitedbetter syngas and hydrogen generation capacity.

  12. Effect of Codoping Cl Anion and 5-AVA Cation on Performance of Large-Area Perovskite Solar Cells with Double-Mesoporous Layers

    Directory of Open Access Journals (Sweden)

    Yaxian Pei

    2016-01-01

    Full Text Available For the perovskite solar cells (PSCs, the performance of the PSCs has become the focus of the research by improving the quality of the perovskite absorption layer. So far, the performance of the large-area PSCs is lower than that of small-area PSCs. In the paper, the experiments were designed to improve the photovoltaic performance of the large-area PSCs by improved processing technique. Here we investigated the optoelectronic properties of the prototypical CH3NH3PbI3 (MAPbI3 further modulated by introducing other extrinsic ions (specifically codoped Cl− and 5-AVA+. Moreover, we used inorganic electron extraction layer to achieve very rapid photogenerated carrier extraction eliminating local structural defects over large areas. Ultimately, we fabricated a best-performing perovskite solar cell based on codoping Cl anion and 5-AVA cation which uses a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated with perovskite and does not require a hole-conducting layer. The experiment results indicated that an average efficiency of double-mesoporous layer-based devices with codoping Cl anion and 5-AVA cation was obtained with exceeding 50% enhancement, compared to that of pure single-mesoporous layer-based device.

  13. Ferrimagnetic and Long Period Antiferromagnetic Phases in High Spin Heisenberg Chains with D-Modulation

    Science.gov (United States)

    Hida, Kazuo

    2007-02-01

    The ground state properties of the high spin Heisenberg chains with alternating single site anisotropy are investigated by means of the numerical exact daigonaization and DMRG method. It is found that the ferrimagnetic state appears between the Haldane phase and period doubled Néel phase for the integer spin chains. On the other hand, the transition from the Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous magnetization varies continuously with the modulation amplitude of the single site anisotropy. Eventually, the magnetization is locked to fractional values of the saturated magnetization. These fractional values satisfy the Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to reveal the physical nature of each state. In contrast to the case of frustration induced ferrimagnetism, no incommensurate magnetic superstructure is found.

  14. 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.

  15. Magnetism and spin-orbit coupling in Ir-based double perovskites La2-xSrxCoIrO6

    Science.gov (United States)

    Kolchinskaya, A.; Komissinskiy, P.; Yazdi, M. Baghaie; Vafaee, M.; Mikhailova, D.; Narayanan, N.; Ehrenberg, H.; Wilhelm, F.; Rogalev, A.; Alff, L.

    2012-06-01

    We have studied Ir spin and orbital magnetic moments in the double perovskites La2-xSrxCoIrO6 by x-ray magnetic circular dichroism. In La2CoIrO6, Ir4+ couples antiferromagnetically to the weak ferromagnetic moment of the canted Co2+ sublattice and shows an unusually large negative total magnetic moment (-0.38 μB/f.u.) combined with strong spin-orbit interaction. In contrast, in Sr2CoIrO6, Ir5+ has a paramagnetic moment with almost no orbital contribution. A simple kinetic-energy-driven mechanism including spin-orbit coupling explains why Ir is susceptible to the induction of substantial magnetic moments in the double perovskite structure.

  16. 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.

  17. Enhanced performance of planar perovskite solar cells via incorporation of Bphen/Cs2CO3-MoO3 double interlayers

    Science.gov (United States)

    Jiang, Yurong; Liu, Hairui; Gong, Xiu; Li, Chen; Qin, Ruiping; Ma, Heng

    2016-11-01

    This work proposes a new perovskite solar cell structure by inserting the double modified interlayers consisting of the 4,7-diphenyl-1,10-phenanthroline (Bphen) and cesium carbonate (Cs2CO3)-MoO3 layer between perovskite (CH3NH3PbI3-xClx)/PCBM (phenyl-C61-butyric acid methylester) and an Ag electrode. The double interlayers improve the photovoltaic efficiency to 15.59%, which is higher than that of reference devices with Bphen (13.41%) or alone, the champion PCE of 16.01% is obtained. The enhanced opening circuit voltage (Voc) is ascribed as the main factor to improve the efficiency. Further studies show, the reduced work function of cathode by means of the Cs2CO3-MoO3 could effectively extract the electrons and reduce the carrier recombination and thus result in a higher Voc.

  18. 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.

  19. Growth of {110}-one-axis-oriented perovskite-type oxide films using self-aligned epitaxial (101)PdO//(111) Pd double layers

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Hiroki [Department of Innovative and Engineered Material, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan); Kariya, Tetsuro [Department of Innovative and Engineered Material, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan); Sanyo Special Steel Co., Ltd, 3007, Nakashima, Shikama-ku, Himeji, Hyogo 672-8677 (Japan); Shimizu, Takao [Department of Innovative and Engineered Material, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan); Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503 (Japan); Uchiyama, Kiyoshi, E-mail: uchiyama@tsuruoka-nct.ac.jp [Department of Creative Engineering, National Institute of Technology, Tsuruoka College, 104 Inooka Sawada, Tsuruoka, Yamagata 997-8511 (Japan); Funakubo, Hiroshi [Department of Innovative and Engineered Material, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan); Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503 (Japan)

    2016-01-29

    Self-aligned (101)-one-axis-oriented PdO layer was obtained on (111) Pd films prepared on (111)Pt/TiO{sub x}/SiO{sub 2}/Si [abbreviated as (111)Pt/Si] substrates by the heat treatment at 750 °C under atmospheric oxygen flow. Films with (110){sub c}-oriented SrRuO{sub 3} with perovskite structure were successfully deposited at 500 °C on a (101)-oriented PdO layer by an RF magnetron sputtering method due to their relatively small lattice mismatch. A (101)-oriented Sr(Zr{sub 0.8}Y{sub 0.2})O{sub 3-δ} (SZYO) film can be successfully prepared on (110){sub c}-oriented SrRuO{sub 3} and its proton conductivity is almost the same as that of (111){sub c}-oriented SZYO but slightly smaller than that of (111){sub c}-oriented one. As the conductivity is strongly affected by the film crystallinity, we can conclude that the newly fabricated (110){sub c}-oriented SZYO has almost the same crystallinity comparing to the films with other orientation. We have successfully demonstrated that the use of (101)PdO//(111)Pd double layer is a good candidate to grow {110}-one-axis-oriented perovskite thin films on Si substrates. - Highlights: • Self-aligned (101)-one-axis-oriented PdO layer were obtained on (111) Pd films • (110){sub c}SrRuO{sub 3} perovskite can be deposited successfully on (101) PdO//Pd double layer • (101){sub c}Sr(Zr{sub 0.8}Y{sub 0.2})O{sub 3–δ} perovskite is also prepared by using (110){sub c} SrRuO{sub 3} layer • (101)PdO//(111)Pd is quite effective for growing {110}-oriented perovskite films.

  20. Reaction kinetics of the double perovskite Sr{sub 2}FeMoO{sub 6} by gas–solid reactions

    Energy Technology Data Exchange (ETDEWEB)

    Valenzuela, J.L. [Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Ro, C.P. 58030 Morelia (Mexico); Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 Mexico D.F. (Mexico); Soto, T.E. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 Mexico D.F. (Mexico); Facultad de Ciencias Físico-Matemáticas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Río, C.P. 58030 Morelia (Mexico); Lemus, J. [Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Ro, C.P. 58030 Morelia (Mexico); Navarro, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 Mexico D.F. (Mexico); Morales, R., E-mail: rmorales@umich.mx [Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Ro, C.P. 58030 Morelia (Mexico)

    2014-12-15

    Double perovskite Sr{sub 2}FeMoO{sub 6} is characterized by its colossal magnetoresistance, however, its production route is not well established. Therefore, the objective of this work is to study the reaction kinetics involved in the formation of Sr{sub 2}FeMoO{sub 6}. Firstly, precursor phases Sr{sub 2}Fe{sub 2}O{sub 5} and SrMoO{sub 4} were synthesized by gas-solid reactions from starting reagents such as SrCO{sub 3}, Fe{sub 2}O{sub 3} y MoO{sub 3}. The thermogravimetric technique was employed to analyze the kinetics of formation of the double perovskite from the precursor phases given the optimized process variables. Microstructural characterization of the products obtained was performed by X-ray diffraction and Rietveld analysis. Results showed that the instability of SrFeO{sub 2.5} during the reduction stage led to a formation of a disordered double perovskite Sr{sub 2}Fe{sub 0.71}Mo{sub 1.29}O{sub 6}.

  1. Magnetic order and spin-orbit coupled Mott state in double perovskite (La$_{1-x}$Sr$_x$)$_2$CuIrO$_6$

    CERN Document Server

    Zhu, W K; Tong, W; Ling, L; Starr, M; Wang, J M; Yang, W C; Losovyj, Y; Zhou, H D; Wang, Y Q; Lee, P -H; Wang, Y -K; Lu, Chi-Ken; Zhang, S X

    2016-01-01

    Double-perovskite oxides that contain both 3d and 5d transition metal elements have attracted growing interest as they provide a model system to study the interplay of strong electron interaction and large spin-orbit coupling (SOC). Here, we report on experimental and theoretical studies of the magnetic and electronic properties of double-perovskites (La$_{1-x}$Sr$_x$)$_2$CuIrO$_6$ ($x$ = 0.0, 0.1, 0.2, and 0.3). The undoped La$_2$CuIrO$_6$ undergoes a magnetic phase transition from paramagnetism to antiferromagnetism at T$_N$ $\\sim$ 74 K and exhibits a weak ferromagnetic behavior below $T_C$ $\\sim$ 52 K. Two-dimensional magnetism that was observed in many other Cu-based double-perovskites is absent in our samples, which may be due to the existence of weak Cu-Ir exchange interaction. First-principle density-functional theory (DFT) calculations show canted antiferromagnetic (AFM) order in both Cu$^{2+}$ and Ir$^{4+}$ sublattices, which gives rise to weak ferromagnetism. Electronic structure calculations sugges...

  2. Electrical properties of double perovskite oxide Sr2LaSbO6: An impedance spectroscopic study

    Science.gov (United States)

    Dutta, Alo; Kumari, Premlata; Sinha, T. P.

    2015-09-01

    The Rietveld refinement of the room temperature x-ray diffraction pattern of double perovskite oxide, Sr2LaSbO6 (SLS) synthesized by the solid-state reaction technique shows monoclinic phase with P21/ n symmetry, which is substantiated by the Raman spectrum of the sample. The dielectric relaxation of SLS is investigated in the temperature range from 30°C to 300°C and in the frequency range from 50 Hz to 1 MHz. The Cole-Cole model is used to explain the dielectric relaxation of SLS. The most probable relaxation frequencies at various temperatures are found to obey the Arrhenius law with an activation energy of 0.36 eV, which indicates that the polaron hopping plays the main role in the dielectric relaxation of SLS. The complex impedance plane plots are analyzed by an electrical equivalent circuit consisting of a resistance and a constant phase element. The frequency dependent conductivity spectra obey the power law. [Figure not available: see fulltext.

  3. Structural and electrical characterizations of cerium (Ce3+)-doped double perovskite system Sr2NiMoO6- δ

    Science.gov (United States)

    Kumar, Pravin; Singh, Nitish Kumar; Sinha, A. S. K.; Singh, Prabhakar

    2016-09-01

    The double perovskite system Sr2- x Ce x NiMoO6- δ (SCNM) with 0.01 ≤ x ≤ 0.05 was synthesized by the citrate-nitrate auto-combustion synthesis route. Thermal studies were carried out by simultaneous differential scanning calorimetry and thermal gravimetry. Phase constitution was analyzed by powder X-ray diffraction (XRD). Rietveld refinement showed that the major phase exists in tetragonal form with space group I4/m. Microstructural investigations revealed the formation of uniform grains. The electrical conductivity studied by impedance spectroscopy in the temperature range 300-600 °C was found to follow a thermally activated process. The sample with x = 0.01 showed the highest conductivity with lowest activation energy. The electrical conductivity of the system was discussed in terms of identified impurity phases and charge density [{{{Mo}}_{{{{Mo}}^{6 +}}}^{5 +} {}^' ]. The variation of electrical conductivity with composition was explained on the basis of X-ray photoelectron spectroscopy and XRD studies.

  4. 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.

  5. Magnetoelectric Coupling, Ferroelectricity, and Magnetic Memory Effect in Double Perovskite La3Ni2NbO9.

    Science.gov (United States)

    Dey, K; Indra, A; De, D; Majumdar, S; Giri, S

    2016-05-25

    We observe ferroelectricity in an almost unexplored double perovskite La3Ni2NbO9. Ferroelectricity appears below ∼60 K, which is found to be correlated with the significant magnetostriction. A reasonably large value of spontaneous electric polarization is recorded to be ∼260 μC/m(2) at 10 K for E = 5 kV/cm, which decreases signifi- cantly upon application of a magnetic field (H), suggesting considerable magnetoelectric coupling. The dielectric permittivity is also influenced by H below the ferroelectric transition. The magnetodielectric response scales linearly to the squared magnetization, as described by the Ginzburg-Landau theory. Meticulous studies of static and dynamic features of dc magnetization and frequency dependent ac susceptibility results suggest spin-glass state below 29 K. Intrinsic magnetic memory effect is observed from zero-field cooled magnetization and isothermal remanent magnetization studies, also pointing spin-glass state below 29 K. Appearance of ferroelectricity together with a significant magnetoelectric coupling in absence of conventional long-range magnetic order is promising for searching new magnetoelectric materials.

  6. 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).

  7. Specific heat study of the iridium double perovskite Sr{sub 2}YIrO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Corredor, Laura T.; Manna, Kaustuv; Aslan Cansever, Gizem; Gass, Sebastian; Zimmermann, Andreas; Dey, Tushar; Blum, Christian; Maljuk, Andrey; Wurmehl, Sabine; Wolter, Anja; Buechner, Bernd [Leibniz Institute for Solid State and Materials Research Dresden, IFW Dresden (Germany)

    2016-07-01

    Recently, Mott insulators with a d{sup 4} electronic configuration were predicted to show superexchange-driven quantum phase transitions. Double perovskites R{sub 2}MM{sup '}O{sub 6} with M{sup '3+} ion, yielding a formal oxidation state of Ir{sup 5+} with 5d{sup 4} electronic configuration, may be candidates to verify or discard such transitions and its impact on the magnetic structure. According to the strong spin-orbit coupling J{sub eff} model, a non-magnetic ground state is expected. Such material is realized in Sr{sub 2}YIrO{sub 6}. Nevertheless, it is claimed that a strong non-cubic crystal field together with a ''intermediate-strength'' spin-orbit coupling, would lead to a different ground state configuration and to antiferromagnetic behavior with T{sub N} = 1.3 K. Also, anomalies in the specific heat were associated to this novel magnetism. In this work, we present magnetic and thermodynamic characterization of Sr{sub 2}YIrO{sub 6} single crystals. No long magnetic order was found. The magnetic contribution to the specific heat was calculated, finding a Schottky anomaly due to magnetic impurities. Further analysis suggests non-negligible spin correlations, which nonetheless, are not associated with long range magnetic ordering.

  8. Thermodynamic analysis of defect equilibration in double perovskites based on PrBaCo2O6-δ cobaltite

    Science.gov (United States)

    Politov, B. V.; Suntsov, A. Yu.; Leonidov, I. A.; Patrakeev, M. V.; Kozhevnikov, V. L.

    2017-05-01

    The double perovskite praseodymium cobaltite lightly doped with yttrium Pr0.9Y0.1BaCo2O6-δ (PYBCO) was obtained by combustion of organo-metallic precursors and shown to have a tetragonal structure with the crystalline lattice parameters a=b=3.903 and c=7.621 Å. The PYBCO composition occurs remarkably stable as show coulometric titration measurements of oxygen content (6-δ) in the oxygen pressure range 10-13-0.21 atm and at temperatures variations within 650-950°С. The experimental data were utilized in order to derive partial thermodynamic functions of oxygen that govern equilibration of defects in PYBCO. The oxygen partial enthalpy ΔHbarO (δ) and entropy ΔSbarO (δ) both experience strong changes near (6-δ)=5. The observed behavior of ΔHbarO (δ) and ΔSbarO (δ) is explained in frameworks of the defect formation model, which involves reactions of charge disproportionation of Co3+ cations, oxygen exchange with the gas phase and oxygen disordering over O2 and O3 structural positions. The verification of the suggested approach is carried out by comparison with independently obtained thermochemical data.

  9. Thermal Diffusivity of Ordered Double Perovskite A2FeMoO6 (A = Ca, Sr and Ba)

    Institute of Scientific and Technical Information of China (English)

    LIU Xiao-Jun; HUANG Qiao-Jian; NIU Dong-Lin; XU Sheng; ZHANG Shu-Yi

    2004-01-01

    @@ Thermal diffusivity has been investigated in ordered double perovskite Sr2FeMoO6 by means of transient surface grating technique in the temperature range of 300-450 K. The thermal diffusivity shows an appreciable decrease from 39mm2/s at 300 K to 37mm2/s at 360K in the ferromagnetic phase, and then steeply drops to 10mm2/s with further increasing temperature above the critical temperature Tc ~ 380 K. Such an abrupt decrease of the thermal diffusivity has been ascribed to the structural phase transition at Tc. We further investigate the lattice effect on the thermal diffusivity in A2FeMoO6 (A = Ca, Sr and Ba) by substitution of Ca2+ or Ba2+ ions for Sr2+ions at 300K. We find that the thermal diffusivity increases from 35mm2/s for A = Ca to 41 mm2/s for A = Ba.Considering the change of the Fe-O-Mo bond angle from 152.4° for A = Ca to 180° for A = Ba, the increased thermal diffusivity for Ba compound has been ascribed to the enhanced hybridization between transition-metal d and oxygen p states due to the larger Fe-O-Mo bond angle and hence the wider one-electron bandwidth W.

  10. Characterization of nonOhmic electrical transport in double perovskite compounds through bias scale and nonlinearity exponent

    Science.gov (United States)

    Chakraborty, D.; Nandi, U. N.; Jana, D.; Dasgupta, P.; Poddar, A.

    2017-01-01

    Scaling analysis of nonOhmic electrical transport in double perovskite (DP) compounds like La2NiMnO6 and Sr2Fe0.3Mn0.7MoO6 is presented over a wide range of electric bias and temperatures. It is shown that the voltage V0(T) at which conductance deviates from its Ohmic value Σ0(T) scales with Σ0(T) as V0(T) ∼Σ0(T) xT , xT being the onset exponent characterizing the onset of nonOhmic conduction. Interestingly, it was found that xT is negative and insensitive to the nature of conduction mechanism in DPs but is related to the characteristic temperature T0 and the mean hopping length Hm. We provide a scaling formalism in terms of the parameters V0(T) and xT in DPs for deeper understanding of the spintronic application and the electrode functioning in solid oxide fuel cells (SOFC). Inelastic multi-step tunneling is found to be the suitable mechanism of electronic transport characterized completely by these two parameters.

  11. 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).

  12. High-pressure synthesis of the double perovskite Sr{sub 2}FeMoO{sub 6}: increment of the cationic ordering and enhanced magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Retuerto, M; Martinez-Lope, M J; Garcia-Hernandez, M; Alonso, J A [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain)

    2009-05-06

    The double perovskite Sr{sub 2}FeMoO{sub 6} has been prepared in polycrystalline form by high-pressure methods, starting from a precursor developed via a citrate technique, containing an elevated degree of anti-site disordering. The application of high external pressure (2 GPa) to Sr{sub 2}FeMoO{sub 6} promotes the long distance Fe/Mo cationic order, due to the smaller lattice volume of the ordered sample. Both the disordered perovskite obtained at ambient pressure and the sample synthesized under high-pressure methods have been characterized by means of x-ray diffraction, neutron powder diffraction and magnetic measurements. The magnetic properties of the two oxides have been compared; the specimen prepared under high pressure not only presents an improved cationic ordering, but also displays a superior saturation magnetization and a sharpener ferromagnetic transition at a significantly high temperature of 430 K.

  13. Defect Tolerance to Intolerance in the Vacancy-Ordered Double Perovskite Semiconductors Cs2SnI6 and Cs2TeI6.

    Science.gov (United States)

    Maughan, Annalise E; Ganose, Alex M; Bordelon, Mitchell M; Miller, Elisa M; Scanlon, David O; Neilson, James R

    2016-07-13

    Vacancy-ordered double perovskites of the general formula A2BX6 are a family of perovskite derivatives composed of a face-centered lattice of nearly isolated [BX6] units with A-site cations occupying the cuboctahedral voids. Despite the presence of isolated octahedral units, the close-packed iodide lattice provides significant electronic dispersion, such that Cs2SnI6 has recently been explored for applications in photovoltaic devices. To elucidate the structure-property relationships of these materials, we have synthesized solid-solution Cs2Sn1-xTexI6. However, even though tellurium substitution increases electronic dispersion via closer I-I contact distances, the substitution experimentally yields insulating behavior from a significant decrease in carrier concentration and mobility. Density functional calculations of native defects in Cs2SnI6 reveal that iodine vacancies exhibit a low enthalpy of formation, and that the defect energy level is a shallow donor to the conduction band rendering the material tolerant to these defect states. The increased covalency of Te-I bonding renders the formation of iodine vacancy states unfavorable and is responsible for the reduction in conductivity upon Te substitution. Additionally, Cs2TeI6 is intolerant to the formation of these defects, because the defect level occurs deep within the band gap and thus localizes potential mobile charge carriers. In these vacancy-ordered double perovskites, the close-packed lattice of iodine provides significant electronic dispersion, while the interaction of the B- and X-site ions dictates the properties as they pertain to electronic structure and defect tolerance. This simplified perspective based on extensive experimental and theoretical analysis provides a platform from which to understand structure-property relationships in functional perovskite halides.

  14. Defect Tolerance to Intolerance in the Vacancy-Ordered Double Perovskite Semiconductors Cs2SnI6 and Cs2TeI6

    Energy Technology Data Exchange (ETDEWEB)

    Maughan, Annalise E.; Ganose, Alex M.; Bordelon, Mitchell M.; Miller, Elisa M.; Scanlon, David O.; Neilson, James R.

    2016-07-13

    Vacancy-ordered double perovskites of the general formula, A2BX6, are a family of perovskite derivatives composed of a face-centered lattice of nearly isolated [BX6] units with A-site cations occupying the cuboctahedral voids. Despite the presence of isolated octahedral units, the close-packed iodide lattice provides significant electronic dispersion, such that Cs2SnI6 has recently been explored for applications in photovoltaic devices. To elucidate the structure-property relationships of these materials, we have synthesized the solid solution Cs2Sn1-xTexI6. However, even though tellurium substitution increases electronic dispersion via closer I-I contact distances, the substitution experimentally yields insulating behavior from a significant decrease in carrier concentration and mobility. Density functional calculations of native defects in Cs2SnI6 reveal that iodine vacancies exhibit a low enthalpy of formation and the defect energy level is a shallow donor to the conduction band, rendering the material tolerant to these defect states. The increased covalency of Te-I bonding renders the formation of iodine vacancy states unfavorable, and is responsible for the reduction in conductivity upon Te substitution. Additionally, Cs2TeI6 is intolerant to the formation of these defects, as the defect level occurs deep within the band gap and thus localizes potential mobile charge carriers. In these vacancy-ordered double perovskites, the close-packed lattice of iodine provides significant electronic dispersion, while the interaction of the B- and X-site ions dictates the properties as they pertain to electronic structure and defect tolerance. This simplified perspective -- based on extensive experimental and theoretical analysis -- provides a platform from which to understand structure-property relationships in functional perovskite halides.

  15. 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.

  16. Equations of state and phase transitions in (Mg,Fe)SiO3 perovskite and post-perovskites, position of the phase boundary and its double crossing, by Quantum Monte Carlo

    Science.gov (United States)

    Cohen, R. E.; Lin, Y.

    2015-12-01

    We have performed quantum Monte Carlo (QMC) simulations and density functional theory calculations to study the equations of state and phase transitions in (Mg,Fe)SiO3 perovskite (Pv, bridgmanite) and post-perovskite (PPv) .[1] The ground-state energies were derived using quantum QMC simulations and the temperature-dependent Helmholtz free energies were calculated within the quasiharmonic approximation and density functional perturbation theory. Quantum Monte Carlo (QMC) within Diffusion Monte Carlo (DMC) is a stochastic numerical solution of Schrödinger's equation within the fixed many-particle nodes obtained, in our case, from a determinant of DFT orbitals. Agreement with experiments is improved over DFT alone. Furthermore, we obtain statistical error bounds on the results, rather than the unconstrained errors of DFT. The Pv-PPv phase boundary calculated from our QMC equations of state is also consistent with experiments, and better than previous DFT computations. In order to understand the H-phase reported in (Mg,Fe)SiO3 [2], we have performed evolutionary structure searching for FeSiO3.[3] We find a new structure type which may be consistent with the experimental observations, but is a lower pressure, less dense, phase. We have built a thermodynamic model for (Mg,Fe)SiO3 perovskite as a function of P and T, and will discuss implications for the location of the phase boundary in D'' and its double crossing [4]. This work is supported by NSF and the ERC Advanced Grant ToMCaT. [1] Y. Lin, R. E. Cohen, S. Stackhouse, K. P. Driver, B. Militzer, L. Shulenburger, and J. Kim, Phys. Rev. B 90 (2014). [2] L. Zhang et al., Science 344, 877 (2014). [3] R. E. Cohen and Y. Lin, Phys. Rev. B 90 (2014). [4] J.W. Hernlund, C. Thomas and P.J. Tackley, Nature 434, 882 (2005).

  17. Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6

    OpenAIRE

    Avijit Kumar Paul; Manfred Reehuis; Vadim Ksenofontov; Binghai Yan; Andreas Hoser; Többens, Daniel M.; Abdala, Paula M.; Peter Adler; Martin Jansen; Claudia Felser

    2013-01-01

    The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron - osmium layers along the tetragonal c-axis. Neutron powder diffraction experiments, 57Fe M\\"ossbauer spectra, and density-functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an examp...

  18. Magnetism, hysteresis cycle, and Ir-substitution doping of Sr2CrIrO6 double perovskite: A Monte Carlo simulation

    Science.gov (United States)

    El Rhazouani, O.; El Khatabi, M.; Zarhri, Z.; Slassi, A.; Benyoussef, A.; El Kenz, A.

    2016-12-01

    Iridium-based double perovskite (DP) Sr2CrIrO6 is expected to have the highest Curie temperatures (Tc) among all DPs and a high spin-polarization at room temperature, thanks to the more extended 5d orbitals of Ir, which makes it potential candidate in spintronic applications. Several publications have appeared in recent years documenting Ir-based double perovskites, but very few have explored the promising compound Sr2CrIrO6. In this paper, a Monte Carlo simulation has been carried out in the framework of Ising model to make an exploratory study of Sr2CrIrO6. Thermal magnetization, magnetic susceptibility, internal energy and specific heat have been studied. Effect of crystal field of Ir on the magnetic properties has been explored. Magnetic hysteresis cycle has been studied in relation to the exchange coupling values. Effects of Ir-substitution doping by Os "Sr2CrIrxOs1 - xO6" and by Re "Sr2CrIrxRe1 - xO6" (0.1 ≤ x ≤ 0.5) on the magnetic behavior have been investigated.

  19. Double perovskite oxides A{sub 2}FeMoO{sub 6-{delta}} (A=Ca, Sr and Ba) as catalysts for methane combustion

    Energy Technology Data Exchange (ETDEWEB)

    Falcon, H. [Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Instituto de Investigaciones en Fisicoquimica de Cordoba INFIQC, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba (Argentina); Barbero, J.A.; Araujo, G.; Fierro, J.L.G. [Instituto de Catalisis y Petroleoquimica, CSIC, Cantoblanco, 28049 Madrid (Spain); Casais, M.T.; Martinez-Lope, M.J.; Alonso, J.A. [Instituto de Ciencia de Materiales, CSIC, Cantoblanco, 28049 Madrid (Spain)

    2004-10-15

    Double perovskites of composition A{sub 2}FeMoO{sub 6-{delta}} (A, alkali earths) have been prepared by soft-chemistry procedures, followed by annealing under reducing conditions (H{sub 2}/N{sub 2} flow). These materials are half metallic ferromagnets, well known for their colossal magnetoresistance properties. The samples have been characterized by X-ray diffraction; temperature-programmed oxidation, specific surface measurements and XPS. The Sr compound, of tetragonal symmetry, exhibits a significant amount of oxygen vacancies, as assessed by TPO. The materials have been tested as catalysts for methane oxidation. At moderate temperatures, a significantly higher catalytic activity is observed for the Sr double perovskite, for which a 80% of conversion is reached at 800K; by contrast the Ca and Ba materials are found to display much poorer characteristics, hardly achieving 50% of conversion rate at 1000K. The much superior characteristics of Sr{sub 2}FeMoO{sub 6-{delta}} are believed to be related to the presence of oxygen vacancies in the crystal structure.

  20. High performance planar p-i-n perovskite solar cells with crown-ether functionalized fullerene and LiF as double cathode buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiaodong; Zhou, Yi, E-mail: yizhou@suda.edu.cn, E-mail: songbo@suda.edu.cn, E-mail: liyf@iccas.ac.cn; Song, Bo, E-mail: yizhou@suda.edu.cn, E-mail: songbo@suda.edu.cn, E-mail: liyf@iccas.ac.cn [Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu 215123 (China); Lei, Ming [Department of Chemistry, Zhejiang University, Hangzhou 310027 (China); Li, Yongfang, E-mail: yizhou@suda.edu.cn, E-mail: songbo@suda.edu.cn, E-mail: liyf@iccas.ac.cn [Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu 215123 (China); Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-08-10

    Double cathode buffer layers (CBLs) composed of fullerene derivative functionalized with a crown-ether end group in its side chain (denoted as PCBC) and a LiF layer were introduced between the PCBM acceptor layer and the top cathode in planar p-i-n perovskite solar cells (pero-SCs) based on CH{sub 3}NH{sub 3}PbI{sub 3−X}Cl{sub X}. The devices with the PCBC/LiF double CBLs showed significant improvements in power conversion efficiency (PCE) and long-term stability when compared to the device with LiF single CBL. Through optimizing the spin-coating speed of PCBC, a maximum PCE of 15.53% has been achieved, which is approximately 15% higher than that of the device with single LiF CBL. The remarkable improvement in PCE can be attributed to the formation of a better ohmic contact in the CBL between PCBC and LiF/Al electrode arising from the dipole moment of PCBC, leading to the enhanced fill factor and short-circuit current density (J{sub sc}). Besides the PCE, the long-term stability of the devices with PCBC interlayer is also superior to that of the device with LiF single CBL, which is due to the more effective protection for the perovskite/PCBM interface.

  1. 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.

  2. 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.

  3. Interplay between spin-orbit coupling and strong correlation effects: Comparison of the three osmate double perovskites Ba2A OsO6 (A =Na , Ca, Y)

    Science.gov (United States)

    Gangopadhyay, Shruba; Pickett, Warren E.

    2016-04-01

    High formal valence Os-based double perovskites are a focus of current interest because they display strong interplay of large spin-orbit coupling and strong electronic correlation. Here we present the electronic and magnetic characteristics of a sequence of three cubic Os based double perovskites Ba2A OsO6 (A =Na , Ca, Y), with formal valences of Os +7(d1) ,Os +6(d2) , and Os +5(d3) . For these first principles based calculations we apply an "exact exchange for correlated electrons" functional, with exact exchange applied in a hybrid fashion solely to the Os (5 d ) states. While Ba2NaOsO6 is a reported ferromagnetic Dirac-Mott insulator studied previously, the other two show antiferromagnetic ordering while all retain the undistorted cubic structure. For comparison purposes we have investigated only the ferromagnetic ordered phase. A metal-insulator transition is predicted to occur upon rotating the direction of magnetization in all three materials, reflecting the central role of spin-orbit coupling in these small gap osmates. Surprises arising from comparing formal charge states with the radial charge densities are discussed. Chemical shielding factors and orbital susceptibilities are provided for comparison with future nuclear magnetic resonance data.

  4. Influence of Ni/Mo ratio on structural and electrical properties of double perovskite system Sr2Ni1+ x Mo1- x O6- δ

    Science.gov (United States)

    Kumar, Pravin; Singh, Nitish Kumar; Singh, Rajesh Kumar; Singh, Prabhakar

    2015-11-01

    Technologically important double perovskite system Sr2Ni1+ x Mo1- x O6- δ with x = 0.00, 0.05, 0.10, and 0.15 was prepared by solution combustion method. The structural and the Rietveld analysis of compositions revealed the formation of double perovskite tetragonal phase Sr2NiMoO6 with space group I4/m as a major phase. SrMoO4 and NiO were also observed as minor phases. Microstructural studies depicted the formation of uniform grains for all the samples. The average grain size was found to lie between the ranges of 1-4 μm. XPS analysis of the synthesized compositions showed the decreasing ratio of Mo5+ to Mo6+ ions in the system with increasing Ni content, which played an important role in the conduction mechanism. The thermal expansion coefficient (TEC) of all compositions indicated that it is more compatible to the TEC of standard electrolytes. The electrical conductivity for all the compositions was studied using impedance spectroscopy in the temperature range 200-600 °C. Composition with x = 0.05 showed better electrical conductivity with good catalytic activity.

  5. Magnetoelastic coupling in Sr{sub 2}(Fe{sub 1-x}Cr{sub x})ReO{sub 6} double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Serrate, D [Instituto de Ciencia de Materiales de Aragon, CSIC and Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza (Spain); Teresa, J M De [Instituto de Ciencia de Materiales de Aragon, CSIC and Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza (Spain); Algarabel, P A [Instituto de Ciencia de Materiales de Aragon, CSIC and Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza (Spain); Marquina, C [Instituto de Ciencia de Materiales de Aragon, CSIC and Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza (Spain); Blasco, J [Instituto de Ciencia de Materiales de Aragon, CSIC and Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza (Spain); Ibarra, M R [Instituto de Ciencia de Materiales de Aragon, CSIC and Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza (Spain); Galibert, J [Laboratoire National des Champs Magnetiques Pulses, Universite Paul Sabatier, CNRS- UPS-INSA, UMR 5147, 143, Avenue de Rangueil, F-31400 Toulouse (France)

    2007-10-31

    We have investigated magnetoelastic coupling in Sr{sub 2}(Fe{sub 1-x}Cr{sub x})ReO{sub 6} polycrystalline double perovskites. The end compound, Sr{sub 2}CrReO{sub 6}, shows a high ferromagnetic transition temperature of 635 K and is thought to exhibit a nearly half-metallic conduction band. We probed the unexpected high orbital moment borne by the Re atom by means of volume and anisotropic magnetostriction measurements in magnetic fields up to 12 T. Our magnetostriction results can be explained by the existence of a large spin-orbit coupling which, in combination with crystal-field effects, produces a single-ion type magnetostrictive response. The Re orbital moment triggers a greatly enhanced magnetocrystalline anisotropy compared to other ferromagnetic double perovskites. From our magnetostriction data, the temperature dependence of the coercive field as a function of Cr-doping is obtained. We discovered that the coercive field increases as Fe is replaced with Cr, which is linked to a strong enhancement of the magnetic anisotropy. This suggests a close relationship between the Fe[Cr]-O-Re coupling and the magnetic anisotropy. We also analysed the impact of the Re orbital moment on the spin-dependent transport across Sr{sub 2}CrReO{sub 6} grain boundaries. The present work opens up the possible use of these compounds for magnetostrictive applications in a wide temperature and magnetic field range.

  6. 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.

  7. Magnetic entropy change and critical exponents in double perovskite Y{sub 2}NiMnO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, G. [School of Physical Sciences, Jawaharlal Nehru University, New Delhi-110067 (India); Tripathi, T.S. [Inter-University Accelerator Centre, New Delhi-110067 (India); Saha, J. [School of Physical Sciences, Jawaharlal Nehru University, New Delhi-110067 (India); Patnaik, S., E-mail: spatnaik@mail.jnu.ac.in [School of Physical Sciences, Jawaharlal Nehru University, New Delhi-110067 (India)

    2014-11-15

    We report the magnetic entropy change (ΔS{sub M}) and the critical exponents in the double perovskite manganite Y{sub 2}NiMnO{sub 6} with a ferromagnetic to paramagnetic transition T{sub C}∼85K. For a magnetic field change ΔH=80kOe, a maximum magnetic entropy change ΔS{sub M}=−6.57J/kgK is recorded around T{sub C}. The critical exponents β=0.363±0.05 and γ=1.331±0.09 obtained from power law fitting to spontaneous magnetization M{sub S}(T) and the inverse initial susceptibility χ{sub 0}{sup −1}(T) satisfy well to values derived for a 3D-Heisenberg ferromagnet. The critical exponent δ=4.761±0.129 is determined from the isothermal magnetization at T{sub C}. The scaling exponents corresponding to second order phase transition are consistent with the exponents from Kouvel–Fisher analysis and satisfy Widom's scaling relation δ=1+(γ/β). Additionally, they also satisfy the single scaling equation M(H,ϵ)=ϵ{sup β}f±(H/ϵ{sup β+γ}) according to which the magnetization-field-temperature data around T{sub C} should collapse into two curves for temperatures below and above T{sub C}. - Highlights: • The magneto-caloric (MC) effect and the critical exponent analysis in Y{sub 2}NiMnO{sub 6} are studied. • Methods such as Kouvel–Fisher, Widom's and Mean-Field scaling are used. • The magnetic ground state in Y{sub 2}NiMnO{sub 6} is based on isotropic 3D Heisenberg model. • The large MC effect can be utilized towards magnetic refrigeration around 77 K. • The nearest neighbor interaction in Y{sub 2}NiMnO{sub 6} rules out ferroelectricity.

  8. Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells.

    Science.gov (United States)

    Jacobsson, T Jesper; Correa-Baena, Juan-Pablo; Halvani Anaraki, Elham; Philippe, Bertrand; Stranks, Samuel D; Bouduban, Marine E F; Tress, Wolfgang; Schenk, Kurt; Teuscher, Joël; Moser, Jacques-E; Rensmo, Håkan; Hagfeldt, Anders

    2016-08-17

    Lead halide perovskites have over the past few years attracted considerable interest as photo absorbers in PV applications with record efficiencies now reaching 22%. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-vis, electroluminescence (EL), photoluminescence (PL), and confocal PL mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices were over 18% efficient, and had in line with previous results a small amount of excess PbI2. For the PbI2-deficient samples, the photocurrent dropped, which could be attributed to accumulation of organic species at the grain boundaries, low charge carrier mobility, and decreased electron injection into the TiO2. The PbI2-deficient compositions did, however, also have advantages. The record Voc was as high as 1.20 V and was found in PbI2-deficient samples. This was correlated with high crystal quality, longer charge carrier lifetimes, and high PL yields and was rationalized as a consequence of the dynamics of the perovskite formation. We further found the ion migration to be obstructed in the PbI2-deficient samples, which decreased the JV hysteresis and increased the photostability. PbI2-deficient synthesis conditions can thus be used to deposit perovskites with excellent crystal quality but with the downside of grain boundaries enriched in organic species, which act as a barrier toward

  9. 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...

  10. Poling-Written Ferroelectricity in Bulk Multiferroic Double-Perovskite BiFe0.5Mn0.5O3.

    Science.gov (United States)

    Delmonte, Davide; Mezzadri, Francesco; Gilioli, Edmondo; Solzi, Massimo; Calestani, Gianluca; Bolzoni, Fulvio; Cabassi, Riccardo

    2016-06-20

    We present a comprehensive study of the electrical properties of bulk polycrystalline BiFe0.5Mn0.5O3, a double perovskite synthesized in high-pressure and high-temperature conditions. BiFe0.5Mn0.5O3 shows an antiferromagnetic character with TN = 288 K overlapped with an intrinsic antiferroelectricity due to the Bi(3+) stereochemical effect. Beyond this, the observation of a semiconductor-insulator transition at TP ≈ 140 K allows one to define three distinct temperature ranges with completely different electrical properties. For T > TN, electric transport follows an ordinary thermally activated Arrhenius behavior; the system behaves as a paramagnetic semiconductor. At intermediate temperatures (TP perovskite. Finally, for T < TP, the material becomes a dielectric insulator, showing very unusual poling-induced soft ferroelectricity with high saturation polarization, similar to the parent compound BiFeO3. Under external electric poling, the system irreversibly evolves from antiferroelectric to polar arrangement.

  11. 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.

  12. Increasing the Curie temperature of Ca{sub 2}FeMoO{sub 6} double perovskite by introducing near-neighbour antiferromagnetic interactions

    Energy Technology Data Exchange (ETDEWEB)

    Rubi, D [Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, 08193, Bellaterra (Spain); Frontera, C [Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, 08193, Bellaterra (Spain); Roig, A [Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, 08193, Bellaterra (Spain); Nogues, J [Institut Catala de Recerca i Estudis Avancats (ICREA), 08193, Bellaterra, Catalunya (Spain); Munoz, J S [Departament de Fisica, Universitat Autonoma de Barcelona, 08193, Bellaterra, Catalunya (Spain); Fontcuberta, J [Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, 08193, Bellaterra (Spain)

    2005-12-21

    We report on the magnetic, magnetotransport and structural characterization of (Ca{sub 1-y}Nd{sub y}){sub 2}Fe{sub 1+x}Mo{sub 1-x}O{sub 6} (x<0.5) ferromagnetic double perovskites. It is found that the presence of an excess (x>0) of Fe ions in the metallic sublattice produces a remarkable increase, by more than 90 K, of the Curie temperature. Moessbauer spectroscopy data indicate a reinforcement of the magnetic interactions. We argue that this dramatic enhancement of the ferromagnetic order is due to the strong antiferromagnetic superexchange coupling between near-neighbour Fe-Fe occupying regular and antisite positions in the structure. Moreover, the results indicate that the excess of magnetic ions (Fe) is essential to overcome the dilution effects caused by antisite defects.

  13. 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.

  14. Exotic magnetism on the quasi-fcc lattices of the d3 double Perovskites La2NaB'O6 (B'=Ru, Os).

    Science.gov (United States)

    Aczel, A A; Baker, P J; Bugaris, D E; Yeon, J; Zur Loye, H-C; Guidi, T; Adroja, D T

    2014-03-21

    We find evidence for long-range and short-range (ζ=70 Å at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (fcc) lattices of the monoclinic double perovskites La2NaRuO6 and La2NaOsO6, respectively. Incommensurate magnetic order on the fcc lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbor and next nearest neighbor exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap Δ ∼ 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally coordinated 3d3 systems, so the large gap observed for La2NaRuO6 may result from the significantly enhanced value of spin-orbit coupling in this 4d(3) material.

  15. Atomic ordering and magnetic properties of non-stoichiometric double-perovskite Sr sub 2 Fe sub x Mo sub 2 sub - sub x O sub 6

    CERN Document Server

    Liu, G Y; Feng, X M; Yang, H F; Ouyang, Z W; Liu, W F; Liang, J K

    2003-01-01

    The crystal structure and magnetic properties of a new series of ordered double-perovskite oxides Sr sub 2 Fe sub x Mo sub 2 sub - sub x O sub 6 (0.8 <= x <= 1.5) have been studied. The crystal structure changes from a tetragonal I4/mmm lattice to a cubic Fm3-bar m lattice around x = 1.2. The degree of ordering in Sr sub 2 Fe sub x Mo sub 2 sub - sub x O sub 6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95. The saturated magnetization increases from x = 0.8 to 0.95 and then decreases from x = 0.95 to 1.5. The Curie temperature exhibits an abrupt drop around x = 1.2, where the structural transition takes place. These complex behaviours are strongly correlated to antisite defect concentration in the compounds.

  16. Single Crystal Growth of Multiferroic Double Perovskites: Yb2CoMnO6 and Lu2CoMnO6

    Directory of Open Access Journals (Sweden)

    Hwan Young Choi

    2017-02-01

    Full Text Available We report on the growth of multiferroic Yb2CoMnO6 and Lu2CoMnO6 single crystals which were synthesized by the flux method with Bi2O3. Yb2CoMnO6 and Lu2CoMnO6 crystallize in a double-perovskite structure with a monoclinic P21/n space group. Bulk magnetization measurements of both specimens revealed strong magnetic anisotropy and metamagnetic transitions. We observed a dielectric anomaly perpendicular to the c axis. The strongly coupled magnetic and dielectric states resulted in the variation of both the dielectric constant and the magnetization by applying magnetic fields, offering an efficient approach to accomplish intrinsically coupled functionality in multiferroics.

  17. XMCD study of Ir based double perovskite La{sub 2-x}Sr{sub x}CoIrO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Kolchyns' ka, Anastasiya; Komissinskiy, Philipp; Alff, Lambert [Institute of Materials Science, Technische Universitaet, Darmstadt (Germany); Mikhailova, Daria; Narayanan, Naren [Institute of Materials Science, Technische Universitaet, Darmstadt (Germany); Institute of Complex Materials, IFW Dresden (Germany); Ehrenberg, Helmut [Institute of Complex Materials, IFW Dresden (Germany); Wilhelm, Fabrice [ESRF, ID-12, Grenoble (France)

    2011-07-01

    Double perovskites La{sub 2-x}Sr{sub x}CoIrO{sub 6} with 0{<=}x{<=}2 were studied by X-ray Magnetic Circular Dichroism (XMCD). Neutron scattering has revealed a canted antiferromagnetic order of the Co ions. Only by XMCD the magnetic moments within the Ir sublattice could be determined: For x=0 we observe a magnetization on the Ir site of about 0.2 {mu}{sub B} which is coupled antiferromagnetically to the residual Co magnetization. This indicates a kinetically driven induced magnetism at the Ir site similar as in compounds such as Sr{sub 2}CrOsO{sub 6}. With increasing Sr content x, the induced magnetic moment decreases and finally vanishes for x=2.

  18. Physical properties and crystal structure analysis of double-perovskite NdBaMn2O6 by using single crystals

    Science.gov (United States)

    Yamada, S.; Sagayama, H.; Higuchi, K.; Sasaki, T.; Sugimoto, K.; Arima, T.

    2017-01-01

    We have succeeded in growing large single crystals of double-perovskite NdBaMn2O6 with the c axis aligned, and carried out a crystal structure analysis and measurements of resistivity and magnetization. A first-order metal-insulator transition at TM I≃290 K is accompanied by a large jump of magnetization and lattice constants. The distortion of MnO6 octahedra is consistent with a ferroic orbital order of x2-y2 type, although other orbital orders cannot be completely discarded. Néel temperature TN is determined to be 235 K, which is fairly lower than TM I, on the basis of the onset of a large magnetic anisotropy. Another structural phase transition from tetragonal to orthorhombic is found at 370 K, which arises from staggered tilting of MnO6 octahedra and little affects the transport and magnetic properties.

  19. Bandgap engineering of lead-free double perovskite Cs{sub 2}AgBiBr{sub 6} through trivalent metal alloying

    Energy Technology Data Exchange (ETDEWEB)

    Du, Ke-zhao; Mitzi, David B. [Department of Mechanical Engineering and Materials Science, and Department of Chemistry, Duke University, Durham, NC (United States); Meng, Weiwei; Wang, Xiaoming; Yan, Yanfa [Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, OH (United States)

    2017-07-03

    The double perovskite family, A{sub 2}M{sup I}M{sup III}X{sub 6}, is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH{sub 3}NH{sub 3}PbI{sub 3}. Given the generally large indirect band gap within most known double perovskites, band-gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs{sub 2}AgBiBr{sub 6} as host, band-gap engineering through alloying of In{sup III}/Sb{sup III} has been demonstrated in the current work. Cs{sub 2}Ag(Bi{sub 1-x}M{sub x})Br{sub 6} (M=In, Sb) accommodates up to 75 % In{sup III} with increased band gap, and up to 37.5 % Sb{sup III} with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs{sub 2}Ag(Bi{sub 0.625}Sb{sub 0.375})Br{sub 6}. Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. 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.

  1. Room temperature relaxor ferroelectricity and spin glass behavior in Sr{sub 2}FeTiO{sub 6} double perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Neenu Lekshmi, P.; Savitha Pillai, S. [Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology NIIST, CSIR, Trivandrum 695 019 (India); Suresh, K.G. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400 076 (India); Santhosh, P.N. [Department of Physics, Indian Institute of Technology Madras, Chennai 600 036 (India); Varma, Manoj Raama, E-mail: manojraamavarma@yahoo.co.uk [Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology NIIST, CSIR, Trivandrum 695 019 (India)

    2012-05-05

    Highlights: Black-Right-Pointing-Pointer Studied the structure, dielectric and magnetic properties of Sr{sub 2}FeTiO{sub 6} complex double perovskite. Black-Right-Pointing-Pointer The thermal evolution of the lattice parameter and volume shows no structural phase transition. Black-Right-Pointing-Pointer Dielectric data analysis shows a diffuse phase transition characteristics. Black-Right-Pointing-Pointer The diffusion-assisted small-polaron hopping conduction evidences an intermediate-valence state and semiconductor like behaviour. Black-Right-Pointing-Pointer The magnetic characterisation exhibits a non-metallic spin-glass-like state below 16 K. - Abstract: The structure, dielectric and magnetic properties of complex Sr{sub 2}FeTiO{sub 6} double perovskite have been investigated. Reitveld analysis of X-ray powder diffraction pattern reveals that the material is stabilized in a cubic perovskite phase with Pm3{sup Macron }m space group without the B-site cations ordering. The temperature evolution of crystal structural studies indicates the absence of structural changes with temperature. The scanning electron micrograph exhibits heterogeneous grain distribution with average grain size of 1-7.5 {mu}m. The bond valence sum calculations and diffusion-assisted small-polaron hopping conduction mechanism confirm the mixed valence state of Fe/Ti ions. Dielectric spectra show a broad dielectric anomaly coupled with a shift in dielectric maxima towards higher temperature with frequency, exhibiting a typical relaxor ferroelectric behavior. The relaxor behavior has been quantitatively characterized based on the phenomenological parameters (T{sub m}, T{sub B}, {gamma}, {Delta}T{sub relax}). The agreement of dielectric relaxation with non-linear Vogel Fulcher relation indicates that the system is indeed a relaxor exhibiting glassy characteristics. The transport studies show a semiconductor like behavior and a negligible magnetoresistance. Furthermore, the magnetic

  2. 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.

