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Sample records for cubic fluorite structure

  1. Platinum nitride with fluorite structure

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Rong; Zhang, Xiao-Feng

    2005-01-31

    The mechanical stability of platinum nitride has been studied using first-principles calculations. By calculating the single-crystal elastic constants, we show that platinum nitride can be stabilized in the fluorite structure, in which the nitrogen atoms occupy all the tetrahedral interstitial sites of the metal lattice. The stability is attributed to the pseudogap effect from analysis of the electronic structure.

  2. Ion conductivity in cubically-stabilized fluorite-like structured Er5CeMoO12.5 and Yb5MMoO12.5 (M = Ce, Zr) solid solutions

    Science.gov (United States)

    Schildhammer, Daniel; Fuhrmann, Gerda; Petschnig, Lucas; Kogler, Michaela; Penner, Simon; Weinberger, Nikolaus; Schottenberger, Herwig; Huppertz, Hubert

    2016-12-01

    For the first time, the usually rhombohedral R 3 bar (no. 148) defect fluorite structured rare earth molybdenum oxides RE6MoO12 (RE = Er, Yb) could be stabilized in the cubic defect fluorite structure Fm 3 bar m (no. 225) through partial substitution of Er3+ and Yb3+ by M4+ cations with M4+ = Ce for Er6MoO12 and M4+ = Ce, Zr for Yb6MoO12. The solution combustion (SC) method and the classical solid state reaction are the synthetic approaches that were used (ambient atmosphere and temperatures of 1250 °C). The obtained oxide powders were characterized by energy dispersive X-ray (EDX) analysis, powder X-ray diffraction (PXRD), IR, and UV-Vis spectroscopy. The PXRD-data were used for Rietveld refinements. Electrochemical impedance spectroscopy (EIS) was conducted to identify oxygen vacancies in the cubic structure type, revealing oxygen ion conductivity starting at 500 °C. Additionally, the influence on ion conductivity by the cation substitutions are discussed. Calculation of the contributing activation energies for the bulk (best value for Yb5CeMoO12.5 is 119.8 kJmol-1), and the grain boundary (e.g. Er5CeMoO12.5: 152.1 kJmol-1) analyzed by means of the Arrhenius plot, shows similarities to the conventional stabilization of zirconia with yttrium (8-YSZ) (110 kJ mol-1 and 110-163 kJmol-1 respectively). The best-calculated conductivity values σ = 1.03 × 10-4 Scm-1 obtained for Er5CeMoO12.5 at 1000 °C are comparable to the values published for 8-YSZ with σ = 3.94 × 10-5 Scm-1 at similar temperatures. These promising preliminary results underline the potential of the title compounds for application in solid oxide fuel cells (SOFCs).

  3. Configurational Model for Conductivity of Stabilized Fluorite Structure Oxides

    DEFF Research Database (Denmark)

    Poulsen, Finn Willy

    1981-01-01

    The formalism developed here furnishes means by which ionic configurations, solid solution limits, and conductivity mechanisms in doped fluorite structures can be described. The present model differs markedly from previous models but reproduces qualitatively reality. The analysis reported...

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

    DEFF Research Database (Denmark)

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

    2015-01-01

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

  5. Giant Mechanocaloric Effects in Fluorite-Structured Superionic Materials

    Science.gov (United States)

    Cazorla, Claudio; Errandonea, Daniel

    2016-05-01

    Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterised by a large entropy increase of the order of 100 J/K*Kg, can be externally tuned with hydrostatic, biaxial or uniaxial stresses. In particular, Ts can be reduced several hundreds of degrees through the application of moderate tensile stresses due to the concomitant drop in the formation energy of Frenkel pair defects. We predict that the adiabatic temperature change in CaF2 and PbF2, two archetypal fluorite-structured FIC, close to their critical points are of the order of 100 and 10 K, respectively. This work advocates that FIC constitute a new family of mechanocaloric materials showing great promise for prospective solid-state refrigeration applications.

  6. New cubic structure compounds as actinide host phases

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-03-15

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

  7. Surface modelling on heavy atom crystalline compounds: HfO{sub 2} and UO{sub 2} fluorite structures

    Energy Technology Data Exchange (ETDEWEB)

    Evarestov, Robert [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)], E-mail: re1973@re1973.spb.edu; Bandura, Andrei; Blokhin, Eugeny [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)

    2009-01-15

    The study of the bulk and surface properties of cubic (fluorite structure) HfO{sub 2} and UO{sub 2} was performed using the hybrid Hartree-Fock density functional theory linear combination of atomic orbitals simulations via the CRYSTAL06 computer code. The Stuttgart small-core pseudopotentials and corresponding basis sets were used for the core-valence interactions. The influence of relativistic effects on the structure and properties of the systems was studied. It was found that surface properties of Mott-Hubbard dielectric UO{sub 2} differ from those found for other metal oxides with the closed-shell configuration of d-electrons.

  8. Importance of surface structure on dissolution of fluorite

    DEFF Research Database (Denmark)

    Godinho, Jose; Piazolo, Sandra; Balic Zunic, Tonci

    2014-01-01

    Dissolution rates are usually calculated as a function of surface area, which is assumed to remain constant ignoring the changes occurring on the surface during dissolution. Here we present a study of how topography of natural fluorite surfaces with different orientation changes during up to 3200 h...... of dissolution. Results are analyzed in terms of changes in surface area, surface reactivity and dissolution rates. All surfaces studied present fast changes in topography during the initial 200 h of dissolution. The controlling factors that cause the development of topography are the stability of the step edges...... forming the initial surface and its inclination to the closest stable planes, which are specific for each surface orientation. During an initial dissolution regime dissolution rates decrease significantly, even though the total surface area increases. During a second dissolution regime, some surfaces...

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

    DEFF Research Database (Denmark)

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

    2004-01-01

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

  10. Optical properties of Cr3+ in fluorite-structure hosts and in MgF*2

    Science.gov (United States)

    Payne, Stephen A.; Chase, L. L.; Krupke, William F.

    1987-03-01

    We have examined the optical properties of Cr3+ in MgF2 and in the fluorite-structure hosts: CdF2, CaF2, SrF2, and BaF2. The properties of Cr3+ in MgF2 are similar to those observed for other fluoride crystals that have octahedral substitutional metal sites. Interestingly, Cr3+ is also found to be sixfold coordinated in the fluorite hosts, despite the fact that the metal sites of these crystal lattices are eightfold coordinated. The smaller ionic radius of Cr3+ compared to, say, Ca2+, undoubtedly results in considerable relaxation at the metal site. However, the crystal field stabilization energy present in the 4A2(d3) ground state also provides for the energetic preference of sixfold vs eightfold coordination. The similarity of the observed absorption spectra of Cr3+ in MgF2 and in fluorite give evidence that the ground state is octahedrally coordinated in all of these hosts. The reduction of this electronic stabilization energy in the 4T2(d3) excited state is considered to produce a configurational shift relative to the ground state. This shift may be the reason why Cr3+ luminesces effectively in MgF2 whereas it is largely quenched in the fluorite-structure materials.

  11. Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7

    Science.gov (United States)

    Aidhy, Dilpuneet S.; Sachan, Ritesh; Zarkadoula, Eva; Pakarinen, Olli; Chisholm, Matthew F.; Zhang, Yanwen; Weber, William J.