  3. Origin of metallic behavior in NiCo2O4 ferrimagnet

    Science.gov (United States)

    Bitla, Yugandhar; Chin, Yi-Ying; Lin, Jheng-Cyuan; van, Chien Nguyen; Liu, Ruirui; Zhu, Yuanmin; Liu, Heng-Jui; Zhan, Qian; Lin, Hong-Ji; Chen, Chien-Te; Chu, Ying-Hao; He, Qing

    2015-10-01

    Predicting and understanding the cation distribution in spinels has been one of the most interesting problems in materials science. The present work investigates the effect of cation redistribution on the structural, electrical, optical and magnetic properties of mixed-valent inverse spinel NiCo2O4(NCO) thin films. It is observed that the films grown at low temperatures (T  400 °C) are insulators with lower ferrimagnetic-paramagnetic phase transition temperature. So far, n-type Fe3O4 has been used as a conducting layer for the spinel thin films based devices and the search for a p-type counterpart still remains elusive. The inherent coexistence and coupling of ferrimagnetic order and the metallic nature in p-type NCO makes it a promising candidate for spintronic devices. Detailed X-ray Absorption and X-ray Magnetic Circular Dichroism studies revealed a strong correlation between the mixed-valent cation distribution and the resulting ferrimagnetic-metallic/insulating behavior. Our study clearly demonstrates that it is the concentration of Ni3+ions and the Ni3+-O2-Ni2+ double exchange interaction that is crucial in dictating the metallic behavior in NCO ferrimagnet. The metal-insulator and the associated magnetic order-disorder transitions can be tuned by the degree of cation site disorder via growth conditions.

  4. Dielectric relaxation and electrical conduction mechanism in A2HoSbO6 (A=Ba, Sr, Ca) Double Perovskite Ceramics: An impedance spectroscopic analysis

    Science.gov (United States)

    Halder, Saswata; Dutta, Alo; Sinha, T. P.

    2017-03-01

    The AC electrical properties of polycrystalline double perovskite oxides A2HoSbO6 (A=Ba, Sr, Ca; AHS) synthesized by solid state reaction technique has been explored by using impedance spectroscopic studies. The Rietveld refinement of the room temperature X-ray diffraction data show that Ba2HoSbO6 (BHS) has cubic phase and Sr2HoSbO6 (SHS) and Ca2HoSbO6 (CHS) crystallize in monoclinic phase. The samples show significant frequency dispersion in their dielectric properties. The polydispersive nature of the relaxation mechanism is explained by the modified Cole-Cole model. The scaling behavior of dielectric loss indicate the temperature independence of the relaxation mechanism. The magnitude of the activation energy indicates that the hopping mechanism is responsible for carrier transport in AHS. The frequency dependent conductivity spectra follow the double power law. Impedance spectroscopic data presented in the Nyquist plot (Z" versus Z‧) are used to identify an equivalent circuit along with to know the grain, grain boundary and interface contributions. The constant phase element (CPE) is used to analyze the experimental response of BHS, SHS and CHS comprehending the contribution of different microstructural features to the conduction process. The temperature dependent electrical conductivity shows a semiconducting behavior.

  5. Mapping chemical/structural order in double perovskite Sr2-xGdxMnTiO6 by atomic resolution electron microscopy

    Science.gov (United States)

    Alvarez, Inmaculada; Biskup, Neven; Lopez, Maria; Garcia-Hernandez, Mar; Veiga, Luisa; Varela, Maria; UCM Collaboration; ORNL Collaboration; CSIC Collaboration

    2013-03-01

    We report on visualizing the chemical and structural order of double perovskite Sr2-xGdxMnTiO6. The antisite disorder of Mn and Ti is detected even at atomic scale at all x, resulting in Mn-rich and Ti-rich regions. For x ?0.75, the majority of manganese ions are in Mn3+ state and are centered in Jahn-Teller distorted MnO6octahedra. The Fourier transformation of atomic resolution images along the [110] zone axis reveals a superstructure that corresponds to the tilting of oxygen octahedra and that doubles the unit cell along [001]c. This superstructure is spatially inhomogeneous and coincides with the regions where B-site ion (Mn/Ti) is displaced along the [110] direction. We discuss these findings in the frame of possible local ferroelectricity and in the light of strong electroresistance observed in Sr1.25Gd0.75MnTiO6. Research at ORNL supported by the U.S. DOE-BES, Materials Sciences and Engineering Division, and also by ORNL's ShaRE User Program (sponsored by DOE-BES). Research at UCM supported by the ERC Starting Investigator Award and MAT2010-20117.

  6. 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.)

  7. High-pressure synthesis, crystal structures, and magnetic properties of 5d double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6.

    Science.gov (United States)

    Yuan, Yahua; Feng, Hai L; Ghimire, Madhav Prasad; Matsushita, Yoshitaka; Tsujimoto, Yoshihiro; He, Jianfeng; Tanaka, Masahiko; Katsuya, Yoshio; Yamaura, Kazunari

    2015-04-06

    Double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 have been synthesized under high-pressure and high-temperature conditions (6 GPa and 1500 °C). Their crystal structures and magnetic properties were studied by a synchrotron X-ray diffraction experiment and by magnetic susceptibility, specific heat, isothermal magnetization, and electrical resistivity measurements. Ca2MgOsO6 and Sr2MgOsO6 crystallized in monoclinic (P21/n) and tetragonal (I4/m) double-perovskite structures, respectively; the degree of order of the Os and Mg arrangement was 96% or higher. Although Ca2MgOsO6 and Sr2MgOsO6 are isoelectric, a magnetic-glass transition was observed for Ca2MgOsO6 at 19 K, while Sr2MgOsO6 showed an antiferromagnetic transition at 110 K. The antiferromagnetic-transition temperature is the highest in the family. A first-principles density functional approach revealed that Ca2MgOsO6 and Sr2MgOsO6 are likely to be antiferromagnetic Mott insulators in which the band gaps open, with Coulomb correlations of ∼1.8-3.0 eV. These compounds offer a better opportunity for the clarification of the basis of 5d magnetic sublattices, with regard to the possible use of perovskite-related oxides in multifunctional devices. The double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 are likely to be Mott insulators with a magnetic-glass (MG) transition at ∼19 K and an antiferromagnetic (AFM) transition at ∼110 K, respectively. This AFM transition temperature is the highest among double-perovskite oxides containing single magnetic sublattices. Thus, these compounds offer valuable opportunities for studying the magnetic nature of 5d perovskite-related oxides, with regard to their possible use in multifunctional devices.

  8. 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.

  9. Green's function approach of an anisotropic Heisenberg ferrimagnetic system

    Energy Technology Data Exchange (ETDEWEB)

    Mert, Gülistan, E-mail: gmert@selcuk.edu.tr

    2013-12-15

    We have investigated the influence of the exchange anisotropy parameter on the magnetization, critical and compensation temperatures and susceptibility of the anisotropic Heisenberg ferrimagnetic system with the single-ion anisotropy under an external magnetic field using the double-time temperature-dependent Green's function theory. In order to decouple the higher order Green's functions, Anderson-Callen's decoupling and random phase approximations have been used. This model is useful for understanding the temperature dependence of total magnetization of Lithium-chromium ferrites Li{sub 0.5}Fe{sub 1.25}Cr{sub 1.25}O{sub 4} for which negative magnetization is characteristic. We observe that the critical temperature increases when the exchange anisotropy increases. When the system is under an external magnetic field, one obtains the first-order phase transition where the magnetization jumps for all the values of the exchange anisotropy parameters. - Highlights: • We investigated the magnetic properties of an anisotropic Heisenberg ferrimagnetic system on a square lattice. • We used the double-time temperature-dependent Green's function technique. • We discussed the influence of the exchange anisotropy parameter on the magnetization, critical and compensation temperatures and susceptibility of the anisotropic Heisenberg ferrimagnetic system. • We observed that the critical temperature increases when the exchange anisotropy increases.

  10. Magnetic and Electrical Transport Properties of Double Perovskite Sr2FeMoO6 Prepared by Sol-Gel Method

    Directory of Open Access Journals (Sweden)

    Yong-Qing Zhai

    2011-01-01

    Full Text Available With activated carbon for reducing agent, the sol-gel method was used to prepare the giant magnetoresistance materials Sr2FeMoO6, which is the double Perovskite oxide. The structure, morphology, magnetic and electrical transport properties were investigated respectively by x-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The as-synthesized sample is Sr2FeMoO6 with tetragonal crystal structure and I4/mmm space group and unit cell parameter is a = 5.580Å, c = 7.882Å. The primary particles are spherical in shape and the grain size is below 100 nm. The curie temperature is above room temperature and the saturation magnetization is 13.321 A·m2/kg under 1.0 T at room temperature. The sample exhibit typical semiconductor behavior and the conductive mechanism can be described by small polaron variable range hopping model. The room temperature magnetoresistance of the sample under 1.0 T field is up to -10.02%. Moreover, it is found the dosage of citric acid and the amount of reducing agent has great effect on the phase structure and magnetic properties of the samples.

  11. Effects of electron doping on the structure and magnetic properties in Ca{sub 2-x}Ce{sub x}FeMoO{sub 6} double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Xi Li, E-mail: xili@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, 222, South Tianshui Road, Lanzhou 730000 (China); Qiao Wen; Yan Shiming; Peng Caidao; Shi Xiaoning; Ge Shihui [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, 222, South Tianshui Road, Lanzhou 730000 (China); Du Jun; Ge Jianjian [National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China)

    2010-06-15

    A sol-gel method has been used to prepare a series of polycrystalline Ca{sub 2-x}Ce{sub x}FeMoO{sub 6} (x = 0-0.4) double perovskites. Rietveld refinement of X-ray diffraction data indicates that although cell parameters increase slightly, the symmetry of the crystalline structure is preserved upon Ce doping. The partial substitution of Ce{sup 3+} for Ca{sup 2+} reduces the saturation magnetization, however it considerably enhances the Curie temperature (T{sub C}) from 365 K for x = 0 to 393 K for x = 0.4. Transport measurement shows that Ca{sub 2-x}Ce{sub x}FeMoO{sub 6} exhibits metallic behavior, and the resistivity of Ca{sub 2-x}Ce{sub x}FeMoO{sub 6} increases first, and then decreases with the increasing of x. The behavior of the increasing of T{sub C} and the decreasing of resistivity upon Ce doping was explained by the electron doping effects.

  12. Surface structure and catalytic performance of Sr-doped La2NiAlO6 double perovskite catalysts for methane combustion

    Institute of Scientific and Technical Information of China (English)

    胡瑞生; 白雅琴; 杜航宇; 张慧敏; 杜燕飞; 张俊阁; 周啟华

    2015-01-01

    A species of novel Sr-doped rare earth double perovskite catalysts (La2–xSrxNiAlO6,x=0, 0.1) were prepared by the sol-gel method using citric acid as a complexing agent and calcined at 1100 ºC for 3 h, then investigated for methane catalytic combustion. The as-prepared catalysts were characterized by X-ray diffraction patterns (XRD), H2-temperature-programmed reduction (H2-TPR), specific surface area (BET), magnetic property measurement technology (M-H), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Experimental results showed that La1.9Sr0.1NiAlO6 catalyst exhibited significantly improved cata-lytic activity (T10=378.7 ºC,T90=602.9 ºC) compared with that of La2NiAlO6, whoseT10 decreased by 74.4 ºC andT90 decreased by 66.8 ºC, respectively. The excellent catalytic activity of La1.9Sr0.1NiAlO6caused by Sr-doping could be explained by the larger num-ber of adsorption oxygen on the catalyst surface, which could be proven by XPS analysis.

  13. First-principles study of the double perovskites Sr$_2$XOsO$_6$ (X = Li, Na, Ca) for spintronics applications

    Indian Academy of Sciences (India)

    M FAIZAN; G MURTAZA; S H KHAN; A KHAN; ASIF MEHMOOD; R KHENATA; S HUSSAIN

    2016-10-01

    We investigated double perovskite compounds of the form Sr$_2$XOsO$_6$ (X = Li, Na, Ca) using the fullpotential linearized augmented plane wave (FP-LAPW) method. For the exchange-correlation energy, Wu andCohen generalized gradient approximation (WC-GGA), Perdew, Burke and Ernzerhof GGA (PBE-GGA), Engel and Vosko GGA (EV-GGA), and GGA plus Hubbard U-parameter (GGA $+$ U) were used. The calculated structuralparameters are in good agreement with the existing experimental results. Calculation of different elastic constants and elastic moduli reveals that these compounds are elastically stable and possess ductile nature. The GGA $+$ Uapproach yields quite accurate results of the bandgap as compared with the simple GGA schemes. The density of states plot shows that Sr-4d, Os-5d and O-2p states predominantly contribute to the conduction and valence bands.Further, our results regarding to the magnetic properties of these compounds reveal their ferromagnetic nature. In addition, these compounds seem to possess half-metallic properties, making them useful candidates for applicationsin spintronics devices.

  14. Structure and thermoelectric properties of Ca2−xSrxFeMoO6 (0 ≤ x ≤ 0.3) double-perovskite oxides

    DEFF Research Database (Denmark)

    Sugahara, Tohru; Van Nong, Ngo; Ohtaki, Michitaka

    2012-01-01

    The thermoelectric properties of double perovskite-type oxides Ca2FeMoO6 are investigated in terms of Sr substitution at the A site of the oxides. The electrical conductivity, , of Ca2−xSrxFeMoO6 (0 ≤ x ≤ 0.3) showed a metallic behavior, decreasing monotonically from ca. 103 S cm−1 at room.......3 abruptly increase at around 1000 K. The Rietveld refinement of the XRD patterns of the oxides indicated that the anti-site defects in the oxides decreased with increasing Sr concentration. The power factor, S2, of the oxides largely increased with increasing temperature; the S2 value of Ca2FeMoO6 was ca. 0...... temperature to ca. 102 S cm−1 at 1250 K. At room temperature, although the values of the oxides increased with increasing substitution level, x, the values maintained almost the same values at high temperature range of 1000–1250 K. The absolute values of the Seebeck coefficient, S, for the samples at x

  15. 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.

  16. Structural distortions, orbital ordering and physical properties of double perovskite R2CoMnO6 calculated by first-principles

    Science.gov (United States)

    Zhou, Hai Yang; Chen, Xiang Ming

    2017-04-01

    The structural distortions, orbital ordering, magnetic and electronic properties of double perovskite R2CoMnO6 (R  =  rare-earth element) have been systematically calculated by first-principles. Structural distortions, including Co–O and Mn–O bond length splitting, the antiferroelectric motions of R ions, the tilting of octahedral (the resulted Co–O–Mn bond angle) are obviously affected by the rare-earth ions’ radius. The bond length splitting behavior of Co–O and Mn–O are rather different because of the Jahn–Teller active ion Co2+ and the Jahn–Teller nonactive ion Mn4+. Taking Gd2CoMnO6 as an example, the t 2g orbitals of Co ions are predicted to be orbital ordered. That is, the spin down channel of d xz orbital for one Co ion and d yz orbital for another Co ion are basically vacant. Finally, the physical properties, including the magnetic Curie temperature and electronic band gap of R2CoMnO6 are almost linear dependent on the average value of cos2 θ (θ is the Co–O–Mn exchange-angle).

  17. Photophysical electronic structure of double-perovskites A{sub 2}GdTaO{sub 6} (A = Ba and Sr)

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Binita, E-mail: ghosh.binita@gmail.com [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India); Dutta, Alo [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India); Shannigrahi, Santiranjan [Institute of Materials Research and Engineering, Agency for Science Technology and Research, 3 Research Link, Singapore 117602 (Singapore); Sinha, T.P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India)

    2015-11-05

    X-ray photoemission spectroscopy (XPS) measurements of double perovskite oxides, Ba{sub 2}GdTaO{sub 6} and Sr{sub 2}GdTaO{sub 6} are performed in the energy window of 0–1300 eV. Density functional theory calculations are initiated with the Vienna ab initio Simulation Package to understand the electronic structure of the systems. The calculated DOS has been compared with the experimental valence band XPS spectra. It has been observed that the Ta-5d and O-2p states are hybridized in the valence band. The chemical shifts of these compounds suggest a mixed ionic and covalent character of the bonds, which has been used to explain the electrical conduction mechanism of the systems. The calculated ratio of the spin-orbit interaction energy for Ba 3d and 4d states matches well with the observed experimental results. - Highlights: • DFT calculations of Ba{sub 2}GdTaO{sub 6} and Sr{sub 2}GdTaO{sub 6} have been performed with VASP. • XPS measurements are performed in the energy window of 0–1300 eV. • The calculated DOS has been compared with the valence band XPS spectra. • Chemical shifts from XPS spectra have been used to explain the conduction mechanism.

  18. Enhanced photoelectrical performance of dye-sensitized solar cells with double-layer TiO2 on perovskite SrTiO3 substrate

    Science.gov (United States)

    Liu, Qiuhong; Sun, Qiong; Zhang, Min; Li, Yang; Zhao, Mei; Dong, Lifeng

    2016-04-01

    In this research, perovskite SrTiO3 particles are synthesized by a hydrothermal method, and TiO2 with a double-layer structure is grown on the SrTiO3 surface by a hydrolysis-condensation process. Structural characterizations reveal that TiO2 comprises of two phases: anatase film at the bottom and single-crystal rutile nanorods grown along the [110] direction on top. The TiO2-SrTiO3 composite film is investigated as photoanode material for dye-sensitized solar cells. In comparison with pure TiO2 and SrTiO3, the composite photoanode shows a much better performance in photoelectric conversion efficiency (1.35 %), which is about 2 and 100 times as efficient as pure TiO2 and SrTiO3, respectively. This indicates that the composite structure can facilitate charge carrier transfer and reduce electron-hole recombination to enhance photoelectrical properties of TiO2-based photoanode materials.

  19. Enhanced ferromagnetic interactions in electron doped Nd{sub x}Sr{sub 2-x}FeMoO{sub 6} double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Rubi, D [Institut de Ciencia de Materials de Barcelona (CSIC), Campus Universitat Autonoma de Barcelona, E-08193, Bellaterra, Catalunya (Spain); Frontera, C [Institut de Ciencia de Materials de Barcelona (CSIC), Campus Universitat Autonoma de Barcelona, E-08193, Bellaterra, Catalunya (Spain); Nogues, J [Institucio Catalana de Recerca i Estudis Avancats (ICREA) and Departament de FIsica, Universitat Autonoma de Barcelona, E-08193, Bellaterra, Catalunya (Spain); Fontcuberta, J [Institut de Ciencia de Materials de Barcelona (CSIC), Campus Universitat Autonoma de Barcelona, E-08193, Bellaterra, Catalunya (Spain)

    2004-05-12

    We report on the structural, magnetic and magnetotransport effects promoted by Nd{sup 3+} substitution in Nd{sub x}Sr{sub 2-x}FeMoO{sub 6}. In spite of the fact that the ionic radius of Nd{sup 3+} is smaller than that of Sr{sup 2+}, the unit cell volume remains constant across the series. We also show that the incorporation of Nd{sup 3+} induces a substantial rising of the Curie temperature from T{sub C} = 400 K for x = 0 to T{sub C} = 440 K for x = 0.6. On the basis of the structural data we argue that this enhancement is due to the injection of itinerant carriers into the conduction band. Nd doping promotes the appearance of antisite (AS) defects in the Fe-Mo sublattice. It turns out that the concentration of AS is mainly controlled by the donor character of the substituting ions rather than by their ionic radii. Antisites are found to reduce the saturation magnetization and the magnetoresistance. This observation, which sharply contrasts with expectations based on electronic rigid band models, indicates that the half-metallic character of double perovskites may be unstable in the presence of antisites. This is in agreement with some recent proposals and the implications of these findings are discussed.

  20. Model-free kinetic analysis of Sr2FeMoO6 re-crystallization process used for double-perovskite monocrystals grown by Bridgman method

    Science.gov (United States)

    Bartha, Cristina; Plapcianu, Carmen; Palade, Petru; Vizman, Daniel

    2015-12-01

    The synthesis routes for polycrystalline bulk Sr2FeMoO6 (SFMO), offer various possibilities, but in all the cases it is difficult to obtain a single phase of this compound. A new challenge in the field is to achieve mono-crystals using different growing routes and the Bridgman method represents one of them. In order to establish the optimal conditions of mono-crystals growing process, a complex thermal investigation of bulk double perovskite has been performed. Differential thermal analysis investigation in argon inert atmosphere, starting from room temperature up to 1650°C provided information about melting and re-crystallization temperature range. Both, the activation energy of Sr2FeMoO6 re-crystallization process and the re-crystallization mechanism were comparatively analyzed by two free-model estimations (Friedman and Ozawa-Flynn-Wall analysis). The resulted data are very important in order to set up the heating program of Bridgman furnace.

  1. Temperature and composition induced phase transitions in Sr2-xCa1+xTeO6 (0 ≤ x ≤ 2) double perovskite oxides

    Science.gov (United States)

    Tamraoui, Y.; Manoun, Bouchaib; Mirinioui, F.; Saadoune, I.; Haloui, R.; Elhachmi, A.; Saad, E.; Lazor, P.

    2017-03-01

    Structures of Sr2-xCa1+xTeO6 double perovskites have been studied by the profile analysis of X-ray diffraction data and Raman spectroscopy at room temperature. This series adopts a monoclinic symmetry for the compositions (0 ≤ x ≤ 0.5) with P21/n as space group and a triclinic system with P 1 bar space group for the compositions (0.5 < x ≤ 2). These results were confirmed by the observed tolerance factor calculated from the distances obtained from the Rietveld refinements which indicates that the true tilt system for the compositions range (0.5 < x ≤ 2) is the triclinic tilt system. Clear changes in the Raman modes centered at 600, 610 and 620 cm-1 and the FWHM of Osbnd Tesbnd O bending vibrations, centered at 738 cm-1 confirmed that the triclinic symmetry takes place between the compositions x = 0.5 and x = 1. Furthermore, Raman spectroscopy studies at high temperature were done for Ca3TeO6. For this compound, considerable changes in the temperature dependence of the modes were well illustrated.

  2. Effects of dynamic diffraction conditions on magnetic parameter determination in a double perovskite Sr2FeMoO6 using electron energy-loss magnetic chiral dichroism.

    Science.gov (United States)

    Wang, Z C; Zhong, X Y; Jin, L; Chen, X F; Moritomo, Y; Mayer, J

    2017-05-01

    Electron energy-loss magnetic chiral dichroism (EMCD) spectroscopy, which is similar to the well-established X-ray magnetic circular dichroism spectroscopy (XMCD), can determine the quantitative magnetic parameters of materials with high spatial resolution. One of the major obstacles in quantitative analysis using the EMCD technique is the relatively poor signal-to-noise ratio (SNR), compared to XMCD. Here, in the example of a double perovskite Sr2FeMoO6, we predicted the optimal dynamical diffraction conditions such as sample thickness, crystallographic orientation and detection aperture position by theoretical simulations. By using the optimized conditions, we showed that the SNR of experimental EMCD spectra can be significantly improved and the error of quantitative magnetic parameter determined by EMCD technique can be remarkably lowered. Our results demonstrate that, with enhanced SNR, the EMCD technique can be a unique tool to understand the structure-property relationship of magnetic materials particularly in the high-density magnetic recording and spintronic devices by quantitatively determining magnetic structure and properties at the nanometer scale. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. Observation of semiconductor to metallic transition and polaron hopping in double perovskite Pr{sub 2}CoTiO{sub 6} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Mahato, Dev K., E-mail: drdevkumar@yahoo.com [Department of Physics, National Institute of Technology Patna, Patna 800005 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1, APC Road, Kolkata 700009 (India)

    2017-05-01

    This paper describes semiconductor to metal transition and polaron conduction in double perovskite Pr{sub 2}CoTiO{sub 6} (PCTO) ceramics. The XRD pattern recorded at room temperature confirmed the pure phase, single crystalline structure. The semicircle arc in the impedance plot at each temperature can be attributed to the grain boundary contribution, indicating one dominating response in the measurement frequency range. The semiconductor to metallic transition was also confirmed by the variation of grain boundary resistance (R{sub gb}) with temperature. The activation energy estimated from the imaginary part of electrical modulus and impedance are found to be the characteristic of polaron conduction in PCTO. Ac conductivity followed power law dependence σ{sub ac} = Bω{sup n}. The observed variation of the exponent ‘n’ with temperature suggests the typical of charge transport assisted by a hopping process. The observed minimum in the temperature dependence of frequency exponent ‘n’ strongly suggests that the large polaron tunneling is the dominant transport process.

  4. Magnetic and electronic properties of double perovskites La{sub 2-x}Sr{sub x}CoIrO{sub 6}(0{<=} x {<=}1)

    Energy Technology Data Exchange (ETDEWEB)

    Narayanan, Narendirakumar; Mikhailova, Daria; Ehrenberg, Helmut [Darmstadt University of Technology, Department of Materials Science (Germany); IFW Dresden, Institute for Complex Materials (Germany); Laskowski, Robert; Blaha, Peter; Schwarz, Karlheinz [Vienna University of Technology, Institute of Materials Chemistry (Austria); Senyshin, Anatoly; Fuess, Hartmut [Darmstadt University of Technology, Department of Materials Science (Germany)

    2009-07-01

    Double Perovskites (DP) A{sub 2}BB{sup '}O{sub 6} with 3d transition metals at B-site and 4d or 5d transition metals at B{sup '}-site have been extensively studied due to their interesting physical properties, that could be tuned by the partial substitution of the ions involved. The ability of Iridium to display different oxidation states and structural constraints (distortion of bond angles) on 5d orbitals, which are generally considered more extended in nature compared to the 3d or 4d ones promise interesting physical properties. We discuss the composition La{sub 2}CoIrO{sub 6} in terms of density functional theory (DFT). We focus mainly on two open aspects. The first one concerns the realization of an insulating state in this material. We show that insulating state can develop only, if we apply LDA/GGA+U method for both B and B{sup '} atoms. The second aspect concerns the magnetic properties. Calculations indicate that this DP has a non-collinear magnetic structure.

  5. Structural and electrical characterizations of cerium (Ce{sup 3+})-doped double perovskite system Sr{sub 2}NiMoO{sub 6-δ}

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Pravin; Singh, Nitish Kumar; Singh, Prabhakar [Indian Institute of Technology (BHU), Department of Physics, Varanasi (India); Sinha, A.S.K. [Indian Institute of Technology (BHU), Department of Chemical Engineering and Technology, Varanasi (India)

    2016-09-15

    The double perovskite system Sr{sub 2-x} Ce{sub x} NiMoO{sub 6-δ} (SCNM) with 0.01 ≤ x ≤ 0.05 was synthesized by the citrate-nitrate auto-combustion synthesis route. Thermal studies were carried out by simultaneous differential scanning calorimetry and thermal gravimetry. Phase constitution was analyzed by powder X-ray diffraction (XRD). Rietveld refinement showed that the major phase exists in tetragonal form with space group I4/m. Microstructural investigations revealed the formation of uniform grains. The electrical conductivity studied by impedance spectroscopy in the temperature range 300-600 C was found to follow a thermally activated process. The sample with x = 0.01 showed the highest conductivity with lowest activation energy. The electrical conductivity of the system was discussed in terms of identified impurity phases and charge density [Mo{sup 5+}{sub Mo}{sup {sub 6}{sub +}}']. The variation of electrical conductivity with composition was explained on the basis of X-ray photoelectron spectroscopy and XRD studies. (orig.)

  6. Electrical transport mechanism in a newly synthesized rare earth double perovskite oxide Sr{sub 2}CeTaO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Bharti, Chandrahas, E-mail: bharti.chandrahas@gmail.com [Sensor and Actuator Division, CSIR-Central Glass and Ceramic Research Institute, 196, Raja SC Mullick Road, Kolkata 700032 (India); Chanda, Sadhan; Sinha, T.P. [Department of Physics, Bose Institute, 93/1, Acharya Prafulla Chandra Road, Kolkata 700009 (India)

    2013-01-15

    A rare earth double perovskite oxide strontium cerium tantalate, Sr{sub 2}CeTaO{sub 6} (SCT) is synthesized by the solid state reaction technique for the first time. The determination of lattice parameters and the identification of phase are carried out by the Rietveld refinement method (RRM) using the Fullprof program in the space group P2{sub 1}/n (C{sup 5}{sub 2h}). A structure of SCT is obtained from RRM. The bond angle and bond length are calculated and listed in Table 1 for SCT. A small amount of impurity of CeO{sub 2} is found in the refinement with space group Fm3m. The scanning electron micrograph shows the average grain size {approx}2 {mu}m. The ac electrical property is investigated in the temperature range from 303 to 703 K and in the frequency range from 0.1 kHz to 1 MHz using impedance spectroscopy. The relaxation mechanism of SCT is explained in detail by fitting experimental impedance and electric modulus data with the modified Debye (Cole-Cole) model. The frequency-dependent electrical data are analyzed in the framework of the conductivity and modulus formalisms. The {sigma}{sub ac} data are fitted with Jonscher's universal power law. The dc conductivity ({sigma}{sub dc}) (calculated from {sigma}{sub ac}) follows an Arrhenius law with the estimated conduction activation energy =0.78 eV. The scaling behavior of imaginary part of electrical impedance (Z Double-Prime ) shows that the relaxation describes the same mechanism at various temperatures.

  7. Structures and magnetic properties of rare earth double perovskites containing antimony or bismuth Ba{sub 2}LnMO{sub 6} (Ln=rare earths; M=Sb, Bi)

    Energy Technology Data Exchange (ETDEWEB)

    Otsuka, Shumpei, E-mail: m-nis-s-o@ec.hokudai.ac.jp; Hinatsu, Yukio

    2015-07-15

    A series of double perovskite-type oxides Ba{sub 2}LnMO{sub 6} (Ln=lanthanides; M=Sb, Bi) were synthesized and their structures were studied. The Ln and M are structurally ordered in the rock-salt type at the B-site of the perovskite ABO{sub 3}. For Ba{sub 2}PrBiO{sub 6} and Ba{sub 2}TbBiO{sub 6}, it has been found that the disordering between Ln ion and Bi ion occurs at the B-site of the double perovskite and both the Pr (Tb) and Bi exist in two oxidation state in the same compound from the analysis of the X-ray diffraction and magnetic susceptibility data. Magnetic susceptibility measurements show that all these compounds are paramagnetic and have no magnetic ordering down to 1.8 K. - Graphical abstract: Tolerance factor for Ba{sub 2}LnMO{sub 6} (M=Sb, Bi) plotted against the ionic radius of Ln{sup 3+}. We have found that there is a clear relation between crystal structures and tolerance factors. - Highlights: • The Ln and M ions are structurally ordered in the rock-salt type at the B-site. • The disordering between Pr (Tb) ion and Bi ion occurs at the B-site. • Ba{sub 2}LnMO{sub 6} (M=Sb, Bi) have no magnetic ordering down to 1.8 K.

  8. Magnetization reversal and ferrimagnetism in Pr,1–NdMnO3

    Indian Academy of Sciences (India)

    Sanjay Biswas; Momin Hossain Khan; Sudipta Pal

    2014-06-01

    Detailed magnetic properties of Pr1–NdMnO3 ( = 0.3, 0.5 and 0.7) have been reported. All the samples crystallize in orthorhombic perovskite structure with Pnma space group. Magnetization measurements under field cooled (FC) protocal reveal magnetization reversal at low temperatures and low magnetic field. This indicates clear evidence of two magnetic sublattices aligned opposite to each other. There is a well-defined maximum around 48 K in the = 0.7 sample (i.e. Pr0.3Nd0.7MnO3) in the ' value which is identified as paramagnetic to ferrimagnetic transition. The peak value shifts to higher temperature with decrease of and width of the maximum broadened. It is also observable that with decrease of Nd, both the value of ' and " decrease. An attempt is made to explain the magnetization reversal within the framework of available models

  9. Nonlinear Excitation in a Ferrimagnetic Zigzag Chain

    Institute of Scientific and Technical Information of China (English)

    王为忠

    2003-01-01

    We study the nonlinear excitation(solitons)in a ferrimagnetic polymer chain by using a total Hamiltonian consisting of Su-Schrieffer-Heeger Hamiltonian and a Hubbard term.At half-filling,the distortion of lattices forms domain wall solitons,while the spin configuration forms envelope solitons.The soliton pair is obtained in a range of the electron-electron(e-e)interaction U,which depends on the electron-phonon(e-ph)interaction.The spin solitons corresponding to the left domain wall and the right domain wall of the displacement are quite different.

  10. Ultrafast angular momentum transfer in multisublattice ferrimagnets.

    Science.gov (United States)

    Bergeard, N; López-Flores, V; Halté, V; Hehn, M; Stamm, C; Pontius, N; Beaurepaire, E; Boeglin, C

    2014-03-11

    Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time-resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange-coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by ~150 fs.

  11. 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.

  12. Theoretical study on the electronic and magnetic properties of double perovskite La2-xSrxMnCoO6 (x = 0,1,2)

    Science.gov (United States)

    Lan, X.; Kong, S.; Zhang, W. Y.

    2011-12-01

    In this paper, the electronic and magnetic properties of double perovskite La2- x Sr x MnCoO6 ( x = 0,1,2) have been studied using the local-spin-density approximation + U method. For the three compositions investigated, the low symmetry P21/ n structure yields consistently lower energy than that of the high symmetry Fmbar{3m} Fm3̅ m structure. The strong electronic correlation and the orbital polarization of Co- d electrons play crucial roles. In agreement with experiments, we find that La2MnCoO6 is a ferromagnetic insulator with both Mn and Co ions in their high-spin states. The tilting of oxygen octahedrons is most significant in this case and is responsible for its insulating behavior; for LaSrMnCoO6, the ground state remains a ferromagnetic insulator with Mn and Co ions in their high-spin states. The optimized P21/ n and Fmbar{3m} Fm3̅ m crystal structures are nearly the same, and the P21/ n structure is stabilized by the spontaneous layer-wise antiferro-orbital ordering of Co- d electrons. We also predict that Sr2MnCoO6 is a ferromagnetic metal, and its electronic structure can be viewed as a rigid band shifting from that of LaSrMnCoO6. Due to the strong covalency between transition metal and oxygen ions, the valences of Mn and Co ions differ considerably from those derived from purely ionic model. Also, doping induced holes mainly go to oxygen sites though the density of states near the Fermi energy has strong mixed character. This feature, together with the orbital ordering phenomenon, should be observable via the X-ray near-edge absorption spectroscopy and the polarized X-ray diffraction spectra.

  13. Cationic ordering, relaxation dynamics and polaron hopping in a new double perovskite oxide: BaPrCoTaO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Bharti, Chandrahas, E-mail: bharti.chandrahas@gmail.com [Sensor and Actuator Division, CSIR-Central Glass and Ceramic Research Institute, 196, Raja SC Mullick Road, Kolkata 700032 (India); Das, Mrinmoy K.; Sen, A. [Sensor and Actuator Division, CSIR-Central Glass and Ceramic Research Institute, 196, Raja SC Mullick Road, Kolkata 700032 (India); Chanda, Sadhan; Sinha, T.P. [Department of Physics, Bose Institute, 93/1, Acharya Prafulla Chandra Road, Kolkata 700009 (India)

    2014-12-25

    Highlights: • BaPrCoTaO{sub 6} (BPCT) is synthesized for the first time. • Rietveld refinement of XRD data confirms monoclinic phase. • XRD confirms the presence of B-type cation ordering in BPCT. • The activation energy of BPCT is ∼0.36 eV. • The conduction mechanism for BPCT is polaron hopping. - Abstract: The Rietveld refinement method is used to investigate the cationic ordering of a new double perovskite oxide BaPrCoTaO{sub 6} (BPCT) synthesized by the solid-state reaction technique. X-ray diffraction pattern of BPCT shows monoclinic phase P2{sub 1}/n (C{sub 2}{sup 5}{sub h}) at room temperature with ordering of the B-cations. The superlattice reflections suggest the existence of simultaneous in-phase and out-of-phase tilting. Scanning electron micrograph shows an average grain size ∼3 μm. The Fourier transform infrared spectra suggest two phonon modes. Impedance spectroscopy is used to investigate the relaxation dynamics and hopping mechanism in the temperature range of 303–523 K and in the frequency range of 0.1 kHz–1 MHz. Experimental electric modulus and electrical impedance data are fitted to the Cole–Cole model. The electrical conductivity data are fitted to Jonscher’s universal power law. The activation energy (E{sub a}) calculated from the Arrhenius plots is found to be ∼0.36 eV which shows polaron hopping in BPCT. Impedance data that have capacitive and resistive components is represented by Nyquist diagram.

  14. Magnetodielectric effect in relaxor/ferrimagnetic composites

    Energy Technology Data Exchange (ETDEWEB)

    Naveed Ul-Haq, M., E-mail: naveedulhaq07@gmail.com [Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Institute for Materials Sciences and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Essen 45141 (Germany); Yunus, Tayyaba; Mumtaz, Arif [Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Shvartsman, V.V.; Lupascu, Doru C. [Institute for Materials Sciences and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Essen 45141 (Germany)

    2015-08-15

    Highlights: • Single phase ferroelectric (relaxor)/ferrimagnetic composites are synthesized. • The composite shows magnetodielectric effect. • Effect of interface strain is discussed. • MD is explained via defining a local order parameter q(T). - Abstract: We report on the effect of an applied static magnetic field on the dielectric properties of ferroelectric relaxor/ferrimagnetic composites consisting of [Ba(Sn{sub 0.3}Ti{sub 0.7})O{sub 3}]{sub 0.8}–[CoFe{sub 2}O{sub 4}]{sub 0.2} (BST{sub 0.8}–CFO{sub 0.2}). The pure Ba(Sn{sub 0.3}Ti{sub 0.7})O{sub 3} (BST30) as well as the composites, were synthesized by solid state reaction method. The X-ray diffraction analysis confirmed that BST30 and CFO coexist in the composite without any secondary phase. The real and the imaginary part of the dielectric permittivity were studied as a function of temperature, with and without static magnetic field, respectively. Relaxor characteristics such as dielectric permittivity and its peak temperature are observed to vary with the magnetic field. This is explained in the context that the applied magnetic field creates magnetostriction in the ferrite phase which is transferred to the relaxor phase via the interface coupling. The strain in the relaxor phase results in the reorientation of local polarization entities, polar nano regions (PNRs), which alters the dielectric characteristics of the sample. This effect is explained in relation to local order parameter q(T) which is found to increase in a certain temperature range above the typical ferroelectric temperature regime with the application of magnetic field.

  15. Double functions of porous TiO2 electrodes on CH3NH3PbI3 perovskite solar cells: Enhancement of perovskite crystal transformation and prohibition of short circuiting

    Directory of Open Access Journals (Sweden)

    Govindhasamy Murugadoss

    2014-08-01

    Full Text Available In order to analyze the crystal transformation from hexagonal PbI2 to CH3NH3PbI3 by the sequential (two-step deposition process, perovskite CH3NH3PbI3 layers were deposited on flat and/or porous TiO2 layers. Although the narrower pores using small nanoparticles prohibited the effective transformation, the porous-TiO2 matrix was able to help the crystal transformation of PbI2 to CH3NH3PbI3 by sequential two-step deposition. The resulting PbI2 crystals in porous TiO2 electrodes did not deteriorate the photovoltaic effects. Moreover, it is confirmed that the porous TiO2 electrode had served the function of prohibiting short circuits between working and counter electrodes in perovskite solar cells.

  16. Influence of the B-site ordering on the magnetic properties of the new La{sub 3}Co{sub 2}MO{sub 9} double perovskites with M = Nb or Ta

    Energy Technology Data Exchange (ETDEWEB)

    Fuertes, V.C.; Blanco, M.C.; Franco, D.G. [INFIQC (CONICET), Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA Cordoba (Argentina); De Paoli, J.M.; Sanchez, R.D. [Centro Atomico Bariloche, CNEA and Instituto Balseiro, Universidad Nacional de Cuyo, Av. Bustillo 9500, 8400 Rio Negro (Argentina); Carbonio, R.E., E-mail: carbonio@mail.fcq.unc.edu.ar [INFIQC (CONICET), Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA Cordoba (Argentina)

    2011-01-15

    Double perovskites La{sub 3}Co{sub 2}NbO{sub 9} and La{sub 3}Co{sub 2}TaO{sub 9} have been prepared by both solid state and sol-gel synthesis. The crystal structures have been studied from X-ray and neutron powder diffraction data. Rietveld refinements show that the crystal structure is monoclinic (P2{sub 1}/n), with different degrees of ordering of B' and B'' cations, with octahedra tilted according to the Glazer notation a{sup -}b{sup -}c{sup +}. Occupancy refinements show that the solid state materials are more B-site ordered than the sol-gel ones. Magnetization measurements show that these perovskites show two magnetic contributions, one with spontaneous magnetization and other with linear behaviour with the magnetic field associated to antiferromagnetic correlations. In the samples synthesized by solid state the spontaneous magnetization is more important than those synthesized by the sol-gel and present T{sub C} of 62 K for Nb and 72 K for Ta. On the other hand, materials prepared by sol-gel have T{sub C} 20 K for Nb and 40 K for Ta, respectively and major presence of the antiferromagnetic contribution. The competition between these magnetic behaviours is interpreted, by a microscopic point of view, as to be due to the different degrees of Co{sup 2+} ions disorder on the B site of the double perovskite structure. This disorder affects the ratio between the antiferromagnetic Co{sup 2+}-O-Co{sup 2+} and the ferromagnetic Co{sup 2+}-O-M{sup 5+}-O-Co{sup 2+} couplings proposed for the system.

  17. B-site ordered double perovskite LaBa1-xSrxZnSbO6 (0 ≤ x ≤ 1): Sr(2+)-doping-induced symmetry evolution and structure-luminescence correlations.

    Science.gov (United States)

    Jiang, Pengfei; Zhou, Zhengyang; Gao, Wenliang; Cong, Rihong; Yang, Tao

    2016-03-07

    The study of perovskites has been active for a long time. Here, we rationally designed and prepared a double perovskite, LaBaZnSbO6, by selecting Zn(2+) and Sb(5+) with large size and charge differences, and, indeed, complete B-site ordering can be achieved. Careful study using powder X-ray diffraction data pinpointed its space group to be I2/m, which has rarely been seen in double perovskites. Thereafter, an interesting observation of Sr(2+)-doping-induced symmetry evolution from I2/m to P21/n was confirmed in the complete solid solutions LaBa1-xSrxZnSbO6, where the tilting system also transferred from a(-)a(-)c(0) to a(-)a(-)c(+). The transition boundary is around x = 0.4. It can also be visualized by the variation of θ (defined as c/[(a + b)/2]), which is associated with the anisotropic shrinkage of the unit cell lattice and indeed shows a minimum at x = 0.4. Such a successive modulation of both the structural symmetry and the average La/Ba/Sr-O bond distances (revealed by Rietveld refinements) motivated us to study the Eu(3+) luminescence in La0.95Eu0.05Ba1-xSrxZnSbO6. Interestingly, the maximum of charge transfer absorption of Eu(3+) shows a precise changing tendency with the A-O bond distances along with the Sr(2+) doping, clearly revealing the structure-luminescence correlations.

  18. Influence of Ni/Mo ratio on structural and electrical properties of double perovskite system Sr{sub 2}Ni{sub 1+x}Mo{sub 1-x}O{sub 6-δ}

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Pravin; Singh, Nitish Kumar; Singh, Rajesh Kumar; Singh, Prabhakar [Indian Institute of Technology (BHU), Department of Physics, Varanasi (India)

    2015-11-15

    Technologically important double perovskite system Sr{sub 2}Ni{sub 1+x}Mo{sub 1-x}O{sub 6-δ} with x = 0.00, 0.05, 0.10, and 0.15 was prepared by solution combustion method. The structural and the Rietveld analysis of compositions revealed the formation of double perovskite tetragonal phase Sr{sub 2}NiMoO{sub 6} with space group I4/m as a major phase. SrMoO{sub 4} and NiO were also observed as minor phases. Microstructural studies depicted the formation of uniform grains for all the samples. The average grain size was found to lie between the ranges of 1-4 μm. XPS analysis of the synthesized compositions showed the decreasing ratio of Mo{sup 5+} to Mo{sup 6+} ions in the system with increasing Ni content, which played an important role in the conduction mechanism. The thermal expansion coefficient (TEC) of all compositions indicated that it is more compatible to the TEC of standard electrolytes. The electrical conductivity for all the compositions was studied using impedance spectroscopy in the temperature range 200-600 C. Composition with x = 0.05 showed better electrical conductivity with good catalytic activity. (orig.)

  19. Cationic ordering and role of the B-site lanthanide(III) and molybdenum(V) cations on the structure and magnetism of double perovskites Sr{sub 2}LnMoO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Pinacca, R.M.; Larrégola, S.A.; López, C.A. [INTEQUI-Área de Química General e Inorgánica “Dr. G.F. Puelles”, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina); Pedregosa, J.C., E-mail: jpedreg@gmail.com [INTEQUI-Área de Química General e Inorgánica “Dr. G.F. Puelles”, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis (Argentina); Pomjakushin, Vladimir [Laboratory for Neutron Scattering, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Sánchez, R.D. [Centro Atómico Bariloche, Comisión Nacional de Energía Atómica and Instituto Balseiro, Universidad Nacional de Cuyo, 8400 S.C. de Bariloche, Río Negro (Argentina); Alonso, J.A. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain)

    2015-06-15

    Highlights: • Five new double perovskites of formula Sr{sub 2}LnMoO{sub 6} were synthesized. • All the samples crystallize in the monoclinic P2{sub 1}/n space group. • Strong reducing conditions were used in order to stabilized Mo(V) cations. • A complete ordering between the rare earth and molybdenum ions was observed. • Magnetism agrees with the crystal distortions observed from Rietveld analysis. - Abstract: We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr{sub 2}LnMoO{sub 6} (Ln = Eu, Gd, Dy, Ho, Er, Yb) with Mo{sup 5+} and Ln{sup 3+} electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo{sup 5+} cations. Structural characterization by XRPD and NPD was performed when Ln = Ho, Er, Yb and just XRPD for absorbing Ln = Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P2{sub 1}/n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25 K and the determined effective magnetic moments are consistent with those expected for the pair Ln{sup 3+}–Mo{sup 5+}. All the phases have negative values​​ of the Weiss temperature indicating dominance of antiferromagnetic interactions.

  20. Evidence of cluster-glass-like state at low temperature in anti-site disordered La1.5Ca0.5CoMnO6 double perovskite

    Science.gov (United States)

    Sahoo, R. C.; Giri, S. K.; Paladhi, D.; Das, A.; Nath, T. K.

    2016-07-01

    We have investigated structural and magnetic properties having cluster-glass (CG) like ordering at low temperature in a polycrystalline La1.5Ca0.5CoMnO6 double perovskite sample. In this anti-site disordered double perovskite, ferromagnetic (FM) ordering is observed at ˜157 K. From temperature variation linear ac susceptibility measurements, a CG state is clearly observed below a freezing temperature of ˜50.1 K, the origin of which can be best explained through (1) structural disorder and (2) consequence of the coexistence and competition of antiferromagnetic and FM interactions. The linear complex ac susceptibility data near the freezing temperature are best fitted to a critical slowing down model characterized by the dynamic exponents zυ ˜ 4.95(5) and τ0 ˜ 1.23 × 10-7 s. These values are very similar to what is generally observed in a CG system. The glassy transition temperature versus Hd c 2/3 behaviour follows the Almeida-Thouless line. The time dependent slow relaxation dynamics and aging effect have also been investigated to confirm a CG-like state formation in this compound.

  1. Synthesis, structure and magnetic properties of La{sub 3}Co{sub 2}SbO{sub 9}: A double perovskite with competing antiferromagnetic and ferromagnetic interactions

    Energy Technology Data Exchange (ETDEWEB)

    Franco, D.G.; Fuertes, V.C.; Blanco, M.C. [INFIQC (CONICET), Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA Cordoba (Argentina); Fernandez-Diaz, M.T. [Institute Laue-Langevin (ILL) 156X, F-38042 Grenoble Cedex 9 (France); Sanchez, R.D., E-mail: rodo@cab.cnea.gov.ar [Centro Atomico Bariloche, CNEA and Instituto Balseiro, Universidad Nacional de Cuyo, Av. Bustillo 9500, 8400 Rio Negro (Argentina); Carbonio, R.E., E-mail: carbonio@fcq.unc.edu.ar [INFIQC (CONICET), Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA Cordoba (Argentina)

    2012-10-15

    The synthesis, structural characterization, and magnetic properties of La{sub 3}Co{sub 2}SbO{sub 9} double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P2{sub 1}/n. Co{sup 2+} and Sb{sup 5+} have the maximum order allowed for the La{sub 3}Co{sub 2}SbO{sub 9} stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) A, b=5.6842(2) A, c=7.9748(2) A and {beta}=89.999(3) Degree-Sign . Magnetization measurements indicate the presence of ferromagnetic correlations with T{sub C}=55 K attributed to the exchange interactions for non-linear Co{sup 2+}-O-Sb{sup 5+}-O-Co{sup 2+} paths. The effective magnetic moment obtained experimentally is {mu}{sub exp}=4.38 {mu}{sub B} (per mol Co{sup 2+}), between the theoretical one for spin only (3.87 {mu}{sub B}) and spin-orbit value (6.63 {mu}{sub B}), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 {mu}{sub B}/f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration. - Graphical abstract: Co-O-Co (Yellow octahedra only) rich zones (antiferromagnetic) are in contact with Co-O-Sb-O-Co (Red and yellow octahedra) rich zones (Ferromagnetic) to give the peculiar magnetic properties, as a consequence, a complex hysteresis loop can be observed composed by a main and irreversible curve in all the measured range, superimposed with a ferromagnetic component at low fields. Highlights: Black-Right-Pointing-Pointer La{sub 3}Co{sub 2}SbO{sub 9} has small Goldschmidt Tolerance Factor (t) due to the small size of La{sup 3+}. Black-Right-Pointing-Pointer Small t determines an angle for the path Co{sup 2+}-O-Sb{sup 5+}-O-Co{sup 2+} of 153 Degree-Sign . Black

  2. Electrical properties and scaling behaviour of rare earth based Ho{sub 2}CoZrO{sub 6} double perovskite ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Mahato, Dev K., E-mail: drdevkumar@yahoo.com [Department of Physics, National Institute of Technology Patna, Patna 800005 (India); Dutta, Alo; Sinha, T.P. [Department of Physics, Bose Institute, 93/1, Acharya Prafulla Chandra Road, Kolkata 700 009 (India)

    2012-12-15

    Graphical abstract: The X-ray diffraction analysis suggests that the compound crystallizes in monoclinic phase at room temperature with β = 108.51 ± 0.021° (a = 8.1858 ± 0.0023 Å, b = 5.2599 ± 0.0027 Å, c = 7.9874 ± 0.0031 Å) and cell volume = 324.17 Å{sup 3}. The SEM image indicates the uniformity of the grains in the samples. The grain size of the microstructure of HCZ is found to be ∼0.48 μm on average. Display Omitted Highlights: ► The conduction mechanism in HCZ may be due to hopping of small polaron. ► The material shows semiconducting behaviour. ► Conductivity obeys Jonscher's power law with high frequency dispersion. ► Both long-range and localized relaxation are present. -- Abstract: The Ho{sub 2}CoZrO{sub 6} (HCZ) double perovskite has been prepared in polycrystalline form by solid state reaction technique. The analysis of the X-ray powder diffraction pattern indicates that the crystal structure is monoclinic at room temperature with cell parameters a = 8.1858 ± 0.0023 Å, b = 5.2599 ± 0.0027 Å, c = 7.9874 ± 0.0031 Å and β = 108.51 ± 0.021°. The compound shows significant frequency dispersion in its dielectric properties. The Cole–Cole model is used to determine the polydispersive nature of dielectric relaxation. The scaling behaviour of dielectric loss and imaginary electric modulus suggest that the relaxation describe same mechanism at various temperatures. Impedance data presented in the Nyquist plot (Z″ versus Z′) are used to identify an equivalent circuit and to know the bulk and interface contributions. The complex impedance analysis of HCZ exhibits the appearance of both the grain and the grain-boundary contribution. The frequency dependent conductivity spectra follow the universal power law. The magnitude of the activation energy indicates that the carrier transport is due to the hopping conduction.