    2015-11-01

    The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density functional theory calculations show that the non-equilibrium defect-fluorite structure can be stabilized by tensile strain. The pyrochlore to defect-fluorite structure transformation in the ring region is predicted to be induced by recrystallization during a melt-quench process and stabilized by tensile strain. Static pair-potential calculations show that planar tensile strain lowers oxygen vacancy migration barriers in pyrochlores, in agreement with recent studies on fluorite and perovskite materials. In view of these results, it is suggested that strain engineering could be simultaneously used to stabilize the defect-fluorite structure and gain control over its high ion-conducting properties.

  12. Special quasirandom structure modeling of fluorite-structured oxide solid solutions with aliovalent cation substitutions

    Science.gov (United States)

    Wolff-Goodrich, Silas; Hanken, Benjamin E.; Solomon, Jonathan M.; Asta, Mark

    2015-07-01

    The accuracy of the special quasirandom structure (SQS) approach for modeling the structure and energetics of fluorite-structured oxide solid solutions with aliovalent cation substitutions is assessed in an ionic-pair potential study of urania and ceria based systems mixed with trivalent rare-earth ions. Mixing enthalpies for SQS supercells containing 96 and 324 lattice sites were calculated using ionic pair potentials for U0.5La0.5O1.75, U0.5Y0.5O1.75, Ce0.5La0.5O1.75, Ce0.5Y0.5O1.75, and Ce0.5Gd0.5O1.75, which all have stoichiometries of pyrochlores. The SQS results were compared to benchmark values for random substitutional disorder obtained using large supercell models. The calculations show significant improvement of the mixing enthalpy for the larger 324 site SQS, which is attributed to a better description of the structural distortions, as characterized by the radial distribution functions in relaxed systems.

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

    Science.gov (United States)

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

    2015-01-01

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

  14. The special symplectic structure of binary cubics

    CERN Document Server

    Slupinski, Marcus

    2009-01-01

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

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

    Science.gov (United States)

    Cady, Susan G.

    1997-01-01

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

  16. Local atomic structure in cubic stabilized zirconia

    Energy Technology Data Exchange (ETDEWEB)

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

    2001-09-01

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

  17. Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures

    Science.gov (United States)

    Sadykov, Vladislav; Mezentseva, Natalia; Usoltsev, Vladimir; Sadovskaya, Ekaterina; Ishchenko, Arkady; Pavlova, Svetlana; Bespalko, Yulia; Kharlamova, Tamara; Zevak, Ekaterina; Salanov, Aleksei; Krieger, Tamara; Belyaev, Vladimir; Bobrenok, Oleg; Uvarov, Nikolai; Okhlupin, Yury; Smorygo, Oleg; Smirnova, Alevtina; Singh, Prabhakar; Vlasov, Aleksandr; Korobeynikov, Mikhail; Bryazgin, Aleksandr; Kalinin, Peter; Arzhannikov, Andrei

    This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm -2 at 700 °C in wet H 2/air feeds was demonstrated.

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

    Science.gov (United States)

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

    1963-01-11

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

  19. Investigating the Electronic Structure of Fluorite Oxides: Comparsion of EELS and First Principles Calculations

    Energy Technology Data Exchange (ETDEWEB)

    Aguiar, J; Asta, M; Gronbech-Jensen, N; Perlov, A; Milman, V; Gao, S; Pickard, C; Browning, N

    2009-06-05

    Energy loss spectra from a variety of cubic oxides are compared with ab-initio calculations based on the density functional plane wave method (CASTEP). In order to obtain agreement between experimental and theoretical spectra, unique material specific considerations were taken into account. The spectra were calculated using various approximations to describe core-hole effects and electronic correlations. All the calculations are based on the local spin density approximation to show qualitative agreement with the sensitive oxygen K-edge spectra in ceria, zirconia, and urania. Comparison of experimental and theoretical results let us characterize the main electronic interactions responsible for both the electronic structure and the resulting EEL spectra of the compounds in question.

  20. Synthesis of the Nanotublar Cubic Fluorite CeO2%纳米管状结构立方萤石型CeO2的合成

    Institute of Scientific and Technical Information of China (English)

    杨儒; 郭亮

    2004-01-01

    低温水热条件下,Ce4+离子经尿素水解均匀沉淀,在十八胺分子模板导向下形成了多层有序排列的纳米管状结构的立方萤石型CeO2,采用粉末X射线衍射(PXRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)以及选区电子衍射(SEAD)等手段对产物进行了表征.结果表明,该结构是由单根外、内径分别为10~20 nm、5~6 am左右的纳米管有序排列形成的纳米管束构成,且产物具有结晶性良好的立方萤石型CeO2晶体结构.在管束的生长过程中,反应体系首先形成单根纳米管,继而管与管之间又相互缔合生长成多层有序排列的纳米管束.控制尿素的水解,获得了不同pH值下的反应产物,发现反应体系pH值在5~6之间时产物为立方萤石型CeO2、6~8时为立方萤石型CeO2与六方型Ce(OH)CO3的混合物、大于8则为六方型Ce(OH)CO3.%Under hydrothermal condition,nitrate cerium(IV) was used as a cerium source,octadecylamine (C18H37NH2)as the molecular template and urea as a precipitating agent, and the hierarchically well-aligned nanotublar bunches of the cubic fluorite ceria were successfully synthesized.The materials have been characterized by Powder X-ray diffraction (PXRD),transmission electron microscopy (TEM),high-resolution transmission electron microscopy (HRTEM)and the selected area electron diffraction (SAED).The products exhibited the hierarchically well-aligned nanotublar bunch which was composed of single nanotube with outer and inner diameter 10~20 and 5~6 nm. The growth process of nanotublar hunches was monitored.Firstly, the separated nanotube appeared in the reaction system. Subsequently, the separated nanotubes integrated into the hierarchically well-aligned nanotublar bunch each other. In addition, the products have different crystalline phase and composition ad increasing the final pH value of reaction system; And when the final pH values of reaction system were at 5~6,6~8 and >8 respectively, the

  1. Solid State Structure-Reactivity Studies on Bixbyites, Fluorites and Perovskites Belonging to the Vanadate, Titanate and Cerate Families

    Science.gov (United States)

    Shafi, Shahid P.

    This thesis primarily focuses on the systematic understanding of structure-reactivity relationships in two representative systems: bixbyite and related structures as well as indium doped CeO2. Topotactic reaction routes have gained significant attention over the past two decades due to their potential to access kinetically controlled metastable materials. This has contributed substantially to the understanding of solid state reaction pathways and provided first insights into mechanisms. Contrary to the widely used ex-situ methods, in-situ techniques including powder x-ray diffraction and thermogravimetric-differential thermal analysis have been employed extensively throughout this work in order to follow the reaction pathways in real time. Detailed analysis of the AVO3 (A = In, Sc) bixbyite reactivity under oxidative conditions has been carried out and a variety of novel metastable oxygen defect phases have been identified and characterized. The novel metastable materials have oxygen deficient fluorite structures and consequently are potential ion conductors. Structural aspects of the topotactic vs. reconstructive transformations are illustrated with this model system. The structure-reactivity study of AVO3 phases was extended to AVO3 perovskite family. Based on the research methodologies and results from AVO3 bixbyite reactivity studies a generalized mechanistic oxidation pathway has been established with a non-vanadium phase, ScTiO3 bixbyite. However, there is stark contrast in terms of structural stability and features beyond this stability limit during AVO3 and ScTiO3 bixbyite reaction pathways. A series of complex reaction sequences including phase separation and phase transitions were identified during the investigation of ScTiO3 reactivity. The two-step formation pathway for the fluorite-type oxide ion conductor Ce1-xInxO2-delta (0 ≤ x ≤ 0.3) is being reported. The formation of the BaCe1-xInxO 3-delta perovskites and the subsequent CO2-capture reaction