  3. First-principles study of the structural, electronic, and magnetic properties of double perovskite Sr2FeReO6 containing various imperfections

    Science.gov (United States)

    Yan, Zhang; Li, Duan; Vincent, Ji; Ke-Wei, Xu

    2016-05-01

    The structural, electronic, and magnetic properties of double perovskite Sr2FeReO6 containing eight different imperfections of FeRe or ReFe antisites, Fe1-Re1 or Fe1-Re4 interchanges, VFe, VRe, VO or VSr vacancies have been studied by using the first-principles projector augmented wave (PAW) within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction (GGA+U). No obvious structural changes are observed for the imperfect Sr2FeReO6 containing FeRe or ReFe antisites, Fe1-Re1 or Fe1-Re4 interchanges, or VSr vacancy defects. However, the six (eight) nearest oxygen neighbors of the vacancy move away from (close to) VFe or VRe (VO) vacancies. The half-metallic (HM) character is maintained for the imperfect Sr2FeReO6 containing FeRe or ReFe antisites, Fe1-Re4 interchange, VFe, VO or VSr vacancies, while it vanishes when the Fe1-Re1 interchange or VRe vacancy is presented. So the Fe1-Re1 interchange and the VRe vacancy defects should be avoided to preserve the HM character of Sr2FeReO6 and thus usage in spintronic devices. In the FeRe or ReFe antisites, Fe1-Re1 or Fe1-Re4 interchanges cases, the spin moments of the Fe (Re) cations situated on Re (Fe) antisites are in an antiferromagnetic coupling with those of the Fe (Re) cations on the regular sites. In the VFe, VRe, VO, or VSr vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice, while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μ tot (μ B/f.u.) of the imperfect Sr2FeReO6 containing eight different defects decrease in the sequence of VSr vacancy (3.50), VRe vacancy (3.43), FeRe antisite (2.74), VO vacancy (2.64), VFe vacancy (2.51), ReFe antisite (2.29), Fe1-Re4 interchange (1.96), Fe1-Re1 interchange (1.87), and the mechanisms of the saturation magnetization reduction have been analyzed. Project supported by the National Natural Science Foundation of China (Grant No. 51501017).

  4. 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.

  5. Band Gaps of the Lead-Free Halide Double Perovskites Cs2BiAgCl6 and Cs2BiAgBr6 from Theory and Experiment.

    Science.gov (United States)

    Filip, Marina R; Hillman, Samuel; Haghighirad, Amir Abbas; Snaith, Henry J; Giustino, Feliciano

    2016-07-07

    The recent discovery of lead-free halide double perovskites with band gaps in the visible represents an important step forward in the design of environmentally friendly perovskite solar cells. Within this new family of semiconductors, Cs2BiAgCl6 and Cs2BiAgBr6 are stable compounds crystallizing in the elpasolite structure. Following the recent computational discovery and experimental synthesis of these compounds, a detailed investigation of their electronic properties is warranted in order to establish their potential as optoelectronic materials. In this work, we perform many-body perturbation theory calculations and obtain high accuracy band gaps for both compounds. In addition, we report on the synthesis of Cs2BiAgBr6 single crystals, which are stable in ambient conditions. From our complementary theoretical and experimental analysis, we are able to assign the indirect character of the band gaps and obtain both experimental and theoretical band gaps of these novel semiconductors that are in close agreement.

  6. Optical spectroscopy and crystal field studies of the Mn{sup 4+} ion (3d{sup 3}) in the double perovskite NaLaMgTeO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Alok M.; Camardello, Samuel J.; Comanzo, Holly A.; Garcia-Santamaria, Florencio [GE Global Research, Niskayuna, NY (United States); Brik, Mikhail G. [Tartu Univ. (Estonia). Inst. of Physics

    2014-02-15

    The spectroscopic properties of the Mn{sup 4+} ion (3d{sup 3}) in the double perovskite NaLaMgTeO{sub 6} are reported in this work. Evidence is presented for the occupation by the Mn{sup 4+} ion of both the six coordinated Mg{sup 2+} and Te{sup 6+} sites in the host structure. The Mn{sup 4+} energy levels are calculated using the exchange charge model of crystal field theory for both occupied sites. The results of our calculations yield the crystal field splitting and Racah parameters of Dq =2008 cm{sup -1}, B =790 cm{sup -1}, C =2881 cm{sup -1}, with C/B = 3.65 (Mg{sup 2+} site) and Dq =2008 cm{sup -1}, B =790 cm{sup -1}, C =2949 cm{sup -1}, with C/B = 3.73 (Te{sup 6+} site). A cross-cutting comparative study of the variations in the crystal field splitting and the Racah parameters of the six-coordinated Mn{sup 4+} ion in a series of materials with the perovskite structure are presented. (orig.)

  7. Existence of solutions for the dynamic equation of ferrimagnets

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Ferrimagnet is a kind of basic and important multi-sublattice magnet material. It has attracted more and more attention of physicists and mathematicians. Many results of solitons and numerical computations on this topic have appeared. In this article, the dynamic equation for an isotropic ferrimagnet with two non-equivalent sublattices is studied, existence of weak solutions in multi dimension case is proved through the penalized method, the uniqueness and smoothness of the solution in one dimension case are also obtained by the relation between this equation and hyperbolic equation.

  8. Study of LnBaCo{sub 2}O{sub 6-d}elta (Ln = Pr, Nd, Sm and Gd) double perovskites as new cathode material for IT-SOFC

    Energy Technology Data Exchange (ETDEWEB)

    Chavez, E; Mueller, M; Mogni, L; Caneiro, A, E-mail: mogni@cab.cnea.gov.a [Centro Atomico Bariloche-CNEA, Instituto Balseiro. Av. Bustillo 9500, S. C. de Bariloche 8400 (Argentina)

    2009-05-01

    Oxides with double perovskites structures of general composition LnBaCo{sub 2}O{sub 6-d}elta (Ln = Pr, Nd, Sm and Gd) were synthesized by solid state reaction with the purpose to evaluate new materials to be used as cathodes in intermediate temperature solid oxide fuel cell (IT-SOFC). A preliminary study about electrochemical properties was performed by impedance spectroscopy between 500 and 800 deg. C under atmosphere of pure O{sub 2}. Symmetrical cells were obtained by spray deposition of LnBaCo{sub 2}O{sub 6-d}elta (Ln = Pr, Nd, Sm and Gd) at both sides of a dense ceramic electrolyte. The impedance spectroscopy measurements as a function of temperatures show a hysteresis loop which could be associated to a tetragonal/orthorhombic phase transition. The existence of this transition was corroborated by high temperature X-Ray diffraction and Differential Scanning Calorimetry measurements.

  9. 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.

  10. Large change in thermopower with temperature driven p-n type conduction switching in environment friendly BaxSr2-xTi0.8Fe0.8Nb0.4O6 double perovskites.

    Science.gov (United States)

    Roy, Pinku; Waghmare, Vikram; Tanwar, Khagesh; Maiti, Tanmoy

    2017-02-22

    Oxide based thermoelectric materials have gained some interest in recent times due to their low thermal conductivity, environment friendly nature and high temperature durability. In the present work, the effect of Nb(5+) doping on the thermoelectric properties of BaxSr2-xTiFeO6 based double perovskites was investigated. BaxSr2-xTi0.8Fe0.8Nb0.4O6 (BSTFN) double perovskites with stoichiometric compositions of 0.0 ≤ x ≤ 0.25 were synthesized by the solid-state reaction method. Rietveld refinement powder XRD data confirmed single-phase solid solutions with cubic crystal symmetry for all the BSTFN compositions. Dense microstructures with fine grain-sizes were observed in SEM studies of the as-synthesized oxide samples. Thermoelectric parameters like the Seebeck coefficient (S), the electrical conductivity (σ) and thermal diffusivity of these oxide samples were measured in the temperature range from 300 K to 1223 K. All the BSTFN compositions exhibited temperature driven p-n type conduction switching along with a colossal change in thermopower. The maximum drop in thermopower (ΔS) of ∼1146 μV K(-1) was observed for BaxSr2-xTi0.8Fe0.8Nb0.4O6 with composition of x = 0.25. From the temperature dependent conductivity studies it is evident that all the compositions underwent intermediate semiconductor to metal-like transition before it showed conversion from p-type to n-type semiconductor behavior in the thermo-power (S) measurement. The conduction mechanisms of these oxides were further explained by the small polaron hopping model.

  11. Electrical conductivity of Sr{sub 2−x}VMoO{sub 6−y} (x = 0.0, 0.1, 0.2) double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Childs, Nicholas B.; Smith, Richard; Key, Camas [Department of Physics, EPS 264, Montana State University, Bozeman, Montana 59717 (United States); Weisenstein, Adam; Sofie, Stephen [Department of Mechanical Engineering, Roberts 220, Montana State University, Bozeman, Montana 59717 (United States)

    2013-06-28

    Electrical conductivity of Sr{sub 2-x}VMoO{sub 6-y} (x = 0.0, 0.1, 0.2) double perovskites has been investigated in a reducing atmosphere at temperatures up to 800 °C. This material has a key application in solid oxide fuel cell anodes as a mixed ion and electron conductor. A solid state synthesis technique was used to fabricate materials and crystal structure was verified through x-ray diffraction. Subsequent to conventional sintering in a reducing environment, elemental valence states were indentified through x-ray photoemission spectroscopy on the double perovskite material before and after annealing in a hydrogen environment. Samples exhibited metallic like conduction with electrical conductivities of 1250 S/cm (Sr{sub 2}VMoO{sub 6-y′}), 2530 S/cm (Sr{sub 1.8}VMoO{sub 6-y″}), and 3610 S/cm (Sr{sub 1.9}VMoO{sub 6-y‴}) at 800 °C in 5% H{sub 2}/95% N{sub 2}, with a substantial increase in conductivity upon cooling to room temperature. Room temperature electrical conductivity values for Sr{sub 1.9}VMoO{sub 6-y‴} make it a candidate as the highest electrically conductive oxide known. Highly insulating secondary surface phases, Sr{sub 3}V{sub 2}O{sub 8}, and SrMoO{sub 4}, begin to reduce at 400 °C in a hydrogen environment, as confirmed by X-ray photoemission and thermal gravimetric analysis. This reduction, from V{sup 5+} and Mo{sup 6+} to lower valence states, leads to a large increase in sample electrical conductivity.

  12. Origin of the spin Seebeck effect in compensated ferrimagnets

    NARCIS (Netherlands)

    Geprägs, S.; Kehlberger, A.; Coletta, F.D.; Qiu, Z.; Guo, E.J.; Schulz, T.; Mix, C.; Meyer, S.; Kamra, A.; Althammer, M.; Huebl, H.; Jakob, G.; Ohnuma, Y.; Adachi, H.; Barker, J.; Maekawa, S.; Bauer, G.E.W.; Saitoh, E.; Gross, R.; Goennenwein, S.T.B.; Kläui, M.

    2016-01-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist t

  13. Giant orthorhombic distortions by Cu+ in ferrimagnetic spinel Mn334

    Science.gov (United States)

    Chung, Jae-Ho; Lee, Kee Hwan; Chang, Hun; Hwang, In Yong; Kang, Hyun Wook; Kim, Su Jae; Lee, Seongsu

    2015-03-01

    Mn3O4 is a tetragonal (c > a) spinel that exhibits noncollinear Yafet-Kittel ferrimagnetic ordering at low temperatures. We report large orthorhombic distortions in its ferrimagnetic phase stabilized by a few percent of Cu doping. The orthorhombic strains of the ferrimagnetic phases increased linearly to the doping and reached up to ɛ ~ 8 . 2 ×10-3 for x = 0.19, which is three times larger than the saturated value under external magnetic fields. For high doping (xagt 0 . 17), the distortions first appeared in the paramagnetic phases and underwent further enhancement simultaneously with the onset of the noncollinear ferrimagnetic ordering. We present the rich magnetostructural phase diagram of CuxMn3-xO4, and argue that the diluted t2 orbital degeneracy of Cu2+ under tetrahedral crystal field breaks the global symmetry and triggers the orthorhombic instability inherent in Mn3O4. This work was supported by the National Research Foundation of Korea through the ARCNEX (NRF-2011-0031933).

  14. Interrelation Between the Structural, Magnetic and Magnetoresistive Properties of Double-Perovskite Sr2FeMoO6-δ Thin Films

    Science.gov (United States)

    Kalanda, N. A.; Demyanov, S. E.; Petrov, A. V.; Karpinsky, D. V.; Yarmolich, M. V.; Oh, S. K.; Yu, S. C.; Kim, D.-H.

    2016-07-01

    Investigations of the formation conditions of Sr2FeMoO6-δ compound films, depending on the substrate temperature and sputtering rate with their subsequent thermal treatment, have made it possible to obtain the single-phase homogeneous films. The analysis of x-ray diffractometry and magnetic force microscopy data has made it possible to reveal the superstructural ordering of Fe and Mo cations, determine the spin polarization degree of conduction electrons and magnetic structure of the films. Studies of temperature and magnetic field dependences of magnetization in the zero-field cooling and field-cooling modes have shown the existence of magnetic regions with low coercitive force, which bears witness of the domination of the ferrimagnetic state at temperatures above the blocking temperature. Lower than this temperature, the nanosized grains are present, where homogeneous magnetization promotes the realization of a superparamagnetic state, which is "obscured" at the higher temperatures. The negative magnetoresistive effect, reaching 14% at low temperatures in a magnetic field of 8 T, is by its nature the giant magnetoresistance with monodirectional spin-polarized electrons.

  15. First-principles study on half-metallic properties of the Sr{sub 2}GdReO{sub 6} double perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Berri, Saadi, E-mail: berrisaadi12@yahoo.fr

    2015-07-01

    A first-principles approach is used to study the structural, electronic and magnetic properties of Sr{sub 2}GdReO{sub 6}, using full-potential linearized augmented plane wave (FP-LAPW) method within the spin density functional theory. At the equilibrium lattice constant, our calculations predict that Sr{sub 2}GdReO{sub 6} is half-metallic (HM) with a magnetic moment of 9 µ{sub B}/fu and HM flip gap of 1.82 eV. In addition, the ferromagnetic phase is found to be energetically more favorable than paramagnetic phase. Therefore, the Sr{sub 2}GdReO{sub 6} compound is a promising material for future spintronic application. - Highlights: • First principles FP-LAPW approach based on (GGA)+U is used for this purpose. • The electronic and magnetic properties of Sr{sub 2}GdReO{sub 6} have been investigated. • Sr{sub 2}GdReO{sub 6} compound is a half-metallic ferrimagnet.

  16. Magnetic Response and Hyperfine Magnetic Fields at Fe Sites of Sr{sub 3}Fe{sub 2}MO{sub 9} (M = Mo, Te, W, U) Double-Perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Baum, L. A.; Stewart, S. J.; Mercader, R. C. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina); Greneche, J. M., E-mail: greneche@univ-lemans.fr [Universite du Maine, Laboratoire de Physique de L' Etat Condense UMR CNRS 6087 (France)

    2004-12-15

    We have studied the isostructural series of double-perovskites Sr{sub 3}Fe{sub 2}MO{sub 9} (M=Mo, Te, W, U) by Moessbauer spectrometry and AC susceptibility measurements. The hyperfine structure of Moessbauer spectra at room temperature is attributed to the presence of high spin state Fe{sup 3+} ions sensing both static and fluctuating magnetic hyperfine fields with different relative areas that depend on M. The magnetically split signal - indistinguishable from the background in the Mo compound spectrum - increases with the Fe-site disorder in the sequence Moperovskite sample is already magnetically fully ordered, while the other three cations suggest ordering temperatures that increase from Te to U to Mo. At 4.2 K all the spectra are completely magnetically split and display hyperfine fields that range from 49 up to 53 T. Coincident with the X-ray and neutron diffraction results, the hyperfine parameters are consistent with Fe atoms centered in oxygen octahedral units, coordinated to different numbers of M-centered octahedra. The AC susceptibility response is {chi}'{sub max} {approx}3.5x10{sup -5} emu/g.Oe for the Mo compound and increases for the W, Te and U compounds with values of {chi}'{sub max} 1.6x10{sup -4}, 3.0x10{sup -4}, and 9.4x10{sup -3} emu/g.Oe, respectively. The out-of-phase component, {chi}'', could only be detected for the U compound. Its frequency dependence displays a shift that denotes a spin-glass-like state arising from the chemical disorder.

  17. Origin of the spin Seebeck effect in compensated ferrimagnets

    Science.gov (United States)

    Geprägs, Stephan; Kehlberger, Andreas; Coletta, Francesco Della; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E. W.; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T. B.; Kläui, Mathias

    2016-02-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE.

  18. Ferrimagnetism in delta chain with anisotropic ferromagnetic and antiferromagnetic interactions

    Science.gov (United States)

    Dmitriev, D. V.; Krivnov, V. Ya

    2016-12-01

    We consider analytically and numerically an anisotropic spin-\\frac{1}{2} delta-chain (sawtooth chain) in which exchange interactions between apical and basal spins are ferromagnetic and those between basal spins are antiferromagnetic. In the limit of strong anisotropy of exchange interactions this model can be considered as the Ising delta chain with macroscopic degenerate ground state perturbed by transverse quantum fluctuations. These perturbations lift the ground state degeneracy and the model reduces to the basal XXZ spin chain in the magnetic field induced by static apical spins. We show that the ground state of such a model is ferrimagnetic. The excitations of the model are formed by ferrimagnetic domains separated by domain walls with a finite energy. At low temperatures the system is effectively divided into two independent subsystems, the apical subsystem described by the Ising spin-\\frac{1}{2} chain and the basal subsystem described by the XXZ chain with infinite zz interactions.

  19. Perovskites with the Framework-Forming Xenon.

    Science.gov (United States)

    Britvin, Sergey N; Kashtanov, Sergei A; Krzhizhanovskaya, Maria G; Gurinov, Andrey A; Glumov, Oleg V; Strekopytov, Stanislav; Kretser, Yury L; Zaitsev, Anatoly N; Chukanov, Nikita V; Krivovichev, Sergey V

    2015-11-23

    The Group 18 elements (noble gases) were the last ones in the periodic system to have not been encountered in perovskite structures. We herein report the synthesis of a new group of double perovskites KM(XeNaO6) (M = Ca, Sr, Ba) containing framework-forming xenon. The structures of the new compounds, like other double perovskites, are built up of the alternating sequence of corner-sharing (XeO6) and (NaO6) octahedra arranged in a three-dimensional rocksalt order. The fact that xenon can be incorporated into the perovskite structure provides new insights into the problem of Xe depletion in the atmosphere. Since octahedrally coordinated Xe(VIII) and Si(IV) exhibit close values of ionic radii (0.48 and 0.40 Å, respectively), one could assume that Xe(VIII) can be incorporated into hyperbaric frameworks such as MgSiO3 perovskite. The ability of Xe to form stable inorganic frameworks can further extend the rich and still enigmatic chemistry of this noble gas.

  20. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    OpenAIRE

    Ma, Q.L.; X. M. Zhang; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rar...

  1. Compensated Ferrimagnetic Tetragonal Heusler Thin Films for Antiferromagnetic Spintronics.

    Science.gov (United States)

    Sahoo, Roshnee; Wollmann, Lukas; Selle, Susanne; Höche, Thomas; Ernst, Benedikt; Kalache, Adel; Shekhar, Chandra; Kumar, Nitesh; Chadov, Stanislav; Felser, Claudia; Parkin, Stuart S P; Nayak, Ajaya K

    2016-10-01

    Fully compensated ferrimagnets with tetragonal crystal structure have the potential for large spin-polarization and strong out-of-plane magnetic anisotropy; hence, they are ideal candidates for high-density-memory applications. Tetragonal Heusler thin films with compensated magnetic state are realized by substitution of Pt in Mn3-x Ptx Ga. Furthermore, the bilayer formed from compensated/uncompensated Mn-Pt-Ga layers is utilized to accomplish exchange bias up to room temperature.

  2. A study of the crystal structures and the phase transitions of the ordered double perovskites Sr{sub 2}ScSbO{sub 6} and Ca{sub 2}ScSbO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Faik, A., E-mail: afaik@cicenergigune.com [Fisika Aplikatua II Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, P.O.Box 644, Bilbao 48080 (Spain); CICenergigune, Parque Tecnologico, Albert Einstein 48, 01510 Minano, Alava (Spain); Orobengoa, D. [Departamento de Fisica de la Materia Condensada, Universidad del Pais Vasco, E-48080 Bilbao (Spain); Iturbe-Zabalo, E.; Igartua, J.M. [Fisika Aplikatua II Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, P.O.Box 644, Bilbao 48080 (Spain)

    2012-08-15

    The crystal structures and phase transitions of the two ordered double perovskites Sr{sub 2}ScSbO{sub 6} and Ca{sub 2}ScSbO{sub 6} were studied using conventional X-ray and neutron powder-diffraction methods. The crystal structures of both compounds have the P2{sub 1}/n space group symmetry at room temperature, resulting from Sc/Sb ordering. The evolution with temperature of the structure of the Sr containing compound shows the presence of three phase transitions with the following sequence: P2{sub 1}/n{yields}I2/m{yields}I4/m{yields}Fm3{sup Macron }m, at about 400, 560 and 650 K, respectively. The smaller size of Ca cation, with respect to that of Sr cation, leads to a large distortion of Ca{sub 2}ScSbO{sub 6} at room temperature. This fact in turn causes that the Ca containing compound shows only the first phase transition from P2{sub 1}/n to I2/m at high temperature at about 1440 K. The analysis of the phase transitions and the refinements have done using the symmetry-adapted modes and the tools of the Bilbao Crystallographic Server. - Graphical abstract: Representation of the new structure resulting from the coupling of the unidimensional GM{sup 4+} and X{sup 3+} modes with the a{sup +}b{sup -}b{sup -} tilting scheme associated to P2{sub 1}/n and the temperature evolution of the amplitudes of the GM{sup 1+}, GM{sup 3+}, GM{sup 4+} and GM{sup 5+} modes of I2/m and I4/m space groups obtained from the NPD data of Sr{sub 2}ScSbO{sub 6}. Highlights: Black-Right-Pointing-Pointer Study of two compounds of the antimony double perovskite family. Black-Right-Pointing-Pointer Determination of the structures at room temperature. Black-Right-Pointing-Pointer Determination of high-temperature phase transitions by X-ray and neutron powder diffraction. Black-Right-Pointing-Pointer Using the symmetry-adapted modes to study the phase transitions.

  3. 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.

  4. Performance of cobalt-free double-perovskite NdBaFe{sub 2−x}Mn{sub x}O{sub 5+δ} cathode materials for proton-conducting IT-SOFC

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Xinbo; Yu, Tian; Ma, Guilin, E-mail: 32uumagl@suda.edu.cn

    2015-07-15

    Highlights: • A novel series of double-perovskite NdBaFe{sub 2−x}Mn{sub x}O{sub 5+δ} cathode materials were prepared. • Among the materials, the NBFM10 exhibits the highest conductivity of 114 S cm{sup −1}. • P-type electronic conduction is dominant in the oxygen partial pressure range tested. • Peak power density of the cell using NBFM10–BZCY composite cathode reached 453 mW cm{sup −2}. • The interfacial polarization resistance (R{sub p}) is as low as 0.06 Ω cm{sup 2} at 700 °C. - Abstract: A novel series of cobalt-free cathode materials, NdBaFe{sub 2−x}Mn{sub x}O{sub 5+δ} (0.0 x 0.3), are prepared by a citric acid–nitrate process. X-ray diffraction (XRD) analysis indicates that all the samples are double-perovskite phases with cubic structure. The conductivity dependence of the cathode materials on temperature (300–800 °C) and oxygen partial pressure (1–10{sup −10} atm) is investigated. Among the tested samples, NdBaFe{sub 1.9}Mn{sub 0.1}O{sub 5+δ} (NBFM10) exhibits the highest conductivity of 114 S cm{sup −1} in air at 550 °C. The H{sub 2}/air fuel cell with the NBFM10–BZCY composite cathode and NiO–BZCY composite anode as well as BaZr{sub 0.1}Ce{sub 0.7}Y{sub 0.2}O{sub 3−α} (BZCY) electrolyte membrane (ca. 30 μm thickness) was assembled and tested at 500–700 °C. The peak power density of the cell reaches 453 mW cm{sup −2}, and the interfacial polarization resistance R{sub p} is only 0.06 Ω cm{sup 2} under open circuit conditions, at 700 °C.

  5. Magnon Mode Selective Spin Transport in Compensated Ferrimagnets

    KAUST Repository

    Cramer, Joel

    2017-04-13

    We investigate the generation of magnonic thermal spin currents and their mode selective spin transport across interfaces in insulating, compensated ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal exhibits a nonmonotonic temperature dependence with two sign changes of the detected voltage signals. Using different ferrimagnetic garnets, we demonstrate the universality of the observed complex temperature dependence of the spin Seebeck effect. To understand its origin, we systematically vary the interface between the ferrimagnetic garnet and the metallic layer, and by using different metal layers we establish that interface effects play a dominating role. They do not only modify the magnitude of the spin Seebeck effect signal but in particular also alter its temperature dependence. By varying the temperature, we can select the dominating magnon mode and we analyze our results to reveal the mode selective interface transmission probabilities for different magnon modes and interfaces. The comparison of selected systems reveals semiquantitative details of the interfacial coupling depending on the materials involved, supported by the obtained field dependence of the signal.

  6. Some Lower Valence Vanadium Fluorides: Their Crystal Distortions, Domain Structures, Modulated Structures, Ferrimagnetism, and Composition Dependence.

    Science.gov (United States)

    Hong, Y. S.; And Others

    1980-01-01

    Describes some contemporary concepts unique to the structure of advanced solids, i.e., their crystal distortions, domain structures, modulated structures, ferrimagnetism, and composition dependence. (Author/CS)

  7. Green's function study of a mixed spin-1 and spin-3/2 Heisenberg ferrimagnetic system

    Energy Technology Data Exchange (ETDEWEB)

    Mert, Guelistan, E-mail: gmert@selcuk.edu.tr [Department of Physics, Selcuk University, 42075 Kampues Konya (Turkey)

    2012-09-15

    The magnetic properties of a mixed spin-1 and spin-3/2 Heisenberg ferrimagnetic system on a square lattice are investigated by using the double-time temperature-dependent Green's function technique. In order to decouple the higher order Green's functions, Anderson and Callen's decoupling and random phase approximations have been used. The nearest- and next-nearest-neighbor interactions and the single-ion anisotropies are considered and their effects on compensation and critical temperature are studied. - Highlights: Black-Right-Pointing-Pointer We investigate the magnetic properties of a mixed spin-1 and spin-3/2 Heisenberg ferrimagnetic system on a square lattice. Black-Right-Pointing-Pointer We use the double-time temperature-dependent Green's function technique. Black-Right-Pointing-Pointer Nearest- and next-nearest-neighbor interactions and single-ion anisotropies are considered. Black-Right-Pointing-Pointer Their effects on compensation and critical temperature are studied. Black-Right-Pointing-Pointer We determined the conditions satisfied by critical and compensation temperatures.

  8. 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.

  9. A redox-stable direct-methane solid oxide fuel cell (SOFC) with Sr2FeNb0.2Mo0.8O6-δ double perovskite as anode material

    Science.gov (United States)

    Ding, Hanping; Tao, Zetian; Liu, Shun; Yang, Yating

    2016-09-01

    Development of high-performing and redox-stable ceramic oxide electrode materials is a crucial technical step for direct hydrocarbon solid oxide fuel cells (SOFCs) operating at intermediate temperatures (550-700 °C). Here we report a nickel-free double perovskite, Sr2FeNb0.2Mo0.8O6-δ (SFNM20), for SOFC anode, and this anode shows outstanding performances with high resistance against carbon build-up and redox cycling in hydrocarbon fuels. At 800 °C, the SFNM20 anode shows electrical conductivity of 5.3 S cm-1 in 5% H2 and peak power densities of 520 and 380 mW cm-2 using H2 and CH4 as the fuel, respectively. The cell exhibits a very stable performance under different constant current loads in H2 and CH4 at 700 °C and high redox stability against the gas environment changes in the anode chamber. In addition, the electrode is structurally stable in various fuels, suggesting that it is a feasible material candidate for the electrode of high-performing SOFCs.

  10. Molybdenum doped Pr0.5Ba0.5MnO3-δ (Mo-PBMO) double perovskite as a potential solid oxide fuel cell anode material

    Science.gov (United States)

    Sun, Yi-Fei; Zhang, Ya-Qian; Hua, Bin; Behnamian, Yashar; Li, Jian; Cui, Shao-Hua; Li, Jian-Hui; Luo, Jing-Li

    2016-01-01

    A layered Mo doped Pr0.5Ba0.5MnO3-δ (Mo-PBMO) double perovskite oxide was prepared by a modified sol-gel method and the properties of the fabricated material are characterized by various technologies. The results of X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), and thermogravimetric analysis (TGA) demonstrate that the treatment in reducing atmosphere at high temperature lead to a significant phase transformation of the material to a single cubic phase as well as with the Mo in multiple oxidized states. Such character leads to the production of large amount of oxygen deficiency with facilitated oxygen diffusion. The electrochemical performance tests of half-cell and single cell SOFCs exhibit the promoted effect of Mo on catalytic activity for the oxidation of H2 and CH4, indicating that Mo-PBMO could serve as an anode material candidate for SOFCs.

  11. Cation distribution in Ba{sub 2}(Fe,W{sub 0.5}Mo{sub 0.5}){sub 2}O{sub 6} double-perovskites: A combined synchrotron and neutron diffraction, magnetization and Moessbauer spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Rammeh, N. [Laboratoire de Physique des Materiaux, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia); Institute for Materials Science, University of Technology, D-64287 Darmstadt (Germany); Ehrenberg, H. [Institute for Materials Science, University of Technology, D-64287 Darmstadt (Germany); Ritter, C. [Institut Laue Langevin, BP 156, F-38042 Grenoble Cedex 9 (France); Fuess, H. [Institute for Materials Science, University of Technology, D-64287 Darmstadt (Germany); Cheikhrouhou, A. [Laboratoire de Physique des Materiaux, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia)], E-mail: abdcheikhrouhou@yahoo.fr

    2009-03-20

    The crystallographic and magnetic structures of polycrystalline Ba{sub 2}(Fe,W){sub 2}O{sub 6} and Ba{sub 2}(Fe,W{sub 0.5}Mo{sub 0.5}){sub 2}O{sub 6} double-perovskites have been investigated by X-ray and neutron powder diffraction (NPD), magnetization and Moessbauer spectroscopy. The samples were synthesized by conventional solid-state reaction at temperatures about 1273 K. The compounds crystallize in the cubic structure with space group Fm3-barm. The magnetic structures were determined by neutron powder diffraction between 5 K and 310 K. Evidence for an antiferromagnetic behavior has been observed for Ba{sub 2}(Fe,W){sub 2}O{sub 6} with T{sub N} = 24.7 K and a two-phase separation for Ba{sub 2}(Fe,W{sub 0.5}Mo{sub 0.5}){sub 2}O{sub 6} into an antiferromagnetic structure of the W-type with T{sub N} = 24.7 K and the ferromagnetic Mo-type with T{sub C} = 270 K.

  12. Nanorod Self-Assembly in High Jc YBa2Cu3O7−x Films with Ru-Based Double Perovskites

    Directory of Open Access Journals (Sweden)

    Javier F. Baca

    2011-11-01

    Full Text Available Many second phase additions to YBa2Cu3O7−x (YBCO films, in particular those that self-assemble into aligned nanorod and nanoparticle structures, enhance performance in self and applied fields. Of particular interest for additions are Ba-containing perovskites that are compatible with YBCO. In this report, we discuss the addition of Ba2YRuO6 to bulk and thick-film YBCO. Sub-micron, randomly oriented particles of this phase were found to form around grain boundaries and within YBCO grains in bulk sintered pellets. Within the limits of EDS, no Ru substitution into the YBCO was observed. Thick YBCO films were grown by pulsed laser deposition from a target consisting of YBa2Cu3Oy with 5 and 2.5 mole percent additions of Ba2YRuO6 and Y2O3, respectively. Films with enhanced in-field performance contained aligned, self-assembled Ba2YRuO6 nanorods and strained Y2O3 nanoparticle layers. A 0.9 µm thick film was found to have a self-field critical current density (Jc of 5.1 MA/cm2 with minimum Jc(Q, H=1T of 0.75 MA/cm2. Conversely, Jc characteristics were similar to YBCO films without additions when these secondary phases formed as large, disordered phases within the film. A 2.3 µm thick film with such a distribution of secondary phases was found to have reduced self-field Jc values of 3.4 MA/cm2 at 75.5 K and Jc(min, Q, 1T of 0.4 MA/cm2.

  13. Review of magnetocaloric effect in perovskite-type oxides

    Institute of Scientific and Technical Information of China (English)

    Zhong Wei; Au Chak-Tong; Du You-Wei

    2013-01-01

    We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO3-type manganese oxides,A3B2O7-type two-layered perovskite oxides,and A2B'B''O6-type ordered double-perovskite oxides).Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La(Ⅰ)-xCaxMnO3 and alkali-metal (Na or K)doped La0.8Ca0.2MnO3 perovskite-type manganese oxides.The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature.Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+δ(0 < x < 0.5),and double-perovskite Ba2Fe1+xMo1-xO6(0 ≤ x ≤ 0.3) near their respective Curie temperatures.Compared with rare earth metals and their alloys,the perovskite-type oxides are lower in cost,and they exhibit higher chemical stability and higher electrical resistivity,which together favor lower eddy-current heating.They are potential magnetic refrigerants at high temperatures,especially near room temperature.

  14. Magnetic properties of a single transverse Ising ferrimagnetic nanoparticle

    Energy Technology Data Exchange (ETDEWEB)

    Bouhou, S.; El Hamri, M. [Laboratoire de Physique des Matériaux et Modélisation des Systèmes, (LP2MS), Unité Associée au CNRST-URAC 08, University of Moulay Ismail, Physics Department, Faculty of Sciences, B.P. 11201 Meknes (Morocco); Essaoudi, I. [Laboratoire de Physique des Matériaux et Modélisation des Systèmes, (LP2MS), Unité Associée au CNRST-URAC 08, University of Moulay Ismail, Physics Department, Faculty of Sciences, B.P. 11201 Meknes (Morocco); Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, 75120 Uppsala (Sweden); Ainane, A., E-mail: ainane@pks.mpg.de [Laboratoire de Physique des Matériaux et Modélisation des Systèmes, (LP2MS), Unité Associée au CNRST-URAC 08, University of Moulay Ismail, Physics Department, Faculty of Sciences, B.P. 11201 Meknes (Morocco); Max-Planck-Institut für Physik Complexer Systeme, Nöthnitzer Str. 38 D-01187 Dresden (Germany); Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, 75120 Uppsala (Sweden); Ahuja, R. [Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, 75120 Uppsala (Sweden)

    2015-01-01

    Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation function, the thermal and the magnetic properties of a single Ising nanoparticle consisting of a ferromagnetic core, a ferromagnetic surface shell and a ferrimagnetic interface coupling are examined. The effect of the transverse field in the surface shell, the exchange interactions between core/shell and in surface shell on the free energy, thermal magnetization, specific heat and susceptibility are studied. A number of interesting phenomena have been found such as the existence of the compensation phenomenon and the magnetization profiles exhibit P-type, N-type and Q-type behaviors.

  15. High-sensitivity piezoelectric perovskites for magnetoelectric composites

    Science.gov (United States)

    Amorín, Harvey; Algueró, Miguel; Campo, Rubén Del; Vila, Eladio; Ramos, Pablo; Dollé, Mickael; Romaguera-Barcelay, Yonny; Cruz, Javier Pérez De La; Castro, Alicia

    2015-01-01

    A highly topical set of perovskite oxides are high-sensitivity piezoelectric ones, among which Pb(Zr,Ti)O3 at the morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal polymorphic phases is reckoned a case study. Piezoelectric ceramics are used in a wide range of mature, electromechanical transduction technologies like piezoelectric sensors, actuators and ultrasound generation, to name only a few examples, and more recently for demonstrating novel applications like magnetoelectric composites. In this case, piezoelectric perovskites are combined with magnetostrictive materials to provide magnetoelectricity as a product property of the piezoelectricity and piezomagnetism of the component phases. Interfaces play a key issue, for they control the mechanical coupling between the piezoresponsive phases. We present here main results of our investigation on the suitability of the high sensitivity MPB piezoelectric perovskite BiScO3–PbTiO3 in combination with ferrimagnetic spinel oxides for magnetoelectric composites. Emphasis has been put on the processing at low temperature to control reactions and interdiffusion between the two oxides. The role of the grain size effects is extensively addressed. PMID:27877758

  16. Polar Behavior in a Magnetic Perovskite Via A-Site Size Disorder

    Energy Technology Data Exchange (ETDEWEB)

    Park, Chul-Hong [ORNL; Singh, David J [ORNL

    2008-01-01

    We elucidate a mechanism for obtaining polar behavior in magnetic perovskites based on A-site disorder and demonstrate this mechanism by density functional calculations for the double perovskite (La,Lu)MnNiO{sub 6} with Lu concentrations at and below 50%. We show that this material combines polar behavior and ferromagnetism. The mechanism is quite general and may be applicable to a wide range of magnetic perovskites.

  17. Polar Behavior in a Magnetic Perovskite from A-Site Size Disorder: A Density Functional Study

    Science.gov (United States)

    Singh, D. J.; Park, Chul Hong

    2008-02-01

    We elucidate a mechanism for obtaining polar behavior in magnetic perovskites based on A-site disorder and demonstrate this mechanism by density functional calculations for the double perovskite (La,Lu)MnNiO6 with Lu concentrations at and below 50%. We show that this material combines polar behavior and ferromagnetism. The mechanism is quite general and may be applicable to a wide range of magnetic perovskites.

  18. Experimental studies of magnetic perovskites

    Science.gov (United States)

    Golovanov, Vladimir Valentinovich

    1998-11-01

    The present work addresses the phenomenon of Giant Magnetoresistance (GMR) and the role of Jahn-Teller distortion in the conduction mechanism of GMR materials. For this purpose, GMR and related perovskites are studied experimentally using infrared reflection spectroscopy, synchrotron x-ray diffraction, and electrical transport measurements. Reflectivity and x-ray diffraction studies of a vacancy doped rhombohedrally distorted GMR material, La0.936Mn0.982O3, indicate the presence of dynamic Jahn-Teller distortion above the magnetic ordering temperature (Tc = 225K) and a substantial reduction of the distortion below Tc. In particular, above Tc, the optical conductivity of large single crystals of the material shows the broad peak around 10,000 cm-1, which shifts towards zero frequency as the ferromagnetic state develops. The peak is attributed to the Jahn-Teller splitting of the two-fold degenerate eg level. Powder x-ray diffraction measurements performed on the same material reveal a sharp 3% reduction of the rhombohedral distortion at the magnetic ordering temperature. This reduction reflects the decrease in the magnitude of the dynamic Jahn-Teller distortion at the magnetic ordering. The transport and magnetic measurements on non Jahn-Teller active La1-xSrxCoO3 perovskites show much lower magnetoresistance, compatible with the conventional double-exchange theory. The relatively high values of magnetoresistance for low doped (x ≤ 0.15) compounds at low temperatures are also interpreted in terms of the double-exchange model.

  19. Critical temperature of a mixed ferro-ferrimagnetic ternary alloy

    Science.gov (United States)

    Dely, Ján; Bobák, Andrej; Žukovič, Milan

    2010-01-01

    We study the critical properties of a mixed ferro-ferrimagnetic ternary alloy of the type ABpC1-p on a cubic lattice consisting of three different Ising spins SA = 3/2, SB = 2, and SC = 5/2. The A ions are linked with either the B or C ions which are randomly distributed in the lattice with the concentration p or 1-p, respectively. The exchange interactions between nearest neighbours only, JAB > 0 and JAC JAC|JAB and concentration p on the critical behaviour of the system are investigated and the results from both methods are compared. We find that the critical temperature of the mixed ferro-ferrimagnet for a special value of R does not depend on the concentration p. The relation between the studied model and the structure of the Prussian blue analog such as (Fe11pMn111-p)1.5[Cr111(CN)6] · nH2O is also discussed.

  20. Magnetic vortex nucleation/annihilation in artificial-ferrimagnet microdisks

    Science.gov (United States)

    Lapa, Pavel N.; Ding, Junjia; Phatak, Charudatta; Pearson, John E.; Jiang, J. S.; Hoffmann, Axel; Novosad, Valentine

    2017-08-01

    The topological nature of the magnetic-vortex state gives rise to peculiar magnetization reversal observed in magnetic microdisks. Interestingly, magnetostatic and exchange, energies which, drive this reversal can be effectively controlled in artificial ferrimagnet heterostructures composed of rare-earth and transition metals. [Py(t)/Gd(t)]25 (t = 1 or 2 nm) superlattices demonstrate a pronounced change of the magnetization and exchange stiffness in a 10-300 K temperature range as well as very small magnetic anisotropy. Due to these properties, the magnetization of cylindrical microdisks composed of these artificial ferrimagnets can be transformed from the vortex to uniformly magnetized states in a permanent magnetic field by changing the temperature. We explored the behavior of magnetization in 1.5-μm [Py(t)/Gd(t)]25 (t = 1 or 2 nm) disks at different temperatures and magnetic fields and observed that due to the energy barrier separating vortex and uniformly magnetized states, the vortex nucleation and annihilation occur at different temperatures. This causes the temperature dependences of the magnetization in these Py/Gd disks to demonstrate a unique hysteretic behavior in a narrow temperature range. It was discovered that for the [Py(2 nm)/Gd(2 nm)]25 microdisks, the vortex can be metastable within a certain temperature range.

  1. Ultrafast heating-induced magnetization switching in ferrimagnets

    Science.gov (United States)

    Gridnev, V. N.

    2016-11-01

    We study theoretically the light-induced magnetization switching in a binary ferrimagnet of the type {{A}p} {{B}1-p} , randomly occupied by two different species of magnetic ions. The localized spins are coupled with spins of itinerant electrons via s-d exchange interaction. Model parameters are chosen so that to achieve similarity between magnetic characteristics of the model and those of ferrimagnetic rare-earth-transition metal GdFeCo alloys. The switching is triggered by heating of the itinerant electrons by a laser pulse. The spin dynamics is governed by the cooling of itinerant electrons, exchange scattering, induced by the s-d exchange interaction and spin-lattice relaxation of the itinerant spins with a characteristic time {τs} . The dynamics of the localized and itinerant spins is described by coupled rate equations. The main conclusion of this study is that the switching occurs only in a certain temperature range depending on {τs} . For long {τs} the switching occurs only below the magnetisation compensation temperature T K. For physically reasonable values of {τs} this temperature range extends from 0 K to {{T}f} ≤ft({τs}\\right) , where {{T}f} ≤ft({τs}\\right) is slightly higher than the compensation temperature T K. With further decrease of {τs} this temperature range shifts to temperatures higher than T K.

  2. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    Science.gov (United States)

    Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  3. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy.

    Science.gov (United States)

    Ma, Q L; Zhang, X M; Miyazaki, T; Mizukami, S

    2015-01-19

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (K(u)(eff)) over 6 Merg/cm(3) is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and K(u)(eff) of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  4. Evidence of spin-glass like ordering and exchange bias effect in antisite-disordered nanometric La1.5Ca0.5CoMnO6 double perovskite

    Science.gov (United States)

    Sahoo, R. C.; Paladhi, D.; Nath, T. K.

    2017-08-01

    Single-phase polycrystalline La1.5Ca0.5CoMnO6 double perovskite nanoparticles (∼25 nm) have been synthesized by chemical sol-gel method. We report here the structural, magnetic and transport properties using X-ray diffraction, dc magnetization, ac susceptibility, exchange bias and dc resistivity measurements. The Rietveld refinement of X-ray diffraction pattern reveals that the La1.5Ca0.5CoMnO6 (LCCMO) system crystallizes in orthorhombic structure with pbnm space group. Mn and Co ions are not completely ordered on the B sites due to the presence of about 30% antisite-disorder in the system. The ordering of Co2+ and Mn4+ gives rise to the ferromagnetism below 145 K. A spin glass like ground state has also been observed near 37.6(4) K, arising mainly due to the presence of competing magnetic interactions and antisite-disorder in the LCCMO nanoparticles. The frequency dependence peak shift of the Ac-susceptibility peak in the glassy state follows the critical slowing down model. The observed memory effect in ac susceptibility data reveals the existence of interacting clusters in a competing magnetic interactions state. The presence of noticeable exchange bias effect can be best explained on the basis of uncompensated interface (ferromagnetic/spin-glass) spins of antisite-disordered LCCMO system. This anti-site disordered nanocompound exhibits semiconducting behavior with variable range hopping kind of electronic conduction mechanism in the temperature range of 200-300 K. We have also observed large negative magnetoresistance (-30% at 100 K and 60 kOe) mainly due to the spin-polarized transport across the grain boundaries.

  5. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

    Science.gov (United States)

    Marini, C; Noked, O; Kantor, I; Joseph, B; Mathon, O; Shuker, R; Kennedy, B J; Pascarelli, S; Sterer, E

    2016-02-03

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa.

  6. 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.

  7. Noncollinear antiferromagnetism of coupled spins and pseudospins in the double perovskite La2CuIrO6

    Energy Technology Data Exchange (ETDEWEB)

    Manna, Kaustuv [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Sarkar, R. [Technische Univ. Dresden (Germany); Fuchs, S. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Onykiienko, Y. A. [Technische Univ. Dresden (Germany); Bera, A. K. [Bhabha Atomic Research Centre (BARC), Mumbai (India); Cansever, G. Aslan [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Kamusella, S. [Technische Univ. Dresden (Germany); Maljuk, A. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Blum, C. G. F. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Corredor, L. T. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Wolter, A. U. B. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Yusuf, S. M. [Bhabha Atomic Research Centre (BARC), Mumbai (India); Frontzek, M. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Keller, L. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Iakovleva, M. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Russian Academy of Sciences (RAS), Kazan (Russian Federation); Vavilova, E. [Russian Academy of Sciences (RAS), Kazan (Russian Federation); Grafe, H. -J. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Kataev, V. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Klauss, H. -H. [Technische Univ. Dresden (Germany); Inosov, D. S. [Technische Univ. Dresden (Germany); Wurmehl, S. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Technische Univ. Dresden (Germany); Büchner, B. [Leibniz Inst. for Solid State and Materials Research (IFW), Dresden (Germany); Technische Univ. Dresden (Germany)

    2016-10-01

    This article reports the structural, magnetic, and thermodynamic properties of the double perovskite compound La2CuIrO6 from x-ray, neutron diffraction, neutron depolarization, dc magnetization, ac susceptibility, specific heat, muon-spin-relaxation ( μ SR ) , electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below ~113 K, short-range spin-spin correlations occur within the Cu2+ sublattice.

  8. A Review on Visible Light Active Perovskite-Based Photocatalysts

    Directory of Open Access Journals (Sweden)

    Pushkar Kanhere

    2014-12-01

    Full Text Available 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.

  9. The double-well oscillating potential of oxygen atoms in perovskite system Ba(K)BiO sub 3 : EXAFS - analysis results

    CERN Document Server

    Menushenkov, A P; Konarev, P V; Meshkov, A A; Benazeth, S; Purans, J

    2000-01-01

    Temperature-dependent X-ray absorption investigations were made on the Bi L sub 3 -edge in Ba sub 1 sub - sub x K sub x BiO sub 3 with x=0.0, 0.4 and 0.5. For the superconducting samples (x=0.4 and 0.5) it has been found that the local structure differs from the ideal cubic in contrast to the neutron and X-ray diffraction data. The provided analysis of the EXAFS spectra indicates that the oxygen atoms move in double-well potential produced by the existence of two non-equivalent octahedral types of the oxygen environment of bismuth. The vibrations in such a potential lead to modulations of the Bi-O lengths with low frequency which is determined by the soft oxygen octahedron rotation mode frequency. This induces strong electron-phonon interaction and may be the reason for relatively high-temperature transition (T sub c approx 30 K) to the superconducting state.

  10. Ferrimagnetic properties of Co/(Gd-Co) multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Svalov, A.V. [Institute of Physics and Applied Mathematics, Ural State University, Lenin Avenue 51, 620083, Ekaterinburg (Russian Federation) and Departamento de Fisica, Universidad de Oviedo, Avenida Calvo Sotelo s/n, 33007, Oviedo, Asturias (Spain)]. E-mail: andrey.svalov@usu.ru; Fernandez, A. [Departamento de Fisica, Universidad de Oviedo, Avenida Calvo Sotelo s/n, 33007, Oviedo, Asturias (Spain); Vas' kovskiy, V.O. [Institute of Physics and Applied Mathematics, Ural State University, Lenin Avenue 51, 620083, Ekaterinburg (Russian Federation); Tejedor, M. [Departamento de Fisica, Universidad de Oviedo, Avenida Calvo Sotelo s/n, 33007, Oviedo, Asturias (Spain); Barandiaran, J.M. [Departamento de Electricidad y Electronica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco, UPV/EHU, P.O. Box 644, 48080, Bilbao (Spain); Orue, I. [Departamento de Electricidad y Electronica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco, UPV/EHU, P.O. Box 644, 48080, Bilbao (Spain); Kurlyandskaya, G.V. [Departamento de Electricidad y Electronica, Facultad de Ciencia y Tecnologia, Universidad del Pais Vasco, UPV/EHU, P.O. Box 644, 48080, Bilbao (Spain)

    2006-09-15

    Co/(Gd-Co) multilayers have been prepared by rf-sputtering and investigated by means of Transverse Magnetooptic Kerr Effect (TMOKE), SQUID and VSM magnetometry. The composition of amorphous Gd{sub 0.36}Co{sub 0.64} layers was chosen so that their saturation magnetization was dominated by Gd moments in all the temperature range. Co and Gd-Co layers formed a macroscopic ferrimagnetically coupled system displaying a compensation temperature. Complete magnetic moment compensation was found at such point. An inversion of TMOKE hysteresis loops and a divergent behaviour of coercivity were also observed. By changing the layers thickness it has been possible to control the magnetic characteristics of the Co/(Gd-Co) structures, in particular the compensation takes place at different temperatures.