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

    Directory of Open Access Journals (Sweden)

    Eduardo A. Castro

    2005-05-01

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

  3. Competing structural instabilities in cubic perovskites

    CERN Document Server

    Vanderbilt, D

    1994-01-01

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

  4. Optical studies of cubic III-nitride structures

    OpenAIRE

    Powell, Ross E L

    2014-01-01

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

  5. Determination of the structure of the cubic phase in high-ZrO{sub 2}Y{sub 2}O{sub 2}-ZrO{sub 2} alloys by CBED

    Energy Technology Data Exchange (ETDEWEB)

    McClellan, K.J.; Xiao, S.Q.; Lagerlof, K.P.D.; Heuer, A.H. [Case Western Reserve Univ., Cleveland, OH (United States)

    1993-06-20

    Convergent beam electron diffraction (CBED) was used to determine the space group of 9.9 and 18 mol% Y{sub 2}O{sub 3}-stabilized cubic ZrO{sub 2} (Y-CSZ) single crystals. The result (P43m space group) is different from the known tetragonal structure (P4{sub 2}/nmc space group) present in lower solute (3.2 mol% Y{sub 2}O{sub 3}) alloys, and the cubic structure (space group Fm3m) traditionally assumed for cubic ZrO{sub 2}. The oxygen sublattice of the cubic structure is distorted from Fm3m, relative to the cation sublattice, by displacements along the <111> directions. Computer simulations of the CBED patterns agree with experiment and suggest an anion displacement of {approximately}0.3 {Angstrom} from the (1/4,1/4,1/4) positions of the ideal fluorite structure.

  6. Fluorite and mixed-metal Kagome-related topologies in metal-organic framework compounds: synthesis, structure, and properties.

    Science.gov (United States)

    Mahata, Partha; Raghunathan, Rajamani; Banerjee, Debamalya; Sen, Diptiman; Ramasesha, S; Bhat, S V; Natarajan, S

    2009-06-01

    Two new three-dimensional metal-organic frameworks (MOFs) [Mn(2)(mu(3)-OH)(H(2)O)(2)(BTC)] x 2 H(2)O, I, and [NaMn(BTC)], II (BTC = 1,2,4-benzenetricarboxylate = trimellitate) were synthesized and their structures determined by single-crystal X-ray diffraction (XRD). In I, the Mn(4) cluster, [Mn(4)(mu(3)-OH)(2)(H(2)O)(4)O(12)], is connected with eight trimellitate anions and each trimellitate anion connects to four different Mn(4) clusters, resulting in a fluorite-like structure. In II, the Mn(2)O(8) dimer is connected with two Na(+) ions through carboxylate oxygen to form mixed-metal distorted Kagome-related two-dimensional -M-O-M- layers, which are pillared by the trimellitate anions forming the three-dimensional structure. The extra-framework water molecules in I are reversibly adsorbed and are also corroborated by powder XRD studies. The formation of octameric water clusters involving free and coordinated water molecules appears to be new. Interesting magnetic behavior has been observed for both compounds. Electron spin resonance (ESR) studies indicate a broadening of the signal below the ordering temperature and appear to support the findings of the magnetic studies.

  7. Structures and stabilities of trivalent and tetravalent rare earth ions in sevenfold and eightfold coordination in fluorite-related complex oxides

    Energy Technology Data Exchange (ETDEWEB)

    Morss, L.R.

    1991-12-31

    This paper reports the preparation and characterization of a series of oxides containing 3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M{sup 4+}/M{sup 3+} reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M{sup 3+} and M{sup 4+} lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxides. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x}. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi{sub 2}O{sub 7} is a pyrochlore, a = 10.142(4) {Angstrom}, with Ce{sup 4+} much more easily reducible than in the perovskite BaCeO{sub 3}. By contrast, a preparation with the stoichiometry ``CaPbTi{sub 2}O{sub 7-x}`` is a two-phase mixture-of perovskite CaTiCo{sub 3} and a presumably Pr{sup 3+}-rich pyrochlore Pr{sub 2}Ti{sub 2}O{sub 7}(?). CaTbTi{sub 2}O{sub 7-x} appears to be a Tb{sup 3+} pyrochlore, a = 10.149(2) {Angstrom}. CaCeZr{sub 2}O{sub 7} is a pyrochlore, a = 10.524(1) {Angstrom}. A preparation of ``CaPbZr{sub 2}O{sub 7-x}`` also appeared to yield a two-phase mixture, perovskite CaZrO{sub 3} and pyrochlore Pr{sub 2}Zr{sub 2}O{sub 7}. In this paper, the structures, f-element ion sites, and M(4)-M(3) stability trends in the CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x} oxides are compared with the structural and stability trends in the perovskites BaMO{sub 3} which have M{sup 4+} ions in sixfold (tilted octahedra) coordination.

  8. Structures and stabilities of trivalent and tetravalent rare earth ions in sevenfold and eightfold coordination in fluorite-related complex oxides

    Energy Technology Data Exchange (ETDEWEB)

    Morss, L.R.

    1991-01-01

    This paper reports the preparation and characterization of a series of oxides containing 3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M{sup 4+}/M{sup 3+} reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M{sup 3+} and M{sup 4+} lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxides. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x}. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi{sub 2}O{sub 7} is a pyrochlore, a = 10.142(4) {Angstrom}, with Ce{sup 4+} much more easily reducible than in the perovskite BaCeO{sub 3}. By contrast, a preparation with the stoichiometry CaPbTi{sub 2}O{sub 7-x}'' is a two-phase mixture-of perovskite CaTiCo{sub 3} and a presumably Pr{sup 3+}-rich pyrochlore Pr{sub 2}Ti{sub 2}O{sub 7}( ). CaTbTi{sub 2}O{sub 7-x} appears to be a Tb{sup 3+} pyrochlore, a = 10.149(2) {Angstrom}. CaCeZr{sub 2}O{sub 7} is a pyrochlore, a = 10.524(1) {Angstrom}. A preparation of CaPbZr{sub 2}O{sub 7-x}'' also appeared to yield a two-phase mixture, perovskite CaZrO{sub 3} and pyrochlore Pr{sub 2}Zr{sub 2}O{sub 7}. In this paper, the structures, f-element ion sites, and M(4)-M(3) stability trends in the CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x} oxides are compared with the structural and stability trends in the perovskites BaMO{sub 3} which have M{sup 4+} ions in sixfold (tilted octahedra) coordination.

  9. Electronic, elastic, acoustic and optical properties of cubic TiO{sub 2}: A DFT approach

    Energy Technology Data Exchange (ETDEWEB)

    Mahmood, Tariq, E-mail: tariq_mahmood78@hotmail.com [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Cao, Chuanbao, E-mail: cbcao@bit.edu.cn [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Tahir, Muhammad; Idrees, Faryal [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Ahmed, Maqsood [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Tanveer, M.; Aslam, Imran; Usman, Zahid; Ali, Zulfiqar; Hussain, Sajad [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China)

    2013-07-01

    The electronic, elastic, acoustic and optical properties of cubic phases TiO{sub 2} fluorite and pyrite are investigated using the first principles calculations. We have employed five different exchange–correlation functions within the local density and generalized gradient approximations using the ultrasoft plane wave pseudopotential method. The calculated band structures of cubic-TiO{sub 2} elucidate that the TiO{sub 2} fluorite and pyrite are direct and indirect semiconductors in contrast to the previous findings. From our studied properties such as bulk and shear moduli, elastic constants C{sub 44} and Debye temperature for TiO{sub 2} fluorite and pyrite, we infer that both the cubic phases are not superhard materials and the pyrite phase is harder than fluorite. The longitudinal and transversal acoustic wave speeds for both phases in the directions [100], [110] and [111] are determined using the pre-calculated elastic constants. In addition, we also calculate the optical properties such as dielectric function, absorption spectrum, refractive index and energy loss function using the pre-optimized structure. On the observation of optical properties TiO{sub 2} fluorite phase turn out to be more photocatalytic than pyrite.

  10. Highly Aminated Mesoporous Silica Nanoparticles with Cubic Pore Structure

    KAUST Repository

    Suteewong, Teeraporn

    2011-01-19

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

  11. Water orientation and hydrogen-bond structure at the fluorite/water interface

    CERN Document Server

    Khatib, Rémi; Bonn, Mischa; Perez-Haro, María-José; Gaigeot, Marie-Pierre; Sulpizi1, Marialore

    2016-01-01

    Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical-experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important flourite-water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the free OH signature in the SFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of flourite-water interfa...

  12. Nonlinear structure formation in the Cubic Galileon gravity model

    CERN Document Server

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

    2013-01-01

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

  13. Structure and energetics of nanotwins in cubic boron nitrides

    Science.gov (United States)

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

    2016-08-01

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

  14. Structure and energetics of nanotwins in cubic boron nitrides

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-08-22

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

  15. The reasons for the color green fluorite Mehmandooye cover using UV spectroscopy and XRF results

    Science.gov (United States)

    Pirzadeh, Sara; Zahiri, Reza

    2016-04-01

    Fluorite mineral or fluorine with chemical formula CaF2 is most important mineralfluor in nature. This mineral crystallization to colors yellow, green, pink, blue, purple, colorless and sometimes black andin cubic system crystallized.assemi transparent and glass with polished.fluoritethe purity include 48/9% fluoreand 51/9% calcium. How the creation colors in minerals different greatly indebted to Kurt Nassau research from Bell Labs, Murray Hill, New Jersey.almostall the mechanisms that cause color in minerals, are the result of the interaction of light waves with the electrons The main factors affecting the color generation include the following: 1)the presence of a constructive element inherent (essential ingredient mineral composition) 2)The presence of a minor impurities (such a element as involved in latticesolid solution) 3) appearancedefects in the crystal structure 4) There are some physical boundaries with distances very small and delicate, like blades out of the solution (which may be the play of colors or Chatvyansy) 5) Mixing mechanical impurities dispersed in a host mineral Based on the results of the analysis, XRF and UV spectrum and also based on the results of ICP, because the color green fluorite examined, the focus color (F_center) and also the presence of some elementsintermediate (such as Y (yttrium). [1] Bill, H., Calas, G. Color centres associated rare earth ions and the origin of coloration in natural fluorites// PhysChem Min, (1978), v 3, pp. 117-131.

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

    KAUST Repository

    Li, Yangyang

    2013-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-01-13

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

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

    Science.gov (United States)

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

    2014-03-07

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

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

    Science.gov (United States)

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

    2014-03-01

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

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

    Science.gov (United States)

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

    2008-01-01

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

  1. Electronic structures of (Pb sub 2 Cu)Sr sub 2 Eu sub x Ce sub n sub - sub x Cu sub 2 O sub 2 sub n sub + sub 6 (n=2, 3): Effect of fluorite blocks between adjacent CuO sub 2 layers

    CERN Document Server

    Arai, M

    2003-01-01

    The electronic structures of (Pb sub 2 Cu)Sr sub 2 Eu sub x Ce sub n sub - sub x Cu sub 2 O sub 2 sub n sub + sub 6 (n = 2, 3) compounds which have fluorite blocks between two adjacent CuO sub 2 layers have been studied by using ab-initio method. It is found that the anisotropy is enhanced by inserting the fluorite blocks. The Fermi velocity perpendicular to the CuO sub 2 layers decreases as the thickness of fluorite blocks increases. The Eu substitution is found to affect both the atomic positions and electronic structures. The distance between apical oxygen and copper becomes shorter by the Eu substitution. The energy bands derived from oxygens in the fluorite blocks approach Fermi energy as the content of Eu substitution increases. (author)

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

    Science.gov (United States)

    Saludjian, P; Reiss-Husson, F

    1980-12-01

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

  3. Synthesis, crystal structures and magnetic properties of fluorite-related compounds Ce3MO7 (M = Nb, Ta)

    Science.gov (United States)

    Inabayashi, Masaki; Doi, Yoshihiro; Wakeshima, Makoto; Hinatsu, Yukio

    2017-10-01

    Ternary oxides Ce3NbO7 and Ce3TaO7 were successfully synthesized by the solid state reaction under flowing hydrogen atmosphere. The structures were determined by the powder X-ray diffraction. Both the compounds were crystallized in the orthorhombic space groups Pnma (for Ce3NbO7) and Cmcm (for Ce3TaO7). Both the structures have similar features: two kinds of infinite chains formed by corner-sharing NbO6 (TaO6) octahedra and edge-sharing Ce(1)O8 cubes, the slabs consisting of alternate chains, and 7-coordinated Ce(2) ions existing between the slabs. In the structure of Ce3NbO7, the NbO6 octahedra running along the a-axis are titled towards the 0 0 1 direction, while in the Ce3TaO7 structure, the TaO6 octahedra running along the c-axis are titled towards the 0 1 0 direction. Magnetic susceptibility measurements for Ce3NbO7 and Ce3TaO7 show that both compounds are paramagnetic down to 1.8 K, and confirm that the Ce ion is in the trivalent state. From specific heat (Cp) measurements, a rapid increase of Cp/T has been observed below 3 K for both the compounds, indicating the onset of magnetic ordering between Ce3+ ions at further lower temperatures.

  4. Phonons in mixed superionic fluorites (BaF2)1–(LaF3)

    Indian Academy of Sciences (India)

    M M Sinha

    2002-11-01

    In recent years, the fluorite-structured solid solutions with the general formula, (MF2)1–(RF3) (M = Ca, Sr, Ba, Pb and R is a rare-earth element or Y), have been the subject of numerous experimental studies focussed on their superionic properties. The overall cubic crystal symmetry (space group 3) is conserved up to ≤ max, where max 0.4–0.5 depending on M and R. The zone centre phonons and phonon dispersion along three symmetry directions of the mixed superionic compound (BaF2)1–(LaF3) have been investigated by applying de Launey angular force model for ≤ max. The calculated results are compared and explained with available experimental results.

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

    Institute of Scientific and Technical Information of China (English)

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

    2004-01-01

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

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

    Science.gov (United States)

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

    2015-03-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2001-01-01

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

  8. Microstructural characterization of the stabilized fluorite phases formed in the Ca 1- yLa yU 2O 6+ x (0 ≤ y ≤ 0.8) system

    Science.gov (United States)

    Gómez-Rebollo, E.; Herrero, P.; Rojas, R. M.