  11. Benign-by-Design Solventless Mechanochemical Synthesis of Three-, Two-, and One-Dimensional Hybrid Perovskites.

    Science.gov (United States)

    Jodlowski, Alexander D; Yépez, Alfonso; Luque, Rafael; Camacho, Luis; de Miguel, Gustavo

    2016-11-21

    Organic-inorganic hybrid perovskites have attracted significant attention owing to their extraordinary optoelectronic properties with applications in the fields of solar energy, lighting, photodetectors, and lasers. The rational design of these hybrid materials is a key factor in the optimization of their performance in perovskite-based devices. Herein, a mechanochemical approach is proposed as a highly efficient, simple, and reproducible method for the preparation of four types of hybrid perovskites, which were obtained in large amounts as polycrystalline powders with high purity and excellent optoelectronics properties. Two archetypal three-dimensional (3D) perovskites (MAPbI3 and FAPbI3 ) were synthesized, together with a bidimensional (2D) perovskite (Gua2 PbI4 ) and a "double-chain" one-dimensional (1D) perovskite (GuaPbI3 ), whose structure was elucidated by X-ray diffraction.

  12. Monte Carlo study of magnetic and thermodynamic properties of a ferrimagnetic Ising nanoparticle with hexagonal core-shell structure

    Science.gov (United States)

    Wang, Wei; Chen, Dong-dong; Lv, Dan; Liu, Jin-ping; Li, Qi; Peng, Zhou

    2017-09-01

    The Monte Carlo method has been used to study the magnetic and thermodynamic properties of a hexagonal ferrimagnetic Ising nanoparticle with spin-3/2 inner core surrounded by spin-1 surface shell layers. The effects of exchange couplings and crystal-fields on the compensation behaviors and critical phenomena of the system have been investigated in detail. Many types of the magnetization curves have been found, depending on the competitions among the exchange couplings, the crystal-fields and the temperature. The phase diagrams for different exchange couplings and crystal-fields have been also obtained. In Particular, we have discovered the double and triple hysteresis loops for certain physical parameters in the present system. An excellent agreement has been achieved from the comparison between our results and the previous studies.

  13. Ferroelectric ultrathin perovskite films

    Science.gov (United States)

    Rappe, Andrew M; Kolpak, Alexie Michelle

    2013-12-10

    Disclosed herein are perovskite ferroelectric thin-film. Also disclosed are methods of controlling the properties of ferroelectric thin films. These films can be used in a variety materials and devices, such as catalysts and storage media, respectively.

  14. 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)

  15. PEROVSKITE SOLAR CELLS (REVIEW ARTICLE)

    OpenAIRE

    Benli, Deniz Ahmet

    2015-01-01

    A solar cell is a device that converts sunlight into electricity. There are different types of solar cells but this report mainly focuses on a type of new generation solar cell that has the name organo-metal halide perovskite, shortly perovskite solar cells. In this respect, the efficiency of power conversion is taken into account to replace the dominancy of traditional and second generation solar cell fields by perovskite solar cells. Perovskite solar cell is a type of solar cell including a...

  16. In Vitro Evaluation of Some Types of Ferrimagnetic Glass Ceramics

    Directory of Open Access Journals (Sweden)

    S. A. M. Abdel-Hameed

    2014-01-01

    Full Text Available The present study aimed at studying the acceleration of the bioactive layer on the surface of ferrimagnetic glass ceramic with a basic composition 40Fe2O3–15P2O5–20SiO2–5TiO2 through the addition of 20% of different types of metal oxides like MgO or CaO or MnO or CuO or ZnO or CeO2. SEM, EDAX, and ICP were applied to present the results of the study. SEM and EDAX measurements indicated the presence of apatite layer formed on the surface of the prepared glass ceramics after immersion in SBF within 7 to 30 days. The investigation of the results clarified that the addition of CaO or ZnO accelerated the formation of apatite on the surfaces of the samples in the simulated body fluid faster than other metal oxides. Inductive coupled plasma (ICP analysis shows the evolution of ion extraction by the simulated body fluid solution (SBF with time in relation to the elemental composition.

  17. Engineered Heusler Ferrimagnets with a Large Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Reza Ranjbar

    2015-09-01

    Full Text Available Synthetic perpendicular magnetic anisotropy (PMA ferrimagnets consisting of 30-nm-thick D022-MnGa and Co2MnSi (CMS cubic Heusler alloys with different thicknesses of 1, 3, 5, 10 and 20 nm, buffered and capped with a Cr film, are successfully grown epitaxially on MgO substrate. Two series samples with and without post annealing at 400 °C are fabricated. The (002 peak of the cubic L21 structure of CMS films on the MnGa layer is observed, even for the 3-nm-thick CMS film for both un-annealed and annealed samples. The smaller remnant magnetization and larger switching field values of CMS (1–20 nm/MnGa (30 nm bilayers compared with 30-nm-thick MnGa indicates antiferromagnetic (AFM interfacial exchange coupling (Jex between MnGa and CMS films for both un-annealed and annealed samples. The critical thickness of the CMS film for observing PMA with AFM coupling in the CMS/MnGa bilayer is less than 10 nm, which is relatively large compared to previous studies.

  18. Machine learning bandgaps of double perovskites

    National Research Council Canada - National Science Library

    Pilania, G; Mannodi-Kanakkithodi, A; Uberuaga, B P; Ramprasad, R; Gubernatis, J E; Lookman, T

    2016-01-01

    .... While quantum mechanical computations for high-fidelity bandgaps are enormously computation-time intensive and thus impractical in high throughput studies, informatics-based statistical learning...

  19. New statistical lattice model with double honeycomb symmetry

    Science.gov (United States)

    Naji, S.; Belhaj, A.; Labrim, H.; Bhihi, M.; Benyoussef, A.; El Kenz, A.

    2014-04-01

    Inspired from the connection between Lie symmetries and two-dimensional materials, we propose a new statistical lattice model based on a double hexagonal structure appearing in the G2 symmetry. We first construct an Ising-1/2 model, with spin values σ = ±1, exhibiting such a symmetry. The corresponding ground state shows the ferromagnetic, the antiferromagnetic, the partial ferrimagnetic and the topological ferrimagnetic phases depending on the exchange couplings. Then, we examine the phase diagrams and the magnetization using the mean field approximation (MFA). Among others, it has been suggested that the present model could be localized between systems involving the triangular and the single hexagonal lattice geometries.

  20. Synthesis, structure and magnetic properties of Sr{sub 2}Fe{sub 1-x}Ga{sub x}MoO{sub 6} (0 {<=} x {<=} 0.6) double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Azad, Abul K., E-mail: aka7@st-andrews.ac.uk [School of Chemistry, University of St-Andrews, St-Andrews KY16 9ST (United Kingdom); Khan, Abdullah [Department of Chemistry, University of Balochistan (Pakistan); Eriksson, Sten-G. [Department of Environmental Inorganic Chemistry, Chalmers University of Technology, SE 412 96 Goeteborg (Sweden); Irvine, John T.S. [School of Chemistry, University of St-Andrews, St-Andrews KY16 9ST (United Kingdom)

    2009-12-15

    Polycrystalline Sr{sub 2}Fe{sub 1-x}Ga{sub x}MoO{sub 6} (0 {<=} x {<=} 0.6) materials have been synthesized by solid state reaction method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature dependent NPD data shows that the compounds crystallize in the tetragonal symmetry in the space group I4/m. The anti-site (AS) defects concentration increases with Ga doping, giving rise to highly B-site disordered materials. Ga doping at the Fe-site decreases the cell volume. The evolution of bond lengths and the cation oxidation states was determined from the Rietveld refinement data. The saturation magnetization and Curie temperature decreased with the increasing Ga content in the samples. Low temperature neutron diffraction data analysis and magnetization measurements confirm the magnetic interaction as ferrimagnetic in the sample.

  1. Perovskite photonic sources

    Science.gov (United States)

    Sutherland, Brandon R.; Sargent, Edward H.

    2016-05-01

    The field of solution-processed semiconductors has made great strides; however, it has yet to enable electrically driven lasers. To achieve this goal, improved materials are required that combine efficient (>50% quantum yield) radiative recombination under high injection, large and balanced charge-carrier mobilities in excess of 10 cm2 V-1 s-1, free-carrier densities greater than 1017 cm-3 and gain coefficients exceeding 104 cm-1. Solid-state perovskites are -- in addition to galvanizing the field of solar electricity -- showing great promise in photonic sources, and may be the answer to realizing solution-cast laser diodes. Here, we discuss the properties of perovskites that benefit light emission, review recent progress in perovskite electroluminescent diodes and optically pumped lasers, and examine the remaining challenges in achieving continuous-wave and electrically driven lasing.

  2. Synthesis and characterization of the double perovskite BaSrCoFe{sub 1}-{sub x}Ni{sub x}O{sub 5.5} like cathode for solid oxide fuel cells; Sintesis y caracterizacion de la doble perovskita BaSrCoFe{sub 1}-{sub x}Ni{sub x}O{sub 5.5} como catodo para celdas SOFC

    Energy Technology Data Exchange (ETDEWEB)

    Alvarado F, J.; Avalos R, L.; Viramontes G, G. [Universidad Michoacana de San Nicolas de Hidalgo, Facultad de Ingenieria Electrica, Santiago Tapia 403, Morelia 58030, Michoacan (Mexico); Reyes R, A. [Centro de Investigacion en Materiales Avanzados, Laboratorio Nacional de Nanotecnologia, Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31109, Chihuahua (Mexico)

    2013-08-01

    Have been synthesized via sol-gel method and characterized by X-ray diffraction, electrical conductivity and thermal expansion coefficient, new material composites BaSrCoFe{sub 1{sub x}}Ni{sub x}O{sub 5.5} (double perovskite type) with the addition of Ni in solid solution Ni{sub x} (x = 0.025, 0.05, 0.075, 0.1 and 0.2), as alternative cathodes for solid oxide fuel cells of intermediate temperature (Sofc-It). X-ray diffraction confirmed the formation of the tetragonal structure perovskite phase BaSrCoFe{sub 1}-{sub x}Ni{sub x}O{sub 5.5}, with the presence of small peaks identified in 2{theta} values below 30 degrees as BaCO{sub 3} and CoFe{sub 2}O{sub 4}. The electrical conductivity increases with the temperature between 350-470 degrees C and then decreases due to the loss of oxygen in the net, which causes differences in conductivity. Semiconductor behavior was obtained in all compositions. Thermal expansion coefficient determination, showed a linear dependence inversely proportional to the concentration of Ni. Our results of electrical conductivity and thermal expansion coefficient, reach to the conclusion that the cathodes between 0.1 and 0.2 Ni, have the greatest possibility for application in Sofc-It. (Author)

  3. Electrospun Perovskite Nanofibers

    Science.gov (United States)

    Chen, Dongsheng; Zhu, Yanyan

    2017-02-01

    CH3NH3PbI3 perovskite nanofibers were synthesized by versatile electrospinning techniques. The synthetic CH3NH3PbI3 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and photoluminescence. As counter electrodes, the synthesized nanofibers increased the performance of the dye-sensitized solar cells from 1.58 to 2.09%. This improvement was attributed to the enhanced smoothness and efficiency of the electron transport path. Thus, CH3NH3PbI3 perovskites nanofibers are potential alternative to platinum counter electrodes in dye-sensitized solar cells.

  4. Synthesis and structural characterization of the Ca2MnReO6 double perovskite Síntese e caracterização estrutural da dupla perovsquita Ca2MnReO6

    Directory of Open Access Journals (Sweden)

    H. P. S Corrêa

    2010-06-01

    Full Text Available The Ca2Mn1Re1O6 double perovskite has been prepared in polycrystalline form by using the encapsulated quartz tube method. The partial oxygen pressure inside the quartz tube revealed this to be a crucial synthesis parameter for the production of a single structural phase sample. This parameter was controlled using the ratio between ReO2 and ReO3 content and the filling factor parameter (ratio between mass and total inner volume of the quartz tube. The morphology and chemical composition was investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The crystal structure parameters were determined by analysis of the synchrotron high-resolution X-ray powder diffraction pattern. The analysis indicates that the sample is an ideal single-phase compound with a monoclinic crystal structure (space group P2(1/n with a = 5.44445(2 Å; b = 5.63957(3 Å; c = 7.77524(3 Å; and β = 90.18(1º. Computer simulations were performed considering two cation valence configurations, namely, (i Mn2+Re6+ or (ii Mn3+Re5+, for the Ca2Mn1Re1O6 compound. XANES analysis measurements indicated +2.3 for the average valence of Mn (a mixture of Mn2+ and Mn3+ and +5.7 for the effective valence of Re (an intermediate valence between Re4+ (ReO2 and Re6+ (ReO3. As a summary, we concluded there is a mixed valence configuration for Mn and Re in Ca2Mn1Re1O6 , taken into account the oxygen content of 6.0±0.1.A dupla perovsquita Ca2MnReO6 na forma policristalina foi preparada utilizando o método do tubo de quartzo encapsulado. A pressão parcial de oxigênio dentro do tubo de quartzo mostrou-se ser um parâmetro crucial para a produção de uma amostra estrutural monofásica. Esse parâmetro foi controlado usando a relação entre o conteúdo dos precursores ReO2 e ReO3 e o parâmetro fator de preenchimento (razão entre a massa e o volume interno total do tubo de quartzo.A morfologia e a composição química foi investigada através da microscopia eletr

  5. Tracing sediment using by enhancing the ferrimagnetic content of soil

    Science.gov (United States)

    Quinton, J.; Armstrong, A.; Maher, B. A.

    2010-12-01

    The last decades has seen the increasing development of new technologies for tracing the movement of sediment across landscapes, including rare earth element oxides, fluorescent particles and DNA tags. These new tracers allow us to tag soil particles using a chemical marker or introduce particles to the soil that mimic its behaviour. Once applied to the soil the particles can be recovered from the landscape or fluvial system and the concentration of tagged particles present quantified. Therefore there is the potential to use different tracers or different ‘species’ of the same tracer to collect data on temporal and spatial patterns of soil redistribution on hillsides and sediment delivery to fluvial systems, with a better resolving power than existing tracers, such as Cs137. Such data could help us in many ways, for example: improving our process understanding of soil erosion processes; understanding rates deposition and their links to biogeochemical cycling; providing spatial data for the validation of erosion models; and getting a better understanding of sediment residence times in catchments. However, there are problems with some of the new generation of tracer which include: different properties to the soil which is being tagged; difficulties with analytical methods; analysis costs; and poor recovery from hillslope scale experiments. In this paper we present initial findings on the use of soil with an enhanced ferrimagnetic content, but with the same physical characteristics as the parent soil, as a sediment tracer. To enhance the soil’s ferromagnetic content the soil was heated under reducing conditions. High and low field susceptibility, anhysteretic remanent magnetization, alternating frequency demagnetisation (10, 20, 30, 40, 60, and 80 mT), and isothermal remanent magnetization (10, 20, 50 100, 200, 300 and 1000 mT) of the bulk soil and the information on size specific erosion. Soil box experiments using rainfall simulation demonstrated the potential

  6. New Physical Deposition Approach for Low Cost Inorganic Hole Transport Layer in Normal Architecture of Durable Perovskite Solar Cells.

    Science.gov (United States)

    Nejand, Bahram Abdollahi; Ahmadi, Vahid; Shahverdi, Hamid Reza

    2015-10-07

    In this work we reported sputter deposited NiOx/Ni double layer as an HTM/contact couple in normal architecture of perovskite solar cell. A perovskite solar cell that is durable for more than 60 days was achieved, with increasing efficiency from 1.3% to 7.28% within 6 days. Moreover, low temperature direct deposition of NiOx layer on perovskite layer was introduced as a potential hole transport material for an efficient cost-effective solar cell applicable for various morphologies of perovskite layers, even for perovskite layers containing pinholes, which is a notable challenge in perovskite solar cells. The angular deposition of NiOx layers by dc reactive magnetron sputtering showed uniform and crack-free coverage of the perovskite layer with no negative impact on perovskite structure that is suitable for nickel back contact layer, surface shielding against moisture, and mechanical damages. Replacing the expensive complex materials in previous perovskite solar cells with low cost available materials introduces cost-effective scalable perovskite solar cells.

  7. Ferrimagnetic states in S = 1/2 frustrated Heisenberg chains with period 3 exchange modulation

    Science.gov (United States)

    Hida, K.

    2007-04-01

    The ground state properties of the S = 1/2 frustrated Heisenberg chain with period 3 exchange modulation are investigated using the numerical diagonalization and density matrix renormalization group (DMRG) method. It is known that this model has a magnetization plateau at one third of the saturation magnetization Ms. On the other hand, the ground state is ferrimagnetic even in the absence of frustration if one of the nearest neighbour bond is ferromagnetic and the others are antiferromagnetic. In the present work, we show that this ferrimagnetic state continues to the region in which all bonds are antiferromagnetic if the frustration is strong. This state further continues to the above-mentioned 1/3 plateau state. In between, we also find the noncollinear ferrimagnetic phase in which the spontaneous magnetization is finite but less than Ms/3. The intuitive interpretation for the phase diagram is given and the physical properties of these phases are discussed.

  8. Ferrimagnetic states in S = 1/2 frustrated Heisenberg chains with period 3 exchange modulation

    Energy Technology Data Exchange (ETDEWEB)

    Hida, K [Divison of Material Science, Graduate School of Science and Engineering, Saitama University, Saitama, Saitama, 338-8570 (Japan)

    2007-04-11

    The ground state properties of the S = 1/2 frustrated Heisenberg chain with period 3 exchange modulation are investigated using the numerical diagonalization and density matrix renormalization group (DMRG) method. It is known that this model has a magnetization plateau at one third of the saturation magnetization M{sub s}. On the other hand, the ground state is ferrimagnetic even in the absence of frustration if one of the nearest neighbour bond is ferromagnetic and the others are antiferromagnetic. In the present work, we show that this ferrimagnetic state continues to the region in which all bonds are antiferromagnetic if the frustration is strong. This state further continues to the above-mentioned 1/3 plateau state. In between, we also find the noncollinear ferrimagnetic phase in which the spontaneous magnetization is finite but less than M{sub s}/3. The intuitive interpretation for the phase diagram is given and the physical properties of these phases are discussed.

  9. An investigation of low-field magnetoresistance in the double perovskites Sr{sub 2}Fe{sub 1-x}Zn{sub x}MoO{sub 6}, x = 0, 0.05, 0.15 and 0.25

    Energy Technology Data Exchange (ETDEWEB)

    Lue Minfeng [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100049 (China); Wang Jingping [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Liu Jianfen [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Song Wei [Analysis Centre, Tianjin University, Tianjin 300072 (China); Hao Xianfeng [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Zhou Defeng [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Liu Xiaojuan [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Wu Zhijian [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

    2006-02-08

    The electrical, magnetic and transport properties of Zn doped polycrystalline samples of Sr{sub 2}Fe{sub 1-x}Zn{sub x}MoO{sub 6} (x = 0,0.05,0.15 and 0.25) with the double perovskite structure have been investigated. The subtle replacement of Fe{sup 3+} ions by Zn{sup 2+} ions facilitates the formation of a more ordered structure, while further substitution leads to disordered structure because of the presence of a striped phase. Analysis of the x-ray powder diffraction patterns based on Rietveld analysis indicates that the replacement of Fe{sup 3+} by Zn{sup 2+} ions favours the formation of Mo{sup 6+} ions. The spin-glass behaviour can be explained on the basis of the competition between the antiferromagnetic superexchange and the ferromagnetic double-exchange interaction. The low-field magnetoresistance was moderately enhanced at x = 0.05, and its origin was found to be the competition between the decrease of the concentration of the itinerant electrons and the weaker antiferromagnetic superexchange in the antiphase boundaries. An almost linear negative magnetoresistance in moderate field has been observed for x = 0.25. A possible double-exchange mechanism is proposed for elucidating the observations; it also suggests a coexistence of (Fe{sup 3+},Mo{sup 5+}) and (Zn{sup 2+},Mo{sup 6+}) valence pairs.

  10. High Performance Perovskite Solar Cells.

    Science.gov (United States)

    Tong, Xin; Lin, Feng; Wu, Jiang; Wang, Zhiming M

    2016-05-01

    Perovskite solar cells fabricated from organometal halide light harvesters have captured significant attention due to their tremendously low device costs as well as unprecedented rapid progress on power conversion efficiency (PCE). A certified PCE of 20.1% was achieved in late 2014 following the first study of long-term stable all-solid-state perovskite solar cell with a PCE of 9.7% in 2012, showing their promising potential towards future cost-effective and high performance solar cells. Here, notable achievements of primary device configuration involving perovskite layer, hole-transporting materials (HTMs) and electron-transporting materials (ETMs) are reviewed. Numerous strategies for enhancing photovoltaic parameters of perovskite solar cells, including morphology and crystallization control of perovskite layer, HTMs design and ETMs modifications are discussed in detail. In addition, perovskite solar cells outside of HTMs and ETMs are mentioned as well, providing guidelines for further simplification of device processing and hence cost reduction.

  11. Crystal structure, thermal expansion and high-temperature electrical conductivity of A-site deficient La{sub 2−z}Co{sub 1+y}(Mg{sub x}Nb{sub 1−x}){sub 1−y}O{sub 6} double perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Shafeie, S. [Department of Materials and Manufacturing Technology, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Dreyer, B.; Awater, R.H.P [Department of Materials and Environmental Chemistry, Stockholm University, S-106 91 Stockholm (Sweden); Golod, T. [Department of Physics, Albanova University Center, Stockholm University, S-106 91 Stockholm (Sweden); Grins, J. [Department of Materials and Environmental Chemistry, Stockholm University, S-106 91 Stockholm (Sweden); Biendicho, J.J. [Department of Materials and Environmental Chemistry, Stockholm University, S-106 91 Stockholm (Sweden); The ISIS Facility, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX (United Kingdom); Istomin, S.Ya. [Department of Chemistry, M.V. Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Svensson, G., E-mail: gunnar@mmk.su.se [Department of Materials and Environmental Chemistry, Stockholm University, S-106 91 Stockholm (Sweden)

    2015-09-15

    New La-deficient double perovskites with P2{sub 1}/n symmetry, La{sub ∼1.90}(Co{sup 2+}{sub 1−x}Mg{sup 2+}{sub x})(Co{sup 3+}{sub 1/3}Nb{sup 5+}{sub 2/3})O{sub 6} with x=0, 0.13 and 0.33, and La{sub 2}(Co{sup 2+}{sub 1/2}Mg{sup 2+}{sub 1/2}) (Co{sup 3+}{sub 1/2}Nb{sup 5+}{sub 1/2})O{sub 6} were prepared by solid state reaction at 1450 °C. Their crystal structures were refined using time-of-flight neutron powder diffraction data. Our results show that certain cations such as Nb{sup 5+}, with very strong B–O bonds in the perovskite structure, can induce A-site vacancies in double perovskites. Upon heating in N{sub 2} gas atmosphere at 1200 °C ∼1% O atom vacancies are formed together with a partial reduction of the Co{sup 3+} content. The average thermal expansion coefficient between 25 and 900 °C of La{sub 1.90}(Co{sup 2+}{sub 2/3}Mg{sup 2+}{sub 1/3})(Co{sup 3+}{sub 1/3}Nb{sup 5+}{sub 2/3})O{sub 6} was determined to be 17.4 ppm K{sup −1}. Four-point electronic conductivity measurements showed that the compounds are semiconductors, with conductivities varying between 3.7·10{sup −2} and 7.7·10{sup −2} S cm{sup −1} at 600 °C and activation energies between 0.77 and 0.81 eV. Partial replacement of La{sup 3+} with Sr{sup 2+} does not lead to any increase of conductivity, while replacement of Mg{sup 2+} with Cu{sup 2+} in La{sub 1.9}CoCu{sub 1/3}Nb{sub 2/3}O{sub 6} and La{sub 1.8}CoCu{sub 1/2}Nb{sub 1/2}O{sub 6} leads to ∼100 times larger conductivities at 600 °C, 0.35 and 1.0 S cm{sup −1}, respectively, and lower activation energies, 0.57 and 0.73 eV, respectively. - Highlights: • Double perovskites, P2{sub 1}/n, La{sub 2−z}(Co{sup 2+}{sub 1−x}Mg{sup 2+}{sub x})(Co{sup 3+}{sub 1/3}Nb{sup 5+}{sub 2/3})O{sub 6} have been synthesized. • Crystal structures have been refined using neutron powder diffraction data. • Strong Nb–O bond and size ordering of Mg{sup 2+}/Co{sup 2+} and Nb{sup 5+}/Co{sup ~3+} leads to La-deficiency. • The

  12. 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.

  13. Fast vortex oscillations in a ferrimagnetic disk near the angular momentum compensation point

    Science.gov (United States)

    Kim, Se Kwon; Tserkovnyak, Yaroslav

    2017-07-01

    We theoretically study the oscillatory dynamics of a vortex core in a ferrimagnetic disk near its angular momentum compensation point, where the spin density vanishes but the magnetization is finite. Due to the finite magnetostatic energy, a ferrimagnetic disk of suitable geometry can support a vortex as a ground state similar to a ferromagnetic disk. In the vicinity of the angular momentum compensation point, the dynamics of the vortex resemble those of an antiferromagnetic vortex, which is described by equations of motion analogous to Newton's second law for the motion of particles. Owing to the antiferromagnetic nature of the dynamics, the vortex oscillation frequency can be an order of magnitude larger than the frequency of a ferromagnetic vortex, amounting to tens of GHz in common transition-metal based alloys. We show that the frequency can be controlled either by applying an external field or by changing the temperature. In particular, the latter property allows us to detect the angular momentum compensation temperature, at which the lowest eigenfrequency attains its maximum, by performing ferromagnetic resonance measurements on the vortex disk. Our work proposes a ferrimagnetic vortex disk as a tunable source of fast magnetic oscillations and a useful platform to study the properties of ferrimagnets.

  14. Magnetoelectric coupling in the cubic ferrimagnet Cu(2)OSeO(3)

    NARCIS (Netherlands)

    Bos, Jan-Willem G.; Colin, Claire V.; Palstra, Thomas T. M.

    2008-01-01

    We have investigated the magnetoelectric coupling in the lone pair containing piezoelectric ferrimagnet Cu(2)OSeO(3). Significant magnetocapacitance develops in the magnetically ordered state (T(c) = 60 K). We find critical behavior near T(c) and a divergence near the metamagnetic transition at 500

  15. Spin Canting and Transverse Relaxation at Surfaces and in the Interior of Ferrimagnetic Particles

    DEFF Research Database (Denmark)

    Mørup, Steen

    2003-01-01

    Analytical expressions for the magnetic energy and the spin-canting angles in some simple ferrimagnetic bulk and surface structures are presented. It is shown that the energy barriers separating different spin-canted states often will be very small. Therefore, the spin canting may be static only ...

  16. Ionic liquid-modulated synthesis of ferrimagnetic Fe(3)S(4) hierarchical superstructures.

    Science.gov (United States)

    Ma, Jianmin; Chang, Liao; Lian, Jiabiao; Huang, Zheng; Duan, Xiaochuan; Liu, Xiaodi; Peng, Peng; Kim, Tongil; Liu, Zhifang; Zheng, Wenjun

    2010-07-21

    Ferrimagnetic Fe(3)S(4) nanowalls and triple hierarchical microspheres have been fabricated via an ionic liquid-modulated solution-phase process, respectively. Magnetic hysteresis measurements demonstrate that their morphology-dependent magnetic properties might be originated from their unique nanostructures.

  17. Phase diagram of a three-sublattice mixed ferro-ferrimagnetic Heisenberg system

    Science.gov (United States)

    Mert, H. Şevki; Mert, Gülistan

    2013-10-01

    We present a numerical study of a three-sublattice mixed ferro-ferrimagnetic Heisenberg system. Green's function technique is used to calculate the magnetization as a function of temperature. The technique involves the random phase approximation and Anderson-Callen's decoupling. We obtain phase diagram and the first-order phase transition.

  18. Green's function study of a three-sublattice mixed-spin Heisenberg ferromagnetic and ferrimagnetic system

    Energy Technology Data Exchange (ETDEWEB)

    Mert, Gülistan, E-mail: gmert@selcuk.edu.tr

    2014-08-01

    The magnetic properties of a three-sublattice mixed-spin Heisenberg ferromagnetic and ferrimagnetic system are investigated with the help of the Green's function technique in order to clarify some characteristic magnetic behaviors of Prussian-blue compounds. Various types of magnetization curves are obtained, which exhibits one- and two-compensation temperatures. The first-order phase transitions from ferrimagnetic to ferromagnetic state have been observed. There are zero-temperature quantum fluctuations for the ferrimagnet at the absolute state while not for ferromagnet. Moreover, in the case of ferrimagnet, inverted magnetic hysteresis loop with negative coercivity is observed at a certain temperature range and the coercivity takes the value zero at the compensation point. - Highlights: • We investigate a three-sublattice Heisenberg ferromagnetic and ferrimagnetic system. • System exhibits one- and two-compensation temperatures. • One observes the first-order phase transitions. • Inverted hysteresis loop for ferrimagnet is obtained. • Coercive field for ferrimagnet reaches zero at compensation temperature.

  19. Tunable perovskite microdisk lasers.

    Science.gov (United States)

    Sun, Wenzhao; Wang, Kaiyang; Gu, Zhiyuan; Xiao, Shumin; Song, Qinghai

    2016-04-28

    Perovskite microdisk lasers have been intensively studied recently. But their lasing properties are usually fixed once the devices are synthesized. Here, for the first time, we demonstrated the switchable and tunable perovskite microdisk lasers by surrounding them with 5CB liquid crystals. With the increase of the environmental temperature from 24 °C to 34 °C, the lasing wavelength slightly changed from 552.91 nm to 552.11 nm at the beginning and suddenly shifted to around 552.54 nm at T = 32 °C, where the phase transition of liquid crystals occurs. Our numerical calculation shows that the wavelength shift is caused by the changes of the refractive index of liquid crystals. More than tuning of the wavelength, a more dramatic wavelength transition from ∼554 nm to 550 nm has also been observed. This sudden transition is mainly induced by the reduction of scattering rather than the change in the refractive index when the liquid crystals are changed from the nematic phase to the isotropic phase. We believe that our research can shed light on the applications of perovskite optoelectronics.

  20. Interplay of Cation Ordering and Ferroelectricity in Perovskite Tin Iodides: Designing a Polar Halide Perovskite for Photovoltaic Applications

    Energy Technology Data Exchange (ETDEWEB)

    Gou, Gaoyang; Young, Joshua; Liu, Xian; Rondinelli, James M.

    2016-09-28

    Owing to its ideal semiconducting band gap and good carrier transport properties, the fully inorganic perovskite CsSnI3 has been proposed as a visible-light absorber for photovoltaic (PV) applications. However, compared to the organic inorganic lead halide perovskite CH3NH3PbI3, CsSnI3 solar cells display very low energy conversion efficiency. In this work, we propose a potential route to improve the PV properties of CsSnI3. Using first-principles calculations, we examine the crystal structures and electronic properties of CsSnI3, including its structural polymorphs. Next, we purposefully order Cs and Rb cations on the A site to create the double perovskite (CsRb)Sn2I6. We find that a stable ferroelectric polarization arises from the nontrivial coupling between polar displacements and octahedral rotations of the SnI6 network. These ferroelectric double perovskites are predicted to have energy band gaps and carrier effective masses similar to those of CsSnI3. More importantly, unlike nonpolar CsSnI3, the electric polarization present in ferroelectric (CsRb)Sn2I6 can effectively separate the photoexcited carriers, leading to novel ferroelectric PV materials with,potentially enhanced energy conversion efficiency.

  1. Stabilisation of Fe2O3-rich Perovskite Nanophase in Epitaxial Rare-earth Doped BiFeO3 Films.

    Science.gov (United States)

    Zhang, Huairuo; Reaney, Ian M; Marincel, Daniel M; Trolier-McKinstry, Susan; Ramasse, Quentin M; MacLaren, Ian; Findlay, Scott D; Fraleigh, Robert D; Ross, Ian M; Hu, Shunbo; Ren, Wei; Rainforth, W Mark

    2015-08-14

    Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)(3+) Fe(3+)O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community.

  2. 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.

  3. 新型复合钙钛矿 Ba(Sb Ⅲ,Sb Ⅴ)O3的水热合成和表征%Hydrothermal Synthesis of a Novel Double Perovskite-type Oxide Ba(Sb Ⅲ, Sb Ⅴ)O3

    Institute of Scientific and Technical Information of China (English)

    郑文君; 庞文琴

    2000-01-01

    采用水热晶化法制备了Ba(Sb Ⅲ,Sb Ⅴ)O3新型钙钛矿型氧化物,并通过XRD、IR、SEM和ICP等方法对产物物相、形貌和组成等进行了表征. 结果表明,产物为立方钙钛矿结构,晶胞参数为a=0.415nm,粒度为1~2μm具有一定团聚的多晶粉末. 产物中锑为三价和五价两种价态. 水热条件对合成影响的研究结果表明,Ba(Sb Ⅲ,SbⅤ)O3合成的适宜碱度和n Sb(Ⅴ)/n Sb(Ⅲ)分别为8~10mol/L KOH和0~1.%A novel double perovskite-type oxide Ba(Sb Ⅲ, Sb Ⅴ)O3 was synthesized by hydrothermal crystallization methods. The phase, morphology and particle size of the product were characterized by XRD, IR, SEM and ICP techniques. The results indicated that the Ba(Sb Ⅲ,Sb Ⅴ)O3 oxide shows a cubic perovskite-type structure with a cell parameter a=0.415nm, and has a particle size in the range from 1 to 2 μm. The product has trivalent and pentavalent two states antimony ions. The influence of hydrothermal conditions exhibited that the optimum alkalinity and n Sb(Ⅲ)/n Sb(Ⅴ) are 8~10 mol/L KOH medium and 0~1 respectively.

  4. 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.

  5. Magnetotransport Properties of Thin Films of Magnetic Perovskites

    Science.gov (United States)

    Jakob, Gerhard; Westerburg, Wilhelm; Martin, Frank; Reisinger, Daniel; Auth, Nicole

    In this article we show magnetotransport of two prototypical (nearly) half metallic perowskites La2/3Ca1/3MnO3 and Sr2FeMoO6. In a half metal the spin polarisation at the Fermi energy is complete and tunneling magnetoresistive devices of high sensitivity can be realized with small external magnetic fields. In the vicinity of the metal-insulator phase transition (MIT) temperature of the manganite an external magnetic field can induce 'colossal' magnetoresistive effects. In the simple perovskites La1-xCaxMnO3 the charge transport above the MIT is of polaronic nature. Hall-effect measurements on the compound La0.67Ca0.33MnO3 below the MIT show a compensated Fermi-surface consisting of electron and hole contributions and an unusual quadratic temperature dependence of the resistivity. In Sr2FeMoO6 we found a clear correlation between electrical conductivity and ordered occupation of the Fe, Mo atomic positions. While the low temperature ferrimagnetic phase shows similar transport the high temperature phase stays metallic.

  6. Internal energy and specific heat in a ferromagnetic-antiferromagnetic double layers

    Institute of Scientific and Technical Information of China (English)

    Jiang Wei; Guo An-Bang

    2007-01-01

    The internal energy and specific heat of a Heisenberg ferro- antiferromagnetic double-layer system are studied by using spin-wave theory and the retarded Green function method at low temperatures. Numerical results show that the antiferromagnetic intralayer coupling J2 has an important influence on internal energy and specific heat for a four-sublattice system with antiferromagnetic (or ferrimagnetic) interlayer couplings.

  7. Multidimensional Perovskites: A Mixed Cation Approach Towards Ambient Stable and Tunable Perovskite Photovoltaics.

    Science.gov (United States)

    Koh, Teck Ming; Thirumal, Krishnamoorthy; Soo, Han Sen; Mathews, Nripan

    2016-09-22

    Although halide perovskites are able to deliver high power conversion efficiencies, their ambient stability still remains an obstacle for commercialization. Thus, promoting the ambient stability of perovskites has become a key research focus. In this review, we highlight the sources of instability in conventional 3 D perovskites, including water intercalation, ion migration, and thermal decomposition. Recently, the multidimensional perovskites approach has become one of the most promising strategies to enhance the stability of perovskites. As compared to pure 2 D perovskites, multidimensional perovskites typically possess more ideal band gaps, better charge transport, and lower exciton binding energy, which are essential for photovoltaic applications. The larger organic cations in multidimensional perovskites could also be more chemically stable at higher temperatures than the commonly used methylammonium cation. By combining 3 D and 2 D perovskites to form multidimensional perovskites, halide perovskite photovoltaics can attain both high efficiency and increased stability.

  8. Methodologies for high efficiency perovskite solar cells.

    Science.gov (United States)

    Park, Nam-Gyu

    2016-01-01

    Since the report on long-term durable solid-state perovskite solar cell in 2012, perovskite solar cells based on lead halide perovskites having organic cations such as methylammonium CH3NH3PbI3 or formamidinium HC(NH2)2PbI3 have received great attention because of superb photovoltaic performance with power conversion efficiency exceeding 22 %. In this review, emergence of perovskite solar cell is briefly introduced. Since understanding fundamentals of light absorbers is directly related to their photovoltaic performance, opto-electronic properties of organo lead halide perovskites are investigated in order to provide insight into design of higher efficiency perovskite solar cells. Since the conversion efficiency of perovskite solar cell is found to depend significantly on perovskite film quality, methodologies for fabricating high quality perovskite films are particularly emphasized, including various solution-processes and vacuum deposition method.

  9. Methodologies for high efficiency perovskite solar cells

    Science.gov (United States)

    Park, Nam-Gyu

    2016-06-01

    Since the report on long-term durable solid-state perovskite solar cell in 2012, perovskite solar cells based on lead halide perovskites having organic cations such as methylammonium CH3NH3PbI3 or formamidinium HC(NH2)2PbI3 have received great attention because of superb photovoltaic performance with power conversion efficiency exceeding 22 %. In this review, emergence of perovskite solar cell is briefly introduced. Since understanding fundamentals of light absorbers is directly related to their photovoltaic performance, opto-electronic properties of organo lead halide perovskites are investigated in order to provide insight into design of higher efficiency perovskite solar cells. Since the conversion efficiency of perovskite solar cell is found to depend significantly on perovskite film quality, methodologies for fabricating high quality perovskite films are particularly emphasized, including various solution-processes and vacuum deposition method.

  10. 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.

  11. Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet

    Energy Technology Data Exchange (ETDEWEB)

    Mizukami, S., E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Sugihara, A.; Suzuki, K. Z.; Miyazaki, T. [WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Iihama, S.; Sasaki, Y. [Department of Applied Physics, Tohoku University, Sendai 980-8579 (Japan)

    2016-01-04

    Laser-induced magnetization precessional dynamics was investigated in epitaxial films of Mn{sub 3}Ge, which is a tetragonal Heusler-like nearly compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed, the precession frequency for which exceeded 0.5 THz and originated from the large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet. The effective damping constant was approximately 0.03. The corresponding effective Landau-Lifshitz constant is approximately 60 Mrad/s and is comparable with those of the similar Mn-Ga materials. The physical mechanisms for the Gilbert damping and for the laser-induced excitation of the FMR mode were also discussed in terms of the spin-orbit-induced damping and the laser-induced ultrafast modulation of the magnetic anisotropy, respectively.

  12. Interlayer Coupling in Co/Ti/(Gd-Co)/Ti Artificial Layered Ferrimagnet

    Institute of Scientific and Technical Information of China (English)

    A.V.Svalov; A.Fernández; V.O.Vas'kovskiy; M.Tejedor; R.Lopez Anton; J.M.Barandiarán; G.V.Kurlyandskaya

    2005-01-01

    @@ The magnetic properties and the structure of [Co/Ti/Gd0.36Co0.64/Ti]4/Co multilayers are investigated by means of torque magnetometer, vibrating sample magnetometer and transverse magneto-optic Kerr effect (TMOKE)measurements and the atomic force microscopy. Due to interlayer exchange interaction, Co and Gd-Co layers form a macroscopic ferrimagnetic system. The change in the sign of the TMOKE hysteresis loops near the compensation temperature and field induced magnetic phase transitions are found. The latter can be characterized by a critical field which shows a linear variation with the temperature. The magnetic properties of these multilayers from many points of view are similar to those of bulk ferrimagnets.

  13. Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet

    Science.gov (United States)

    Mizukami, S.; Sugihara, A.; Iihama, S.; Sasaki, Y.; Suzuki, K. Z.; Miyazaki, T.

    2016-01-01

    Laser-induced magnetization precessional dynamics was investigated in epitaxial films of Mn3Ge, which is a tetragonal Heusler-like nearly compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed, the precession frequency for which exceeded 0.5 THz and originated from the large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet. The effective damping constant was approximately 0.03. The corresponding effective Landau-Lifshitz constant is approximately 60 Mrad/s and is comparable with those of the similar Mn-Ga materials. The physical mechanisms for the Gilbert damping and for the laser-induced excitation of the FMR mode were also discussed in terms of the spin-orbit-induced damping and the laser-induced ultrafast modulation of the magnetic anisotropy, respectively.

  14. Epitaxial Growth of Hard Ferrimagnetic Mn3Ge Film on Rhodium Buffer Layer

    Directory of Open Access Journals (Sweden)

    Atsushi Sugihara

    2015-06-01

    Full Text Available Mn\\(_3\\Ge has a tetragonal Heusler-like D0\\(_{22}\\ crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\\(_3\\Ge film on a Rh buffer layer was investigated for comparison with that of a film on a Cr buffer layer in terms of the lattice mismatch between Mn\\(_3\\Ge and the buffer layer. The film grown on Rh had much better crystalline quality than that grown on Cr, which can be attributed to the small lattice mismatch. Epitaxial films of Mn\\(_3\\Ge on Rh show somewhat small coercivity (\\(H_{\\rm c}\\ = 12.6 kOe and a large perpendicular magnetic anisotropy (\\(K_{\\rm u}\\ = 11.6 Merg/cm\\(^3\\, comparable to that of the film grown on Cr.

  15. Schwinger-boson approach to anisotropy ferrimagnetic chain with bond alternation

    Institute of Scientific and Technical Information of China (English)

    李殷翔; 陈斌

    2015-01-01

    We use the Schwinger-boson approach to study the anisotropy ferrimagnetic spin-(1/2,1) chain with bond alternation. Based on the effect of bond alternationδ, we obtain energy gap, free energy, and specific heat, respectively. The specific heat with larger bond alternation (δ >0.7) displays a peak at low temperature. Based on the effect of X X Z anisotropy parameter∆, we present excited spectrums, free energy, and specific heat, respectively.

  16. Lattice thermal conductivity of MgSiO3 perovskite and post-perovskite at the core-mantle boundary

    Science.gov (United States)

    Ohta, K.; Yagi, T.; Taketoshi, N.; Hirose, K.; Komabayashi, T.; Baba, T.; Ohishi, Y.; Hernlund, J. W.

    2011-12-01

    Heat in the Earth's interior is transported dominantly by convection in the mantle and core, and by conduction at thermal boundary layers. The thermal conductivity of the bottom thermal boundary layer of the mantle determines the magnitude of heat flux from the core, and is intimately related to the formation of mantle plumes, the long-term thermal evolution of both mantle and core, and the driving force for generation of the geomagnetic field (Lay et al. 2008). However, the thermal conductivity and diffusivity have been poorly constrained at the high pressures of Earth's lowermost mantle. Previous estimates of the thermal conductivity in this region ranged widely between 5 and 30 W/m/K, and it has been often assumed to be 10 W/m/K (Lay et al. 2006). The lattice thermal diffusivity of MgSiO3 perovskite, a primary mineral in the Earth's lower mantle, has only been measured at 1 bar (Osako and Ito 1991). And the thermal diffusivity of post-perovskite has not been investigated so far. We measured the lattice component of thermal diffusivities of both MgSiO3 perovskite and post-perovskite to 144 GPa using a light pulse thermoreflectance technique in a diamond anvil cell (Yagi et al. 2011). The estimated lattice thermal conductivity of perovskite-dominant lowermost mantle is about 9 W/m/K, while post-perovskite-dominant one exhibits ~50% higher diffusivity than perovskite at equivalent pressure. Since many previous calculations assumed a lowermost mantle conductivity of 10 W/m/K, compatible with values obtained in this study, the present findings do not significantly alter the magnitude of heat flow from the core estimated using the post-perovskite double-crossing model (e.g., Lay et al. 2006). Indeed, the present results continue to support the notion of high core-mantle boundary heat flow along with a large degree of secular cooling necessary to sustain a geodynamo even in the absence of an inner core.

  17. Magnetic order and interactions in ferrimagnetic Mn3Si2Te6

    Science.gov (United States)

    May, Andrew F.; Liu, Yaohua; Calder, Stuart; Parker, David S.; Pandey, Tribhuwan; Cakmak, Ercan; Cao, Huibo; Yan, Jiaqiang; McGuire, Michael A.

    2017-05-01

    The magnetism in Mn3Si2Te6 has been investigated using thermodynamic measurements, first-principles calculations, neutron diffraction, and diffuse neutron scattering on single crystals. These data confirm that Mn3Si2Te6 is a ferrimagnet below TC ≈78 K. The magnetism is anisotropic, with magnetization and neutron diffraction demonstrating that the moments lie within the basal plane of the trigonal structure. The saturation magnetization of ≈1.6 μB /Mn at 5 K originates from the different multiplicities of the two antiferromagnetically aligned Mn sites. First-principles calculations reveal antiferromagnetic exchange for the three nearest Mn-Mn pairs, which leads to a competition between the ferrimagnetic ground state and three other magnetic configurations. The ferrimagnetic state results from the energy associated with the third-nearest-neighbor interaction, and thus long-range interactions are essential for the observed behavior. Diffuse magnetic scattering is observed around the 002 Bragg reflection at 120 K, which indicates the presence of strong spin correlations well above TC. These are promoted by the competing ground states that result in a relative suppression of TC and may be associated with a small ferromagnetic component that produces anisotropic magnetism below ≈330 K .

  18. 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.

  19. Perovskite photovoltaics: Slow recombination unveiled

    Science.gov (United States)

    Moser, Jacques-E.

    2017-01-01

    One of the most salient features of hybrid lead halide perovskites is the extended lifetime of their photogenerated charge carriers. This property has now been shown experimentally to originate from a slow, thermally activated recombination process.

  20. Perovskite solar cells: Stability lies at interfaces

    Science.gov (United States)

    Lira-Cantú, Mónica

    2017-07-01

    Perovskite solar cells are developing fast but their lifetimes must be extended. Now, large-area printed perovskite solar modules have been shown to be stable for more than 10,000 hours under continuous illumination.

  1. Photocatalysis: HI-time for perovskites

    DEFF Research Database (Denmark)

    Vesborg, Peter Christian Kjærgaard

    2017-01-01

    Organolead halide perovskite solar absorbers demonstrate high photovoltaic efficiencies but they are notorious for their intolerance to water. Now, methylammonium lead iodide perovskites are used to harvest solar energy — in water — via photocatalytic generation of hydrogen from solutions...

  2. Accelerated Degradation Due to Weakened Adhesion from Li-TFSI Additives in Perovskite Solar Cells.

    Science.gov (United States)

    Lee, Inhwa; Yun, Jae Hoon; Son, Hae Jung; Kim, Taek-Soo

    2017-03-01

    Reliable integration of organometallic halide perovskite in photovoltaic devices is critically limited by its low stability in humid environments. Furthermore, additives to increase the mobility in the hole transport material (HTM) have deliquescence and hygroscopic properties, which attract water molecules and result in accelerated degradation of the perovskite devices. In this study, a double cantilever beam (DCB) test is used to investigate the effects of additives in the HTM layer on the perovskite layer through neatly delaminating the interface between the perovskite and HTM layers. Using the DCB test, the bottom surface of the HTM layers is directly observed, and it is found that the additives are accumulated at the bottom along the thickness (i.e., through-plane direction) of the films. It is also found that the additives significantly decrease the adhesion at the interface between the perovskite and HTM layers by more than 60% through hardening the HTM films. Finally, the adhesion-based degradation mechanism of perovskite devices according to the existence of additives is proposed for humid environments.

  3. 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.

  4. Perovskite-perovskite tandem photovoltaics with optimized band gaps

    Science.gov (United States)

    Eperon, Giles E.; Leijtens, Tomas; Bush, Kevin A.; Prasanna, Rohit; Green, Thomas; Wang, Jacob Tse-Wei; McMeekin, David P.; Volonakis, George; Milot, Rebecca L.; May, Richard; Palmstrom, Axel; Slotcavage, Daniel J.; Belisle, Rebecca A.; Patel, Jay B.; Parrott, Elizabeth S.; Sutton, Rebecca J.; Ma, Wen; Moghadam, Farhad; Conings, Bert; Babayigit, Aslihan; Boyen, Hans-Gerd; Bent, Stacey; Giustino, Feliciano; Herz, Laura M.; Johnston, Michael B.; McGehee, Michael D.; Snaith, Henry J.

    2016-11-01

    We demonstrate four- and two-terminal perovskite-perovskite tandem solar cells with ideally matched band gaps. We develop an infrared-absorbing 1.2-electron volt band-gap perovskite, FA0.75Cs0.25Sn0.5Pb0.5I3, that can deliver 14.8% efficiency. By combining this material with a wider-band gap FA0.83Cs0.17Pb(I0.5Br0.5)3 material, we achieve monolithic two-terminal tandem efficiencies of 17.0% with >1.65-volt open-circuit voltage. We also make mechanically stacked four-terminal tandem cells and obtain 20.3% efficiency. Notably, we find that our infrared-absorbing perovskite cells exhibit excellent thermal and atmospheric stability, not previously achieved for Sn-based perovskites. This device architecture and materials set will enable “all-perovskite” thin-film solar cells to reach the highest efficiencies in the long term at the lowest costs.

  5. Novel Solvent-free Perovskite Deposition in Fabrication of Normal and Inverted Architectures of Perovskite Solar Cells

    OpenAIRE

    Bahram Abdollahi Nejand; Saba Gharibzadeh; Vahid Ahmadi; H. Reza Shahverdi

    2016-01-01

    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 s...

  6. Graded bandgap perovskite solar cells

    Science.gov (United States)

    Ergen, Onur; Gilbert, S. Matt; Pham, Thang; Turner, Sally J.; Tan, Mark Tian Zhi; Worsley, Marcus A.; Zettl, Alex

    2017-05-01

    Organic-inorganic halide perovskite materials have emerged as attractive alternatives to conventional solar cell building blocks. Their high light absorption coefficients and long diffusion lengths suggest high power conversion efficiencies, and indeed perovskite-based single bandgap and tandem solar cell designs have yielded impressive performances. One approach to further enhance solar spectrum utilization is the graded bandgap, but this has not been previously achieved for perovskites. In this study, we demonstrate graded bandgap perovskite solar cells with steady-state conversion efficiencies averaging 18.4%, with a best of 21.7%, all without reflective coatings. An analysis of the experimental data yields high fill factors of ~75% and high short-circuit current densities up to 42.1 mA cm-2. The cells are based on an architecture of two perovskite layers (CH3NH3SnI3 and CH3NH3PbI3-xBrx), incorporating GaN, monolayer hexagonal boron nitride, and graphene aerogel.