    1997-06-01

    The thermal behaviour and stability of the fluorite structure in the Ca 1- yLa yU 2O 6+ x (0 ≤ y ≤ 0.8) system during ageing have been studied by thermal analysis and X-ray powder diffraction. When the amount of La 3+ incorporated into the Ca 1- yLa yU 2O 6+ x structure is ≥ 0.6 the complete stabilization of the fluorite phase is achieved. This phase remains stable over the temperature range from room temperature-1400°C even after being submitted to long term give time. For lower amounts of La 3+ a mixture of cubic fluorite and calcium lanthanum diuranate solid solution is obtained on annealing. The microstructural characterization carried out by electron diffraction and high resolution transmission electron microscopy reveals short range order for the high temperature quenched materials. Annealing of the oxides leads to the formation of ordered nanodomains embedded within the fluorite matrix, but no ordered single phase is isolated. A hexagonal cell of a H = 3.8 and c H = 18.8 Å has been deduced for the domains.

  9. Microstructural characterization of the stabilized fluorite phases formed in the Ca{sub 1-y}La{sub y}U{sub 2}O{sub 6+x} (0{<=}y{<=}0.8) system.

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Rebollo, E. [CSIC, Madrid (Spain). Inst. de Ciencia de Mater.; Herrero, P. [CSIC, Madrid (Spain). Inst. de Ciencia de Mater.; Rojas, R.M. [CSIC, Madrid (Spain). Inst. de Ciencia de Mater.

    1997-06-01

    The thermal behaviour and stability of the fluorite structure in the Ca{sub 1-y}La{sub y}U{sub 2}O{sub 6+x} (0{<=}y{<=}0.8) system during ageing have been studied by thermal analysis and X-ray powder diffraction. When the amount of La{sup 3+} incorporated into the Ca{sub 1-y}La{sub y}U{sub 2}O{sub 6+x} structure is {>=}0.6 the complete stabilization of the fluorite phase is achieved. This phase remains stable over the temperature range from room temperature-1400 C even after being submitted to long term give time. For lower amounts of La{sup 3+} a mixture of cubic fluorite and calcium lanthanum diuranate solid solution is obtained on annealing. The microstructural characterization carried out by electron diffraction and high resolution transmission electron microscopy reveals short range order for the high temperature quenched materials. Annealing of the oxides leads to the formation of ordered nanodomains embedded within the fluorite matrix, but no ordered single phase is isolated. A hexagonal cell of a{sub H}=3.8 and c{sub H}=18.8 A has been deduced for the domains. (orig.).

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

    Science.gov (United States)

    Efrat, R; Aserin, A; Garti, N

    2008-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-10-17

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

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

    Science.gov (United States)

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

    2008-03-19

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2004-01-01

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

  14. Optical properties of a new Bi38Mo7O78 semiconductor with fluorite-type δ-Bi2O3 structure

    Science.gov (United States)

    Wang, Zuoshan; Bi, Shala; Wan, Yingpeng; Huang, Pengjie; Zheng, Min

    2017-03-01

    Bi3+-containing inorganic materials usually show rich optical and electronic properties due to the hybridization between 6s and 6p electronic components together with the lone pair in Bi3+ ions. In this work, a new semiconductor of bismuth molybdate Bi38Mo7O78 (19Bi2O3·7MoO3) was synthesized by the sol-gel film coating and the following heat process. The samples developed into nanoparticles with average size of 40 nm. The phase formation was verified via the XRD Rietveld structural refinement. Orthorhombic Bi38Mo7O78 can be regarded to be derived from the cubic δ-phase Bi2O3 structure. The microstructure was investigated by SEM, EDX, TEM, BET and XPS measurements. The UV-vis absorption spectra showed that the band gap of Bi38Mo7O78 (2.38 eV) was greatly narrowed in comparison with Bi2O3 (2.6 eV). This enhances the efficient absorption of visible light. Meanwhile, the conduction band of is wider and shows more dispersion, which greatly benefits the mobility of the light-induced charges taking part in the photocatalytic reactions. Bi38Mo7O78 nanoparticles possess efficient activities on the photodegradation of methylene blue (MB) solutions under the excitation of visible-light. The photocatalysis activities and mechanisms were discussed on the crystal structure characteristics and the measurements such as photoluminescence, exciton lifetime and XPS results.

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

    Directory of Open Access Journals (Sweden)

    Lu Qingshan

    2010-01-01

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

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

    Science.gov (United States)

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

    2010-02-11

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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

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

    2016-03-15

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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Directory of Open Access Journals (Sweden)

    Jinming Liu

    2016-05-01

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

  1. Cubic AlGaN/GaN structures for device application

    Energy Technology Data Exchange (ETDEWEB)

    Schoermann, Joerg

    2007-05-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-09-07

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-01-01

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

  4. Variable helium diffusion characteristics in fluorite

    Science.gov (United States)

    Wolff, R.; Dunkl, I.; Kempe, U.; Stockli, D.; Wiedenbeck, M.; von Eynatten, H.

    2016-09-01

    Precise analysis of the diffusion characteristics of helium in fluorite is crucial for establishing the new fluorite (U-Th-Sm)/He thermochronometer (FHe), which potentially provides a powerful tool for dating ore deposits unsuitable for the application of conventional geochronometers. Incremental helium outgassing experiments performed on fluorites derived from a spectrum of geological environments suggest a thermally activated volume diffusion mechanism. The diffusion behaviour is highly variable and the parameters range between log D0/a2 = 0.30 ± 0.27-7.27 ± 0.46 s-1 and Ea = 96 ± 3.5-182 ± 3.8 kJ/mol. Despite the fact that the CaF2 content of natural fluorites in most cases exceeds 99 weight percent, the closure temperature (Tc) of the fluorite (U-Th-Sm)/He thermochronometer as calculated from these diffusion parameters varies between 46 ± 14 °C and 169 ± 9 °C, considering a 125 μm fragment size. Here we establish that minor substitutions of calcium by rare earth elements and yttrium (REE + Y) and related charge compensation by sodium, fluorine, oxygen and/or vacancies in the fluorite crystal lattice have a significant impact on the diffusivity of helium in the mineral. With increasing REE + Y concentrations F vacancies are reduced and key diffusion pathways are narrowed. Consequently, a higher closure temperature is to be expected. An empirical case study confirms this variability: two fluorite samples from the same deposit (Horni Krupka, Czech Republic) with ca. 170 °C and ca. 43 °C Tc yield highly different (U-Th-Sm)/He ages of 290 ± 10 Ma and 79 ± 10 Ma, respectively. Accordingly, the fluorite sample with the high Tc could have quantitatively retained helium since the formation of the fluorite-bearing ores in the Permian, despite subsequent Mesozoic burial and associated regional hydrothermal heating. In contrast, the fluorite with the low Tc yields a Late Cretaceous age close to the apatite fission track (AFT) and apatite (U-Th)/He ages (AHe

  5. Control estructural de las mineralizaciones de fluorita del batolito Cerro Áspero, Sierras Pampeanas de Córdoba Structural control of vein-type fluorite deposits of Cerro Áspero batholith, Sierras Pampeanas of Córdoba

    Directory of Open Access Journals (Sweden)

    Jorge E Coniglio

    2010-12-01

    , NE, EW, and NW strike-slip regional fault zones, with thicknesses generally less than 3 metres. They can be continued up to 200 m deep below surface. The geometry and distributions of the veins were tectonically controlled by divergent shear zones, probably linked with the opening of the south Atlantic ocean. In the study area, this regional situation established a dextral simple shear system related to NNE lineaments, that is characterized by N70ºE striking extensional structures, less than 1 km long, and NE and NW striking shear systems, more than 4 km long. These shear systems show typical patterns of transcurrent faults such as stepovers, offsets, bends and horsetail splay. Four successive mineralizing stages were recognized on the basis of textural and structural analyses of the veins. The emplacement of these mineralizing stages were controlled by a discontinuous activity of dextral couple, with the minimum paleostress (σ3 always oriented toward NNW. The fact that some of the fluorite stages are absent in several veins in the investigated areas, confirm that the mineralized structures had different times of opening and sealing, and thus the depositional sequence established could be used as an effective prospection criteria. The main ore bodies are related to extensional zones (releasing bends and extensional structures, which registered the whole mineralizing sequence.