  7. Search for fully compensated ferrimagnet in Co substituted Mn{sub 2}VGa alloy

    Energy Technology Data Exchange (ETDEWEB)

    Deka, Bhargab, E-mail: d.bhargab@iitg.ernet.in [Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039 (India); Singh, R.K., E-mail: ranjan@dmrl.drdo.in [Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058 (India); Srinivasan, A., E-mail: asrini@iitg.ernet.in [Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039 (India)

    2015-12-01

    Crystallographic and magnetic properties of bulk (Mn{sub 1−x}Co{sub x}){sub 2}VGa alloys with 0≤x≤0.50 are reported in this work. All the alloys exhibit stable L2{sub 1} structure. Unit cell volume of this series of alloys decreased from 207.5 Å{sup 3} to 195.1 Å{sup 3} as x was increased from 0 to 0.50. All the alloys shows ferrimagnetic behavior with Curie temperature decreasing from 763 K to 367 K with increase in x. Saturation magnetization (M{sub s}) measured for the alloys with x=0, 0.25 and 0.50 are 1.84 μ{sub B}/f.u., 0.85 μ{sub B}/f.u. and 0.30 μ{sub B}/f.u., respectively, as compared to the values of 2.00 μ{sub B}/f.u., 1.00 μ{sub B}/f.u. and 0 μ{sub B}/f.u., predicted by the Slater–Pauling (S–P) rule. While explaining the deviations in the M{sub s} from the values predicted by the S–P rule, a fully compensated ferrimagnet is expected in an alloy with total number of valance electrons of 24.1. - Highlights: • (Mn{sub 1−x}Co{sub x}){sub 2} VGa alloys with highly ordered L2{sub 1} structure has been obtained • With Co substitution, magnetization of (Mn{sub 1-x}Co{sub x}){sub 2}VGa alloys reduces to 0.3={sub B}/f.u. • Fully compensated ferrimagnet is expected in the alloy with 24.1 valance electrons.

  8. Double-layered Aurivillius-type ferroelectrics with magnetic moments

    NARCIS (Netherlands)

    Missyul, A. B.; Zvereva, I. A.; Palstra, T. T. M.; Kurbakov, A. I.

    2010-01-01

    We have synthesized the double-layer Aurivillius phase Bi(2)LnNbTiO(9) where Ln = Nd-Gd, Bi. All compounds adopt the orthorhombic polar space group A2(I)am. The magnetic Ln-ion occupies the cuboctahedral position in the middle of the perovskite double-layer, and thus controls the octahedral tilt of

  9. Understanding the inverse magnetocaloric effect in antiferro- and ferrimagnetic arrangements.

    Science.gov (United States)

    von Ranke, P J; de Oliveira, N A; Alho, B P; Plaza, E J R; de Sousa, V S R; Caron, L; Reis, M S

    2009-02-04

    The inverse magnetocaloric effect occurs when a magnetic material cools down under applied magnetic field in an adiabatic process. Although the existence of the inverse magnetocaloric effect was recently reported experimentally, a theoretical microscopic description is almost nonexistent. In this paper we theoretically describe the inverse magnetocaloric effect in antiferro- and ferrimagnetic systems. The inverse magnetocaloric effects were systematically investigated as a function of the model parameters. The influence of the Néel and the compensation temperature on the magnetocaloric effect is also analyzed using a microscopic model.

  10. Phase transition and magnetization of a hexagonal prismatic nanoisland with a ferrimagnetic spin configuration

    Science.gov (United States)

    Jiang, Wei; Wang, Ya-Ning

    2017-03-01

    Magnetic properties of a nanoisland with a ferrimagnetic spin configuration, described by the transverse Ising model, are studied by the effective-field theory with correlations. The hexagonal prismatic nanoisland consists of the bilayer with core-shell structure. The phase transition, the magnetization, the susceptibility and the internal energy of the system have been calculated for different values. A lot of novel features, such as the reentrant phenomenon, have been found in the phase transition diagrams of the nanoisland. They are heavily dependent on the exchange coupling, the single-ion anisotropy and the transverse field. These theoretical results may have guiding significance for preparing nanoisland experimentally.

  11. Spin waves in the ferrimagnetic phase of NdCu{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Kramp, S.; Rotter, M.; Loewenhaupt, M. E-mail: loewenhaupt@physik.tu-dresden.de; Pyka, N.M.; Schmidt, W.; Kamp, R. van de

    2001-05-01

    The spin wave dispersion relation in the ferrimagnetic phase F1 of NdCu{sub 2} has been measured by means of inelastic neutron scattering. In a-direction the expected six dispersion branches could be determined. The spin wave dispersion is compared to that of the ferromagnetic phase F3. In F1 the magnetic Brillouin zone is only one-third of that in F3 introducing additional symmetry conditions for the dispersion relation. The experimental results agree well with these conditions.

  12. Spin waves in the ferrimagnetic phase of NdCu 2

    Science.gov (United States)

    Kramp, S.; Rotter, M.; Loewenhaupt, M.; Pyka, N. M.; Schmidt, W.; van de Kamp, R.

    2001-05-01

    The spin wave dispersion relation in the ferrimagnetic phase F1 of NdCu 2 has been measured by means of inelastic neutron scattering. In a-direction the expected six dispersion branches could be determined. The spin wave dispersion is compared to that of the ferromagnetic phase F3. In F1 the magnetic Brillouin zone is only one-third of that in F3 introducing additional symmetry conditions for the dispersion relation. The experimental results agree well with these conditions.

  13. Partial Ferrimagnetism in S = 1/2 Heisenberg Ladders with a Ferromagnetic Leg, an Antiferromagnetic Leg, and Antiferromagnetic Rungs

    Science.gov (United States)

    Sekiguchi, Kazutaka; Hida, Kazuo

    2017-08-01

    Ground-state and finite-temperature properties of S = 1/2 Heisenberg ladders with a ferromagnetic leg, an antiferromagnetic leg, and antiferromagnetic rungs are studied. It is shown that a partial ferrimagnetic phase extends over a wide parameter range in the ground state. The numerical results are supported by an analytical calculation based on a mapping onto the nonlinear σ model and a perturbation calculation from the strong-rung limit. It is shown that the partial ferrimagnetic state is a spontaneously magnetized Tomonaga-Luttinger liquid with incommensurate magnetic correlation, which is confirmed by a DMRG calculation. The finite-temperature magnetic susceptibility is calculated using the thermal pure quantum state method. It is suggested that the susceptibility diverges as T-2 in the ferrimagnetic phases as in the case of ferromagnetic Heisenberg chains.

  14. Stability Issues on Perovskite Solar Cells

    Directory of Open Access Journals (Sweden)

    Xing Zhao

    2015-11-01

    Full Text Available Organo lead halide perovskite materials like methylammonium lead iodide (CH3NH3PbI3 and formamidinium lead iodide (HC(NH22PbI3 show superb opto-electronic properties. Based on these perovskite light absorbers, power conversion efficiencies of the perovskite solar cells employing hole transporting layers have increased from 9.7% to 20.1% within just three years. Thus, it is apparent that perovskite solar cell is a promising next generation photovoltaic technology. However, the unstable nature of perovskite was observed when exposing it to continuous illumination, moisture and high temperature, impeding the commercial development in the long run and thus becoming the main issue that needs to be solved urgently. Here, we discuss the factors affecting instability of perovskite and give some perspectives about further enhancement of stability of perovskite solar cell.

  15. Patterning of Perovskite Single Crystals

    KAUST Repository

    Corzo, Daniel

    2017-06-12

    As the internet-of-things hardware integration continues to develop and the requirements for electronics keep diversifying and expanding, the necessity for specialized properties other than the classical semiconductor performance becomes apparent. The success of emerging semiconductor materials depends on the manufacturability and cost as much as on the properties and performance they offer. Solution-based semiconductors are an emerging concept that offers the advantage of being compatible with large-scale manufacturing techniques and have the potential to yield high-quality electronic devices at a lower cost than currently available solutions. In this work, patterns of high-quality MAPbBr3 perovskite single crystals in specific locations are achieved through the modification of the substrate properties and solvent engineering. The fabrication of the substrates involved modifying the surface adhesion forces through functionalization with self-assembled monolayers and patterning them by photolithography processes. Spin coating and blade coating were used to deposit the perovskite solution on the modified silicon substrates. While single crystal perovskites were obtained with the modification of substrates alone, solvent engineering helped with improving the Marangoni flows in the deposited droplets by increasing the contact angle and lowering the evaporation rate, therefore controlling and improving the shape of the grown perovskite crystals. The methodology is extended to other types of perovskites such as the transparent MAPbCl3 and the lead-free MABi2I9, demonstrating the adaptability of the process. Adapting the process to electrode arrays opened up the path towards the fabrication of optoelectronic devices including photodetectors and field-effect transistors, for which the first iterations are demonstrated. Overall, manufacturing and integration techniques permitting the fabrication of single crystalline devices, such as the method in this thesis work, are

  16. 均相有序双钙钛矿Sr2CaMoO6:Eu3+荧光粉的制备及其发光性能%Preparation of homogeneous and ordered double-perovskite Sr2CaMoO6 :Eu3+ phosphors and its luminescent properties

    Institute of Scientific and Technical Information of China (English)

    张乐; 李月; 刘金秋; 韩朋德; 张其土

    2012-01-01

    Eu3+ doped double perovskite Sr2CaMo06 orange-red phosphor was prepared by EDTA-citric acid complexing method at a lower temperature. The X-ray diffraction, scanning electron microscope, UV-Vis diffuse reflection spectrum, and photoluminescent spectra were used to characterize the structure and luminescent properties of phosphors at different calcination temperatures, and the structure refinement of the prepared powder and its first principle calculations for density of states were displayed. Results showed that the highly B site-ordered ions-doped double perovskite powder obtained only at 900 t and its structure with P21/n space group had a interval arrangement of BO6 octahedron with a slight tilting. The strong and wide absorption in UV region was resulted in the charge transfer from 0 2p orbit to Mo 4d orbit and the resulted emission was dominated by magnetic dipole transition of orange light without prohibiting. The emission excited by blue light was dominated by the electronic dipole transition of red light with partial remove of parity. With increasing the calcination temperature,the grain size,the degree of B site-order and the particlal size were all grown up and the phosphor calcined at 1 100 ℃ had the highest luminescent intensity.%采用乙二胺四乙酸(EDTA)-柠檬酸联合配位法在较低温度下制备Eu3+掺杂的双钙钛矿Sr2CaMoO6橙红色荧光粉,借助X线衍射、扫描电镜、紫外可见漫反射光谱和荧光光谱研究不同煅烧温度下粉体的结构和发光性能,并进行结构精修和态密度的第一性原理计算.结果表明:在900℃下即得到B位高度有序的离子掺杂的双钙钛矿粉体,其结构为BO6八面体周期性间隔排列且小角度倾斜的空间群为P21/n的正交双钙钛矿结构;粉体在近紫外区强而宽的吸收源于MoO6八面体中O2p轨道到Mo4d轨道的电荷迁移,并由此发射以无禁戒的磁偶极跃迁橙光为主,但在蓝光激发下以发射宇称禁戒部

  17. Study of Properties of Mixed Ferro-Ferrimagnetic Ising Compounds with (AxB1-x)yC

    Institute of Scientific and Technical Information of China (English)

    XINZi-Hua; WEIGuo-Zhu; LIANGYa-Qiu; ZHANGQi

    2004-01-01

    The magnetic properties of the mixed ferro-ferrimagnetic compounds with (AxB1-x)yC, where A, B,and C are three different magnetic ions and form three different sublattices, are studied by using the standardmean-field theory. The phase diagram which is related to experimental work of molecule-based ferro-ferrimagnet(NiⅡxMnⅡ1-x)1.5[CrⅢ(CN)6] · zH2O is obtained. The magnetization curves, internal energy, and specific heat of thesame mixed (AxB1-x)y C system are also investigated.

  18. Study of Properties of Mixed Ferro-Ferrimagnetic Ising Compounds with (AxB1-x)yC

    Institute of Scientific and Technical Information of China (English)

    XIN Zi-Hua; WEI Guo-Zhu; LIANG Ya-Qiu; ZHANG Qi

    2004-01-01

    The magnetic properties of the mixed ferro-ferrimagnetic compounds with (AxB1-x)yC, where A, B, and C are three different magnetic ions and form three different sublattices, are studied by using the standard mean-field theory. The phase diagram which is related to experimental work of molecule-based ferro-ferrimagnet (NiⅡxMn1Ⅱ-x)1.5[CrⅢ(CN)6]· zH2O is obtained. The magnetization curves, internal energy, and specific heat of the same mixed (Ax B1- x) y C system are also investigated.

  19. Ferrimagnetic Properties of Bond Dilution Mixed Blume-Capel Model with Random Single-Ion Anisotropy

    Institute of Scientific and Technical Information of China (English)

    LIU Lei; YAN Shi-Lei

    2005-01-01

    We study the ferrimagnetic properties of spin 1/2 and spin-1 systems by means of the effective field theory.The system is considered in the framework of bond dilution mixed Blume-Capel model (BCM) with random single-ion anisotropy. The investigation of phase diagrams and magnetization curves indicates the existence of induced magnetic ordering and single or multi-compensation points. Special emphasis is placed on the influence of bond dilution and random single-ion anisotropy on normal or induced magnetic ordering states and single or multi-compensation points.Normal magnetic ordering states take on new phase diagrams with increasing randomness (bond and anisotropy), while anisotropy induced magnetic ordering states are always occurrence no matter whether concentration of anisotropy is large or small. Existence and disappearance of compensation points rely strongly on bond dilution and random single-ion anisotropy.Some results have not been revealed in Previous papers and predicted by Néel theory of ferrimagnetism.

  20. Competing exchange interactions in multiferroic and ferrimagnetic CaBaCo4O7

    Science.gov (United States)

    Fishman, R. S.; Bordács, S.; Kocsis, V.; Kézsmárki, I.; Viirok, J.; Nagel, U.; Rõõm, T.; Puri, A.; Zeitler, U.; Tokunaga, Y.; Taguchi, Y.; Tokura, Y.

    2017-01-01

    Competing exchange interactions can produce complex magnetic states together with spin-induced electric polarizations. With competing interactions on alternating triangular and kagome layers, the swedenborgite CaBaCo4O7 may have one of the largest measured spin-induced polarizations of ˜1700 nC/cm2 below its ferrimagnetic transition temperature at 70 K. Upon rotating our sample about c =[0 ,0 ,1 ] while the magnetic field is fixed along [1 ,0 ,0 ] , the threefold splitting of the spin-wave frequencies indicates that our sample is hexagonally twinned. Magnetization measurements then suggest that roughly 20% of the sample is in a domain with the a axis along [1 ,0 ,0 ] and that 80% of the sample is in one of two other domains with the a axis along either [-1 /2 ,√{3 }/2 ,0 ] or [-1 /2 ,-√{3 }/2 ,0 ] . Powder neutron-diffraction data, magnetization measurements, and terahertz (THz) absorption spectroscopy reveal that the complex spin order in each domain can be described as a triangular array of bitetrahedral c -axis chains ferrimagnetically coupled to each other in the a b plane. The electric-field dependence of bonds coupling those chains produces the large spin-induced polarization of CaBaCo4O7 .

  1. Spin time-relaxation within strongly coupled paramagnetic systems exhibiting paramagnetic-ferrimagnetic transitions

    CERN Document Server

    Chahid, M

    2000-01-01

    The purpose of the present work is a quantitative study of the spin time relaxation within superweak ferrimagnetic materials exhibiting a paramagnetic-ferrimagnetic transition, when the temperature is changed from an initial value T sub i to a final one T sub f very close to the critical temperature T sub c. From a magnetic point of view, the material under investigation is considered to be made of two strongly coupled paramagnetic sublattices of respective moments phi (cursive,open) Greek and psi. Calculations are made within a Landau mean-field theory, whose free energy involves, in addition to quadratic and quartic terms in both moments phi (cursive,open) Greek and psi, a lowest-order coupling - Cphi (cursive,open) Greek psi, where C<0 stands for the coupling constant measuring the interaction between the two sublattices. We first determine the time dependence of the shifts of the order parameters delta phi (cursive,open) Greek and delta psi from the equilibrium state. We find that this time dependence ...

  2. Possible martensitic transformation and ferrimagnetic properties in Heusler alloy Mn{sub 2}NiSn

    Energy Technology Data Exchange (ETDEWEB)

    Duan, Ying-Ni, E-mail: duanyingni@163.com [Department of Medical Engineering and Technology, Xinjiang Medical University, Urumqi 830011, Xinjiang (China); Fan, Xiao-Xi; Kutluk, Abdugheni [Department of Medical Engineering and Technology, Xinjiang Medical University, Urumqi 830011, Xinjiang (China); Du, Xiu-Juan [School of Applied Science, Taiyuan University of Science and Technology, Taiyuan 030024, Shanxi (China); Zhang, Zheng-Wei [Chemistry and Chemical Engineering Laboratory, The Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, Urumqi 830011, Xinjiang (China); Song, Yu-Ling [College of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 473061, Henan (China)

    2015-07-15

    The electronic structure and magnetic properties of Hg{sub 2}CuTi-type Mn{sub 2}NiSn have been studied by performing the first-principle calculations. It is found that the phase transformation from the cubic to the tetragonal structure reduces the total energy, indicating that the martensitic phase is more stable and the phase transition from austenite to martensite may happen at low temperature for Hg{sub 2}CuTi-type Mn{sub 2}NiSn. Concerning the magnetism of Hg{sub 2}CuTi-type Mn{sub 2}NiSn, both austenitic and martensitic phases are suggested to be ferrimagnets. Furthermore, martensitic transformation decreases the magnetic moment per formula unit compared with austenitic phase. The results are helpful to accelerate the use of Mn{sub 2}NiSn alloys in the series for magnetic shape memory applications. - Highlights: • It is found that the phase transition from austenite to martensite may happen at low temperature for Mn{sub 2}NiSn with the Hg{sub 2}CuTi-type structure. • Both austenitic and martensitic Mn{sub 2}NiSn are ferrimagnets. • Martensitic transformation decreases the magnetization.

  3. Spin-Orbit-Torque Efficiency in Compensated Ferrimagnetic Cobalt-Terbium Alloys

    Science.gov (United States)

    Finley, Joseph; Liu, Luqiao

    2016-11-01

    Despite the potential advantages of information storage in antiferromagnetically coupled materials, it remains unclear whether one can control the magnetic-moment orientation efficiently because of the canceled magnetic moment. Here, we report spin-orbit-torque-induced magnetization switching of ferrimagnetic Co1 -xTbx films with perpendicular magnetic anisotropy. Current-induced switching is demonstrated in all of the studied film compositions, including those near the magnetization compensation point. The spin-orbit-torque-induced effective field is further quantified in the domain-wall motion regime. A divergent behavior that scales with the inverse of magnetic moment is confirmed close to the compensation point, which is consistent with angular momentum conservation. Moreover, we also quantify the Dzyaloshinskii-Moriya interaction energy in the Ta /Co1 -xTbx system and we find that the energy density increases as a function of the Tb concentration. The demonstrated spin-orbit-torque switching, in combination with the fast magnetic dynamics and minimal net magnetization of ferrimagnetic alloys, promises spintronic devices that are faster and with higher density than traditional ferromagnetic systems.

  4. Systems and methods for scalable perovskite device fabrication

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Jinsong; Dong, Qingfeng; Sao, Yuchuan

    2017-02-28

    Continuous processes for fabricating a perovskite device are described that include using a doctor blade for continuously forming a perovskite layer and using a conductive tape lamination process to form an anode or a cathode layer on the perovskite device.

  5. Monolithic Perovskite Silicon Tandem Solar Cells with Advanced Optics

    Energy Technology Data Exchange (ETDEWEB)

    Goldschmidt, Jan C.; Bett, Alexander J.; Bivour, Martin; Blasi, Benedikt; Eisenlohr, Johannes; Kohlstadt, Markus; Lee, Seunghun; Mastroianni, Simone; Mundt, Laura; Mundus, Markus; Ndione, Paul; Reichel, Christian; Schubert, Martin; Schulze, Patricia S.; Tucher, Nico; Veit, Clemens; Veurman, Welmoed; Wienands, Karl; Winkler, Kristina; Wurfel, Uli; Glunz, Stefan W.; Hermle, Martin

    2016-11-14

    For high efficiency monolithic perovskite silicon tandem solar cells, we develop low-temperature processes for the perovskite top cell, rear-side light trapping, optimized perovskite growth, transparent contacts and adapted characterization methods.

  6. Control of Perovskite Crystal Growth by Methylammonium Lead Chloride Templating.

    Science.gov (United States)

    Binek, Andreas; Grill, Irene; Huber, Niklas; Peters, Kristina; Hufnagel, Alexander G; Handloser, Matthias; Docampo, Pablo; Hartschuh, Achim; Bein, Thomas

    2016-04-20

    State-of-the-art solar cells based on methylammonium lead iodide (MAPbI3 ) now reach efficiencies over 20 %. This fast improvement was possible with intensive research in perovskite processing. In particular, chloride-based precursors are known to have a positive influence on the crystallization of the perovskite. Here, we used a combination of in-situ X-ray diffraction and charge-transport measurements to understand the influence of chloride during perovskite crystallization in planar heterojunction solar cells. We show that MAPbCl3 crystallizes directly after the deposition of the starting solution and acts as a template for the formation of MAPbI3 . Additionally, we show that the charge-carrier mobility doubles by extending the time for the template formation. Our results give a deeper understanding of the influence of chloride in the synthesis of MAPbI3 and illustrate the importance of carefully controlling crystallization for reproducible, high-efficiency solar cells.

  7. 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.

  8. 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.

  9. 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

  10. Vibrational spectra of ordered perovskites

    NARCIS (Netherlands)

    Corsmit, A.F.; Hoefdraad, H.E.; Blasse, G.

    1972-01-01

    The vibrational spectra of the molecular M6+O6 (M = Mo, Te, W) group in ordered perovskites of the type Ba2M2+M6+O6 are reported. These groups have symmetry Oh, whereas their site symmetry is also Oh. An assignment of the internal vibrations is presented.

  11. 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.

  12. Elastic and anelastic anomalies in (Ca,Sr)TiO perovskites: Analogue behaviour for silicate perovskites

    OpenAIRE

    Walsh, J.W.; Taylor, P.A.; Buckley, A.; Darling, T.W.; Schreuer, J.; Carpenter, M.A.

    2008-01-01

    Elastic and anelastic anomalies in (Ca,Sr)TiO3 perovskites: Analogue behaviour for silicate perovskites UNITED KINGDOM (Walsh, J.W.) UNITED KINGDOM Received: 2007-10-30 Revised: 2008-02-18 Accepted: 2008-02-27

  13. Mixed-cation designs of magnetic perovskites for Faraday rotation at IR wavelengths

    Science.gov (United States)

    Dionne, Gerald F.; Taussig, Alexander R.; Bolduc, Martin; Bi, Lei; Ross, Caroline A.

    2007-05-01

    Magnetic garnets with Bi3+ are the standard media of discrete Faraday rotation isolators for IR-laser/fiber-optical transmission at 1.55μm wavelength. For monolithic integration with semiconductors, perovskites of generic formula A[B ]O3 offer promising alternatives that involve combinations of select transition-metal ions in octahedral B sites. In this paper, two concepts are described. In both cases, the 180° B -O-B bonding of the perovskite lattice could provide superexchange fields large enough to maintain spin ordering at room temperature. One model proposes a quasiferrite arrangement with antiferromagnetic alignment between Fe3+ and Ni2+ charge ordered in the double perovskite compound {A3+A'4+}[Fe3+Ni2+]O6. The other concept relies on ferromagnetism through delocalization superexchange with the composition A23+[Mn4+Ni2+]O6. Where appropriate to enhance Faraday rotation, Bi3+ can be used for A3+.

  14. The effect of illumination on the formation of metal halide perovskite films

    Science.gov (United States)

    Ummadisingu, Amita; Steier, Ludmilla; Seo, Ji-Youn; Matsui, Taisuke; Abate, Antonio; Tress, Wolfgang; Grätzel, Michael

    2017-04-01

    Optimizing the morphology of metal halide perovskite films is an important way to improve the performance of solar cells when these materials are used as light harvesters, because film homogeneity is correlated with photovoltaic performance. Many device architectures and processing techniques have been explored with the aim of achieving high-performance devices, including single-step deposition, sequential deposition and anti-solvent methods. Earlier studies have looked at the influence of reaction conditions on film quality, such as the concentration of the reactants and the reaction temperature. However, the precise mechanism of the reaction and the main factors that govern it are poorly understood. The consequent lack of control is the main reason for the large variability observed in perovskite morphology and the related solar-cell performance. Here we show that light has a strong influence on the rate of perovskite formation and on film morphology in both of the main deposition methods currently used: sequential deposition and the anti-solvent method. We study the reaction of a metal halide (lead iodide) with an organic compound (methylammonium iodide) using confocal laser scanning fluorescence microscopy and scanning electron microscopy. The lead iodide crystallizes before the intercalation of methylammonium iodide commences, producing the methylammonium lead iodide perovskite. We find that the formation of perovskite via such a sequential deposition is much accelerated by light. The influence of light on morphology is reflected in a doubling of solar-cell efficiency. Conversely, using the anti-solvent method to form methyl ammonium lead iodide perovskite in a single step from the same starting materials, we find that the best photovoltaic performance is obtained when films are produced in the dark. The discovery of light-activated crystallization not only identifies a previously unknown source of variability in opto-electronic properties, but also opens up

  15. Ferrimagnetic/ferroelastic domain interactions in magnetite below the Verwey transition: Part II. Micromagnetic and image simulations

    DEFF Research Database (Denmark)

    Bryson, James F.J.; Kasama, Takeshi; Dunin-Borkowski, Rafal E.;

    2013-01-01

    Micromagnetic simulations have been used to explore the interaction between ferrimagnetic domain walls (DWs) and ferroelastic twin walls (TWs) below the Verwey transition in magnetite (Fe3O4). Simulations were performed using a thin-foil geometry in order to replicate the domain patterns observed...

  16. Ligand-Stabilized Reduced-Dimensionality Perovskites

    KAUST Repository

    Quan, Li Na

    2016-02-03

    Metal halide perovskites have rapidly advanced thin film photovoltaic performance; as a result, the materials’ observed instabilities urgently require a solution. Using density functional theory (DFT), we show that a low energy of formation, exacerbated in the presence of humidity, explains the propensity of perovskites to decompose back into their precursors. We find, also using DFT, that intercalation of phenylethylammonium between perovskite layers introduces quantitatively appreciable van der Waals interactions; and these drive an increased formation energy and should therefore improve material stability. Here we report the reduced-dimensionality (quasi-2D) perovskite films that exhibit improved stability while retaining the high performance of conventional three-dimensional perovskites. Continuous tuning of the dimensionality, as assessed using photophysical studies, is achieved by the choice of stoichiometry in materials synthesis. We achieved the first certified hysteresis-free solar power conversion in a planar perovskite solar cell, obtaining a 15.3% certified PCE, and observe greatly improved performance longevity.

  17. 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.

  18. Ligand-Stabilized Reduced-Dimensionality Perovskites.

    Science.gov (United States)

    Quan, Li Na; Yuan, Mingjian; Comin, Riccardo; Voznyy, Oleksandr; Beauregard, Eric M; Hoogland, Sjoerd; Buin, Andrei; Kirmani, Ahmad R; Zhao, Kui; Amassian, Aram; Kim, Dong Ha; Sargent, Edward H

    2016-03-02

    Metal halide perovskites have rapidly advanced thin-film photovoltaic performance; as a result, the materials' observed instabilities urgently require a solution. Using density functional theory (DFT), we show that a low energy of formation, exacerbated in the presence of humidity, explains the propensity of perovskites to decompose back into their precursors. We find, also using DFT, that intercalation of phenylethylammonium between perovskite layers introduces quantitatively appreciable van der Waals interactions. These drive an increased formation energy and should therefore improve material stability. Here we report reduced-dimensionality (quasi-2D) perovskite films that exhibit improved stability while retaining the high performance of conventional three-dimensional perovskites. Continuous tuning of the dimensionality, as assessed using photophysical studies, is achieved by the choice of stoichiometry in materials synthesis. We achieve the first certified hysteresis-free solar power conversion in a planar perovskite solar cell, obtaining a 15.3% certified PCE, and observe greatly improved performance longevity.

  19. Design of Lead-Free Inorganic Halide Perovskites for Solar Cells via Cation-Transmutation.

    Science.gov (United States)

    Zhao, Xin-Gang; Yang, Ji-Hui; Fu, Yuhao; Yang, Dongwen; Xu, Qiaoling; Yu, Liping; Wei, Su-Huai; Zhang, Lijun

    2017-02-22

    Hybrid organic-inorganic halide perovskites with the prototype material of CH3NH3PbI3 have recently attracted intense interest as low-cost and high-performance photovoltaic absorbers. Despite the high power conversion efficiency exceeding 20% achieved by their solar cells, two key issues-the poor device stabilities associated with their intrinsic material instability and the toxicity due to water-soluble Pb(2+)-need to be resolved before large-scale commercialization. Here, we address these issues by exploiting the strategy of cation-transmutation to design stable inorganic Pb-free halide perovskites for solar cells. The idea is to convert two divalent Pb(2+) ions into one monovalent M(+) and one trivalent M(3+) ions, forming a rich class of quaternary halides in double-perovskite structure. We find through first-principles calculations this class of materials have good phase stability against decomposition and wide-range tunable optoelectronic properties. With photovoltaic-functionality-directed materials screening, we identify 11 optimal materials with intrinsic thermodynamic stability, suitable band gaps, small carrier effective masses, and low excitons binding energies as promising candidates to replace Pb-based photovoltaic absorbers in perovskite solar cells. The chemical trends of phase stabilities and electronic properties are also established for this class of materials, offering useful guidance for the development of perovskite solar cells fabricated with them.

  20. Stability Issues on Perovskite Solar Cells

    OpenAIRE

    2015-01-01

    Organo lead halide perovskite materials like methylammonium lead iodide (CH3NH3PbI3) and formamidinium lead iodide (HC(NH2)2PbI3) show superb opto-electronic properties. Based on these perovskite light absorbers, power conversion efficiencies of the perovskite solar cells employing hole transporting layers have increased from 9.7% to 20.1% within just three years. Thus, it is apparent that perovskite solar cell is a promising next generation photovoltaic technology. However, the unstable natu...

  1. Spin dynamics in perovskites, pyrochlores, and layered manganites

    Energy Technology Data Exchange (ETDEWEB)

    Oseroff, S. B. [San Diego State University, San Diego, California 29182-8062 (United States); Moreno, N. O. [Instituto de Fisica ' ' Gleb Wataghin' ' UNICAMP, Campinas, Sao Paulo 13083-970, (Brazil); Pagliuso, P. G. [Instituto de Fisica ' ' Gleb Wataghin' ' UNICAMP, Campinas, Sao Paulo 13083-970, (Brazil); Rettori, C. [Instituto de Fisica ' ' Gleb Wataghin' ' UNICAMP, Campinas, Sao Paulo 13083-970, (Brazil); Huber, D. L. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Gardner, J. S. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Sarrao, J. L. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Thompson, J. D. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Causa, M. T. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica and Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, (Argentina); Alejandro, G. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica and Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, (Argentina)] (and others)

    2000-05-01

    High temperature electron spin resonance (ESR) and magnetic susceptibility ({chi}) are analyzed for manganites related with colossal magnetoresistance (CMR). The properties of compounds with different crystalline structures: three-dimensional (3D) perovskites, pyrochlore, and La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}, a two-dimensional layer, are compared. In the paramagnetic regime, and outside the critical regions associated with phase transitions, the temperature dependence of the ESR linewidth presents a universal behavior dominated by the variations of {chi}(T), {delta}H{sub pp}(T)=[C/T{chi}(T)]{delta}H{sub pp}({infinity}). The high temperature limit of the linewidth, {delta}H{sub pp}({infinity}), is related to the parameters of the Hamiltonian describing the interactions of the spin system. The role played by magnetic anisotropy, isotropic superexchange, and double exchange is revealed and discussed in the analysis of the experimental data. In CMR and non-CMR pyrochlores, {delta}H{sub pp}({infinity}){proportional_to}{omega}{sub p}{sup 2}/J where J is proportional to the Curie-Weiss temperature, including the hybridization mechanism producing CMR. Instead, {delta}H{sub pp}({infinity}) of CMR perovskites seems not to be affected by the double-exchange interaction. In contrast with the 3D perovskites, the ESR linewidth and resonance field of La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}, a bilayer compound, although isotropic at high temperatures, becomes anisotropic for T{sub c}=125 K

  2. Metrological Performance of a Ferrimagnetic Resonance Marker for the Field Control of the CERN Proton Synchrotron

    CERN Document Server

    Arpaia, P; Caspers, F; Golluccio, G; Oberson, D

    2012-01-01

    In particle accelerators, “field markers” provide a digital trigger when the magnetic field crosses a given threshold. In this paper, the metrological characterization of a magnetic field marker, based on a ferrimagnetic resonance transducer referencing the flux sensed by a coil, is reported. The experimental results of a validation test campaign at the European Organization for Nuclear Research (CERN) to test the marker in static as well as fast ramping fields (up to 2.5 T/s) are illustrated. The repeatability of ±4 μT attained in the range (60 to 100) mT is very promising to increase the performance of the Proton Synchrotron accelerator at CERN.

  3. Transparent ferrimagnetic semiconducting CuCr2O4 thin films by atomic layer deposition

    Science.gov (United States)

    Tripathi, T. S.; Yadav, C. S.; Karppinen, M.

    2016-04-01

    We report the magnetic and optical properties of CuCr2O4 thin films fabricated by atomic layer deposition (ALD) from Cu(thd)2, Cr(acac)3, and ozone; we deposit 200 nm thick films and anneal them at 700 °C in oxygen atmosphere to crystallize the spinel phase. A ferrimagnetic transition at 140 K and a direct bandgap of 1.36 eV are determined for the films from magnetic and UV-vis spectrophotometric measurements. Electrical transport measurements confirm the p-type semiconducting behavior of the films. As the ALD technique allows the deposition of conformal pin-hole-free coatings on complex 3D surfaces, our CuCr2O4 films are interesting material candidates for various frontier applications.

  4. Magnetic proximity effect features in antiferromagnetic/ferrimagnetic core-shell nanoparticles

    OpenAIRE

    Golosovsky, I. V.; Suriñach, Santiago

    2009-01-01

    A study of “inverted” core-shell, MnO/γ-Mn2O3, nanoparticles is presented. Crystal and magnetic structures and characteristic sizes have been determined by neutron diffraction for the antiferromagnetic core (MnO) and the ferrimagnetic shell (γ-Mn2O3). Remarkably, while the MnO core is found to have a TN not far from its bulk value, the magnetic order of the γ-Mn2O3 shell is stable far above TC, exhibiting two characteristic temperatures, at T~ 40  K [TC(γ-Mn2O3)] and at T~120  K [~ TN(MnO)]. ...

  5. First-principles study on the ferrimagnetic half-metallic Mn2FeAs alloy

    Science.gov (United States)

    Qi, Santao; Zhang, Chuan-Hui; Chen, Bao; Shen, Jiang; Chen, Nanxian

    2015-05-01

    Mn-based full-Heusler alloys are kinds of promising candidates for new half-metallic materials. Basing on first principles, the electronic structures and magnetic properties of the Mn2FeAs full-Heusler alloy have been investigated in detail. The Hg2CuTi-type Mn2FeAs compound obeys the Slater-Pauling rule, while the anti-parallel alignment atomic magnetic moments of Mn locating at different sites indicate it a ferrimagnetic alloy. The calculated spin-down bands behave half-metallic character, exhibiting a direct gap of 0.46 eV with a 100% spin polarization at the Fermi level. More studies show the compound would maintain half-metallic nature in a large range of variational lattice constants. We expect that our calculated results may trigger Mn2FeAs applying in the future spintronics field.

  6. Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy.

    Science.gov (United States)

    Jeong, Jaewoo; Ferrante, Yari; Faleev, Sergey V; Samant, Mahesh G; Felser, Claudia; Parkin, Stuart S P

    2016-01-18

    Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn-Ge termination layers that are oppositely magnetized to the higher moment Mn-Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible.

  7. Micromagnetic simulation of ferrimagnetic TbFeCo films with exchange coupled nanophases

    Science.gov (United States)

    Ma, Chung T.; Li, Xiaopu; Poon, S. Joseph

    2016-11-01

    Amorphous ferrimagnetic TbFeCo thin films are found to exhibit exchange bias effect near the compensation temperature by magnetic hysteresis loop measurement. The observed exchange anisotropy is believed to originate from the exchange interaction between the two nanoscale amorphous phases distributed within the films. Here, we present a computational model of phase-separated TbFeCo using micromagnetic simulation. Two types of cells with different Tb concentration are distributed within the simulated space to obtain a heterogeneous structure consisting of two nanoscale amorphous phases. Each cell contains separated Tb and FeCo components, forming two antiferromagnetically coupled sublattices. Using this model, we are able to show the existence of exchange bias effect, and the shift in hysteresis loops is in agreement with experiment. The micromagnetic model developed herein for a heterogeneous magnetic material may also account for some recent measurements of exchange bias effect in crystalline films.

  8. Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy

    Science.gov (United States)

    Jeong, Jaewoo; Ferrante, Yari; Faleev, Sergey V.; Samant, Mahesh G.; Felser, Claudia; Parkin, Stuart S. P.

    2016-01-01

    Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn-Ge termination layers that are oppositely magnetized to the higher moment Mn-Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible.

  9. Transparent ferrimagnetic semiconducting CuCr2O4 thin films by atomic layer deposition

    Directory of Open Access Journals (Sweden)

    T. S. Tripathi

    2016-04-01

    Full Text Available We report the magnetic and optical properties of CuCr2O4 thin films fabricated by atomic layer deposition (ALD from Cu(thd2, Cr(acac3, and ozone; we deposit 200 nm thick films and anneal them at 700 °C in oxygen atmosphere to crystallize the spinel phase. A ferrimagnetic transition at 140 K and a direct bandgap of 1.36 eV are determined for the films from magnetic and UV-vis spectrophotometric measurements. Electrical transport measurements confirm the p-type semiconducting behavior of the films. As the ALD technique allows the deposition of conformal pin-hole-free coatings on complex 3D surfaces, our CuCr2O4 films are interesting material candidates for various frontier applications.

  10. Interface electronic structure at the topological insulator-ferrimagnetic insulator junction

    Science.gov (United States)

    Kubota, Y.; Murata, K.; Miyawaki, J.; Ozawa, K.; Onbasli, M. C.; Shirasawa, T.; Feng, B.; Yamamoto, Sh; Liu, R.-Y.; Yamamoto, S.; Mahatha, S. K.; Sheverdyaeva, P.; Moras, P.; Ross, C. A.; Suga, S.; Harada, Y.; Wang, K. L.; Matsuda, I.

    2017-02-01

    An interface electron state at the junction between a three-dimensional topological insulator film, Bi2Se3, and a ferrimagnetic insulator film, Y3Fe5O12 (YIG), was investigated by measurements of angle-resolved photoelectron spectroscopy and x-ray absorption magnetic circular dichroism. The surface state of the Bi2Se3 film was directly observed and localized 3d spin states of the Fe3+ in the YIG film were confirmed. The proximity effect is likely described in terms of the exchange interaction between the localized Fe 3d electrons in the YIG film and delocalized electrons of the surface and bulk states in the Bi2Se3 film.

  11. Self-assembled dynamic perovskite composite cathodes for intermediate temperature solid oxide fuel cells

    Science.gov (United States)

    Shin, J. Felix; Xu, Wen; Zanella, Marco; Dawson, Karl; Savvin, Stanislav N.; Claridge, John B.; Rosseinsky, Matthew J.

    2017-01-01

    Electrode materials for intermediate temperature (500-700 ∘C) solid oxide fuel cells require electrical and mechanical stability to maintain performance during the cell lifetime. This has proven difficult to achieve for many candidate cathode materials and their derivatives with good transport and electrocatalytic properties because of reactivity towards cell components, and the fuels and oxidants. Here we present Ba0.5Sr0.5(Co0.7Fe0.3)0.6875W0.3125O3-δ (BSCFW), a self-assembled composite prepared through simple solid state synthesis, consisting of B-site cation ordered double perovskite and disordered single perovskite oxide phases, as a candidate cathode material. These phases interact by dynamic compositional change at the operating temperature, promoting both chemical stability through the increased amount of W in the catalytically active single perovskite provided from the W-reservoir double perovskite, and microstructural stability through reduced sintering of the supported catalytically active phase. This interactive catalyst-support system enabled stable high electrochemical activity through the synergic integration of the distinct properties of the two phases.

  12. Scaffolding, ladders, chains, and rare ferrimagnetism in intermetallic borides: synthesis, crystal chemistry and magnetism.

    Science.gov (United States)

    Goerens, Christian; Brgoch, Jakoah; Miller, Gordon J; Fokwa, Boniface P T

    2011-07-04

    Single-phase polycrystalline samples and single crystals of the complex boride phases Ti(8)Fe(3)Ru(18)B(8) and Ti(7)Fe(4)Ru(18)B(8) have been synthesized by arc melting the elements. The phases were characterized by powder and single-crystal X-ray diffraction as well as energy-dispersive X-ray analysis. They are new substitutional variants of the Zn(11)Rh(18)B(8) structure type, space group P4/mbm (no. 127). The particularity of their crystal structure lies in the simultaneous presence of dumbbells which form ladders of magnetically active iron atoms along the [001] direction and two additional mixed iron/titanium chains occupying Wyckoff sites 4h and 2b. The ladder substructure is ca. 3.0 Å from the two chains at the 4h, which creates the sequence chain-ladder-chain, establishing a new structural and magnetic motif, the scaffold. The other chain (at 2b) is separated by at least 6.5 Å from this scaffold. According to magnetization measurements, Ti(8)Fe(3)Ru(18)B(8) and Ti(7)Fe(4)Ru(18)B(8) order ferrimagnetically below 210 and 220 K, respectively, with the latter having much higher magnetic moments than the former. However, the magnetic moment observed for Ti(8)Fe(3)Ru(18)B(8) is unexpectedly smaller than the recently reported Ti(9)Fe(2)Ru(18)B(8) ferromagnet. The variation of the magnetic moments observed in these new phases can be adequately understood by assuming a ferrimagnetic ordering involving the three different iron sites. Furthermore, the recorded hysteresis loops indicate a semihard magnetic behavior for the two phases. The highest H(c) value (28.6 kA/m), measured for Ti(7)Fe(4)Ru(18)B(8), lies just at the border of those of hard magnetic materials.

  13. High-performance perovskite light-emitting diodes via morphological control of perovskite films.

    Science.gov (United States)

    Yu, Jae Choul; Kim, Da Bin; Jung, Eui Dae; Lee, Bo Ram; Song, Myoung Hoon

    2016-04-07

    Solution-processable perovskite materials have garnered tremendous attention because of their excellent charge carrier mobility, possibility of a tunable optical bandgap, and high photoluminescence quantum efficiency (PLQE). In particular, the uniform morphology of a perovskite film is the most important factor in realizing perovskite light-emitting diodes (PeLEDs) with high efficiency and full-coverage electroluminescence (EL). In this study, we demonstrate highly efficient PeLEDs that contain a perovskite film with a uniform morphology by introducing HBr into the perovskite precursor. The introduction of HBr into the perovskite precursor results in a perovskite film with a uniform, continuous morphology because the HBr increases the solubility of the inorganic component in the perovskite precursor and reduces the crystallization rate of the perovskite film upon spin-coating. Moreover, PeLEDs fabricated using perovskite films with a uniform, continuous morphology, which were deposited using 6 vol% HBr in a dimethylformamide (DMF)/hydrobromic acid (HBr) cosolvent, exhibited full coverage of the green EL emission. Finally, the optimized PeLEDs fabricated with perovskite films deposited using the DMF/HBr cosolvent exhibited a maximum luminance of 3490 cd m(-2) (at 4.3 V) and a luminous efficiency of 0.43 cd A(-1) (at 4.3 V).

  14. Polarization twist in perovskite ferrielectrics.

    Science.gov (United States)

    Kitanaka, Yuuki; Hirano, Kiyotaka; Ogino, Motohiro; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2016-09-02

    Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of 'polarization twist', which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms.

  15. Polarization twist in perovskite ferrielectrics

    Science.gov (United States)

    Kitanaka, Yuuki; Hirano, Kiyotaka; Ogino, Motohiro; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2016-01-01

    Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms. PMID:27586824

  16. Polarization twist in perovskite ferrielectrics

    Science.gov (United States)

    Kitanaka, Yuuki; Hirano, Kiyotaka; Ogino, Motohiro; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2016-09-01

    Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms.

  17. 双钙钛矿Sr2FeMoO6的微波合成、表征及电磁性能%Microwave Synthesis, Characterization, Magnetic and Electrical Properties of Double Perovskite Sr2FeMoO6

    Institute of Scientific and Technical Information of China (English)

    翟永清; 张张; 霍国燕; 任明辉

    2011-01-01

    以SrCO3、Fe2O3、MoO3为原料,MnO2为微波吸收剂,采用微波烧结法成功合成双钙钛矿Sr2FeMoO6粉体.XRD结果表明,产品为四方晶系Sr2FeMoO6,空间群为14/mmm,晶胞参数为:a=0.5571nm,c=0.7872nm,利用X射线衍射数据经Scherrer公式计算所得样品的晶粒尺寸为20nm左右.磁性能测试结果表明,样品表现为铁磁性,磁转变温度高于室温,1T磁场下室温饱和磁化强度为17.949(A·m2)/kg.电性能测试结果表明,样品呈现典型的半导体行为,导电机制属于绝热小极化子导电机制,样品在1T磁场下的室温磁电阻变化率可达-15.63%.%With MnO2 as microwave absorbent, double perovskite Sr2FeMoO6 powder was synthesized by microwave processing using SrC03, Fe2O3 and MoO3 as starting materials.XRD patterns reveal that the as-synthesized product is Sr2FeMoO6 with tetragonal crystal structure and I4/mmm space group, and the unit cell parameter is a =0.5571 nm as well as c = 0.7872 nm.The grain size of the sample is about 20 nm, calculated by the Scherrer formula using the diffraction data.Magnetism testing results show that the sample is ferromagnet,the transition temperature is higher than room temperature and the saturation magnetization is 17.949 (A·m2)kg under 1 T at room temperature.Electrical performance testing results show that the sample exhibit typical semiconductor behavior and the conductive mechanism can be described by adiabatic small polaron model.The room temperature magnetoresistance of the sample under 1 T field is up to -15.63%

  18. 双钙钛矿Sr2Fe1-CrMoO6电子结构与磁学性质的第一性原理研究*%Electronic and magnetic properties of double perovskites Sr2 Fe1- Cr MoO6:the first principles study

    Institute of Scientific and Technical Information of China (English)

    杨小兰

    2014-01-01

    The electronic structure and magnetic properties of double perovskites Sr2 Fe1- Cr MoO6 system in different Cr content (=0,1/3,0.5 and 1)corresponding to the Sr2 Fe1- Cr MoO6 supper cell structure were caculated by the first principle method .The calculation results showed that:the obtained lattice parameters, total magnetic moments and magnetic moments per Fe ion of Sr2 Fe1- Cr MoO6 decrease ,with the increase of Cr doping (=0.5),the spin-up electronic density near the Fermi energy increases,the compounds change to be metallic,but Sr2 Fe1- Cr MoO6 (=0,1/3,and 1)still to be half-metalic.The calculation results coincided with the existing experiments and theories well,which offered theoretical data for application in further.%利用第一性原理系统计算了 Sr2 Fe1-Cr MoO 6体系中不同 Cr 含量(=0,1/3,0.5和1)所对应 Sr2 Fe1- Cr MoO 6晶胞结构的电子结构和磁学性质.计算结果表明,体系的晶格常数、总磁矩及 Fe离子磁矩由于 Cr 掺杂而降低,晶格发生畸变,并发现当 Cr 掺杂含量增加至0.5时自旋向上费米面附近态密度明显增加,超胞呈金属性,但 Sr2 Fe1- Cr MoO 6(=0,1/3,0.5和1)仍保持半金属性.得出的计算结果与现有的实验和理论值吻合较好,该结果为其材料的进一步实际应用提供了理论依据.

  19. Stability and Elasticity of High Iron and Aluminum Post-Perovskite Phases and Their Implications for the D" Layer

    Science.gov (United States)

    Shieh, S. R.; Duffy, T. S.; Kubo, A.; Prakapenka, V. B.

    2008-12-01

    To evaluate the iron and aluminum effects on the post-perovskite phase at deep mantle conditions, it is important to study the potential mantle silicates containing both iron and aluminum. In this study, three different compositions of natural garnet along pyrope-almandine join, Pyr21Alm73Gr5, Pyr43Alm54Gr2, Pyr58Alm38Gr3, were used as starting materials to investigate the stability and elasticity of high iron- and aluminum-bearing post-perovskite phase at deep mantle conditions. In situ high-pressure and high- temperature experiments were conducted at beamline 13-ID-D of GSECARS, Advanced Photon Source. A monochromatic beam with a wavelength of 0.3044 Å and a MAR CCD detector were used for X-ray diffraction data collections. Samples were loaded in the symmetrical diamond-anvil cells and heated by the double-sided laser heating system. Our results showed that the post-perovskite phase can be successfully synthesized from three different compositions at pressure greater than 160 GPa and temperature higher than 1600 K. This indicates that the post-perovskite phase can simultaneously accommodate high aluminum and high iron contents. However, Al2O3-post-perovskite phase can also be observed from some runs for Pyr43Alm54Gr2 and Pyr58Alm38Gr3, showing that there is actually a limit for incorporating the aluminum into the post-perovskite phase but not for iron. In addition, we also found that the volume of post- perovskite phases can also be affected by the incorporated amount of iron. Our pressure-volume results showed that high-iron post-perovskite phases have larger volumes and the iron effect is greater at pressure above 120 GPa.

  20. Flexible Hybrid Organic-Inorganic Perovskite Memory.

    Science.gov (United States)

    Gu, Chungwan; Lee, Jang-Sik

    2016-05-24

    Active research has been done on hybrid organic-inorganic perovskite materials for application to solar cells with high power conversion efficiency. However, this material often shows hysteresis, which is undesirable, shift in the current-voltage curve. The hysteresis may come from formation of defects and their movement in perovskite materials. Here, we utilize the defects in perovskite materials to be used in memory operations. We demonstrate flexible nonvolatile memory devices based on hybrid organic-inorganic perovskite as the resistive switching layer on a plastic substrate. A uniform perovskite layer is formed on a transparent electrode-coated plastic substrate by solvent engineering. Flexible nonvolatile memory based on the perovskite layer shows reproducible and reliable memory characteristics in terms of program/erase operations, data retention, and endurance properties. The memory devices also show good mechanical flexibility. It is suggested that resistive switching is done by migration of vacancy defects and formation of conducting filaments under the electric field in the perovskite layer. It is believed that organic-inorganic perovskite materials have great potential to be used in high-performance, flexible memory devices.