  6. Structural and optoelectronic properties of cubic perovskite RbPbF3

    Indian Academy of Sciences (India)

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

    2014-04-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-02-01

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

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

    Science.gov (United States)

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

    2015-08-01

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

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

    Science.gov (United States)

    Wen, Cai

    2017-03-09

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

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

    Science.gov (United States)

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

    2017-07-01

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

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

    Science.gov (United States)

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

    2012-09-07

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Peterman, D.J.

    1980-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-06-25

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

  14. Reaction kinetics of fluorite in flow systems and surface chemistry

    Institute of Scientific and Technical Information of China (English)

    张荣华; 胡书敏

    1996-01-01

    The kinetic experiments of fluorite in water-HCl solution in an open-flow system at the temperatures ≤100℃ reveal that the variation of flow rate (U) can change the reaction rate orders from 0 to 2 or higher. In the far from equilibrium systems, the dissolution rates of fluorite in aqueous solutions have a zero order.The reaction rates are controlled by pH values of input solutions. In fact, the reaction rates are related to the concentrations of the active sites occupied by H+ on fluorite surface [SOH]. X-ray photospectroscopy observations on fluorite surface before and after reaction indicate that surface chemical processes control the reaction rates: Cl- cations attach on and enter into surface of fluorite besides H+ when fluorites react with HCl solutions, which affect the reaction rates.

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-07-15

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

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

    Science.gov (United States)

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

    2016-07-19

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

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

    Science.gov (United States)

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

    2016-07-01

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

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

    Science.gov (United States)

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

    2016-03-01

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

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

    OpenAIRE

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

    2002-01-01

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

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Directory of Open Access Journals (Sweden)

    Alexander L. Ivanovskii

    2008-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-09-01

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

  4. Selective Flotation of Calcite from Fluorite: A Novel Reagent Schedule

    Directory of Open Access Journals (Sweden)

    Zhiyong Gao

    2016-10-01

    Full Text Available Fluorite is an important strategic mineral. In general, fluorite ores will contain a certain amount of calcite gangue mineral. Thus, they need to be separated from each other. For an economic separation, a reverse flotation process is used to float calcite gangue from fluorite. However, little information on the separation is available. In this study, a novel reagent schedule using citric acid (CA as the depressant, sodium fluoride (NaF as the regulator and sulfoleic acid (SOA as the collector, was developed to separate calcite from fluorite. The results demonstrated a high selectivity for the flotation of calcite from fluorite using this new reagent schedule. The best selective separation for a single mineral and mixed binary minerals was obtained when 200 mg/L of NaF, 50 mg/L of CA, and 6 mg/L of SOA were used at pH 9. In addition, a batch flotation experiment was carried out using a run-of-mine feed material. Selective separation was achieved with 85.18% calcite removal while only 11.2% of fluorite was lost. An attempt was made to understand the effect of the new reagent schedule on the flotation of calcite. The results from both microflotation and bench scale flotation demonstrated a great potential for industrial application using this novel reagent schedule to upgrade fluorite ore.

  5. Geochemistry and microfabrics of syndiagenetic strata-bound fluorite from Eschwege, Germany - Implications for fluorite formation and remobilization in Zechstein carbonates from the Lower Saxony Basin

    Science.gov (United States)

    Duschl, Florian; Wischhöfer, Philipp; Vollbrecht, Axel

    2017-04-01

    Core samples of Stassfurt carbonate rocks (Zechstein, Ca2) from various locations in the Lower Saxony Basin (LSB) often contain fluorite which occurs as pore filling cement, replacement fluorite, or as fault-related fracture mineralizations. Recent studies on fluorite geochemistry and fluid migration in the LSB suggest a sedimentary rather than a hydrothermal fluorite source for some of these deep-seated (> 2500 mbs) accumulations. Outcrop samples from lens-shaped and stratiform fluorite occurrences within oolithic limestone (Ca2) near Eschwege, Germany, give insight into syndiagenetic fluorite formation in Zechstein carbonates. They serve as a shallow-burial analogue for remobilized fluorite within deeply buried carbonate rocks of the LSB. Samples were studied using petrographic microscopy, hot-cathodoluminescence microscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Five different fluorite types were identified: a first generation (I) is represented by a dark brownish to violet fluorite that replaced ooids during early diagenesis. As pressure increased during burial the replacement fluorite recrystallized forming white aggregates of parallel bar-shaped fluorite crystals (type II), type (III) consists of white fluorite grains with rectangular and mostly polygonal grain boundaries; type (IV) is a colorless to blueish pore-filling fluorite, and type (V) is a colorless fracture-hosted fluorite. In-situ LA-ICP-MS analyses of respective fluorite types revealed relatively low REE concentrations in general with Tb/Ca vs. Tb/La signatures that are typical for sediment-hosted fluorite. The REE distribution patterns reflect the processes of recrystallization and remobilization. Though stylolitization affected both host rock and replacement fluorite, only little fluorite remobilization did occur due to pressure solution. Geochemical analyses prove that fluorite formation was controlled by precipitation from a sedimentary parental fluid

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

    Science.gov (United States)

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

    2015-03-01

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

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

    Science.gov (United States)

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

    2017-03-01

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

  8. Fluid Evolution During Mineralization of Atashkuh Fluorite-Barite (±Sulfide Deposit, South of Delijan

    Directory of Open Access Journals (Sweden)

    Seyed Javad Moghaddasi

    2016-07-01

    Full Text Available Introduction More than 30 fluorite occurrences with approximately 1.35 million tons of reserves have been recognized in Iran (Ghorbani, 2013. The Atashkuh fluorite-barite (±sulfide deposit is one of four occurrences located south of the city of Delijan in Markazi province, about 80 km SE of Arak city. The Atashkuh deposit occurs between the central Iran structural zone on the north and the Sanandaj-Sirjan structural zone on the south. The geology of the area is dominated by folded and faulted Jurassic carbonates and shales (Thiele et al., 1968. The lower Jurassic shale and calcareous sandstone of the Shemshak Formation and the Middle to Upper Jurassic dolomite of the Badamu Formation are the main host rocks for the fluorite veins. In this study, 40 samples from fluorite veins and host rocks were collected, from which 25 thin sections and 8 doubly-polished thin sections were prepared. Micro-thermometric studies were conducted on primary fluid inclusions using the Linkam THM600 heating-freezing stage. In addition, 10 samples were analyzed by XRD. Results Fluid inclusion data indicate that the Atashkuh fluorite-barite (±sulfides veins were deposited as a result of mixing a primary multi-component Na-K(-Mg-Ca high-salinity brine (SH type inclusions with less saline calcium-rich connate water (LVHH type inclusions and pressure reduction of ore bearing fluids. Fluid inclusions containing halite in high-salinity brine, and hydrohalite in connate water show suggest a high-salinity brine and connate water before mixing. The main mineralization stage was followed by circulation of low temperature meteoric water, responsible for the late stage mineralization. The micro-thermometry results suggest that the main fluorite mineralization occurred at 250 °C and 150 Mpa pressure. Dolomitization and silicification are the main alteration types associated with the Atashkuh mineralization. The occurrence of chlorite, talc, illite and dolomitized host rock all