  1. Achieving High Performance Perovskite Solar Cells

    Science.gov (United States)

    Yang, Yang

    2015-03-01

    Recently, metal halide perovskite based solar cell with the characteristics of rather low raw materials cost, great potential for simple process and scalable production, and extreme high power conversion efficiency (PCE), have been highlighted as one of the most competitive technologies for next generation thin film photovoltaic (PV). In UCLA, we have realized an efficient pathway to achieve high performance pervoskite solar cells, where the findings are beneficial to this unique materials/devices system. Our recent progress lies in perovskite film formation, defect passivation, transport materials design, interface engineering with respect to high performance solar cell, as well as the exploration of its applications beyond photovoltaics. These achievements include: 1) development of vapor assisted solution process (VASP) and moisture assisted solution process, which produces perovskite film with improved conformity, high crystallinity, reduced recombination rate, and the resulting high performance; 2) examination of the defects property of perovskite materials, and demonstration of a self-induced passivation approach to reduce carrier recombination; 3) interface engineering based on design of the carrier transport materials and the electrodes, in combination with high quality perovskite film, which delivers 15 ~ 20% PCEs; 4) a novel integration of bulk heterojunction to perovskite solar cell to achieve better light harvest; 5) fabrication of inverted solar cell device with high efficiency and flexibility and 6) exploration the application of perovskite materials to photodetector. Further development in film, device architecture, and interfaces will lead to continuous improved perovskite solar cells and other organic-inorganic hybrid optoelectronics.

  2. Photocatalysis: HI-time for perovskites

    Science.gov (United States)

    Vesborg, Peter C. K.

    2017-01-01

    Organolead halide perovskite solar absorbers demonstrate high photovoltaic efficiencies but they are notorious for their intolerance to water. Now, methylammonium lead iodide perovskites are used to harvest solar energy — in water — via photocatalytic generation of hydrogen from solutions of hydriodic acid.

  3. Photocatalysis: HI-time for perovskites

    DEFF Research Database (Denmark)

    Vesborg, Peter Christian Kjærgaard

    2017-01-01

    Organolead halide perovskite solar absorbers demonstrate high photovoltaic efficiencies but they are notorious for their intolerance to water. Now, methylammonium lead iodide perovskites are used to harvest solar energy — in water — via photocatalytic generation of hydrogen from solutions of hydr...

  4. Perovskite solar cells: Danger from within

    Science.gov (United States)

    Wilks, Regan G.; Bär, Marcus

    2017-01-01

    Extensive efforts are under way to increase not only the efficiency but also the stability of organic-inorganic halide perovskite based solar cells. However, research shows that iodine-containing perovskites are vulnerable to a self-degradation pathway that may inherently limit their lifetime.

  5. Perovskite Superlattices as Tunable Microwave Devices

    Science.gov (United States)

    Christen, H. M.; Harshavardhan, K. S.

    2003-01-01

    Experiments have shown that superlattices that comprise alternating epitaxial layers of dissimilar paraelectric perovskites can exhibit large changes in permittivity with the application of electric fields. The superlattices are potentially useful as electrically tunable dielectric components of such microwave devices as filters and phase shifters. The present superlattice approach differs fundamentally from the prior use of homogeneous, isotropic mixtures of base materials and dopants. A superlattice can comprise layers of two or more perovskites in any suitable sequence (e.g., ABAB..., ABCDABCD..., ABACABACA...). Even though a single layer of one of the perovskites by itself is not tunable, the compositions and sequence of the layers can be chosen so that (1) the superlattice exhibits low microwave loss and (2) the interfacial interaction between at least two of the perovskites in the superlattice renders either the entire superlattice or else at least one of the perovskites tunable.

  6. Efficient Luminescence from Perovskite Quantum Dot Solids

    KAUST Repository

    Kim, Younghoon

    2015-11-18

    © 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals\\' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

  7. 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.

  8. Understanding the photostability of perovskite solar cell

    Science.gov (United States)

    Joshi, Pranav H.

    Global climate change and increasing energy demands have led to a greater focus on cheaper photovoltaic energy solutions. Perovskite solar cells and organic solar cells have emerged as promising technologies for alternative cheaper photovoltaics. Perovskite solar cells have shown unprecedentedly rapid improvement in power conversion efficiency, from 3% in 2009 to more than 21% today. High absorption coefficient, long diffusion lengths, low exciton binding energy, low defect density and easy of fabrication has made perovskites near ideal material for economical and efficient photovoltaics. However, stability of perovskite and organic solar cells, especially photostability is still not well understood. In this work, we study the photostability of organic solar cells and of perovskite solar cells. (Abstract shortened by ProQuest.).

  9. Organohalide Lead Perovskites for Photovoltaic Applications.

    Science.gov (United States)

    Yusoff, Abd Rashid Bin Mohd; Nazeeruddin, Mohammad Khaja

    2016-03-03

    Perovskite solar cells have recently exhibited a significant leap in efficiency due to their broad absorption, high optical absorption coefficient, very low exciton binding energy, long carrier diffusion lengths, efficient charge collection, and very high open-circuit potential, similar to that of III-IV semiconductors. Unlike silicon solar cells, perovskite solar cells can be developed from a variety of low-temperature solutions processed from inexpensive raw materials. When the perovskite absorber film formation is optimized using solvent engineering, a power conversion efficiency of over 21% has been demonstrated, highlighting the unique photovoltaic properties of perovskite materials. Here, we review the current progress in perovskite solar cells and charge transport materials. We highlight crucial challenges and provide a summary and prospects.

  10. 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.

  11. Oxyfluoride Chemistry of Layered Perovskite Compounds

    Directory of Open Access Journals (Sweden)

    Yoshihiro Tsujimoto

    2012-03-01

    Full Text Available In this paper, we review recent progress and new challenges in the area of oxyfluoride perovskite, especially layered systems including Ruddlesden-Popper (RP, Dion-Jacobson (DJ and Aurivillius (AV type perovskite families. It is difficult to synthesize oxyfluoride perovskite using a conventional solid-state reaction because of the high chemical stability of the simple fluoride starting materials. Nevertheless, persistent efforts made by solid-state chemists have led to a major breakthrough in stabilizing such a mixed anion system. In particular, it is known that layered perovskite compounds exhibit a rich variety of O/F site occupation according to the synthesis used. We also present the synthetic strategies to further extend RP type perovskite compounds, with particular reference to newly synthesized oxyfluorides, Sr2CoO3F and Sr3Fe2O5+xF2−x (x ~ 0.44.

  12. Magnetic Signatures of Quantum Critical Points of the Ferrimagnetic Mixed Spin-(1/2, S) Heisenberg Chains at Finite Temperatures

    Science.gov (United States)

    Strečka, Jozef; Verkholyak, Taras

    2016-10-01

    Magnetic properties of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are examined using quantum Monte Carlo simulations for two different quantum spin numbers S=1 and 3/2. The calculated magnetization curves at finite temperatures are confronted with zero-temperature magnetization data obtained within the density matrix renormalization group method, which imply an existence of two quantum critical points determining a breakdown of the gapped Lieb-Mattis ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively. While a square root behavior of the magnetization accompanying each quantum critical point is gradually smoothed upon rising temperature, the susceptibility and isothermal entropy change data at low temperatures provide a stronger evidence of the zero-temperature quantum critical points through marked local maxima and minima, respectively.

  13. The phase diagrams and the magnetic properties of a ferrimagnetic mixed spin 1/2 and spin 1 Ising nanowire

    Energy Technology Data Exchange (ETDEWEB)

    Boughrara, M., E-mail: boughrara_mourad@yahoo.fr; Kerouad, M.; Zaim, A.

    2014-06-01

    In this work, we have used Monte Carlo Simulation technique (MCS) and effective field theory (EFT) to study the critical and the compensation behaviors of a ferrimagnetic cylindrical nanowire. The system consists of a ferromagnetic spin S{sub A}=1/2 core and a ferromagnetic spin S{sub B}=1 surface shell coupled with an antiferromagnetic interlayer coupling J{sub 1} to the core. The effects of the uniaxial anisotropy, the shell coupling and the interface negative coupling on both the critical and compensation temperatures are investigated. - Highlights: • Phase diagrams and total magnetizations are examined for a ferrimagnetic mixed spin 1/2 and spin 1 Ising nanowire. • The system is studied by effective-field theory and Monte Carlo (MC) simulation. • The effects of the uniaxial anisotropy, the shell coupling and the interface negative coupling on both the critical and compensation temperatures are investigated.

  14. Magnetic Properties of One-Dimensional Ferrimagnetic Mixed (1,3/2) Spin Chain with Single-Ion Anisotropy

    Institute of Scientific and Technical Information of China (English)

    Ekrem Aydiner

    2004-01-01

    @@ We have carried out Monte Carlo simulations to study the magnetic properties of a mixed S = 1 and S = 3/2ferrimagnetic system interacting antiferromagnetically on a one-dimensional spin chain with single-ion anisotropy.It has been shown that at sufficiently low temperatures, the system has magnetization plateaus near the ground state under an external field. Other interesting physical quantities such as the specific heat and the Neel order at low temperatures are also discussed.

  15. Evaluation of the resistance of DNA immobilized on ferrimagnetic particles of cobalt ferrite nanopowder against nuclease cleavage.

    Science.gov (United States)

    Pershina, A G; Sazonov, A E; Ogorodova, L M

    2010-07-01

    DNA was immobilized on ferrimagnetic particles of cobalt ferrite nanopowder (CoFe(2)O(4)) and its resistance to endonuclease (DNase I) hydrolysis was studied. Immobilization on cobalt ferrite nanoparticles prevented enzymatic cleavage of DNA. This process was not associated with enzyme inactivation under the effect of nanosize cobalt ferrite and was presumably determined by lesser availability of the DNA molecule as a result of its interaction with nanoparticles.

  16. The phase diagrams and the magnetic properties of a ferrimagnetic mixed spin 1/2 and spin 1 Ising nanowire

    Science.gov (United States)

    Boughrara, M.; Kerouad, M.; Zaim, A.

    2014-06-01

    In this work, we have used Monte Carlo Simulation technique (MCS) and effective field theory (EFT) to study the critical and the compensation behaviors of a ferrimagnetic cylindrical nanowire. The system consists of a ferromagnetic spin SA=1/2 core and a ferromagnetic spin SB=1 surface shell coupled with an antiferromagnetic interlayer coupling J1 to the core. The effects of the uniaxial anisotropy, the shell coupling and the interface negative coupling on both the critical and compensation temperatures are investigated.

  17. Spin time-relaxation within strongly coupled paramagnetic systems exhibiting paramagnetic-ferrimagnetic transitions

    Energy Technology Data Exchange (ETDEWEB)

    Chahid, M.; Benhamou, M. E-mail: benhamou.mabrouk@caramail.com

    2000-08-01

    The purpose of the present work is a quantitative study of the spin time relaxation within superweak ferrimagnetic materials exhibiting a paramagnetic-ferrimagnetic transition, when the temperature is changed from an initial value T{sub i} to a final one T{sub f} very close to the critical temperature T{sub c}. From a magnetic point of view, the material under investigation is considered to be made of two strongly coupled paramagnetic sublattices of respective moments phi (cursive,open) Greek and {psi}. Calculations are made within a Landau mean-field theory, whose free energy involves, in addition to quadratic and quartic terms in both moments phi (cursive,open) Greek and {psi}, a lowest-order coupling - Cphi (cursive,open) Greek{psi}, where C<0 stands for the coupling constant measuring the interaction between the two sublattices. We first determine the time dependence of the shifts of the order parameters {delta}phi (cursive,open) Greek and {delta}{psi} from the equilibrium state. We find that this time dependence is completely controlled by two kinds of relaxation times {tau}{sub 1} and {tau}{sub 2}. The former is a long time and the second a short one, and they are associated, respectively, with long and local wavelength fluctuations. We find that, only the first relaxation time is relevant for physics, since it drives the system to undergo a phase transition. Spatial fluctuations are also taken into account. In this case, we find an explicit expression of the relaxation times, which are functions of temperature T, coupling constant C and wave vector q. We find that the critical mode is that given by the zero scattering-angle limit, i.e. q=0. Finally, we emphasize that the appearance of these two relaxation times is in good agreement with results reported in recent experimental work dealt with the Curie-Weiss paramagnet compound Li{sub x}Ni{sub 2-x}O{sub 2}, where the composition x is very close to 1.

  18. Composite bone cements loaded with a bioactive and ferrimagnetic glass-ceramic: Leaching, bioactivity and cytocompatibility

    Energy Technology Data Exchange (ETDEWEB)

    Verné, Enrica, E-mail: enrica.verne@polito.it [Institute of Materials Physics and Engineering, Applied Science and Technology Department, Politecnico di Torino, C. so Duca degli Abruzzi 24, 10129 Torino (Italy); Bruno, Matteo [Institute of Materials Physics and Engineering, Applied Science and Technology Department, Politecnico di Torino, C. so Duca degli Abruzzi 24, 10129 Torino (Italy); Miola, Marta [Institute of Materials Physics and Engineering, Applied Science and Technology Department, Politecnico di Torino, C. so Duca degli Abruzzi 24, 10129 Torino (Italy); Department of Health Sciences, Università del Piemonte Orientale “Amedeo Avogadro”, Via Solaroli 17, 28100 Novara (Italy); Maina, Giovanni; Bianco, Carlotta [Traumatology Orthopedics and Occupational Medicine Dept., Università di Torino, Via G. Zuretti 29, 10126 Torino (Italy); Cochis, Andrea [Department of Health Sciences, Università del Piemonte Orientale “Amedeo Avogadro”, Via Solaroli 17, 28100 Novara (Italy); Rimondini, Lia [Department of Health Sciences, Università del Piemonte Orientale “Amedeo Avogadro”, Via Solaroli 17, 28100 Novara (Italy); Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, Via G. Giusti, 9, 50121 Firenze (Italy)

    2015-08-01

    In this work, composite bone cements, based on a commercial polymethylmethacrylate matrix (Palamed®) loaded with ferrimagnetic bioactive glass-ceramic particles (SC45), were produced and characterized in vitro. The ferrimagnetic bioactive glass-ceramic belongs to the system SiO{sub 2}–Na{sub 2}O–CaO–P{sub 2}O{sub 5}–FeO–Fe{sub 2}O{sub 3} and contains magnetite (Fe{sub 3}O{sub 4}) crystals into a residual amorphous bioactive phase. Three different formulations (containing 10, 15 and 20 wt.% of glass-ceramic particles respectively) have been investigated. These materials are intended to be applied as bone fillers for the hyperthermic treatment of bone tumors. The morphological, compositional, calorimetric and mechanical properties of each formulation have been already discussed in a previous paper. The in vitro properties of the composite bone cements described in the present paper are related to iron ion leaching test (by graphite furnace atomic absorption spectrometer), bioactivity (i.e. the ability to stimulate the formation of a hydroxyapatite – HAp – layer on their surface after soaking in simulated body fluid SBF) and cytocompatibility toward human osteosarcoma cells (ATCC CRL-1427, Mg63). Morphological and chemical characterizations by scanning electron microscopy and energy dispersion spectrometry have been performed on the composite samples after each test. The iron release was negligible and all the tested samples showed the growth of HAp on their surface after 28 days of immersion in a simulated body fluid (SBF). Cells showed good viability, morphology, adhesion, density and the ability to develop bridge-like structures on all investigated samples. A synergistic effect between bioactivity and cell mineralization was also evidenced. - Highlights: • An in vitro biological characterization was carried out on ferromagnetic and bioactive composite cements. • No release of iron was revealed in the physiological solution. • Bioactivity tests

  19. In vitro heat generation by ferrimagnetic maghemite microspheres for hyperthermic treatment of cancer under an alternating magnetic field.

    Science.gov (United States)

    Kawashita, Masakazu; Domi, Shinjiro; Saito, Yasuhiro; Aoki, Masaaki; Ebisawa, Yukihiro; Kokubo, Tadashi; Saito, Takashi; Takano, Mikio; Araki, Norio; Hiraoka, Masahiro

    2008-05-01

    Ferrimagnetic materials can be expected to be useful as thermo seeds for hyperthermic treatment of cancer, especially where the cancer is located in deep parts of body, as they can generate heat by magnetic hysteretic loss when they are placed in an alternating magnetic field. Recently, it was reported that ferrimagnetic maghemite (gamma-Fe2O3) microspheres 20-30 microm in diameter prepared in aqueous solution can show excellent heat generating ability. However, these microspheres have many cracks on their surfaces. In this study, the preparation conditions for the microspheres was further optimized in order to obtain crack-free ferrimagnetic microspheres, and the in vitro heat generation of the obtained microspheres was measured in an agar phantom under an alternating magnetic field. Crack-free gamma-Fe2O3 microspheres 20-30 microm in diameter were obtained successfully. Their saturation magnetization and coercive force were 68 emu g(-1) and 198 Oe, respectively. Their heat generation under an alternating magnetic field of 300 Oe at 100 kHz was estimated to be 42 W g(-1). The microspheres showed in vitro heat generation when they were dispersed in an agar phantom and placed under an alternating magnetic field. It is believed that these microspheres may be useful for the in situ hyperthermic treatment of cancer.

  20. 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.

  1. Spintronics of Organometal Trihalide Perovskites

    OpenAIRE

    Sun, Dali; Zhang, Chuang; Kavand, Marzieh; van Schooten, Kipp J.; Malissa, Hans; Groesbeck, Matthew; McLaughlin, Ryan; Boehme, Christoph; Vardeny, Z. Valy

    2016-01-01

    The family of organometal trihalide perovskite (OTP), CH3NH3PbX3 (where X is halogen) has recently revolutionized the photovoltaics field and shows promise in a variety of optoelectronic applications. The characteristic spin properties of charge and neutral excitations in OTPs are influenced by the large spin-orbit coupling of the Pb atoms, which may lead to spin-based device applications. Here we report the first studies of pure spin-current and spin-aligned carrier injection in OTP spintron...

  2. 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.

  3. Controlled Synthesis and Ferrimagnetism of Homogeneous Hierarchical CoFe2O4 Particles

    Science.gov (United States)

    Long, Nguyen Viet; Yang, Yong; Thi, Cao Minh; Phuc, Le Hong; Lu, Le Trong; Nogami, Masayuki

    2017-10-01

    Uniform, large, spherical, hierarchical CoFe2O4 spinel particles have been successfully prepared by a modified polyol method using NaBH4 and NaOH, revealing controlled size, shape, and morphology with high crystallinity in a certain microscale range. Their inverse AB2O4-type crystal structure was intensively studied by x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Using stock solutions of CoCl2 and FeCl3 precursors in 1:2 ratio, CoFe2O4 particles were formed well with high crystallinity in the best inverse spinel structure in space group Fd-3m. The fascinating ferrimagnetic and hysteretic properties of the as-prepared hierarchical CoFe2O4 spinel particles were investigated by vibrating-sample magnetometry (VSM) at room temperature (RT). The results confirm formation of hierarchical CoFe2O4 microscale particles with inverse-spinel AB2O4-type structure and high magnetization by modified polyol method with heat treatment.

  4. Ferrimagnetic ceramic adsorbents for cleanup of H2S from exhaust gases

    Institute of Scientific and Technical Information of China (English)

    Bernd Halbedel; Apostolos Kontogeorgakos

    2007-01-01

    Adsorbents that exhibit magnetic properties in addition to other required process-relevant characteristics open up new perspectives for the dry reduction and/or elimination of H2S and other sulfur compounds from exhaust gases. These adsorbents eliminate the sulfur compounds from exhaust gases by virtue of their coatings and their magnetic property which makes it possible the use of magnetically assisted and stabilized fluidization in an externally applied magnetic field.In the present paper, the feasibility of the sorptive function of porous ceramic ferrimagnetic beads is ensured by sol-gel coating of zinc oxide without the formation of Zn-Fe-oxides and without considerable decrease of available pore volume. The results of material characterization by SEM, Auger electron spectroscopy, X-ray and mercury-porosity measurements and the loading capacity of a H2S/N2 model gas are presented and discussed. The resulting H2S loading of the functionalized adsorbent beads is more than 10 times larger than that of the starting material.

  5. Strain controlled ferromagnetic-ferrimagnetic transition and vacancy formation energy of defective graphene.

    Science.gov (United States)

    Zhang, Yajun; Sahoo, Mpk; Wang, Jie

    2016-09-23

    Single vacancy (SV)-induced magnetism in graphene has attracted much attention motivated by its potential in achieving new functionalities. However, a much higher vacancy formation energy limits its direct application in electronic devices and the dependency of spin interaction on the strain is unclear. Here, through first-principles density-functional theory calculations, we investigate the possibility of strain engineering towards lowering vacancy formation energy and inducing new magnetic states in defective graphene. It is found that the SV-graphene undergoes a phase transition from an initial ferromagnetic state to a ferrimagnetic state under a biaxial tensile strain. At the same time, the biaxial tensile strain significantly lowers the vacancy formation energy. The charge density, density of states and band theory successfully identify the origin and underlying physics of the transition. The predicted magnetic phase transition is attributed to the strain driven spin flipping at the C-atoms nearest to the SV-site. The magnetic semiconducting graphene induced by defect and strain engineering suggests an effective way to modulate both spin and electronic degrees of freedom in future spintronic devices.

  6. Field theoretical approach to the paramagnetic-ferrimagnetic transition in strongly coupled paramagnetic systems

    CERN Document Server

    Chahid, M

    2000-01-01

    The aim of this paper is the investigation of the critical properties of two strongly coupled paramagnetic sublattices exhibiting a paramagnetic-ferrimagnetic transition, at some critical temperature T sub c greater than the room temperature. In order to take into account the strong fluctuations of the magnetization near the critical point, use is made of the renormalization-group (RG) techniques applied to an elaborated field model describing such a transition, which is of Landau-Ginzburg-Wilson type. The associated free energy or action is a functional of two kinds of order parameters (local magnetizations), which are scalar fields phi (cursive,open) Greek and psi relative to these sublattices. It involves quadratic and quartic terms in both fields, and a lowest-order coupling C sub o phi (cursive,open) Greek psi, where C sub o >0 stands for the coupling constant measuring the interaction between the two sublattices. We first show that the associated field theory is renormalizable at any order of the pertur...

  7. Comparison of the irreversible thermomagnetic behaviour of some ferro- and ferrimagnetic systems

    Indian Academy of Sciences (India)

    P S Anil Kumar; P A Joy; S K Date

    2000-04-01

    The magnetic behaviour of two ferromagnetic oxides and two ferrimagnetic oxides (ferrites) are compared to study the effect of magnetocrystalline anisotropy on thermal-history-dependence of magnetization of these ordered magnetic systems. All four compounds show thermomagnetic irreversibility (FC > ZFC) below a certain temperature, irr. The highly anisotropic ferromagnetic oxide, SrRuO3 and the hard ferrite, SrFe12O19 show sharp peaks below in their ZFC() curves, whereas for the soft ferrite Ni0.8Zn0.2Fe2O4 and the low anisotropic ferromagnetic oxide La0.7Ca0.3MnO3 only a broad maximum is observed in ZFC, when measured in small magnetic fields. The shapes of the ZFC() curves are inversely-related to the magnitude of the coercivities (c) of the compounds in relation to the applied field, and the temperature dependence of (c). FCand ZFC are related through the coercivity for all four magnetic systems.

  8. Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice

    Science.gov (United States)

    Girovsky, Jan; Nowakowski, Jan; Ali, Md. Ehesan; Baljozovic, Milos; Rossmann, Harald R.; Nijs, Thomas; Aeby, Elise A.; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; Wäckerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M.; Jung, Thomas A.; Ballav, Nirmalya

    2017-05-01

    Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.

  9. Evidence for ferromagnetic coupling at the doped topological insulator/ferrimagnetic insulator interface

    Science.gov (United States)

    Liu, Wenqing; He, Liang; Zhou, Yan; Murata, Koichi; Onbasli, Mehmet C.; Ross, Caroline A.; Jiang, Ying; Wang, Yong; Xu, Yongbing; Zhang, Rong; Wang, Kang. L.

    2016-05-01

    One of the major obstacles of the magnetic topological insulators (TIs) impeding their practical use is the low Curie temperature (Tc). Very recently, we have demonstrated the enhancement of the magnetic ordering in Cr-doped Bi2Se3 by means of proximity to the high-Tc ferrimagnetic insulator (FMI) Y3Fe5O12 and found a large and rapidly decreasing penetration depth of the proximity effect, suggestive of a different carrier propagation process near the TI surface. Here we further present a study of the interfacial magnetic interaction of this TI/FMI heterostrucutre. The synchrotron-based X-ray magnetic circular dichroism (XMCD) technique was used to probe the nature of the exchange coupling of the Bi2-xCrxSe3/Y3Fe5O12 interface. We found that the Bi2-xCrxSe3 grown on Y3Fe5O12(111) predominately contains Cr3+ cations, and the spin direction of the Cr3+ is aligned parallel to that of tetrahedral Fe3+ of the YIG, revealing a ferromagnetic exchange coupling between the Bi2-xCrxSe3 and the Y3Fe5O12.

  10. New ferrimagnetic biocomposite film based in collagen and yttrium iron garnet

    Directory of Open Access Journals (Sweden)

    2010-12-01

    Full Text Available In recent years a great interest in the study of the association of magnetic with biological material for bioapplications has been observed in the literature. This work analyses the development of new magnetic biocomposite films from a magnetic ferrite and a biopolymer. Magnetic and dielectric properties of Y3Fe5O12 (YIG/collagen composite films were studied as a function of the YIG concentration. This biocomposite was also characterized by Infrared Spectroscopy (IR, Thermal Analysis (DSC and TG and scanning electron microspcopic (SEM methods. The magnetization and dielectric measurements were performed at room temperature. The results demonstrated that ferrimagnetic garnet (YIG and collagen (Col can be used to obtain a homogeneous composite. All the composite films showed a ferromagnetic behavior and they were characterized as a soft magnet material. These results show that Col-YIG biocomposites are biological films with magnetic properties that can be employed as a versatile performance materials, due to their flexible dielectric and magnetic features. They could be used as electronic devices in biological applications.

  11. Current driven magnetization dynamics of a self-polarised synthetic ferrimagnet

    Energy Technology Data Exchange (ETDEWEB)

    Jenkins, A. S.; Lacoste, B.; Geranton, G.; Gusakova, D.; Dieny, B.; Ebels, U.; Buda-Prejbeanu, L. D. [SPINTEC, UMR-8191, CNRS/CEA-INAC/UJF-Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France)

    2014-02-28

    Spin torque driven excitations in spin valves and tunnel junctions are often investigated for a two magnetic layer system for which a polarizer (fixed magnetization) and a free layer can be distinguished. In the search for improved microwave properties and to understand the role of different coupling mechanisms between the magnetic layers, here, the excitation spectrum of an exchange coupled two layer synthetic ferrimagnet (SyF) system is investigated numerically with spin momentum transfer acting on both layers simultaneously. This self-polarised two layer system does not contain an external polarizer, and excitation of coupled modes arises due to the mutual spin transfer torque and the Ruderman-Kittel-Kasuya-Yosida interlayer exchange coupling. The current-field state diagrams of static and dynamic states are reported as a function of the interlayer exchange coupling strength. The numerically determined critical boundaries are well reproduced by an analytical stability analysis. The dynamic steady states reveal an optic-like mode at low magnetic fields, which becomes progressively acoustic-like for increased magnetic fields and currents. The frequency of these modes can be tuned by the film thickness and the strength of the interlayer exchange interaction. The results presented here will provide an important guide for designing spin torque oscillators that exploit the dynamic coupling between layers and, furthermore, they will provide a basis to test analytical models of spin torque driven coupled excitations.

  12. Strain controlled ferromagnetic-ferrimagnetic transition and vacancy formation energy of defective graphene

    Science.gov (United States)

    Zhang, Yajun; Sahoo, MPK; Wang, Jie

    2016-10-01

    Single vacancy (SV)-induced magnetism in graphene has attracted much attention motivated by its potential in achieving new functionalities. However, a much higher vacancy formation energy limits its direct application in electronic devices and the dependency of spin interaction on the strain is unclear. Here, through first-principles density-functional theory calculations, we investigate the possibility of strain engineering towards lowering vacancy formation energy and inducing new magnetic states in defective graphene. It is found that the SV-graphene undergoes a phase transition from an initial ferromagnetic state to a ferrimagnetic state under a biaxial tensile strain. At the same time, the biaxial tensile strain significantly lowers the vacancy formation energy. The charge density, density of states and band theory successfully identify the origin and underlying physics of the transition. The predicted magnetic phase transition is attributed to the strain driven spin flipping at the C-atoms nearest to the SV-site. The magnetic semiconducting graphene induced by defect and strain engineering suggests an effective way to modulate both spin and electronic degrees of freedom in future spintronic devices.

  13. Synthesis and dielectric properties of ferroelectric-ferrimagnetic PZT-SFMO composites

    Directory of Open Access Journals (Sweden)

    Alexander V. Petrov

    2017-03-01

    Full Text Available Ferrimagnetic-ferroelectric composite materials on the base of Pb0.85Zr0.53Ti0.47O3– Sr2FeMoO6–δ (PZT-SFMO compounds have been prepared by a complex ceramic technology and a modified sol-gel synthesis. The dielectric properties of the PZT-SFMO composites with the PZT concentrations of 55 wt% and less, as well as of pure SFMO, are caused by the Maxwell-Wagner relaxation and a huge electrical conductivity. In contrast, in pure PZT the ferroelectric phase transition is clearly expressed in the static dielectric permittivity anomaly. Moreover, in all investigated composites, similarly to pure SFMO, the electrical conductivity anomaly is observed in the range from 560–540 K. This indicates that the composites with PZT concentrations of 55 wt% and higher are above the electrical and magnetic percolation threshold, in a good agreement with the excluded volume theory. In PZT-SFMO composites the DC electrical conductivity increases with SFMO concentration almost in a power law fashion, while the activation energy of the DC conductivity decreases under certain conditions.

  14. Long-range ferrimagnetic order in a two-dimensional supramolecular Kondo lattice.

    Science.gov (United States)

    Girovsky, Jan; Nowakowski, Jan; Ali, Md Ehesan; Baljozovic, Milos; Rossmann, Harald R; Nijs, Thomas; Aeby, Elise A; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; Wäckerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M; Jung, Thomas A; Ballav, Nirmalya

    2017-05-22

    Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman-Kittel-Kasuya-Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.

  15. Evidence of ferrimagnetic ordering in FeMnO{sub 3} produced by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Seifu, D. E-mail: dseifu@morgan.edu; Kebede, A.; Oliver, F.W.; Hoffman, E.; Hammond, E.; Wynter, C.; Aning, A.; Takacs, L.; Siu, I.-L.; Walker, J.C.; Tessema, G.; Seehra, M.S

    2000-03-01

    Mechanical alloying of {alpha}-Fe{sub 2}O{sub 3} with Mn{sub 2}O{sub 3} is shown to produce FeMnO{sub 3}, whose X-ray diffraction pattern fits the cubic structure (space group Ia3, lattice constant {approx}9.40 A) identical to that of Mn{sub 2}O{sub 3}. Temperature variation of its magnetic susceptibility {chi} shows a phase transition near T{sub c}{approx}40 K and the {chi}{sup -1} versus T data for T>T{sub c} fit the variation expected for a ferrimagnet with a magnetic moment of 2.8 {mu}{sub B} per formula unit. The Moessbauer spectrum for T>T{sub c} is a doublet with quadrupole splitting {approx}1 mm/s and isomer shift {approx}0.4 mm/s, changing to a sextet for T

  16. Monodisperse Dual-Functional Upconversion Nanoparticles Enabled Near-Infrared Organolead Halide Perovskite Solar Cells.

    Science.gov (United States)

    He, Ming; Pang, Xinchang; Liu, Xueqin; Jiang, Beibei; He, Yanjie; Snaith, Henry; Lin, Zhiqun

    2016-03-18

    Extending the spectral absorption of organolead halide perovskite solar cells from visible into near-infrared (NIR) range renders the minimization of non-absorption loss of solar photons with improved energy alignment. Herein, we report on, for the first time, a viable strategy of capitalizing on judiciously synthesized monodisperse NaYF4 :Yb/Er upconversion nanoparticles (UCNPs) as the mesoporous electrode for CH3 NH3 PbI3 perovskite solar cells and more importantly confer perovskite solar cells to be operative under NIR light. Uniform NaYF4 :Yb/Er UCNPs are first crafted by employing rationally designed double hydrophilic star-like poly(acrylic acid)-block-poly(ethylene oxide) (PAA-b-PEO) diblock copolymer as nanoreactor, imparting the solubility of UCNPs and the tunability of film porosity during the manufacturing process. The subsequent incorporation of NaYF4 :Yb/Er UCNPs as the mesoporous electrode led to a high efficiency of 17.8 %, which was further increased to 18.1 % upon NIR irradiation. The in situ integration of upconversion materials as functional components of perovskite solar cells offers the expanded flexibility for engineering the device architecture and broadening the solar spectral use.

  17. Strongly correlated perovskite fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, You; Guan, Xiaofei; Zhou, Hua; Ramadoss, Koushik; Adam, Suhare; Liu, Huajun; Lee, Sungsik; Shi, Jian; Tsuchiya, Masaru; Fong, Dillon D.; Ramanathan, Shriram

    2016-05-16

    Fuel cells convert chemical energy directly into electrical energy with high efficiencies and environmental benefits, as compared with traditional heat engines1, 2, 3, 4. Yttria-stabilized zirconia is perhaps the material with the most potential as an electrolyte in solid oxide fuel cells (SOFCs), owing to its stability and near-unity ionic transference number5. Although there exist materials with superior ionic conductivity, they are often limited by their ability to suppress electronic leakage when exposed to the reducing environment at the fuel interface. Such electronic leakage reduces fuel cell power output and the associated chemo-mechanical stresses can also lead to catastrophic fracture of electrolyte membranes6. Here we depart from traditional electrolyte design that relies on cation substitution to sustain ionic conduction. Instead, we use a perovskite nickelate as an electrolyte with high initial ionic and electronic conductivity. Since many such oxides are also correlated electron systems, we can suppress the electronic conduction through a filling-controlled Mott transition induced by spontaneous hydrogen incorporation. Using such a nickelate as the electrolyte in free-standing membrane geometry, we demonstrate a low-temperature micro-fabricated SOFC with high performance. The ionic conductivity of the nickelate perovskite is comparable to the best-performing solid electrolytes in the same temperature range, with a very low activation energy. The results present a design strategy for high-performance materials exhibiting emergent properties arising from strong electron correlations.

  18. Strongly correlated perovskite fuel cells

    Science.gov (United States)

    Zhou, You; Guan, Xiaofei; Zhou, Hua; Ramadoss, Koushik; Adam, Suhare; Liu, Huajun; Lee, Sungsik; Shi, Jian; Tsuchiya, Masaru; Fong, Dillon D.; Ramanathan, Shriram

    2016-06-01

    Fuel cells convert chemical energy directly into electrical energy with high efficiencies and environmental benefits, as compared with traditional heat engines. Yttria-stabilized zirconia is perhaps the material with the most potential as an electrolyte in solid oxide fuel cells (SOFCs), owing to its stability and near-unity ionic transference number. Although there exist materials with superior ionic conductivity, they are often limited by their ability to suppress electronic leakage when exposed to the reducing environment at the fuel interface. Such electronic leakage reduces fuel cell power output and the associated chemo-mechanical stresses can also lead to catastrophic fracture of electrolyte membranes. Here we depart from traditional electrolyte design that relies on cation substitution to sustain ionic conduction. Instead, we use a perovskite nickelate as an electrolyte with high initial ionic and electronic conductivity. Since many such oxides are also correlated electron systems, we can suppress the electronic conduction through a filling-controlled Mott transition induced by spontaneous hydrogen incorporation. Using such a nickelate as the electrolyte in free-standing membrane geometry, we demonstrate a low-temperature micro-fabricated SOFC with high performance. The ionic conductivity of the nickelate perovskite is comparable to the best-performing solid electrolytes in the same temperature range, with a very low activation energy. The results present a design strategy for high-performance materials exhibiting emergent properties arising from strong electron correlations.

  19. Strongly correlated perovskite fuel cells.

    Science.gov (United States)

    Zhou, You; Guan, Xiaofei; Zhou, Hua; Ramadoss, Koushik; Adam, Suhare; Liu, Huajun; Lee, Sungsik; Shi, Jian; Tsuchiya, Masaru; Fong, Dillon D; Ramanathan, Shriram

    2016-06-09

    Fuel cells convert chemical energy directly into electrical energy with high efficiencies and environmental benefits, as compared with traditional heat engines. Yttria-stabilized zirconia is perhaps the material with the most potential as an electrolyte in solid oxide fuel cells (SOFCs), owing to its stability and near-unity ionic transference number. Although there exist materials with superior ionic conductivity, they are often limited by their ability to suppress electronic leakage when exposed to the reducing environment at the fuel interface. Such electronic leakage reduces fuel cell power output and the associated chemo-mechanical stresses can also lead to catastrophic fracture of electrolyte membranes. Here we depart from traditional electrolyte design that relies on cation substitution to sustain ionic conduction. Instead, we use a perovskite nickelate as an electrolyte with high initial ionic and electronic conductivity. Since many such oxides are also correlated electron systems, we can suppress the electronic conduction through a filling-controlled Mott transition induced by spontaneous hydrogen incorporation. Using such a nickelate as the electrolyte in free-standing membrane geometry, we demonstrate a low-temperature micro-fabricated SOFC with high performance. The ionic conductivity of the nickelate perovskite is comparable to the best-performing solid electrolytes in the same temperature range, with a very low activation energy. The results present a design strategy for high-performance materials exhibiting emergent properties arising from strong electron correlations.

  20. Effect of Gd3+ doping on phase structure,magnetic and electrical properties of double perovskite Sr2FeMoO6%Gd3+掺杂对Sr2FeMoO6结构及电磁性能的影响

    Institute of Scientific and Technical Information of China (English)

    翟永清; 乔静; 张张; 霍国燕; 温静娟

    2011-01-01

    采用微波固相烧结法合成了双钙钛矿Sr2-xGdxFeMoO6(x=0.0、0.1、0.2、0.3)。用XRD和VSM对样品的物相结构和电磁性能进行了研究。结果表明所得Sr2FeMoO6为四方晶系结构,空间群为I4/mmm,随Gd3+掺杂量的增加,Fe、Mo排列的有序度逐渐降低,同时伴有少量Gd2O3杂相生成。样品Sr2-xGdxFeMoO6均表现为铁磁性,磁转变温度均高于室温,Gd3+掺杂使得样品的室温饱和磁化强度降低,但适量Gd3+的掺杂(x=0.3)可明显提高样品的室温磁电阻变化率。样品Sr2-xGdxFeMoO6均呈现典型的半导体行为,当x=0.0、0.1、0.2时,在100~300K,其电输运行为服从小极化子变程跃迁导电机制;当x=0.3时,在150~300K,服从小极化子变程跃迁导电机制;在100~150K,则属于绝热小极化子导电机制。%Double perovskite Sr2-xGdxFeMoO6(x=0.0,0.1,0.2,0.3) were synthesized by microwave sintering method.The phase structure,magnetic and electrical properties of all the samples were investigated by X-ray powder diffraction(XRD) and vibrating-sample magnetometer(VSM) respectively.The results show that the as-synthesized sample is Sr2FeMoO6 with tetragonal crystal structure and I4/mmm space group.With the increase of doped Gd3+,the ordering degree of the Fe and Mo cations decreases gradually,accompanied by a small amount of impurity phase Gd2O3.The samples Sr2-xGdxFeMoO6 are ferromagnetic,and the magnetic transition temperature is above room temperature.The saturation magnetization is decreased with the doping of Gd3+ at room temperature,but magnetoresistance ratio can be improved significantly when the doping concernt of Gd3+ x=0.3.The samples Sr2-xGdxFeMoO6 exhibit typical semiconductor behavior.When x=0.0,0.1,0.2,the electrical transport behavior follows the small polaron variable-range transition model in the range of 100-300K.When x=0.3,it follows the small polaron variable-range transition model in the range of 150-300K;but it is

  1. Semitransparent Fully Air Processed Perovskite Solar Cells.

    Science.gov (United States)

    Bu, Lingling; Liu, Zonghao; Zhang, Meng; Li, Wenhui; Zhu, Aili; Cai, Fensha; Zhao, Zhixin; Zhou, Yinhua

    2015-08-19

    Semitransparent solar cells are highly attractive for application as power-generating windows. In this work, we present semitransparent perovskite solar cells that employ conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PSS) film as the transparent counter electrode. The PSS electrode is prepared by transfer lamination technique using plastic wrap as the transfer medium. The use of the transfer lamination technique avoids the damage of the CH3NH3PbI3 perovskite film by direct contact of PSS aqueous solution. The semitransparent perovskite solar cells yield a power conversion efficiency of 10.1% at an area of about 0.06 cm(2) and 2.9% at an area of 1 cm(2). The device structure and the fabrication technique provide a facile way to produce semitransparent perovskite solar cells.

  2. Perovskite Thin Films via Atomic Layer Deposition

    KAUST Repository

    Sutherland, Brandon R.

    2014-10-30

    © 2014 Wiley-VCH Verlag GmbH & Co. KGaA. (Graph Presented) A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3NH3PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm-1.

  3. Perovskite thin films via atomic layer deposition.

    Science.gov (United States)

    Sutherland, Brandon R; Hoogland, Sjoerd; Adachi, Michael M; Kanjanaboos, Pongsakorn; Wong, Chris T O; McDowell, Jeffrey J; Xu, Jixian; Voznyy, Oleksandr; Ning, Zhijun; Houtepen, Arjan J; Sargent, Edward H

    2015-01-01

    A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3 NH3 PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm(-1) .

  4. Hierarchical Assembly of a {Mn(II)15Mn(III)4} Brucite Disc: Step-by-Step Formation and Ferrimagnetism.

    Science.gov (United States)

    Deng, Yong-Kai; Su, Hai-Feng; Xu, Jia-Heng; Wang, Wen-Guang; Kurmoo, Mohamedally; Lin, Shui-Chao; Tan, Yuan-Zhi; Jia, Jiong; Sun, Di; Zheng, Lan-Sun

    2016-02-03

    In search of functional molecular materials and the study of their formation mechanism, we report the elucidation of a hierarchical step-by-step formation from monomer (Mn) to heptamer (Mn7) to nonadecamer (Mn19) satisfying the relation 1 + Σn6n, where n is the ring number of the Brucite structure using high-resolution electrospray ionization mass spectrometry (HRESI-MS). Three intermediate clusters, Mn10, Mn12, and Mn14, were identified. Furthermore, the Mn19 disc remains intact when dissolved in acetonitrile with a well-resolved general formula of [Mn19(L)x(OH)y(N3)36-x-y](2+) (x = 18, 17, 16; y = 8, 7, 6; HL = 1-(hydroxymethyl)-3,5-dimethylpyrazole) indicating progressive exchange of N3(-) for OH(-). The high symmetry (R-3) Mn19 crystal structure consists of a well-ordered discotic motif where the peripheral organic ligands form a double calix housing the anions and solvent molecules. From the formula and valence bond sums, the charge state is mixed-valent, [Mn(II)15Mn(III)4]. Its magnetic properties and electrochemistry have been studied. It behaves as a ferrimagnet below 40 K and has a coercive field of 2.7 kOe at 1.8 K, which can be possible by either weak exchange between clusters through the anions and solvents or through dipolar interaction through space as confirmed by the lack of ordering in frozen CH3CN. The moment of nearly 50 NμB suggests Mn(II)-Mn(II) and Mn(III)-Mn(III) are ferromagnetically coupled while Mn(II)-Mn(III) is antiferromagnetic which is likely if the Mn(III) are centrally placed in the cluster. This compound displays the rare occurrence of magnetic ordering from nonconnected high-spin molecules.

  5. Perovskite Solar Cells: Beyond Methylammonium Lead Iodide.

    Science.gov (United States)

    Boix, Pablo P; Agarwala, Shweta; Koh, Teck Ming; Mathews, Nripan; Mhaisalkar, Subodh G

    2015-03-05

    Organic-inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH3NH3PbI3, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH3NH3PbI3, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensional families that will provide the next fillip toward market viability of the perovskite solar cells.

  6. Modeling hybrid perovskites by molecular dynamics.

    Science.gov (United States)

    Mattoni, Alessandro; Filippetti, Alessio; Caddeo, Claudia

    2017-02-01

    The topical review describes the recent progress in the modeling of hybrid perovskites by molecular dynamics simulations. Hybrid perovskites and in particular methylammonium lead halide (MAPI) have a tremendous technological relevance representing the fastest-advancing solar material to date. They also represent the paradigm of an organic-inorganic crystalline material with some conceptual peculiarities: an inorganic semiconductor for what concerns the electronic and absorption properties with a hybrid and solution processable organic-inorganic body. After briefly explaining the basic concepts of ab initio and classical molecular dynamics, the model potential recently developed for hybrid perovskites is described together with its physical motivation as a simple ionic model able to reproduce the main dynamical properties of the material. Advantages and limits of the two strategies (either ab initio or classical) are discussed in comparison with the time and length scales (from pico to microsecond scale) necessary to comprehensively study the relevant properties of hybrid perovskites from molecular reorientations to electrocaloric effects. The state-of-the-art of the molecular dynamics modeling of hybrid perovskites is reviewed by focusing on a selection of showcase applications of methylammonium lead halide: molecular cations disorder; temperature evolution of vibrations; thermally activated defects diffusion; thermal transport. We finally discuss the perspectives in the modeling of hybrid perovskites by molecular dynamics.

  7. Ambipolar solution-processed hybrid perovskite phototransistors

    KAUST Repository

    Li, Feng

    2015-09-08

    Organolead halide perovskites have attracted substantial attention because of their excellent physical properties, which enable them to serve as the active material in emerging hybrid solid-state solar cells. Here we investigate the phototransistors based on hybrid perovskite films and provide direct evidence for their superior carrier transport property with ambipolar characteristics. The field-effect mobilities for triiodide perovskites at room temperature are measured as 0.18 (0.17) cm2 V−1 s−1 for holes (electrons), which increase to 1.24 (1.01) cm2 V−1 s−1 for mixed-halide perovskites. The photoresponsivity of our hybrid perovskite devices reaches 320 A W−1, which is among the largest values reported for phototransistors. Importantly, the phototransistors exhibit an ultrafast photoresponse speed of less than 10 μs. The solution-based process and excellent device performance strongly underscore hybrid perovskites as promising material candidates for photoelectronic applications.

  8. Perovskite solar cells: from materials to devices.

    Science.gov (United States)

    Jung, Hyun Suk; Park, Nam-Gyu

    2015-01-07

    Perovskite solar cells based on organometal halide light absorbers have been considered a promising photovoltaic technology due to their superb power conversion efficiency (PCE) along with very low material costs. Since the first report on a long-term durable solid-state perovskite solar cell with a PCE of 9.7% in 2012, a PCE as high as 19.3% was demonstrated in 2014, and a certified PCE of 17.9% was shown in 2014. Such a high photovoltaic performance is attributed to optically high absorption characteristics and balanced charge transport properties with long diffusion lengths. Nevertheless, there are lots of puzzles to unravel the basis for such high photovoltaic performances. The working principle of perovskite solar cells has not been well established by far, which is the most important thing for understanding perovksite solar cells. In this review, basic fundamentals of perovskite materials including opto-electronic and dielectric properties are described to give a better understanding and insight into high-performing perovskite solar cells. In addition, various fabrication techniques and device structures are described toward the further improvement of perovskite solar cells.

  9. Modeling hybrid perovskites by molecular dynamics

    Science.gov (United States)

    Mattoni, Alessandro; Filippetti, Alessio; Caddeo, Claudia

    2017-02-01

    The topical review describes the recent progress in the modeling of hybrid perovskites by molecular dynamics simulations. Hybrid perovskites and in particular methylammonium lead halide (MAPI) have a tremendous technological relevance representing the fastest-advancing solar material to date. They also represent the paradigm of an organic-inorganic crystalline material with some conceptual peculiarities: an inorganic semiconductor for what concerns the electronic and absorption properties with a hybrid and solution processable organic-inorganic body. After briefly explaining the basic concepts of ab initio and classical molecular dynamics, the model potential recently developed for hybrid perovskites is described together with its physical motivation as a simple ionic model able to reproduce the main dynamical properties of the material. Advantages and limits of the two strategies (either ab initio or classical) are discussed in comparison with the time and length scales (from pico to microsecond scale) necessary to comprehensively study the relevant properties of hybrid perovskites from molecular reorientations to electrocaloric effects. The state-of-the-art of the molecular dynamics modeling of hybrid perovskites is reviewed by focusing on a selection of showcase applications of methylammonium lead halide: molecular cations disorder; temperature evolution of vibrations; thermally activated defects diffusion; thermal transport. We finally discuss the perspectives in the modeling of hybrid perovskites by molecular dynamics.

  10. Modeling Anomalous Hysteresis in Perovskite Solar Cells.

    Science.gov (United States)

    van Reenen, Stephan; Kemerink, Martijn; Snaith, Henry J

    2015-10-01

    Organic-inorganic lead halide perovskites are distinct from most other semiconductors because they exhibit characteristics of both electronic and ionic motion. Accurate understanding of the optoelectronic impact of such properties is important to fully optimize devices and be aware of any limitations of perovskite solar cells and broader optoelectronic devices. Here we use a numerical drift-diffusion model to describe device operation of perovskite solar cells. To achieve hysteresis in the modeled current-voltage characteristics, we must include both ion migration and electronic charge traps, serving as recombination centers. Trapped electronic charges recombine with oppositely charged free electronic carriers, of which the density depends on the bias-dependent ion distribution in the perovskite. Our results therefore show that reduction of either the density of mobile ionic species or carrier trapping at the perovskite interface will remove the adverse hysteresis in perovskite solar cells. This gives a clear target for ongoing research effort and unifies previously conflicting experimental observations and theories.

  11. Molecular dynamics simulations of organohalide perovskite precursors: solvent effects in the formation of perovskite solar cells.