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

    Science.gov (United States)

    1992-12-01

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

  10. High-pressure elastic properties of cubic Ir2P from ab initio calculations

    Science.gov (United States)

    Sun, Xiao-Wei; Bioud, Nadhira; Fu, Zhi-Jian; Wei, Xiao-Ping; Song, Ting; Li, Zheng-Wei

    2016-10-01

    A study of the high-pressure elastic properties of new synthetic Ir2P in the anti-fluorite structure is conducted using ab initio calculations based on density functional theory. The elastic constants C11, C12 and C44 for the cubic Ir2P are obtained by the stress-strain method and the elastic stability calculations under pressure indicate that it is stable at least 100 GPa. Additionally, the electronic density of states, the aggregate elastic moduli, that is bulk modulus, shear modulus, and Young's modulus along with the Debye temperature, Poisson's ratio, and elastic anisotropy factor are all successfully obtained. Moreover, the pressure dependence of the longitudinal and shear wave velocities in three different directions [100], [110], and [111] for Ir2P are also predicted for the first time.

  11. Effects of firing schedule on solubility limits and transport properties of ZrO2–TiO2–Y2O3 fluorites

    DEFF Research Database (Denmark)

    Fagg, D.P.; Frade, J.R.; Mogensen, Mogens Bjerg

    2007-01-01

    The low Y/high Zr edge of the cubic defect fluorite solid solution in the system ZrO2–TiO2–Y2O3 in air is reassessed, as it is these compositions which have been suggested to offer the highest levels of mixed conductivity. Vegard's law is obeyed for values of x which lie within the cubic defect...... fluorite phase in Zr1−x−yYyTixO2−δ for values of y=0.2 and 0.25. Measured lattice parameters show good agreement with those calculated from the Kim relation. Deviation from Vegard's law places the limit of the solid solution at x=0.18 and 0.20 for values of y=0.2 and 0.25, respectively, at 1500 °C...

  12. Investigation of thermally induced anion disorder in fluorites using neutron scattering techniques

    DEFF Research Database (Denmark)

    Hutchings, M T; Clausen, Kurt Nørgaard; Dickens, M H

    1984-01-01

    Some materials with the fluorite structures show a pronounced specific heat anomaly well below their melting temperature. This anomaly is a consequence of lattice disorder and is associated with the onset of fast-ion conduction. This paper presents the results of a series of experiments in which ...... anion Frenkel interstitials, anion vacancies and relaxed anions has been developed which satisfactorily accounts for the distribution of intensity....

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

    Science.gov (United States)

    Kong, Bo; Zhang, Yachao

    2016-07-01

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

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

    Directory of Open Access Journals (Sweden)

    Noorhana Yahya

    2009-01-01

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

  15. TL response of a natural fluorite

    CERN Document Server

    Balogun, F A; Ogundare, F O; Fasasi, M K; Hussein, L A

    1999-01-01

    A batch of a naturally occurring fluorite (CaF sub 2) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224 deg. C at a heating rate of 10 deg. C s sup - sup 1. The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224 deg. C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal...

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

    Science.gov (United States)

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

    2013-03-01

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

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

    Indian Academy of Sciences (India)

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

    2016-02-01

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

  18. First-principles study of electronic structures and stability of body-centered cubic Ti-Mo alloys by special quasirandom structures.

    Science.gov (United States)

    Sahara, Ryoji; Emura, Satoshi; Ii, Seiichiro; Ueda, Shigenori; Tsuchiya, Koichi

    2014-06-01

    The electronic structures and structural properties of body-centered cubic Ti-Mo alloys were studied by first-principles calculations. The special quasirandom structures (SQS) model was adopted to emulate the solid solution state of the alloys. The valence band electronic structures of Ti-Mo and Ti-Mo-Fe alloys were measured by hard x-ray photoelectron spectroscopy. The structural parameters and valence band photoelectron spectra were calculated using first-principles calculations. The results obtained with the SQS models showed better agreement with the experimental results than those obtained using the conventional ordered structure models. This indicates that the SQS model is effective for predicting the various properties of solid solution alloys by means of first-principles calculations.

  19. Effects of Temperature on Structure and Mobility of the <100> Edge Dislocation in Body-Centred Cubic Iron

    Energy Technology Data Exchange (ETDEWEB)

    Terentyev, Dmitry [Belgian Nuclear Research Centre, SCK-CEN; Osetskiy, Yury N [ORNL; Bacon, David J [University of Liverpool

    2010-01-01

    Dislocation segments with Burgers vector b = <1 0 0> are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2<1 1 1>. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight <1 0 0> edge dislocation is investigated here by atomic-scale computer simulation for {alpha}-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2<1 1 1> fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the <1 0 0> dislocation. It is concluded that the response of the <1 0 0> edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2<1 1 1> dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples.

  20. Effects of temperature on structure and mobility of the <1 0 0> edge dislocation in body-centred cubic iron

    Energy Technology Data Exchange (ETDEWEB)

    Terentyev, D.A., E-mail: dterenty@sckcen.be [Nuclear Materials Science Institute, SCK CEN, Boeretang 200, B-2400, Mol (Belgium); Osetsky, Yu. N. [Materials Sciences and Technology, ORNL, Oak Ridge, TN 37831 (United States); Bacon, D.J. [Department of Engineering, University of Liverpool, Brownlow Hill, Liverpool L69 3GH (United Kingdom)

    2010-04-15

    Dislocation segments with Burgers vector b = <1 0 0> are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2<1 1 1>. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight <1 0 0> edge dislocation is investigated here by atomic-scale computer simulation for {alpha}-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2<1 1 1> fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the <1 0 0> dislocation. It is concluded that the response of the <1 0 0> edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2<1 1 1> dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples.

  1. Sintering of Spherical Particles of Equal and Different Size Arranged in a Body Centered Cubic Structure

    DEFF Research Database (Denmark)

    Redanz, Pia; McMeeking, R. M.

    2003-01-01

    Solid-state sintering of a bcc structure of spherical particles has been studied numerically by use of simple shape parameters to describe the state of the unit cell. Both free and pressure-assisted sintering of particles of equal and different sizes for various ratios of boundary and surface...... to interact, or the next-nearest neighbours in the particle structure attain contact. Quantative measures of the density at the transition from open pore space between the particles to closed porosity as well as the density at which the next-nearest neighbours start to touch are derived. Furthermore...

  2. Self-focusing and solitonlike structures in materials with competing quadratic and cubic nonlinearities

    DEFF Research Database (Denmark)

    Bergé, L.; Bang, O.; Juul Rasmussen, J.;

    1997-01-01

    , mutually trapped waves can self-focus until collapse whenever their respective powers exceed some thresholds. On the contrary, coupled waves diffracting in a one-dimensional plane never collapse and may evolve towards stable solitonlike structures. For higher transverse dimension numbers, we investigate...