    Science.gov (United States)

    Gutierrez-Sevillano, Juan José; Ahmad, Shahzada; Calero, Sofía; Anta, Juan A

    2015-09-21

    The stability and desirable crystal formation of organohalide perovskite semiconductors is of utmost relevance to ensure the success of perovskites in photovoltaic technology. Herein we have simulated the dynamics of ionic precursors toward the formation of embryonic organohalide perovskite CH3NH3PbI3 units in the presence of solvent molecules using Molecular Dynamics. The calculations involved, a variable amount of Pb(2+), I(-), and CH3NH3(+) ionic precursors in water, pentane and a mixture of these two solvents. Suitable force fields for solvents and precursors have been tested and used to carry out the simulations. Radial distribution functions and mean square displacements confirm the formation of basic perovskite crystalline units in pure pentane - taken as a simple and archetypal organic solvent. In contrast, simulations in water confirm the stability of the solvated ionic precursors, which prevents their aggregation to form the perovskite compound. We have found that in the case of a water/pentane binary solvent, a relatively small amount of water did not hinder the perovskite formation. Thus, our findings suggest that the cause of the poor stability of perovskite films in the presence of moisture is a chemical reaction, rather than the polar nature of the solvents. Based on the results, a set of force-field parameters to study from first principles perovskite formation and stability, also in the solid phase, is proposed.

  12. Hybrid Perovskite Light-Emitting Diodes Based on Perovskite Nanocrystals with Organic-Inorganic Mixed Cations.

    Science.gov (United States)

    Zhang, Xiaoli; Liu, He; Wang, Weigao; Zhang, Jinbao; Xu, Bing; Karen, Ke Lin; Zheng, Yuanjin; Liu, Sheng; Chen, Shuming; Wang, Kai; Sun, Xiao Wei

    2017-03-07

    Organic-inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed-cation perovskite nanocrystals based on FA(1-x) Csx PbBr3 (FA = CH(NH2 )2 ). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA(1-x) Csx PbBr3 , is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed-cation perovskites are employed as light emitters in light-emitting diodes (LEDs). With an optimized composition of FA0.8 Cs0.2 PbBr3 , the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m(-2) and a current efficiency of 10.09 cd A(-1) . This work provides important instructions on the future compositional optimization of mixed-cation perovskite for obtaining high-performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs.

  13. 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.

  14. A first-principle investigation of spin-gapless semiconductivity, half-metallicity, and fully-compensated ferrimagnetism property in Mn2ZnMg inverse Heusler compound

    Science.gov (United States)

    Wang, Xiaotian; Cheng, Zhenxiang; Khenata, Rabah; Rozale, Habib; Wang, Jianli; Wang, Liying; Guo, Ruikang; Liu, Guodong

    2017-02-01

    Recently, spin-gapless semiconductors (SGSs) and half-metallic materials (HMMs) have received considerable interest in the fields of materials sciences and solid-state physics because they can provide a high degree of spin polarization in electron transport. The results on band structure calculations reveal that the metallic fully-compensated ferrimagnet (M-FCF) Mn2ZnMg becomes half-metallic fully-compensated ferrimagnet (HM-FCF), fully-compensated ferrimagnetic semiconductor (FCF-S) and fully-compensated ferrimagnetic spin-gapless semiconductor (FCF-SGS) if the uniform strain applied. However, the metallic fully-compensated ferrimagnetism property of the Mn2ZnMg is robust to the tetragonalization. The structure stability based on the calculations of the cohesion energy and the formation energy of this compound has been tested. Furthermore, a magnetic state transition from antiferromagentic (AFM) state to non-magnetic (NM) state can be observed at the lattice constant of 5.20 Å.

  15. Multiferroicity in Perovskite Manganite Superlattice

    Science.gov (United States)

    Tao, Yong-Mei; Jiang, Xue-Fan; Liu, Jun-Ming

    2016-08-01

    Multiferroic properties of short period perovskite type manganite superlattice ((R1MnO3)n/(R2MnO3)n (n=1,2,3)) are considered within the framework of classical Heisenberg model using Monte Carlo simulation. Our result revealed the interesting behaviors in Mn spins structure in superlattice. Apart from simple plane spin cycloid structure which is shown in all manganites including bulk, film, and superlattice here in low temperature, a non-coplanar spiral spin structure is exhibited in a certain temperature range when n equals 1, 2 or 3. Specific heat, spin-helicity vector, spin correlation function, spin-helicity correlation function, and spin configuration are calculated to confirm this non-coplanar spiral spin structure. These results are associated with the competition among exchange interaction, magnetic anisotropy, and Dzyaloshinskii-Moriya interaction. Supported by the National Natural Science Foundation of China (NSFC) under Grant No. 11447136

  16. In vitro biocompatibility of a ferrimagnetic glass-ceramic for hyperthermia application.

    Science.gov (United States)

    Bretcanu, Oana; Miola, Marta; Bianchi, Claudia L; Marangi, Ida; Carbone, Roberta; Corazzari, Ingrid; Cannas, Mario; Verné, Enrica

    2017-04-01

    Ferrimagnetic glass-ceramics containing magnetite crystals were developed for hyperthermia applications of solid neoplastic tissue. The present work is focused on in vitro evaluation of the biocompatibility of these materials, before and after soaking in a simulated body fluid (SBF). X-ray diffraction, scanning electron microscopy, atomic absorption spectrophotometry, X-ray photoelectron spectrometry and pH measurements were employed in glass-ceramic characterisation. The free-radical mediated reactivity of the glass-ceramic was evaluated by Electron Paramagnetic Resonance (EPR) spin trapping. Cell adhesion and proliferation tests were carried out by using 3T3 murine fibroblasts. Cytotoxicity was performed by qualitative evaluation of human bone osteosarcoma cells U2OS cell line. The results show that almost two times more 3T3 cells proliferated on the samples pre-treated in SBF, compared with the untreated specimens. Moreover a decrease of confluence was observed at 48 and 72h for U2OS cells exposed to the untreated glass-ceramic, while the powder suspensions of glass-ceramic pre-treated in SBF did not influence the cell morphology up to 72h of exposition. The untreated glass-ceramic exhibited Fenton-like reactivity, as well as reactivity towards formate molecule. After pre-treatment with SBF the reactivity towards formate was completely suppressed. The concentration of iron released into the SBF solution was below 0.1ppm at 37°C, during one month of soaking. The different in vitro behaviour of the samples before and after SBF treatment has been correlated to the bioactive glass-ceramic surface modifications as detected by morphological, structural and compositional analyses. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Evidence for ferromagnetic coupling at the doped topological insulator/ferrimagnetic insulator interface

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wenqing [Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD (United Kingdom); York-Nanjing Joint Centre for Spintronics and Nano Engineering (YNJC), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093 (China); Physics Department, Hong Kong University (Hong Kong); He, Liang; Zhang, Rong, E-mail: yongbing.xu@york.ac.uk, E-mail: rzhang@nju.edu.cn, E-mail: wang@seas.ucla.edu [York-Nanjing Joint Centre for Spintronics and Nano Engineering (YNJC), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093 (China); Zhou, Yan [York-Nanjing Joint Centre for Spintronics and Nano Engineering (YNJC), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093 (China); Physics Department, Hong Kong University (Hong Kong); Murata, Koichi; Wang, Kang L., E-mail: yongbing.xu@york.ac.uk, E-mail: rzhang@nju.edu.cn, E-mail: wang@seas.ucla.edu [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Onbasli, Mehmet C.; Ross, Caroline A. [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Jiang, Ying; Wang, Yong [Centre of Electron Microscopy, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027 (China); Xu, Yongbing, E-mail: yongbing.xu@york.ac.uk, E-mail: rzhang@nju.edu.cn, E-mail: wang@seas.ucla.edu [Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD (United Kingdom); York-Nanjing Joint Centre for Spintronics and Nano Engineering (YNJC), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093 (China)

    2016-05-15

    One of the major obstacles of the magnetic topological insulators (TIs) impeding their practical use is the low Curie temperature (T{sub c}). Very recently, we have demonstrated the enhancement of the magnetic ordering in Cr-doped Bi{sub 2}Se{sub 3} by means of proximity to the high-T{sub c} ferrimagnetic insulator (FMI) Y{sub 3}Fe{sub 5}O{sub 12} and found a large and rapidly decreasing penetration depth of the proximity effect, suggestive of a different carrier propagation process near the TI surface. Here we further present a study of the interfacial magnetic interaction of this TI/FMI heterostrucutre. The synchrotron-based X-ray magnetic circular dichroism (XMCD) technique was used to probe the nature of the exchange coupling of the Bi{sub 2−x}Cr{sub x}Se{sub 3}/Y{sub 3}Fe{sub 5}O{sub 12} interface. We found that the Bi{sub 2−x}Cr{sub x}Se{sub 3} grown on Y{sub 3}Fe{sub 5}O{sub 12}(111) predominately contains Cr{sup 3+} cations, and the spin direction of the Cr{sup 3+} is aligned parallel to that of tetrahedral Fe{sup 3+} of the YIG, revealing a ferromagnetic exchange coupling between the Bi{sub 2−x}Cr{sub x}Se{sub 3} and the Y{sub 3}Fe{sub 5}O{sub 12}.

  18. Electrochemical Doping of Halide Perovskites with Ion Intercalation.

    Science.gov (United States)

    Jiang, Qinglong; Chen, Mingming; Li, Junqiang; Wang, Mingchao; Zeng, Xiaoqiao; Besara, Tiglet; Lu, Jun; Xin, Yan; Shan, Xin; Pan, Bicai; Wang, Changchun; Lin, Shangchao; Siegrist, Theo; Xiao, Qiangfeng; Yu, Zhibin

    2017-01-24

    Halide perovskites have recently been investigated for various solution-processed optoelectronic devices. The majority of studies have focused on using intrinsic halide perovskites, and the intentional incoporation of dopants has not been well explored. In this work, we discovered that small alkali ions, including lithium and sodium ions, could be electrochemically intercalated into a variety of halide and pseudohalide perovskites. The ion intercalation caused a lattice expansion of the perovskite crystals and resulted in an n-type doping of the perovskites. Such electrochemical doping improved the conductivity and changed the color of the perovskites, leading to an electrochromism with more than 40% reduction of transmittance in the 450-850 nm wavelength range. The doped perovskites exhibited improved electron injection efficiency into the pristine perovskite crystals, resulting in bright light-emitting diodes with a low turn-on voltage.

  19. Highly Efficient Perovskite-Perovskite Tandem Solar Cells Reaching 80% of the Theoretical Limit in Photovoltage.

    Science.gov (United States)

    Rajagopal, Adharsh; Yang, Zhibin; Jo, Sae Byeok; Braly, Ian L; Liang, Po-Wei; Hillhouse, Hugh W; Jen, Alex K-Y

    2017-09-01

    Organic-inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley-Queisser limit of single-junction solar cells; however, they are limited by large nonideal photovoltage loss (V oc,loss ) in small- and large-bandgap subcells. Here, an integrated approach is utilized to improve the V oc of subcells with optimized bandgaps and fabricate perovskite-perovskite tandem solar cells with small V oc,loss . A fullerene variant, Indene-C60 bis-adduct, is used to achieve optimized interfacial contact in a small-bandgap (≈1.2 eV) subcell, which facilitates higher quasi-Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V oc to 0.84 V. Compositional engineering of large-bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V oc of 1.22 V. The resultant monolithic perovskite-perovskite tandem solar cell shows a high V oc of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V oc,loss is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskite-perovskite tandems for solar-energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar-to-hydrogen efficiencies beyond 15%. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Neutral- and Multi-Colored Semitransparent Perovskite Solar Cells

    OpenAIRE

    Kyu-Tae Lee; L. Jay Guo; Hui Joon Park

    2016-01-01

    In this review, we summarize recent works on perovskite solar cells with neutral- and multi-colored semitransparency for building-integrated photovoltaics and tandem solar cells. The perovskite solar cells exploiting microstructured arrays of perovskite “islands” and transparent electrodes—the latter of which include thin metallic films, metal nanowires, carbon nanotubes, graphenes, and transparent conductive oxides for achieving optical transparency—are investigated. Moreover, the perovskite...

  1. Multicomponent, peptide-targeted glycol chitosan nanoparticles containing ferrimagnetic iron oxide nanocubes for bladder cancer multimodal imaging.

    Science.gov (United States)

    Key, Jaehong; Dhawan, Deepika; Cooper, Christy L; Knapp, Deborah W; Kim, Kwangmeyung; Kwon, Ick Chan; Choi, Kuiwon; Park, Kinam; Decuzzi, Paolo; Leary, James F

    While current imaging modalities, such as magnetic resonance imaging (MRI), computed tomography, and positron emission tomography, play an important role in detecting tumors in the body, no single-modality imaging possesses all the functions needed for a complete diagnostic imaging, such as spatial resolution, signal sensitivity, and tissue penetration depth. For this reason, multimodal imaging strategies have become promising tools for advanced biomedical research and cancer diagnostics and therapeutics. In designing multimodal nanoparticles, the physicochemical properties of the nanoparticles should be engineered so that they successfully accumulate at the tumor site and minimize nonspecific uptake by other organs. Finely altering the nano-scale properties can dramatically change the biodistribution and tumor accumulation of nanoparticles in the body. In this study, we engineered multimodal nanoparticles for both MRI, by using ferrimagnetic nanocubes (NCs), and near infrared fluorescence imaging, by using cyanine 5.5 fluorescence molecules. We changed the physicochemical properties of glycol chitosan nanoparticles by conjugating bladder cancer-targeting peptides and loading many ferrimagnetic iron oxide NCs per glycol chitosan nanoparticle to improve MRI contrast. The 22 nm ferrimagnetic NCs were stabilized in physiological conditions by encapsulating them within modified chitosan nanoparticles. The multimodal nanoparticles were compared with in vivo MRI and near infrared fluorescent systems. We demonstrated significant and important changes in the biodistribution and tumor accumulation of nanoparticles with different physicochemical properties. Finally, we demonstrated that multimodal nanoparticles specifically visualize small tumors and show minimal accumulation in other organs. This work reveals the importance of finely modulating physicochemical properties in designing multimodal nanoparticles for bladder cancer imaging.

  2. Magnetic anisotropy and chemical long-range order in epitaxial ferrimagnetic CrPt{sub 3} films

    Energy Technology Data Exchange (ETDEWEB)

    Maret, M. E-mail: mireille.maret@uni-konstanz.de; Albrecht, M.; Koehler, J.; Poinsot, R.; Ulhaq-Bouillet, C.; Tonnerre, J.M.; Berar, J.F.; Bucher, E

    2000-08-01

    Thin films of CrPt{sub 3} were prepared by molecular beam epitaxy on both Al{sub 2}O{sub 3}(0 0 0 1) and MgO(0 0 1) substrates, either directly by co-deposition of Cr and Pt at high temperatures or after in situ annealing of superlattices [Cr(2 A)/Pt(7 A)]. In situ RHEED observations and X-ray diffraction measurements have allowed us to check the single-crystal quality of CrPt{sub 3} films and to determine the degree of L1{sub 2}-type long-range order (LRO). In films co-deposited between 850 deg. C and 950 deg. C a nearly perfect LRO has been observed. As in bulk alloys, such ordering yields a ferrimagnetic order, while the disordered films are non-magnetic. In contrast with the ferromagnetic L1{sub 2}-type ordered CoPt{sub 3}(1 1 1) films, the ferrimagnetic CrPt{sub 3}(1 1 1) films exhibit perpendicular magnetic anisotropy with quality factors, K{sub u}/K{sub d}, as large as 5 and large coercivities around 450 kA/m. Such anisotropy could be related to the arrangement of Cr atoms, which owing to their large magnetic moment, oppositely directed to the small Pt moment, drive the magnetization. Since the six Cr nearest neighbours around a Cr atom are along the <0 0 1> directions, making an angle of 54.74 deg. with the [1 1 1] growth direction, the overlap of their electron distribution favors an easy axis of magnetization normal to the film plane. This idea is supported by the absence of magnetic anisotropy in ferrimagnetic CrPt{sub 3}(0 0 1) films.

  3. Making and Breaking of Lead Halide Perovskites

    KAUST Repository

    Manser, Joseph S.

    2016-02-16

    A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as organic metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compounds can be processed at low temperature (typically in the range 80–150 °C) and readily self-assemble from the solution phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chemical and structural stability, undergoing rapid degradation in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphology, manipulation of the stoichiometry and chemistry of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degradation mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degradation under operating conditions. This Account provides insight into the lifecycle of organic–inorganic lead halide perovskites, including (i) the nature of the precursor solution, (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chemistry, and thus the lead halide charge-transfer complexes present in solution, crystallization

  4. Making and Breaking of Lead Halide Perovskites.

    Science.gov (United States)

    Manser, Joseph S; Saidaminov, Makhsud I; Christians, Jeffrey A; Bakr, Osman M; Kamat, Prashant V

    2016-02-16

    A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as organic metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compounds can be processed at low temperature (typically in the range 80-150 °C) and readily self-assemble from the solution phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chemical and structural stability, undergoing rapid degradation in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphology, manipulation of the stoichiometry and chemistry of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degradation mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degradation under operating conditions. This Account provides insight into the lifecycle of organic-inorganic lead halide perovskites, including (i) the nature of the precursor solution, (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chemistry, and thus the lead halide charge-transfer complexes present in solution, crystallization

  5. First-principles study of ferroelectricity induced by p-d hybridization in ferrimagnetic NiFe2O4

    Science.gov (United States)

    Jong, Un-Gi; Yu, Chol-Jun; Park, Yong-Su; Ri, Chong-Suk

    2016-09-01

    We investigate the ferrimagnetism and ferroelectricity of bulk NiFe2O4 with tetragonal P41 22 symmetry by means of density functional theory calculations using generalized gradient approximation + Hubbard U approach. Special attention is paid to finding the most energetically favorable configuration on magnetic ordering and further calculating the reliable spontaneous electric polarization. With the fully optimized crystalline structure of the most stable configuration, the spontaneous polarization is obtained to be 23 μC/cm2 along the z direction, which originates from the hybridization between the 3d states of the Fe3+ cation and the 2p states of oxygen induced by Jahn-Teller effect.

  6. Natural and magnetic optical activity of 2-D chiral cyanido-bridged Mn(II)-Nb(IV) molecular ferrimagnets.

    Science.gov (United States)

    Chorazy, Szymon; Podgajny, Robert; Nitek, Wojciech; Fic, Tomasz; Görlich, Edward; Rams, Michał; Sieklucka, Barbara

    2013-08-04

    Unique two dimensional enantiopure cyanido-bridged {[Mn(II)(R-mpm)2]2[Nb(IV)(CN)8]}·4H2O and {[Mn(II)(S-mpm)2]2[Nb(IV)(CN)8]}·4H2O (-S) (mpm = α-methyl-2-pyridine-methanol) ferrimagnets with TC = 23.5 K were synthesized and characterized. They reveal natural optical activity (NOA) due to the chiral crystal structure, and magnetic optical activity (MOA) in the presence of an external magnetic field, with the strong enhancement in the magnetically ordered phase below TC.

  7. Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

    Science.gov (United States)

    Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaolan; Hu, Jin; Ho Kim, Dae

    2012-01-01

    We have grown epitaxial thin films of spinel NiCo2O4 on single crystalline MgAl2O4 (001) substrates by pulsed laser deposition. Magnetization measurement revealed hysteresis loops consistent with the reported ferrimagnetic order. The electrical transport exhibits a metallic behavior with the lowest resistivity of 0.8 mΩ cm and a metal insulator transition around the Néel temperature. The systematic variation in the properties of the films grown at different growth temperatures indicates a close relationship between the magnetic order and electrical transport.

  8. Monte Carlo study of a mixed spin (1, 3/2) ferrimagnetic nanowire with core/shell morphology

    Energy Technology Data Exchange (ETDEWEB)

    Feraoun, A.; Zaim, A., E-mail: ah_zaim@yahoo.fr; Kerouad, M., E-mail: kerouad@fs-umi.ac.ma

    2014-07-15

    In this work, Monte Carlo simulation based on Metropolis algorithm was used to study the magnetic behavior of a ferrimagnetic nanowire on a hexagonal lattice with a spin-3/2 core surrounded by a spin-1 shell layer with antiferromagnetic interface coupling in the presence of the crystal field interactions. The influences of the crystal field interactions, the interfacial and core couplings on the critical and compensation behaviors of the nanowire, are investigated. The results present rich critical behavior, which includes the first-and second-order phase transitions, the tricritical and critical end points. In addition, the compensation points can appear for appropriate values of the system parameters.

  9. Perpendicularly magnetized ferrimagnetic [Mn50Ga50/Co2FeAl] superlattice and the utilization in magnetic tunnel junctions

    Directory of Open Access Journals (Sweden)

    Q. L. Ma

    2015-08-01

    Full Text Available The ferrimagnetic superlattice (SL [MnGa/Co2FeAl]n exhibiting perpendicular magnetic anisotropy opened a new method for spintronics materials used in magnetic random access memory, because of the high anisotropy, small damping constant and tunable magnetization. In this work, we fabricated SLs with different MnGa composition and studied the MnGa composition dependence of the structure and magnetic properties of the SLs. Furthermore, we fabricated fully perpendicular magnetic tunnel junctions with SLs as both top and bottom electrodes. A clear tunnel magnetoresistance (TMR effect with TMR ratio of 1.3% at room temperature was observed.

  10. Patterning of perovskite-polymer films by wrinkling instabilities.

    Science.gov (United States)

    Nasti, G; Sanchez, S; Gunkel, I; Balog, S; Roose, B; Wilts, B D; Teuscher, J; Gentile, G; Cerruti, P; Ambrogi, V; Carfagna, C; Steiner, U; Abate, A

    2017-02-22

    Organic-inorganic perovskites are semiconductors used for applications in optoelectronics and photovoltaics. Micron and submicron perovskite patterns have been explored in semitransparent photovoltaic and lasing applications. In this work, we show that a polymeric medium can be used to create a patterned perovskite, by using a novel and inexpensive approach.

  11. X-ray imaging: Perovskites target X-ray detection

    Science.gov (United States)

    Heiss, Wolfgang; Brabec, Christoph

    2016-05-01

    Single crystals of perovskites are currently of interest to help fathom fundamental physical parameters limiting the performance of perovskite-based polycrystalline solar cells. Now, such perovskites offer a technology platform for optoelectronic devices, such as cheap and sensitive X-ray detectors.

  12. Electrochemical studies of perovskite mixed conductors

    Energy Technology Data Exchange (ETDEWEB)

    Brosha, E.L.; Chung, B.W.; Garzon, F.H. [Los Alamos National Lab., NM (United States). Electronic and Electrochemical Materials and Devices Group

    1994-12-01

    Research into the growth of high-quality single crystal thin films of high transition temperature {Tc} superconductors have stimulated interest in other perovskite metal oxides with a variety of physical properties. Thin films of perovskite materials are among the major focal research areas for optical, sensor, electronic, and superconducting applications. Two lanthanum-based oxygen/electronic conducting perovskite oxides of particular interest for high temperature fuel cell electrodes and interconnects and for other electrochemical applications such as oxygen separation devices are La{sub 1{minus}x}Sr{sub x}MnO{sub 3{minus}y} and La{sub 1{minus}x}Sr{sub x}CoO{sub 3{minus}y}. The La-based perovskites are valuable for these technologies because they reduce interfacial resistances by eliminating the need for a three phase contact area (gas, metal electrode, electrolyte). In addition, these oxides may also serve a valuable role as novel catalysts or catalytic supports; however, little is known about what catalytic properties they may possess. Fundamental study of the electrochemical, diffusional oxygen transport, and surface catalytic properties of these materials can be greatly simplified if the complications associated with the presence of grain boundaries and multiple crystallite orientations can be avoided. Therefore, single crystals of these La-based perovskites become highly desirable. In this work, the authors report the structural and electrical properties of highly oriented thin films of La{sub 0.84}Sr{sub 0.16}MnO{sub 3} and La{sub 0.8}Sr{sub 0.2}CoO{sub 3} grown on single crystal Y-ZrO{sub 2} substrates. An addition, the authors have demonstrated growing, in situ, epitaxial multilayer perovskite/fluorite/perovskite configurations for fundamental fuel cell modeling.

  13. Bismuth centred magnetic perovskite: A projected multiferroic

    Energy Technology Data Exchange (ETDEWEB)

    Kundu, Asish K., E-mail: asish.k@gmail.com [Discipline of Physics, Indian Institute of Information Technology, Design and Manufacturing, Dumna Airport Road, Jabalpur 482005 (India); Seikh, Md. Motin [Department of Chemistry, Visva-Bharati University, Santiniketan, West Bengal 731235 (India); Nautiyal, Pranjal [Discipline of Mechanical Engineering, Indian Institute of Information Technology, Design and Manufacturing, Dumna Airport Road, Jabalpur 482005 (India)

    2015-03-15

    In recent time substantial attention has been initiated to understand the physics behind multiferroism and to design new multiferroic materials. BiMnO{sub 3} and BiFeO{sub 3} are the well-studied Bi-centred multiferroic oxides. BiMnO{sub 3} is a ferromagnetic–ferroelectric (metastable) phase and require drastic conditions to synthesize. However, lanthanum substituted BiMnO{sub 3} phases stabilized at ambient pressure. It is thus of major importance to increase the number of ferromagnetic perovskites with Bi cations that could be designed under ambient conditions. In this article, we have presented an up to date report of investigations on Bi-centred magnetic perovskites, a prospective material for multiferroic application. Central focus is concentrated on La{sub 0.5}Bi{sub 0.5}MnO{sub 3} perovskite with various substitutions at different levels. A few of these perovskites are found to be of practical importance e.g. La{sub 0.5}Bi{sub 0.5}Mn{sub 0.67}Co{sub 0.33}O{sub 3} with high dielectric permittivity coupled with ferromagnetism. A comprehensive analysis of different physical functionalities and their interrelation for a wide range of compositions of these Bi-centred perovskites is presented. It has been found that the complex magnetic behaviour originates from mixed valence metal ions. The ferroelectricity is associated with the 6s{sup 2} lone pair of Bi{sup 3+} cations. The magnetic ground state influences the dielectric properties reflecting the multiferroism in a single material. - Highlights: • Multiferroics have attracted increasing attention due to their possible device applications. • Bismuth centred magnetic perovskite is one kind of such promising multiferroic materials. • Ferromagnetic Bi-perovskites, which are synthesized at ambient conditions, have been discussed.

  14. Rational Strategies for Efficient Perovskite Solar Cells.

    Science.gov (United States)

    Seo, Jangwon; Noh, Jun Hong; Seok, Sang Il

    2016-03-15

    A long-standing dream in the large scale application of solar energy conversion is the fabrication of solar cells with high-efficiency and long-term stability at low cost. The realization of such practical goals depends on the architecture, process and key materials because solar cells are typically constructed from multilayer heterostructures of light harvesters, with electron and hole transporting layers as a major component. Recently, inorganic-organic hybrid lead halide perovskites have attracted significant attention as light absorbers for the fabrication of low-cost and high-efficiency solar cells via a solution process. This mainly stems from long-range ambipolar charge transport properties, low exciton binding energies, and suitable band gap tuning by managing the chemical composition. In our pioneering work, a new photovoltaic platform for efficient perovskite solar cells (PSCs) was proposed, which yielded a high power conversion efficiency (PCE) of 12%. The platform consisted of a pillared architecture of a three-dimensional nanocomposite of perovskites fully infiltrating mesoporous TiO2, resulting in the formation of continuous phases and perovskite domains overlaid with a polymeric hole conductor. Since then, the PCE of our PSCs has been rapidly increased from 3% to over 20% certified efficiency. The unprecedented increase in the PCE can be attributed to the effective integration of the advantageous attributes of the refined bicontinuous architecture, deposition process, and composition of perovskite materials. Specifically, the bicontinuous architectures used in the high efficiency comprise a layer of perovskite sandwiched between mesoporous metal-oxide layer, which is a very thinner than that of used in conventional dye-sensitized solar cells, and hole-conducting contact materials with a metal back contact. The mesoporous scaffold can affect the hysteresis under different scan direction in measurements of PSCs. The hysteresis also greatly depends on

  15. Nanoimprinted Perovskite Nanograting Photodetector with Improved Efficiency.

    Science.gov (United States)

    Wang, Honglei; Haroldson, Ross; Balachandran, Balasubramaniam; Zakhidov, Alex; Sohal, Sandeep; Chan, Julia Y; Zakhidov, Anvar; Hu, Walter

    2016-12-27

    Recently, organolead halide-based perovskites have emerged as promising materials for optoelectronic applications, particularly for photovoltaics, photodetectors, and lasing, with low cost and high performance. Meanwhile, nanoscale photodetectors have attracted tremendous attention toward realizing miniaturized optoelectronic systems, as they offer high sensitivity, ultrafast response, and the capability to detect beyond the diffraction limit. Here we report high-performance nanoscale-patterned perovskite photodetectors implemented by nanoimprint lithography (NIL). The spin-coated lead methylammonium triiodide perovskite shows improved crystallinity and optical properties after NIL. The nanoimprinted metal-semiconductor-metal photodetectors demonstrate significantly improved performance compared to the nonimprinted conventional thin-film devices. The effects of NIL pattern geometries on the optoelectronic characteristics were studied, and the nanograting pattern based photodetectors demonstrated the best performance, showing approximately 35 times improvement on responsivity and 7 times improvement on on/off ratio compared with the nonimprinted devices. The high performance of NIL-nanograting photodetectors likely results from high crystallinity and favored nanostructure morphology, which contribute to higher mobility, longer diffusion length, and better photon absorption. Our results have demonstrated that the NIL is a cost-effective method to fabricate high-performance perovskite nanoscale optoelectronic devices, which may be suitable for manufacturing of high-density perovskite nanophotodetector arrays and to provide integration with state-of-the-art electronic circuits.

  16. Quantum-dot-in-perovskite solids

    KAUST Repository

    Ning, Zhijun

    2015-07-15

    © 2015 Macmillan Publishers Limited. All rights reserved. Heteroepitaxy - atomically aligned growth of a crystalline film atop a different crystalline substrate - is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned \\'dots-in-a-matrix\\' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  17. Trap states in lead iodide perovskites.

    Science.gov (United States)

    Wu, Xiaoxi; Trinh, M Tuan; Niesner, Daniel; Zhu, Haiming; Norman, Zachariah; Owen, Jonathan S; Yaffe, Omer; Kudisch, Bryan J; Zhu, X-Y

    2015-02-11

    Recent discoveries of highly efficient solar cells based on lead iodide perovskites have led to a surge in research activity on understanding photo carrier generation in these materials, but little is known about trap states that may be detrimental to solar cell performance. Here we provide direct evidence for hole traps on the surfaces of three-dimensional (3D) CH3NH3PbI3 perovskite thin films and excitonic traps below the optical gaps in these materials. The excitonic traps possess weak optical transition strengths, can be populated from the relaxation of above gap excitations, and become more significant as dimensionality decreases from 3D CH3NH3PbI3 to two-dimensional (2D) (C4H9NH3I)2(CH3NH3I)(n-1)(PbI2)(n) (n = 1, 2, 3) perovskites and, within the 2D family, as n decreases from 3 to 1. We also show that the density of excitonic traps in CH3NH3PbI3 perovskite thin films grown in the presence of chloride is at least one-order of magnitude lower than that grown in the absence of chloride, thus explaining a widely known mystery on the much better solar cell performance of the former. The trap states are likely caused by electron-phonon coupling and are enhanced at surfaces/interfaces where the perovskite crystal structure is most susceptible to deformation.

  18. Bismuth centred magnetic perovskite: A projected multiferroic

    Science.gov (United States)

    Kundu, Asish K.; Seikh, Md. Motin; Nautiyal, Pranjal

    2015-03-01

    In recent time substantial attention has been initiated to understand the physics behind multiferroism and to design new multiferroic materials. BiMnO3 and BiFeO3 are the well-studied Bi-centred multiferroic oxides. BiMnO3 is a ferromagnetic-ferroelectric (metastable) phase and require drastic conditions to synthesize. However, lanthanum substituted BiMnO3 phases stabilized at ambient pressure. It is thus of major importance to increase the number of ferromagnetic perovskites with Bi cations that could be designed under ambient conditions. In this article, we have presented an up to date report of investigations on Bi-centred magnetic perovskites, a prospective material for multiferroic application. Central focus is concentrated on La0.5Bi0.5MnO3 perovskite with various substitutions at different levels. A few of these perovskites are found to be of practical importance e.g. La0.5Bi0.5Mn0.67Co0.33O3 with high dielectric permittivity coupled with ferromagnetism. A comprehensive analysis of different physical functionalities and their interrelation for a wide range of compositions of these Bi-centred perovskites is presented. It has been found that the complex magnetic behaviour originates from mixed valence metal ions. The ferroelectricity is associated with the 6s2 lone pair of Bi3+ cations. The magnetic ground state influences the dielectric properties reflecting the multiferroism in a single material.

  19. Dissolution-recrystallization method for high efficiency perovskite solar cells

    Science.gov (United States)

    Han, Fei; Luo, Junsheng; Wan, Zhongquan; Liu, Xingzhao; Jia, Chunyang

    2017-06-01

    In this work, a dissolution-recrystallization method (DRM) with chlorobenzene and dimethylsulfoxide treating the perovskite films during the spin-coating process is reported. This is the first time that DRM is used to control perovskite crystallization and improve the device performance. Furthermore, the DRM is good for reducing defects and grain boundaries, improving perovskite crystallization and even improving TiO2/perovskite interface. By optimizing, the DRM2-treated perovskite solar cell (PSC) obtains the best photoelectric conversion efficiency (PCE) of 16.76% under AM 1.5 G illumination (100 mW cm-2) with enhanced Jsc and Voc compared to CB-treated PSC.

  20. Field theoretical approach to the paramagnetic-ferrimagnetic transition in strongly coupled paramagnetic systems

    Energy Technology Data Exchange (ETDEWEB)

    Chahid, M.; Benhamou, M. E-mail: benhamou.mabrouk@caramail.com

    2000-04-01

    The aim of this paper is the investigation of the critical properties of two strongly coupled paramagnetic sublattices exhibiting a paramagnetic-ferrimagnetic transition, at some critical temperature T{sub c} greater than the room temperature. In order to take into account the strong fluctuations of the magnetization near the critical point, use is made of the renormalization-group (RG) techniques applied to an elaborated field model describing such a transition, which is of Landau-Ginzburg-Wilson type. The associated free energy or action is a functional of two kinds of order parameters (local magnetizations), which are scalar fields phi (cursive,open) Greek and {psi} relative to these sublattices. It involves quadratic and quartic terms in both fields, and a lowest-order coupling C{sub o}phi (cursive,open) Greek{psi}, where C{sub o}>0 stands for the coupling constant measuring the interaction between the two sublattices. We first show that the associated field theory is renormalizable at any order of the perturbation series in the coupling constants, up to a critical dimension d{sub c}=4, and that, the corresponding counterterms have the same form as those relative to the usual phi (cursive,open) Greek{sup 4}-theory (C{sub o}=0). The existence of the renormalization theory enables us to write the RG-equations satisfied by the correlation functions. We solve these using the standard characteristics method, to get all critical properties of the system under investigation. We first determine the exact shape of the critical line in the (T,C)-plane, along which the system undergoes a phase transition. Second, we determine the scaling laws of the correlation functions, with respect to relevant parameters of the problem, namely, the wave vector q, the (renormalized) coupling C and the temperature shift T-T{sub c}. We find that these scaling laws are characterized by critical exponents, which are the same as those relative to Ising-like magnetic systems.

  1. Ferrimagnetic spin-1/2 chain of alternating Ising and Heisenberg spins in arbitrarily oriented magnetic field

    Directory of Open Access Journals (Sweden)

    J. Strečka

    2012-12-01

    Full Text Available The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg spins in an arbitrarily oriented magnetic field is exactly solved using the spin-rotation transformation and the transfer-matrix method. It is shown that the low-temperature magnetization process depends basically on a spatial orientation of the magnetic field. A sharp stepwise magnetization curve with a marked intermediate plateau, which emerges for the magnetic field applied along the easy-axis direction of the Ising spins, becomes smoother and the intermediate plateau shrinks if the external field is tilted from the easy-axis direction. The magnetization curve of a polycrystalline system is also calculated by performing powder averaging of the derived magnetization formula. The proposed spin-chain model brings an insight into high-field magnetization data of 3d-4f bimetallic polymeric compound Dy(NO3(DMSO2Cu(opba(DMSO2, which provides an interesting experimental realization of the ferrimagnetic chain composed of two different but regularly alternating spin-1/2 magnetic ions Dy3+ and Cu2+ that are reasonably approximated by the notion of Ising and Heisenberg spins, respectively.

  2. Magnetic anisotropy and chemical long-range order in epitaxial ferrimagnetic CrPt sub 3 films

    CERN Document Server

    Maret, M; Köhler, J; Poinsot, R; Ulhaq-Bouillet, C; Tonnerre, J M; Berar, J F; Bucher, E

    2000-01-01

    Thin films of CrPt sub 3 were prepared by molecular beam epitaxy on both Al sub 2 O sub 3 (0 0 0 1) and MgO(0 0 1) substrates, either directly by co-deposition of Cr and Pt at high temperatures or after in situ annealing of superlattices [Cr(2 A)/Pt(7 A)]. In situ RHEED observations and X-ray diffraction measurements have allowed us to check the single-crystal quality of CrPt sub 3 films and to determine the degree of L1 sub 2 -type long-range order (LRO). In films co-deposited between 850 deg. C and 950 deg. C a nearly perfect LRO has been observed. As in bulk alloys, such ordering yields a ferrimagnetic order, while the disordered films are non-magnetic. In contrast with the ferromagnetic L1 sub 2 -type ordered CoPt sub 3 (1 1 1) films, the ferrimagnetic CrPt sub 3 (1 1 1) films exhibit perpendicular magnetic anisotropy with quality factors, K sub u /K sub d , as large as 5 and large coercivities around 450 kA/m. Such anisotropy could be related to the arrangement of Cr atoms, which owing to their large mag...

  3. 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.

  4. Metal halide perovskites for energy applications

    Science.gov (United States)

    Zhang, Wei; Eperon, Giles E.; Snaith, Henry J.

    2016-06-01

    Exploring prospective materials for energy production and storage is one of the biggest challenges of this century. Solar energy is one of the most important renewable energy resources, due to its wide availability and low environmental impact. Metal halide perovskites have emerged as a class of semiconductor materials with unique properties, including tunable bandgap, high absorption coefficient, broad absorption spectrum, high charge carrier mobility and long charge diffusion lengths, which enable a broad range of photovoltaic and optoelectronic applications. Since the first embodiment of perovskite solar cells showing a power conversion efficiency of 3.8%, the device performance has been boosted up to a certified 22.1% within a few years. In this Perspective, we discuss differing forms of perovskite materials produced via various deposition procedures. We focus on their energy-related applications and discuss current challenges and possible solutions, with the aim of stimulating potential new applications.

  5. Organometallic perovskites for optoelectronic applications (Conference Presentation)

    Science.gov (United States)

    Levchuk, Levgen; Hoegl, Florian; Brandl, Marco; Osvet, Andres; Hock, Rainer; Herre, Patrick; Wolfgang, Wolfgang; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph

    2016-09-01

    Organometallic halide perovskites CH3NH3BX3 (B= Pb, Sn, Ge; X = I, Br, Cl) have become one of the most promising semiconductors for solar cell applications, reaching power conversion efficiencies beyond 20%. Improving our ability to harness the full potential of organometal halide perovskites requires the development of more reliable synthesis routines of well defined, reproducible and defect free reference systems allowing to study the fundamental photo-physical processes. In this study we present size and band gap engineering for organo-lead perovskites crystallites with various shapes and sizes ranging from the 5 nm regime all the way to 1 cm. Colloidal nano-crystals, micro-crystlline particles as well as single crystals are demonstrated with excellent purity and control in shape and size are demonstrated. The structural, optical and photo-physical properties of these reference materials are investigated and analyzed as function of their size and shape.

  6. Atomic Resolution Imaging of Halide Perovskites.

    Science.gov (United States)

    Yu, Yi; Zhang, Dandan; Kisielowski, Christian; Dou, Letian; Kornienko, Nikolay; Bekenstein, Yehonadav; Wong, Andrew B; Alivisatos, A Paul; Yang, Peidong

    2016-12-14

    The radiation-sensitive nature of halide perovskites has hindered structural studies at the atomic scale. We overcome this obstacle by applying low dose-rate in-line holography, which combines aberration-corrected high-resolution transmission electron microscopy with exit-wave reconstruction. This technique successfully yields the genuine atomic structure of ultrathin two-dimensional CsPbBr3 halide perovskites, and a quantitative structure determination was achieved atom column by atom column using the phase information of the reconstructed exit-wave function without causing electron beam-induced sample alterations. An extraordinarily high image quality enables an unambiguous structural analysis of coexisting high-temperature and low-temperature phases of CsPbBr3 in single particles. On a broader level, our approach offers unprecedented opportunities to better understand halide perovskites at the atomic level as well as other radiation-sensitive materials.

  7. Electronic and Ionic Transport Dynamics in Organolead Halide Perovskites.

    Science.gov (United States)

    Li, Dehui; Wu, Hao; Cheng, Hung-Chieh; Wang, Gongming; Huang, Yu; Duan, Xiangfeng

    2016-07-26

    Ion migration has been postulated as the underlying mechanism responsible for the hysteresis in organolead halide perovskite devices. However, the electronic and ionic transport dynamics and how they impact each other in organolead halide perovskites remain elusive to date. Here we report a systematic investigation of the electronic and ionic transport dynamics in organolead halide perovskite microplate crystals and thin films using temperature-dependent transient response measurements. Our study reveals that thermally activated ionic and electronic conduction coexist in perovskite devices. The extracted activation energies suggest that the electronic transport is easier, but ions migrate harder in microplates than in thin films, demonstrating that the crystalline quality and grain boundaries can fundamentally modify electronic and ionic transport in perovskites. These findings offer valuable insight on the electronic and ionic transport dynamics in organolead halide perovskites, which is critical for optimizing perovskite devices with reduced hysteresis and improved stability and efficiency.

  8. Synthesis of solid solutions of perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Dambekalne, M.Y.; Antonova, M.K.; Perro, I.T.; Plaude, A.V.

    1986-03-01

    The authors carry out thermographic studies, using a derivatograph, in order to understand the nature of the processes taking place during the synthesis of solid solutions of perovskites. Based on the detailed studies on the phase transformations occurring in the charges of the PSN-PMN solid solutions and on the selection of the optimum conditions for carrying out their synthesis, the authors obtained a powder containing a minimum quantity of the undesirable pyrochlore phase and by sintering it using the hot pressing method, they produced single phase ceramic specimens containing the perovskite phase alone with a density close to the theoretical value and showing zero apparent porosity and water absorption.

  9. Excited State Properties of Hybrid Perovskites.

    Science.gov (United States)

    Saba, Michele; Quochi, Francesco; Mura, Andrea; Bongiovanni, Giovanni

    2016-01-19

    Metal halide perovskites have come to the attention of the scientific community for the progress achieved in solar light conversion. Energy sustainability is one of the priorities of our society, and materials advancements resulting in low-cost but efficient solar cells and large-area lighting devices represent a major goal for applied research. From a basic point of view, perovskites are an exotic class of hybrid materials combining some merits of organic and inorganic semiconductors: large optical absorption, large mobilities, and tunable band gap together with the possibility to be processed in solution. When a novel class of promising semiconductors comes into the limelight, lively discussions ensue on the photophysics of band-edge excitations, because just the states close to the band edge are entailed in energy/charge transport and light emission. This was the case several decades ago for III-V semiconductors, it has been up to 10 years ago for organics, and it is currently the case for perovskites. Our aim in this Account is to rationalize the body of experimental evidence on perovskite photophysics in a coherent theoretical framework, borrowing from the knowledge acquired over the years in materials optoelectronics. A crucial question is whether photon absorption leads to a population of unbound, conductive free charges or instead excitons, neutral and insulating bound states created by Coulomb interaction just below the energy of the band gap. We first focus on the experimental estimates of the exciton binding energy (Eb): at room temperature, Eb is comparable to the thermal energy kBT in MAPbI3 and increases up to values 2-3kBT in wide band gap MAPbBr3 and MAPbCl3. Statistical considerations predict that these values, even though comparable to or larger than thermal energy, let free carriers prevail over bound excitons for all levels of excitation densities relevant for devices. The analysis of photophysics evidence confirms that all hybrid halide

  10. Research Update: Luminescence in lead halide perovskites

    Directory of Open Access Journals (Sweden)

    Ajay Ram Srimath Kandada

    2016-09-01

    Full Text Available Efficiency and dynamics of radiative recombination of carriers are crucial figures of merit for optoelectronic materials. Following the recent success of lead halide perovskites in efficient photovoltaic and light emitting technologies, here we review some of the noted literature on the luminescence of this emerging class of materials. After outlining the theoretical formalism that is currently used to explain the carrier recombination dynamics, we review a few significant works which use photoluminescence as a tool to understand and optimize the operation of perovskite based optoelectronic devices.

  11. Partial oxidation of 2-propanol on perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Sumathi, R.; Viswanathan, B.; Varadarajan, T.K. [Indian Inst. of Tech., Madras (India). Dept. of Chemistry

    1998-12-31

    Partial oxidation of 2-propanol was carried out on AB{sub 1-x}B`{sub x}O{sub 3} (A=Ba, B=Pb, Ce, Ti; B`=Bi, Sb and Cu) type perovskite oxides. Acetone was the major product observed on all the catalysts. All the catalysts underwent partial reduction during the reaction depending on the composition of the reactant, nature of the B site cation and the extent of substitution at B site. The catalytic activity has been correlated with the reducibility of the perovskite oxides determined from Temperature Programmed Reduction (TPR) studies. (orig.)

  12. Research Update: Luminescence in lead halide perovskites

    Science.gov (United States)

    Srimath Kandada, Ajay Ram; Petrozza, Annamaria

    2016-09-01

    Efficiency and dynamics of radiative recombination of carriers are crucial figures of merit for optoelectronic materials. Following the recent success of lead halide perovskites in efficient photovoltaic and light emitting technologies, here we review some of the noted literature on the luminescence of this emerging class of materials. After outlining the theoretical formalism that is currently used to explain the carrier recombination dynamics, we review a few significant works which use photoluminescence as a tool to understand and optimize the operation of perovskite based optoelectronic devices.

  13. Large area perovskite solar cell module

    Science.gov (United States)

    Cai, Longhua; Liang, Lusheng; Wu, Jifeng; Ding, Bin; Gao, Lili; Fan, Bin

    2017-01-01

    The recent dramatic rise in power conversion efficiencies (PCE) of perovskite solar cells has triggered intense research worldwide. However, their practical development is hampered by poor stability and low PCE values with large areas devices. Here, we developed a gas-pumping method to avoid pinholes and eliminate local structural defects over large areas of perovskite film, even for 5 × 5 cm2 modules, the PCE reached 10.6% and no significant degradation was found after 140 days of outdoor testing. Our approach enables the realization of high performance large-area PSCs for practical application.

  14. Nanoscale investigation of organic - inorganic halide perovskites

    Science.gov (United States)

    Cacovich, S.; Divitini, G.; Vrućinić, M.; Sadhanala, A.; Friend, R. H.; Sirringhaus, H.; Deschler, F.; Ducati, C.

    2015-10-01

    Over the last few years organic - inorganic halide perovskite-based solar cells have exhibited a rapid evolution, reaching certified power conversion efficiencies now surpassing 20%. Nevertheless the understanding of the optical and electronic properties of such systems on the nanoscale is still an open problem. In this work we investigate two model perovskite systems (based on iodine - CH3NH3PbI3 and bromine - CH3NH3PbBr3), analysing the local elemental composition and crystallinity and identifying chemical inhomogeneities.

  15. 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.

  16. 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.

  17. Strain-sensitive spin-state ordering in thin films of perovskite LaCoO3

    Science.gov (United States)

    Fujioka, J.; Yamasaki, Y.; Doi, A.; Nakao, H.; Kumai, R.; Murakami, Y.; Nakamura, M.; Kawasaki, M.; Arima, T.; Tokura, Y.

    2015-11-01

    We have investigated the lattice distortion coupled to the Co 3 d -spin-state ordering in thin films of perovskite LaCoO3 with various epitaxial strains by measurements of the magnetization, x-ray diffraction, and optical spectra. In the system with tensile strain about 0.5%, a lattice distortion characterized by the modulation vector q =(1 /6 ,1 /6 ,1 /6 ) emerges at 40 K, followed by a ferromagnetic ordering at 24 K. Alternatively, in systems with tensile strain exceeding 1%, the lattice distortion characterized by q =(1 /4 ,1 /4 ,1 /4 ) emerges at 120 K or higher, and subsequently the ferromagnetic or ferrimagnetic ordering occurs around 90 K. The evolution of infrared phonon spectra and resonant x-ray scattering at the Co K edge suggests that the population change in the Co 3 d spin state causes the strain-induced switching of spin-state ordering as well as of magnetic ordering in this canonical spin-state crossover system.

  18. Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compound Mn1.5FeV0.5Al

    Science.gov (United States)

    Stinshoff, Rolf; Nayak, Ajaya K.; Fecher, Gerhard H.; Balke, Benjamin; Ouardi, Siham; Skourski, Yurii; Nakamura, Tetsuya; Felser, Claudia

    2017-02-01

    The Slater-Pauling rule states that L 21 Heusler compounds with 24 valence electrons never exhibit a total spin magnetic moment. In the case of strongly localized magnetic moments at one of the atoms (here Mn) they will exhibit a fully compensated half-metallic ferrimagnetic state instead, in particular, when symmetry does not allow for antiferromagnetic order. With the aid of magnetic and anomalous Hall effect measurements, it is experimentally demonstrated that Mn1.5V0.5FeAl follows such a scenario. The ferrimagnetic state is tuned by the composition. A small residual magnetization, which arises due to a slight mismatch of the magnetic moments in the different sublattices, results in a pronounced change of the temperature dependence of the ferrimagnet. A compensation point is confirmed by observation of magnetic reversal and sign change of the anomalous Hall effect. Theoretical models are presented that correlate the electronic structure and the compensation mechanisms of the different half-metallic ferrimagnetic states in the Mn-V-Fe-Al Heusler system.

  19. X-ray structure of [ReCl4(mu-ox)Cu(pyim)2]: a new heterobimetallic Re(IV)Cu(II) ferrimagnetic chain.

    Science.gov (United States)

    Martínez-Lillo, José; Armentano, Donatella; De Munno, Giovanni; Lloret, Francesc; Julve, Miguel; Faus, Juan

    2008-01-01

    A new heterobimetallic Re(IV)Cu(II) compound has been prepared and its crystal structure determined by single-crystal X-ray diffraction; magnetic susceptibility measurements show that this compound behaves as a ferrimagnetic chain with significant antiferromagnetic interactions between Re(IV) and Cu(II) metal ions.

  20. Improving the Stability and Performance of Perovskite Light-Emitting Diodes by Thermal Annealing Treatment.

    Science.gov (United States)

    Yu, Jae Choul; Kim, Dae Woo; Kim, Da Bin; Jung, Eui Dae; Park, Jong Hyun; Lee, Ah-Young; Lee, Bo Ram; Di Nuzzo, Daniele; Friend, Richard H; Song, Myoung Hoon

    2016-08-01

    A perovskite LED with a perovskite film treated under optimum thermal annealing conditions exhibits a significantly enhanced long-term stability with full coverage of the green electroluminescence emission due to the highly uniform morphology of the perovskite film.

  1. Multicomponent, peptide-targeted glycol chitosan nanoparticles containing ferrimagnetic iron oxide nanocubes for bladder cancer multimodal imaging

    Directory of Open Access Journals (Sweden)

    Key J

    2016-08-01

    Full Text Available Jaehong Key,1,2 Deepika Dhawan,3 Christy L Cooper,3,4 Deborah W Knapp,3 Kwangmeyung Kim,5 Ick Chan Kwon,5 Kuiwon Choi,5 Kinam Park,1,6 Paolo Decuzzi,7–9 James F Leary1,3,41Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA; 2Department of Biomedical Engineering, Yonsei University, Wonju, Republic of Korea; 3School of Veterinary Medicine-Department of Basic Medical Sciences, Purdue University, West Lafayette, 4Birck Nanotechnology Center at Discovery Park, Purdue University, West Lafayette, IN, USA; 5Biomedical Research Center, Korea Institute of Science and Technology, Sungbook-Gu, Seoul, Republic of Korea; 6Department of Pharmaceutics, Purdue University, West Lafayette, IN, 7Department of Translational Imaging, 8Department of Nanomedicine, Houston Methodist Research Institute, Houston, TX USA; 9Laboratory of Nanotechnology for Precision Medicine, Fondazione Istituto Italiano di Tecnologia (IIT, Genova, Italy Abstract: While current imaging modalities, such as magnetic resonance imaging (MRI, computed tomography, and positron emission tomography, play an important role in detecting tumors in the body, no single-modality imaging possesses all the functions needed for a complete diagnostic imaging, such as spatial resolution, signal sensitivity, and tissue penetration depth. For this reason, multimodal imaging strategies have become promising tools for advanced biomedical research and cancer diagnostics and therapeutics. In designing multimodal nanoparticles, the physicochemical properties of the nanoparticles should be engineered so that they successfully accumulate at the tumor site and minimize nonspecific uptake by other organs. Finely altering the nano-scale properties can dramatically change the biodistribution and tumor accumulation of nanoparticles in the body. In this study, we engineered multimodal nanoparticles for both MRI, by using ferrimagnetic nanocubes (NCs, and near infrared fluorescence imaging

  2. Material and Device Stability in Perovskite Solar Cells.

    Science.gov (United States)

    Kim, Hui-Seon; Seo, Ja-Young; Park, Nam-Gyu

    2016-09-22

    Organic-inorganic halide perovskite solar cells have attracted great attention because of their superb efficiency reaching 22 % and low-cost, facile fabrication processing. Nevertheless, stability issues in perovskite solar cells seem to block further advancements toward commercialization. Thus, device stability is one of the important topics in perovskite solar cell research. In the beginning, the poor moisture resistivity of the perovskite layer was considered as a main problem that hindered further development of perovskite solar cells, which encouraged engineering of the perovskite or protection of the perovskite by a buffer layer. Soon after, other parameters affecting long-term stability were sequentially found and various attempts have been made to enhance intrinsic and extrinsic stability. Here we review the recent progresses addressing stability issues in perovskite solar cells. In this report, we investigated factors affecting stability from material and device points of view. To gain a better understanding of the stability of the bulk perovskite material, decomposition mechanisms were investigated in relation to moisture, photons, and heat. Stability of full device should also be carefully examined because its stability is dependent not only on bulk perovskite but also on the interfaces and selective contacts. In addition, ion migration and current-voltage hysteresis were found to be closely related to stability.

  3. Properties of Perovskites and other oxides

    NARCIS (Netherlands)

    Müller, K.A.; Kool, T.W.

    2010-01-01

    In this book some 50 papers published by K A Müller as author or co-author over several decades, amplified by more recent work mainly by T W Kool with collaborators, are reproduced. The main subject is Electron Paramagnetic Resonance (EPR) applied to the study of perovskites and other oxides with re

  4. 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...

  5. Centrifugal Casting of Tubular Perovskite Membranes

    NARCIS (Netherlands)

    Mertins, Frederic H.B.; Kruidhof, Henk; Bouwmeester, Henny J.M.

    2005-01-01

    Dense tubular membranes were produced by centrifugal casting of an aqueous suspension, containing powder particles of the mixed-conducting perovskite La0.5Sr0.5CoO3−δ and a dispersant. The resulting green bodies were dried and sintered to produce tubes with a maximum length of 12 cm, having a relat

  6. Tilts and Ionic Shifts in Rhombohedral Perovskites

    NARCIS (Netherlands)

    Noheda, Beatriz; Duan, Ning; Cereceda, Noé; Gonzalo, Julio A.

    1998-01-01

    We make a comparative analysis of rhombohedral perovskites (ABO3) with/without oxygen rotations and ionic shifts, within the framework of a generalised effective field approach. We analyse available data on LaAlO3 and LiTaO3 and new data on Zr-rich PZT, examples of three different ways of structural

  7. Hybrid solar cells : Perovskites under the Sun

    NARCIS (Netherlands)

    Loi, Maria Antonietta; Hummelen, Jan C.

    2013-01-01

    Mixed-halide organic–inorganic hybrid perovskites are reported to display electron–hole diffusion lengths over 1 μm. This observation provides important insight into the charge-carrier dynamics of this class of semiconductors and increases the expectations for highly efficient and cheap solar cells.

  8. Electro-optics of perovskite solar cells

    Science.gov (United States)

    Lin, Qianqian; Armin, Ardalan; Nagiri, Ravi Chandra Raju; Burn, Paul L.; Meredith, Paul

    2015-02-01

    Organohalide-perovskite solar cells have emerged as a leading next-generation photovoltaic technology. However, despite surging efficiencies, many questions remain unanswered regarding the mechanisms of operation. Here we report a detailed study of the electro-optics of efficient CH3NH3PbI3-perovskite-only planar devices. We report the dielectric constants over a large frequency range. Importantly, we found the real part of the static dielectric constant to be ∼70, from which we estimate the exciton-binding energy to be of order 2 meV, which strongly indicates a non-excitonic mechanism. Also, Jonscher's Law behaviour was consistent with the perovskite having ionic character. Accurate knowledge of the cell's optical constants allowed improved modelling and design, and using this information we fabricated an optimized device with an efficiency of 16.5%. The optimized devices have ∼100% spectrally flat internal quantum efficiencies and minimal bimolecular recombination. These findings establish systematic design rules to achieve silicon-like efficiencies in simple perovskite solar cells.

  9. High performance magnetocaloric perovskites for magnetic refrigeration

    DEFF Research Database (Denmark)

    Bahl, Christian R. H.; Velazquez, David; Nielsen, Kaspar K.

    2012-01-01

    We have applied mixed valance manganite perovskites as magnetocaloric materials in a magnetic refrigeration device. Relying on exact control of the composition and a technique to process the materials into single adjoined pieces, we have observed temperature spans above 9 K with two materials. Re...

  10. 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

  11. Photovoltaic Rudorffites: Lead-Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites.

    Science.gov (United States)

    Turkevych, Ivan; Kazaoui, Said; Ito, Eisuke; Urano, Toshiyuki; Yamada, Koji; Tomiyasu, Hiroshi; Yamagishi, Hideo; Kondo, Michio; Aramaki, Shinji

    2017-06-28

    Hybrid CPbX3 (C: Cs, CH3 NH3 ; X: Br, I) perovskites possess excellent photovoltaic properties but are highly toxic, which hinders their practical application. Unfortunately, all Pb-free alternatives based on Sn and Ge are extremely unstable. Although stable and non-toxic C2 ABX6 double perovskites based on alternating corner-shared AX6 and BX6 octahedra (A=Ag, Cu; B=Bi, Sb) are possible, they have indirect and wide band gaps of over 2 eV. However, is it necessary to keep the corner-shared perovskite structure to retain good photovoltaic properties? Here, we demonstrate another family of photovoltaic halides based on edge-shared AX6 and BX6 octahedra with the general formula Aa Bb Xx (x=a+3 b) such as Ag3 BiI6 , Ag2 BiI5 , AgBiI4 , AgBi2 I7 . As perovskites were named after their prototype oxide CaTiO3 discovered by Lev Perovski, we propose to name these new ABX halides as rudorffites after Walter Rüdorff, who discovered their prototype oxide NaVO2 . We studied structural and optoelectronic properties of several highly stable and promising Ag-Bi-I photovoltaic rudorffites that feature direct band gaps in the range of 1.79-1.83 eV and demonstrated a proof-of-concept FTO/c-m-TiO2 /Ag3 BiI6 /PTAA/Au (FTO: fluorine-doped tin oxide, PTAA: poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], c: compact, m: mesoporous) solar cell with photoconversion efficiency of 4.3 %. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. New perovskite-based manganite Pb 2Mn 2O 5

    Science.gov (United States)

    Hadermann, Joke; Abakumov, Artem M.; Perkisas, Tyché; D'Hondt, Hans; Tan, Haiyan; Verbeeck, Johan; Filonenko, Vladimir P.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf

    2010-09-01

    A new perovskite based compound Pb 2Mn 2O 5 has been synthesized using a high pressure high temperature technique. The structure model of Pb 2Mn 2O 5 is proposed based on electron diffraction, high angle annular dark field scanning transmission electron microscopy and high resolution transmission electron microscopy. The compound crystallizes in an orthorhombic unit cell with parameters a=5.736(1) Å≈√2 ap, b=3.800(1) Å≈ ap, c=21.562(6) Å≈4√2 ap ( ap—the parameter of the perovskite subcell) and space group Pnma. The Pb 2Mn 2O 5 structure consists of quasi two-dimensional perovskite blocks separated by 1/2[110] p(1¯01) p crystallographic shear planes. The blocks are connected to each other by chains of edge-sharing MnO 5 distorted tetragonal pyramids. The chains of MnO 5 pyramids and the MnO 6 octahedra of the perovskite blocks delimit six-sided tunnels accommodating double chains of Pb atoms. The tunnels and pyramidal chains adopt two mirror-related configurations ("left" L and "right" R) and layers consisting of chains and tunnels of the same configuration alternate in the structure according to an -L-R-L-R-sequence. The sequence is sometimes locally violated by the appearance of -L-L- or -R-R-fragments. A scheme is proposed with a Jahn-Teller distortion of the MnO 6 octahedra with two long and two short bonds lying in the a- c plane, along two perpendicular orientations within this plane, forming a d-type pattern.

  13. Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C 7H 6N 2O 6)(H 2O) 3·2H 2O

    Science.gov (United States)

    Yamamoto, S.

    2000-11-01

    In response to recent nuclear magnetic resonance measurements on a ferrimagnetic chain compound NiCu(C 7H 6N 2O 6)(H 2O) 3·2H 2O [Solid State Commun. 113 (2000) 433], we calculate the nuclear spin-lattice relaxation rate 1/ T1 in terms of a modified spin-wave theory. Emphasizing that the dominant relaxation mechanism arises from the direct (single-magnon) process rather than the Raman (two-magnon) one, we explain the observed temperature and applied-field dependences of 1/ T1. Ferrimagnetic relaxation phenomena are generally discussed and novel ferrimagnets with extremely slow dynamics are predicted.

  14. Metallic transport and large anomalous Hall effect at room temperature in ferrimagnetic Mn{sub 4}N epitaxial thin film

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Xi; Shigematsu, Kei [Department of Chemistry, The University of Tokyo, Tokyo 113-0033 (Japan); Chikamatsu, Akira, E-mail: chikamatsu@chem.s.u-tokyo.ac.jp; Fukumura, Tomoteru [Department of Chemistry, The University of Tokyo, Tokyo 113-0033 (Japan); CREST, Japan Science and Technology Agency (JST), Tokyo 113-0033 (Japan); Hirose, Yasushi; 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)

    2014-08-18

    We report the electrical transport properties of ferrimagnetic Mn{sub 4}N (001) epitaxial thin films grown by pulsed laser deposition on MgO (001) substrates. The Mn{sub 4}N thin films were tetragonally distorted with a ratio of out-of-plane to in-plane lattice constants of 0.987 and showed perpendicular magnetic anisotropy with an effective magnetic anisotropy constant of 0.16 MJ/m{sup 3}, which is comparable with that of a recently reported molecular-beam-epitaxy-grown film. The thin films exhibited metallic transport with a room temperature resistivity of 125 μΩ cm in addition to a large anomalous Hall effect with a Hall angle tangent of 0.023.

  15. Magnetoelectric and transport properties of (GaMn)Sb thin films: A ferrimagnetic phase in dilute alloys

    Science.gov (United States)

    Calderón, Jorge A.; Mesa, F.; Dussan, A.

    2017-02-01

    We studied the electrical, magnetic, and transport properties of (GaMn)Sb thin films fabricated by the direct current magnetron co-sputtering method. Using X-ray powder diffraction measurements, we identified the presence of ferrimagnetic (Mn2Sb) and ferromagnetic (Mn2Sb2) phases within the films. We also measured the magnetization of the films versus an applied magnetic field as well as their hysteresis curves at room temperature. We determined the electrical and transport properties of the films through temperature-dependent resistivity measurements using the Van Der Pauw method. The main contribution to the transport process was variable range hopping. Hopping parameters were calculated using percolation theory and refined using the diffusional model. In addition, we determined that all samples had p type semiconductor behavior, that there was an increase in the density of localized states near the Fermi level, and that the binary magnetic phases influenced the electrical properties and transport mechanisms.

  16. Laser-induced precession of magnetization in ferrimagnetic GdFe thin films with low power excitation

    Directory of Open Access Journals (Sweden)

    K. Nishibayashi

    2013-03-01

    Full Text Available We have investigated thermal effects on the dynamics of laser-induced precession of magnetization in ferrimagnetic GdFe thin films under low-excitation conditions (6-60 μJ/cm2. An increase in quasi-equilibrium temperature by laser heating causes a shift in precession frequency, which is explained analytically by the alteration of the magnetic anisotropy field by 2.2 [Oe] at a pulse fluence of 1 μJ/cm2. We have also demonstrated coherent control of the precession amplitude using a sequence of two laser pulses, each with a fluence of 18 μJ/cm2, and point out the importance of low-power excitation for precise control of the dynamic states.

  17. Phase diagrams and magnetic properties of ferrimagnetic mixed spin-1/2 and spin-3/2 Ising nanowire

    Science.gov (United States)

    Boughazi, B.; Boughrara, M.; Kerouad, M.

    2017-01-01

    A hexagonal nanowire consisting of a ferromagnetic spin-1/2 core and spin-3/2 outer shell coupled with ferrimagnetic interlayer coupling has been studied by the use of the Monte Carlo simulation based on the heat bath algorithm. Particular emphasis is given to the effects of the size, the crystal field, the shell and the interface coupling constants on the critical and the compensation phenomenon. Some interesting behaviors have been observed which include the first and second order phase transitions. The isolated critical points are also observed. We have also found that the system exhibits the compensation phenomenon for appropriate values of the system parameters. The critical exponent has also been calculated.

  18. First-principles study on the ferrimagnetic half-metallic Mn{sub 2}FeAs alloy

    Energy Technology Data Exchange (ETDEWEB)

    Qi, Santao [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Zhang, Chuan-Hui, E-mail: zhangch@ustb.edu.cn [National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083 (China); Chen, Bao; Shen, Jiang [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Chen, Nanxian [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Department of Physics, Tsinghua University, Beijing 100084 (China)

    2015-05-15

    Mn-based full-Heusler alloys are kinds of promising candidates for new half-metallic materials. Basing on first principles, the electronic structures and magnetic properties of the Mn{sub 2}FeAs full-Heusler alloy have been investigated in detail. The Hg{sub 2}CuTi-type Mn{sub 2}FeAs compound obeys the Slater-Pauling rule, while the anti-parallel alignment atomic magnetic moments of Mn locating at different sites indicate it a ferrimagnetic alloy. The calculated spin-down bands behave half-metallic character, exhibiting a direct gap of 0.46 eV with a 100% spin polarization at the Fermi level. More studies show the compound would maintain half-metallic nature in a large range of variational lattice constants. We expect that our calculated results may trigger Mn{sub 2}FeAs applying in the future spintronics field. - Graphical abstract: The d orbitals of Mn and Fe atoms split into multi-degenerated levels which create new bonding and nonbonding states. These exchange splitting shift the Fermi level to origin band gap.▪ - Highlights: • The electronic structure and magnetic properties of Mn{sub 2}FeAs full-Heusler alloy were studied. • A total magnetic moment of 3μ{sub B} was obtained for Mn{sub 2}FeAs alloy, following the SP rule M{sub t}=Z{sub t}−24. • The origin of ferrimagnetism and half-metallic character in Mn{sub 2}FeAs were discussed.

  19. The influence of crystallised Fe3O4 on the magnetic properties of coprecipitation-derived ferrimagnetic glass-ceramics.

    Science.gov (United States)

    Bretcanu, O; Spriano, S; Verné, E; Cöisson, M; Tiberto, P; Allia, P

    2005-07-01

    Ferrimagnetic glass-ceramics are potential candidates for magnetic induction hyperthermia, which is one form of inducing deep-regional hyperthermia, by using a magnetic field. The aim of this work was to analyse the influence of the amount of crystallised magnetite on the magnetic properties of glass-ceramic samples. Thus, two different ferrimagnetic glass-ceramics with the composition of the system Na(2)O-CaO-SiO(2)-P(2)O(5)-FeO-Fe(2)O(3) were prepared by melting at 1500 degrees C for 30 min of the coprecipitation-derived starting products. The X-ray diffraction patterns show the presence of nanometric magnetite crystals in a glassy matrix after cooling from melting temperature. The estimated amount of crystallised magnetite varies between 20 and 45 wt.%, as a function of the chemical composition. The morphology of the crystals was studied by scanning electron micrography and transmission electron micrography. Glass transition temperature and thermal stability were investigated by differential thermal analysis. Magnetic hysteresis cycles were analysed using a vibrating sample magnetometer with a maximum applied field of 17 kOe, at room temperature, in quasi-static conditions. Calorimetric measurements were carried out using a magnetic induction furnace. The power losses estimated from calorimetric measurements under a magnetic field of 40 kA/m and 440 kHz are 65 W/g for the glass-ceramic with lower iron oxides content and 25 W/g for the glass-ceramic with higher iron oxide content.

  20. Recent progress in stability of perovskite solar cells

    Science.gov (United States)

    Qin, Xiaojun; Zhao, Zhiguo; Wang, Yidan; Wu, Junbo; Jiang, Qi; You, Jingbi

    2017-01-01

    Perovskite solar cells have attracted significant attention in just the past few years in solar cell research fields, where the power conversion efficiency was beyond 22.1%. Now, the most important challenge for perovskite solar cells in practical applications is the stability issue. In this mini-review, we will summarize the degradation mechanism of perovskite solar cells, including the perovskite material itself and also the interfaces. While we also provide our opinion on improving the stability of perovskite solar cells. Project supported by China Huaneng Group Project High Performance Perovskite Solar Cells (No. TW-15-HJK01), the National Key Research and Development Program of China (No. 2016YFB0700700), the National 1000 Young Talent Awards, and the National Natural Science Foundation of China (No. 61574133).

  1. Neutral- and Multi-Colored Semitransparent Perovskite Solar Cells

    Directory of Open Access Journals (Sweden)

    Kyu-Tae Lee

    2016-04-01

    Full Text Available In this review, we summarize recent works on perovskite solar cells with neutral- and multi-colored semitransparency for building-integrated photovoltaics and tandem solar cells. The perovskite solar cells exploiting microstructured arrays of perovskite “islands” and transparent electrodes—the latter of which include thin metallic films, metal nanowires, carbon nanotubes, graphenes, and transparent conductive oxides for achieving optical transparency—are investigated. Moreover, the perovskite solar cells with distinctive color generation, which are enabled by engineering the band gap of the perovskite light-harvesting semiconductors with chemical management and integrating with photonic nanostructures, including microcavity, are discussed. We conclude by providing future research directions toward further performance improvements of the semitransparent perovskite solar cells.

  2. Neutral- and Multi-Colored Semitransparent Perovskite Solar Cells.

    Science.gov (United States)

    Lee, Kyu-Tae; Guo, L Jay; Park, Hui Joon

    2016-04-11

    In this review, we summarize recent works on perovskite solar cells with neutral- and multi-colored semitransparency for building-integrated photovoltaics and tandem solar cells. The perovskite solar cells exploiting microstructured arrays of perovskite "islands" and transparent electrodes-the latter of which include thin metallic films, metal nanowires, carbon nanotubes, graphenes, and transparent conductive oxides for achieving optical transparency-are investigated. Moreover, the perovskite solar cells with distinctive color generation, which are enabled by engineering the band gap of the perovskite light-harvesting semiconductors with chemical management and integrating with photonic nanostructures, including microcavity, are discussed. We conclude by providing future research directions toward further performance improvements of the semitransparent perovskite solar cells.

  3. Applications of cesium in the perovskite solar cells

    Science.gov (United States)

    Ye, Fengjun; Yang, Wenqiang; Luo, Deying; Zhu, Rui; Gong, Qihuang

    2017-01-01

    Perovskite solar cells have experienced an unprecedented rapid development in the power conversion efficiency (PCE) during the past 7 years, and the record PCE has been already comparable to the traditional polycrystalline silicon solar cells. Presently, it is more urgent to address the challenge on device stability for the future commercial application. Recently, the inorganic cesium lead halide perovskite has been intensively studied as one of the alternative candidates to improve device stability through controlling the phase transition. The cesium (Cs)-doped perovskites show more superior stability comparing with organic methylammonium (MA) lead halide perovskite or formamidinium (FA) lead halide perovskite. Here, recent progress of the inorganic cesium application in organic–inorganic perovskite solar cells (PSCs) is highlighted from the viewpoints of the device efficiency and the device stability. Project supported by the 973 Program of China (No. 2015CB932203), the National Natural Science Foundation of China (Nos. 61377025, 91433203), and the Young 1000 Talents Global Recruitment Program of China.

  4. Hybrid perovskites: Approaches towards light-emitting devices

    KAUST Repository

    Alias, Mohd Sharizal

    2016-10-06

    The high optical gain and absorption of organic-inorganic hybrid perovskites have attracted extensive research for photonic device applications. Using the bromide halide as an example, we present key approaches of our work towards realizing efficient perovskites based light-emitters. The approaches involved determination of optical constants for the hybrid perovskites thin films, fabrication of photonic nanostructures in the form of subwavelength grating reflector patterned directly on the hybrid perovskites as light manipulation layer, and enhancing the emission property of the hybrid perovskites by using microcavity structure. Our results provide a platform for realization of hybrid perovskites based light-emitting devices for solid-state lighting and display applications. © 2016 IEEE.

  5. LSFM perovskites as cathodes for the electrochemical reduction of NO

    DEFF Research Database (Denmark)

    Kammer Hansen, K.; Skou, E.M.

    2005-01-01

    Six La0.6Sr0.4Fe1-xMnO3-delta (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) perovskite compounds have been synthesised by the citric-acid route. The perovskites have been characterised by powder XRD and are shown to belong to the hexagonal crystal system. The perovskites are also evaluated by TG-measurements ...

  6. A Physics-based Analytical Model for Perovskite Solar Cells

    OpenAIRE

    Sun, Xingshu; Asadpour, Reza; Nie, Wanyi; Mohite, Aditya D.; Alam, Muhammad A.

    2015-01-01

    Perovskites are promising next-generation absorber materials for low-cost and high-efficiency solar cells. Although perovskite cells are configured similar to the classical solar cells, their operation is unique and requires development of a new physical model for characterization, optimization of the cells, and prediction of the panel performance. In this paper, we develop such a physics-based analytical model to describe the operation of different types of perovskite solar cells, explicitly...

  7. 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.

  8. Double Trouble

    NARCIS (Netherlands)

    Elsaesser, Thomas; Kievit, Robert; Simons, Jan

    1994-01-01

    Double Trouble highlights the career of Dutch scriptwriter and television producer Chiem van Houweninge, well-known for his long-running TV comedy series and as author of episodes for TV detective series. Double Trouble gives Van Houweninge's own views on writing and filming in television prime impo

  9. Double Trouble

    NARCIS (Netherlands)

    Elsaesser, Thomas; Kievit, Robert; Simons, Jan

    1994-01-01

    Double Trouble highlights the career of Dutch scriptwriter and television producer Chiem van Houweninge, well-known for his long-running TV comedy series and as author of episodes for TV detective series. Double Trouble gives Van Houweninge's own views on writing and filming in television prime

  10. Perovskite solar cells: Shedding light on film crystallization

    Science.gov (United States)

    Bakr, Osman M.; Mohammed, Omar F.

    2017-06-01

    A study on the formation of methylammonium lead iodide perovskite films reveals that light illumination influences the crystallization kinetics, therefore affecting the final photovoltaic performance of these materials.

  11. 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.

  12. 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.

  13. 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.

  14. Elastic anisotropy of experimental analogues of perovskite and post-perovskite help to interpret D'' diversity.

    Science.gov (United States)

    Yoneda, Akira; Fukui, Hiroshi; Xu, Fang; Nakatsuka, Akihiko; Yoshiasa, Akira; Seto, Yusuke; Ono, Kenya; Tsutsui, Satoshi; Uchiyama, Hiroshi; Baron, Alfred Q R

    2014-03-27

    Recent studies show that the D'' layer, just above the Earth's core-mantle boundary, is composed of MgSiO3 post-perovskite and has significant lateral inhomogeneity. Here we consider the D'' diversity as related to the single-crystal elasticity of the post-perovskite phase. We measure the single-crystal elasticity of the perovskite Pbnm-CaIrO3 and post-perovskite Cmcm-CaIrO3 using inelastic X-ray scattering. These materials are structural analogues to same phases of MgSiO3. Our results show that Cmcm-CaIrO3 is much more elastically anisotropic than Pbnm-CaIrO3, which offers an explanation for the enigmatic seismic wave velocity jump at the D'' discontinuity. Considering the relation between lattice preferred orientation and seismic anisotropy in the D'' layer, we suggest that the c axis of post-perovskite MgSiO3 aligns vertically beneath the Circum-Pacific rim, and the b axis vertically beneath the Central Pacific.

  15. Organohalide Perovskites for Solar Energy Conversion.

    Science.gov (United States)

    Lin, Qianqian; Armin, Ardalan; Burn, Paul L; Meredith, Paul

    2016-03-15

    Lead-based organohalide perovskites have recently emerged as arguably the most promising of all next generation thin film solar cell technologies. Power conversion efficiencies have reached 20% in less than 5 years, and their application to other optoelectronic device platforms such as photodetectors and light emitting diodes is being increasingly reported. Organohalide perovskites can be solution processed or evaporated at low temperatures to form simple thin film photojunctions, thus delivering the potential for the holy grail of high efficiency, low embedded energy, and low cost photovoltaics. The initial device-driven "perovskite fever" has more recently given way to efforts to better understand how these materials work in solar cells, and deeper elucidation of their structure-property relationships. In this Account, we focus on this element of organohalide perovskite chemistry and physics in particular examining critical electro-optical, morphological, and architectural phenomena. We first examine basic crystal and chemical structure, and how this impacts important solar-cell related properties such as the optical gap. We then turn to deeper electronic phenomena such as carrier mobilities, trap densities, and recombination dynamics, as well as examining ionic and dielectric properties and how these two types of physics impact each other. The issue of whether organohalide perovskites are predominantly nonexcitonic at room temperature is currently a matter of some debate, and we summarize the evidence for what appears to be the emerging field consensus: an exciton binding energy of order 10 meV. Having discussed the important basic chemistry and physics we turn to more device-related considerations including processing, morphology, architecture, thin film electro-optics and interfacial energetics. These phenomena directly impact solar cell performance parameters such as open circuit voltage, short circuit current density, internal and external quantum efficiency

  16. Cobalt based layered perovskites as cathode material for intermediate temperature Solid Oxide Fuel Cells: A brief review

    Science.gov (United States)

    Pelosato, Renato; Cordaro, Giulio; Stucchi, Davide; Cristiani, Cinzia; Dotelli, Giovanni

    2015-12-01

    Nowadays, the cathode is the most studied component in Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFCs). Decreasing SOFCs operating temperature implies slow oxygen reduction kinetics and large polarization losses. Double perovskites with general formula REBaCo2O5+δ are promising mixed ionic-electronic conductors, offering a remarkable enhancement of the oxygen diffusivity and surface exchange respect to disordered perovskites. In this review, more than 250 compositions investigated in the literature were analyzed. The evaluation was performed in terms of electrical conductivity, Area Specific Resistance (ASR), chemical compatibility with electrolytes and Thermal Expansion Coefficient (TEC). The most promising materials have been identified as those bearing the mid-sized rare earths (Pr, Nd, Sm, Gd). Doping strategies have been analyzed: Sr doping on A site promotes higher electrical conductivity, but worsen ASR and TECs; B-site doping (Fe, Ni, Mn) helps lowering TECs, but is detrimental for the electrochemical properties. A promising boost of the electrochemical activity is obtained by simply introducing a slight Ba under-stoichiometry. Still, the high sensitivity of the electrochemical properties against slight changes in the stoichiometry hamper a conclusive comparison of all the investigated compounds. Opportunities for an improvement of double perovskite cathodes performance is tentatively foreseen in combining together the diverse effective doping strategies.

  17. 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.

  18. P-V-T Equation of State of (Al,Fe)-bearing Mantle Perovskite and its Implications for Mantle Models

    Science.gov (United States)

    Fei, Y.; Ricolleau, A.; Litasov, K.; Prakapenka, V.

    2008-12-01

    We have made significant progress on accurate measurements of P-V-T equations-of-state of mantle minerals that are of fundamental importance for developing compositional and mineralogical models of the Earth's mantle. In this study, we report new compression data on (Al,Fe)-bearing mantle perovskite up to simultaneous pressure and temperature of 113 GPa and 2120 K. The mantle perovskite was synthesized in the multi-anvil apparatus at 27 GPa and 2073 K, with chemical compositions expected in a peridotitic mantle. It contains 5.86 wt% FeO and 3.84 wt% Al2O3. The pre-synthesized perovsite mixed with Au powder was compressed in neon pressure medium in a symmetric diamond anvil cell. The sample was heated with a double-sided laser-heating system at the GSECARS 13-ID-D beamline (Advanced Photon Source). We performed 8 heating cycles in the pressure range of 30-113 GPa and temperatures up to 2560 K. In-situ synchrotron X-ray diffraction data were collected within a uniformly heated area, using a MAR-CCD area detector. The diffraction pattern contains peaks of orthorhombic perovskite, internal standard Au, and pressure medium Ne. The triplet (020, 112, and 200 diffraction peaks) of the orthorhombic perovskite is well resolve. The present dataset covers the entire P-T range of the lower mantle and requires no extrapolation to compare the mantle density profile derived from seismic observations. In light of the new P-V-T data on the (Al,Fe)-bearing mantle perovskite combined with our recent density data and spin transition of ferropericlase, we finally discuss the compositional and mineralogical models of the lower mantle.

  19. Characterization of Ordering in A-Site Deficient Perovskite Ca1-xLa2x/3TiO3 Using STEM/EELS.

    Science.gov (United States)

    Danaie, Mohsen; Kepaptsoglou, Demie; Ramasse, Quentin M; Ophus, Colin; Whittle, Karl R; Lawson, Sebastian M; Pedrazzini, Stella; Young, Neil P; Bagot, Paul A J; Edmondson, Philip D

    2016-10-03

    The vacancy ordering behavior of an A-site deficient perovskite system, Ca1-xLa2x/3TiO3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown to be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La(3+) ions was observed, with alternating La-rich and La-poor layers on (001)p planes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La(3+), or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. The occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.

  20. Metal halide perovskite nanomaterials: synthesis and applications.

    Science.gov (United States)

    Ha, Son-Tung; Su, Rui; Xing, Jun; Zhang, Qing; Xiong, Qihua

    2017-04-01

    Nanomaterials refer to those with at least one dimension being at the nanoscale (i.e. applications. The different synthesis approaches and growth mechanisms will be discussed along with their novel characteristics and applications. Taking perovskite quantum dots as an example, the quantum confinement effect and high external quantum efficiency are among these novel properties and their excellent performance in applications, such as single photon emitters and LEDs, will be discussed. Understanding the mechanism behind the formation of these nanomaterial forms of perovskite will help researchers to come up with effective strategies to combat the emerging challenges of this family of materials, such as stability under ambient conditions and toxicity, towards next generation applications in photovoltaics and optoelectronics.

  1. Perovskite Materials: Solar Cell and Optoelectronic Applications

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Bin [ORNL; Geohegan, David B [ORNL; Xiao, Kai [ORNL

    2017-01-01

    Hybrid organometallic trihalide perovskites are promising candidates in the applications for next-generation, high-performance, low-cost optoelectronic devices, including photovoltaics, light emitting diodes, and photodetectors. Particularly, the solar cells based on this type of materials have reached 22% lab scale power conversion efficiency in only about seven years, comparable to the other thin film photovoltaic technologies. Hybrid perovskite materials not only exhibit superior optoelectronic properties, but also show many interesting physical properties such as ion migration and defect physics, which may allow the exploration of more device functionalities. In this article, the fundamental understanding of the interrelationships between crystal structure, electronic structure, and material properties is discussed. Various chemical synthesis and processing methods for superior device performance in solar cells and optoelectronic devices are reviewed.

  2. Ferroelectric perovskite nanopowders obtained by mechanochemical synthesis

    Directory of Open Access Journals (Sweden)

    Izabela Szafraniak-Wiza

    2010-09-01

    Full Text Available Simple perovskite nanopowders were fabricated by mechanochemical synthesis. High-energy milling process of respective oxides, leading to production of ferroelectric perovskites, was carefully investigated and characterized by X-ray diffraction, electron microscopy and X-ray excited photoelectron spectroscopy. It has been found that: (i the powder consists of loosely packed grains with a broad distribution of sizes between a few nm and 45 nm, (ii the grains possess core/shell structure, (iii the grain core of sizes larger than about 20 nm exhibits well developed crystalline structure, (iv the grains are coated by structurally disordered (amorphous shell. Intermediate phases have been found in the process of PbTiO3 mechanosynthesis only. The obtained nanopowders were used for preparation of dense ceramics.

  3. Synthesis of a polar ordered oxynitride perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Vadapoo, Rajasekarakumar; Ahart, Muhtar; Somayazulu, Maddury; Holtgrewe, Nicholas; Meng, Yue; Konopkova, Zuzana; Hemley, Russell J.; Cohen, R. E.

    2017-06-01

    For decades, numerous attempts have been made to produce polar oxynitride perovskites, where some of the oxygen is replaced by nitrogen, but a polar ordered oxynitride has never been demonstrated. Caracas and Cohen [Appl. Phys. Lett. 91, 092902 (2007)] studied possible ordered polar oxynitrides within density-functional theory (DFT) and found a few candidates that were predicted to be insulating and at least metastable. YSi O 2 N stood out with huge predicted polarization and nonlinear optic coefficients. In this study, we demonstrate the synthesis of perovskite-structured YSi O 2 N by using a combination of a diamond-anvil cell and in situ laser-heating techniques. Subsequent in situ x-ray diffraction, second-harmonic generation, and Raman-scattering measurements confirm that it is polar and a strong nonlinear optical material, with structure and properties similar to those predicted by DFT.

  4. Left-handed properties of manganite-perovskites La1-xSrxMnO3 at various dopant concentrations

    Directory of Open Access Journals (Sweden)

    D. P. Belozorov

    2014-03-01

    Full Text Available The experimental study of Double Negative (DNG state of electromagnetic wave propagating in lanthanum manganite-perovskites doped with strontium La1-xSrxMnO3 is provided firstly below individual Curie temperatures (in ferromagnetic metal state (FM for La1-xSrxMnO3. Various dopant concentrations are considered for ceramic specimens: x = 0.15;  0.225;  0.3;  0.45;  0.6. It is shown that dependence of the DNG-peak intensity on dopant concentration is sharply non-monotone with maximum at the dopant concentrations x = 0.225 – 0.3. This behaviour follows the change of Curie temperature with increase of dopant concentration in such substances. The obtained dependence of DNG peak intensity supports the opinion concerning the role of disorder in highly doped manganite-perovskite magnetic ceramics under study.

  5. ZrO2/TiO2 Electron Collection Layer for Efficient Meso-Superstructured Hybrid Perovskite Solar Cells.

    Science.gov (United States)

    Mejía Escobar, Mario Alejandro; Pathak, Sandeep; Liu, Jiewei; Snaith, Henry J; Jaramillo, Franklin

    2017-01-25

    Since the first reports of efficient organic-inorganic perovskite solar cells in 2012, an explosion of research activity has emerged around the world, which has led to a rise in the power conversion efficiencies (PCEs) to over 20%. Despite the impressive efficiency, a key area of the device which remains suboptimal is the electron extraction layer and its interface with the photoactive perovskite. Here, we implement an electron collection "bilayer" composed of a thin layer of zirconia coated with titania, sitting upon the transparent conductive oxide fluorine-doped tin oxide (FTO). With this double collection layer we have reached up to 17.9% power conversion efficiency, delivering a stabilized power output (SPO) of 17.0%, measured under simulated AM 1.5 sunlight of 100 mW cm(-2) irradiance. Finally, we propose a mechanism of the charge transfer processes within the fabricated architectures in order to explain the obtained performance of the devices.

  6. 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...

  7. High performance magnetocaloric perovskites for magnetic refrigeration

    OpenAIRE

    Velázquez, David

    2012-01-01

    We have applied mixed valance manganite perovskites as magnetocaloric materials in a magnetic refrigeration device. Relying on exact control of the composition and a technique to process the materials into single adjoined pieces, we have observed temperature spans above 9 K with two materials. Reasonable correspondence is found between experiments and a 2D numerical model, using the measured magnetocaloric properties of the two materials as input. © 2012 American Institute of Physics.

  8. The photophysics of perovskite solar cells

    Science.gov (United States)

    Sum, Tze Chien

    2014-09-01

    Solution-processed hybrid organic-inorganic perovskite solar cells, a newcomer to the photovoltaic arena, have taken the field by storm with their extraordinary power conversion efficiencies exceeding 17%. In this paper, the photophysics and the latest findings on the carrier dynamics and charge transfer mechanisms in this new class of photovoltaic material will be examined and distilled. Some open photophysics questions will also be discussed.

  9. Bond disproportionation and dynamical charge fluctuations in the perovskite rare-earth nickelates

    Science.gov (United States)

    Green, R. J.; Haverkort, M. W.; Sawatzky, G. A.

    2016-11-01

    We present a theory describing the local electronic properties of the perovskite rare-earth nickelates—materials which have negative charge transfer energies, strong O 2 p - Ni 3 d covalence, and breathing-mode lattice distortions at the origin of highly studied metal-insulator and antiferromagnetic ordering transitions. Utilizing a full-orbital, full-correlation double-cluster approach, we find strong charge fluctuations, in agreement with a bond disproportionation interpretation. The double-cluster formulation permits the inclusion of necessary orbital degeneracies and Coulomb interactions to calculate resonant x-ray spectral responses, with which we find excellent agreement with well-established experimental results. This previously absent, crucial link between theory and experiment provides validation of the recently proposed bond disproportionation theory, and provides an analysis methodology for spectroscopic studies of engineered phases of nickelates and other high-valence transition-metal compounds.

  10. Resistance switching memory in perovskite oxides

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Z.B., E-mail: zbyan@nju.edu.cn; Liu, J.-M., E-mail: liujm@nju.edu.cn

    2015-07-15

    The resistance switching behavior has recently attracted great attentions for its application as resistive random access memories (RRAMs) due to a variety of advantages such as simple structure, high-density, high-speed and low-power. As a leading storage media, the transition metal perovskite oxide owns the strong correlation of electrons and the stable crystal structure, which brings out multifunctionality such as ferroelectric, multiferroic, superconductor, and colossal magnetoresistance/electroresistance effect, etc. The existence of rich electronic phases, metal–insulator transition and the nonstoichiometric oxygen in perovskite oxide provides good platforms to insight into the resistive switching mechanisms. In this review, we first introduce the general characteristics of the resistance switching effects, the operation methods and the storage media. Then, the experimental evidences of conductive filaments, the transport and switching mechanisms, and the memory performances and enhancing methods of perovskite oxide based filamentary RRAM cells have been summarized and discussed. Subsequently, the switching mechanisms and the performances of the uniform RRAM cells associating with the carrier trapping/detrapping and the ferroelectric polarization switching have been discussed. Finally, the advices and outlook for further investigating the resistance switching and enhancing the memory performances are given.

  11. Light-trapping in perovskite solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Du, Qing Guo, E-mail: duqi0001@e.ntu.edu.sg [Department of Physics, University of Toronto, 60 ST. George St., Toronto, Ontario, M5S 1A7 (Canada); Institute of High Performance Computing, A* STAR, Singapore, 138632 (Singapore); Shen, Guansheng [Department of Physics, University of Toronto, 60 ST. George St., Toronto, Ontario, M5S 1A7 (Canada); School of Information and Communication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); John, Sajeev [Department of Physics, University of Toronto, 60 ST. George St., Toronto, Ontario, M5S 1A7 (Canada); Department of Physics, Soochow University, Suzhou (China)

    2016-06-15

    We numerically demonstrate enhanced light harvesting efficiency in both CH{sub 3}NH{sub 3}PbI{sub 3} and CH(NH{sub 2}){sub 2}PbI{sub 3}-based perovskite solar cells using inverted vertical-cone photonic-crystal nanostructures. For CH{sub 3}NH{sub 3}PbI{sub 3} perovskite solar cells, the maximum achievable photocurrent density (MAPD) reaches 25.1 mA/cm{sup 2}, corresponding to 92% of the total available photocurrent in the absorption range of 300 nm to 800 nm. Our cell shows 6% absorption enhancement compared to the Lambertian limit (23.7 mA/cm{sup 2}) and has a projected power conversion efficiency of 12.9%. Excellent solar absorption is numerically demonstrated over a broad angular range from 0 to 60 degree for both S- and P- polarizations. For the corresponding CH(NH{sub 2}){sub 2}PbI{sub 3} based perovskite solar cell, with absorption range of 300 nm to 850 nm, we find a MAPD of 29.1 mA/cm{sup 2}, corresponding to 95.4% of the total available photocurrent. The projected power conversion efficiency of the CH(NH{sub 2}){sub 2}PbI{sub 3} based photonic crystal solar cell is 23.4%, well above the current world record efficiency of 20.1%.

  12. Light-trapping in perovskite solar cells

    Directory of Open Access Journals (Sweden)

    Qing Guo Du

    2016-06-01

    Full Text Available We numerically demonstrate enhanced light harvesting efficiency in both CH3NH3PbI3 and CH(NH22PbI3-based perovskite solar cells using inverted vertical-cone photonic-crystal nanostructures. For CH3NH3PbI3 perovskite solar cells, the maximum achievable photocurrent density (MAPD reaches 25.1 mA/cm2, corresponding to 92% of the total available photocurrent in the absorption range of 300 nm to 800 nm. Our cell shows 6% absorption enhancement compared to the Lambertian limit (23.7 mA/cm2 and has a projected power conversion efficiency of 12.9%. Excellent solar absorption is numerically demonstrated over a broad angular range from 0 to 60 degree for both S- and P- polarizations. For the corresponding CH(NH22PbI3 based perovskite solar cell, with absorption range of 300 nm to 850 nm, we find a MAPD of 29.1 mA/cm2, corresponding to 95.4% of the total available photocurrent. The projected power conversion efficiency of the CH(NH22PbI3 based photonic crystal solar cell is 23.4%, well above the current world record efficiency of 20.1%.

  13. Perovskite-related oxynitrides in photocatalysis.

    Science.gov (United States)

    Pokrant, Simone; Maegli, Alexandra E; Chiarello, Gian Luca; Weidenkaff, Anke

    2013-01-01

    Over the last decades photocatalytic water splitting has become of increasing importance for fundamental and applied research, since the direct conversion of sunlight into chemical energy via the production of H2 has the potential to contribute to the world's energy needs without CO2 generation. One of the unsolved challenges consists of finding a highly efficient photocatalyst that is cheap, environmentally friendly, contains exclusively abundant elements, is (photo)chemically stable and absorbs visible light. Photocatalytic efficiency is closely connected to both structural properties like crystallinity, particle size and surface area and to electronic properties like the band gap and the quantum efficiency. Hence extensive control over a large parameter field is necessary to design a good photocatalyst. A material class where the structure-composition-property relations and the influence of substitution effects are well studied is the perovskite-type family of compounds. The perovskite-related oxynitrides belong to this very flexible compound family where many of the necessary characteristics for a photocatalyst are already given and some of the intrinsic properties like the band gap can be tuned within the same crystal structure by substitution. In this work we present materials' design concepts to improve the photocatalytic efficiency of a perovskite-type catalyst and describe their effects on the photocatalytic activity.

  14. Surface Restructuring of Hybrid Perovskite Crystals

    KAUST Repository

    Banavoth, Murali

    2016-11-07

    Hybrid perovskite crystals have emerged as an important class of semiconductors because of their remarkable performance in optoelectronics devices. The interface structure and chemistry of these crystals are key determinants of the device\\'s performance. Unfortunately, little is known about the intrinsic properties of the surfaces of perovskite materials because extrinsic effects, such as complex microstructures, processing conditions, and hydration under ambient conditions, are thought to cause resistive losses and high leakage current in solar cells. We reveal the intrinsic structural and optoelectronic properties of both pristinely cleaved and aged surfaces of single crystals. We identify surface restructuring on the aged surfaces (visualized on the atomic-scale by scanning tunneling microscopy) that lead to compositional and optical bandgap changes as well as degradation of carrier dynamics, photocurrent, and solar cell device performance. The insights reported herein clarify the key variables involved in the performance of perovskite-based solar cells and fabrication of high-quality surface single crystals, thus paving the way toward their future exploitation in highly efficient solar cells.

  15. Intriguing Optoelectronic Properties of Metal Halide Perovskites.

    Science.gov (United States)

    Manser, Joseph S; Christians, Jeffrey A; Kamat, Prashant V

    2016-11-09

    A new chapter in the long and distinguished history of perovskites is being written with the breakthrough success of metal halide perovskites (MHPs) as solution-processed photovoltaic (PV) absorbers. The current surge in MHP research has largely arisen out of their rapid progress in PV devices; however, these materials are potentially suitable for a diverse array of optoelectronic applications. Like oxide perovskites, MHPs have ABX3 stoichiometry, where A and B are cations and X is a halide anion. Here, the underlying physical and photophysical properties of inorganic (A = inorganic) and hybrid organic-inorganic (A = organic) MHPs are reviewed with an eye toward their potential application in emerging optoelectronic technologies. Significant attention is given to the prototypical compound methylammonium lead iodide (CH3NH3PbI3) due to the preponderance of experimental and theoretical studies surrounding this material. We also discuss other salient MHP systems, including 2-dimensional compounds, where relevant. More specifically, this review is a critical account of the interrelation between MHP electronic structure, absorption, emission, carrier dynamics and transport, and other relevant photophysical processes that have propelled these materials to the forefront of modern optoelectronics research.

  16. Defect Tolerance in Methylammonium Lead Triiodide Perovskite

    Energy Technology Data Exchange (ETDEWEB)

    Steirer, K. Xerxes; Schulz, Philip; Teeter, Glenn; Stevanovic, Vladan; Yang, Mengjin; Zhu, Kai; Berry, Joseph J.

    2016-08-12

    Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH3NH3PbI3 (MAPbI3), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO2 appears tolerant to the formation of compensating defect pairs of VI and VMA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide-lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI3 electronic structure to distributed defects that can significantly transform the electronic density of states only when in high concentrations.

  17. Interparticle interactions in composites of nanoparticles of ferrimagnetic (gamma-Fe2O3) and antiferromagnetic (CoO,NiO) materials

    DEFF Research Database (Denmark)

    Frandsen, Cathrine; Ostenfeld, Christopher Worsøe; Xu, M.;

    2004-01-01

    The magnetic properties of mixtures of ferrimagnetic gamma-Fe2O3 (maghemite) and antiferromagnetic NiO or CoO nanoparticles have been studied by use of Fe-57 Mossbauer spectroscopy, neutron powder diffraction and magnetization measurements. The studies showed that the interaction with antiferroma......The magnetic properties of mixtures of ferrimagnetic gamma-Fe2O3 (maghemite) and antiferromagnetic NiO or CoO nanoparticles have been studied by use of Fe-57 Mossbauer spectroscopy, neutron powder diffraction and magnetization measurements. The studies showed that the interaction...... with antiferromagnetic particles has a significant influence on the magnetic properties of the gamma-Fe2O3 nanoparticles. It was found that mixing the gamma-Fe2O3 nanoparticles with NiO nanoparticles resulted in a faster superparamagnetic relaxation and a reduced coercivity compared to a sample consisting solely...

  18. Ferrimagnetism and abnormal spin-lattice coupling in dilute magnetic ferroelectric (Bi0.46Na0.46Ba0.08)TiO3:Co

    Institute of Scientific and Technical Information of China (English)

    Fan Jing; Dong Xin-Wei; Song You; Wang Ke-Feng; Liu Jun-Ming; Jiang Xiang-Ping

    2011-01-01

    We have investigated the low-temperature magnetism and spin-lattice coupling in (Bi0.46Na0.46Ba0.08)TiO3:Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroelectrics. It is revealed that the as-prepared (Bi0.46Na0.46Ba0.08)TiO3:Co at Co content of 20%~30% exhibits fascinating ferrimagnetism which is robust against magnetic field, the abnormal spin-lattice coupling characterized by a negative magnetostriction effect; and the suppressed magnetic moment within the temperature range of 30 K~50 K is identified. These magnetic behaviours at low temperatures can be explained by the competition between the ferrimagnetic response and the magnetic moment suppression induced by the abnormal spin-lattice coupling effect. Finally, the ferroelectric and magnetodielectric properties are also discussed.

  19. Haldane Phases and Ferrimagnetic Phases with Spontaneous Translational Symmetry Breakdown in Distorted Mixed Diamond Chains with Spins 1 and 1/2

    Science.gov (United States)

    Hida, Kazuo; Takano, Ken'ichi; Suzuki, Hidenori

    2010-11-01

    The ground states of two types of distorted mixed diamond chains with spins 1 and 1/2 are investigated using exact diagonalization, DMRG, and mapping onto low-energy effective models. In the undistorted case, the ground state consists of an array of independent spin-1 clusters separated by singlet dimers. The lattice distortion induces an effective interaction between cluster spins. When this effective interaction is antiferromagnetic, several Haldane phases appear with or without spontaneous translational symmetry breakdown (STSB). The transition between the Haldane phase without STSB and that with (n+1)-fold STSB (n=1, 2, and 3) belongs to the same universality class as the (n+1)-clock model. In contrast, when the effective interaction is ferromagnetic, the quantized and partial ferrimagnetic phases appear with or without STSB. An effective low-energy theory for the partial ferrimagnetic phase is presented.

  20. 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.