  3. Origin of the catalytic activity of face-centered-cubic ruthenium nanoparticles determined from an atomic-scale structure.

    Science.gov (United States)

    Kumara, L S R; Sakata, Osami; Kohara, Shinji; Yang, Anli; Song, Chulho; Kusada, Kohei; Kobayashi, Hirokazu; Kitagawa, Hiroshi

    2016-11-09

    The 3-dimensional (3D) atomic-scale structure of newly discovered face-centered cubic (fcc) and conventional hexagonal close packed (hcp) type ruthenium (Ru) nanoparticles (NPs) of 2.2 to 5.4 nm diameter were studied using X-ray pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) modeling. Atomic PDF based high-energy X-ray diffraction measurements show highly diffuse X-ray diffraction patterns for fcc- and hcp-type Ru NPs. We here report the atomic-scale structure of Ru NPs in terms of the total structure factor and Fourier-transformed PDF. It is found that the respective NPs have substantial structural disorder over short- to medium-range order atomic distances from the PDF analysis. The first-nearest-neighbor peak analyses show a significant size dependence for the fcc-type Ru NPs demonstrating the increase in the peak height due to an increase in the number density as a function of particle size. The bond angle and coordination number (CN) distribution for the RMC-simulated fcc- and hcp-type Ru NP models indicated inherited structural features from their bulk counterparts. The CN analysis of the whole NP and surface of each RMC model of Ru NPs show the low activation energy packing sites on the fcc-type Ru NP surface atoms. Finally, our newly defined order parameters for RMC simulated Ru NP models suggested that the enhancement of the CO oxidation activity of fcc-type NPs was due to a decrease in the close packing ordering that resulted from the increased NP size. These structural findings could be positively supported for synthesized low-cost and high performance nano-sized catalysts and have potential application in fuel-cell systems and organic synthesis.

  4. Electronic Structure Studies and Photocatalytic Properties of Cubic Bi1.5ZnNb1.5O7

    Directory of Open Access Journals (Sweden)

    Ganchimeg Perenlei

    2015-01-01

    Full Text Available The photocatalytic ability of cubic Bi1.5ZnNb1.5O7 (BZN pyrochlore for the decolorization of an acid orange 7 (AO7 azo dye in aqueous solution under ultraviolet (UV irradiation has been investigated for the first time. BZN catalyst powders prepared using low temperature sol-gel and higher temperature solid-state methods have been evaluated and their reaction rates have been compared. The experimental band gap energy has been estimated from the optical absorption edge and has been used as reference for theoretical calculations. The electronic band structure of BZN has been investigated using first-principles density functional theory (DFT calculations for random, completely and partially ordered solid solutions of Zn cations in both the A and B sites of the pyrochlore structure. The nature of the orbitals in the valence band (VB and the conduction band (CB has been identified and the theoretical band gap energy has been discussed in terms of the DFT model approximations.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-08-01

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

  6. DFT Study of the Electronic Structure of Cubic-SiC Nanopores with a C-Terminated Surface

    Directory of Open Access Journals (Sweden)

    M. Calvino

    2014-01-01

    Full Text Available A study of the dependence of the electronic structure and energetic stability on the chemical surface passivation of cubic porous silicon carbide (pSiC was performed using density functional theory (DFT and the supercell technique. The pores were modeled by removing atoms in the [001] direction to produce a surface chemistry composed of only carbon atoms (C-phase. Changes in the electronic states of the porous structures were studied by using different passivation schemes: one with hydrogen (H atoms and the others gradually replacing pairs of H atoms with oxygen (O atoms, fluorine (F atoms, and hydroxide (OH radicals. The results indicate that the band gap behavior of the C-phase pSiC depends on the number of passivation agents (other than H per supercell. The band gap decreased with an increasing number of F, O, or OH radical groups. Furthermore, the influence of the passivation of the pSiC on its surface relaxation and the differences in such parameters as bond lengths, bond angles, and cell volume are compared between all surfaces. The results indicate the possibility of nanostructure band gap engineering based on SiC via surface passivation agents.

  7. First-principles study of the structural stability of cubic, tetragonal and hexagonal phases in Mn₃Z (Z=Ga, Sn and Ge) Heusler compounds.

    Science.gov (United States)

    Zhang, Delin; Yan, Binghai; Wu, Shu-Chun; Kübler, Jürgen; Kreiner, Guido; Parkin, Stuart S P; Felser, Claudia

    2013-05-22

    We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.

  8. First-principles study of the structural stability of cubic, tetragonal and hexagonal phases in Mn3Z (Z=Ga, Sn and Ge) Heusler compounds

    Science.gov (United States)

    Zhang, Delin; Yan, Binghai; Wu, Shu-Chun; Kübler, Jürgen; Kreiner, Guido; Parkin, Stuart S. P.; Felser, Claudia

    2013-05-01

    We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

  11. Structural and electronic properties of V-doped cubic BN: A density functional theory study

    Science.gov (United States)

    Espitia R, Miguel J.; Díaz F, John H.; Rodríguez Martínez, Jairo Arbey

    2016-10-01

    The structural, electronic, and magnetic properties of c-BN compound doped with V atoms were calculated by means of the pseudopotential method, employed exactly as implemented in computational Quantum ESPRESSO code. For the description of the electron-electron interaction, generalized gradient approximation (GGA) was used. A half-metallic behavior is predicted for the concentrations B0.9375V0.0625N and B0.875V0.125N, because of the fact that the majority spins are metallic and the minority spins are semiconducting. We found magnetic moments of 2.0 and 4.0 μβ per supercell, respectively. The main contribution to the magnetic moment comes from the V atom, with local moments of 1.61 μβ/V-atom. These compounds are good candidates for potential applications in spintronics and as spin injectors.

  12. Structure of the body-centered cubic phase of lipid systems does not consist of indefinitely long straight rods

    OpenAIRE

    Luzzati, Vittorio; Tardieu, Annette; Gulik-Krzywicki, Tadeusz

    1981-01-01

    The observed intensities of the reflections from the body-centered cubic phase of lipid systems are shown to be incompatible with a recently reported model consisting of straight, indefinitely long rods.

  13. Ab initio density functional theory investigation of the structural, electronic and optical properties of Ca{sub 3}Sb{sub 2} in hexagonal and cubic phases

    Energy Technology Data Exchange (ETDEWEB)

    Arghavani Nia, Borhan, E-mail: b.arghavani@gmail.com [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Sedighi, Matin [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Shahrokhi, Masoud [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Moradian, Rostam [Nano-Science and Nano-Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Computational Physics Science Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-1795, Tehran (Iran, Islamic Republic of)

    2013-11-15

    A density functional theory study of structural, electronical and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. In the exchange–correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca{sub 3}Sb{sub 2} has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated. - Graphical abstract: A density functional theory study of structural, electronic and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. Display Omitted - Highlights: • Physical properties of Ca{sub 3}Sb{sub 2} in hexagonal and cubic phases are investigated. • It is found that the hexagonal phase is an indirect gap semiconductor. • Ca{sub 3}Sb{sub 2} is a direct-gap semiconductor at the Γ point in the cubic phase. • By increasing pressure the semiconducting band gap and anti-symmetry gap are decreased.

  14. Cubical sets and the topological topos

    DEFF Research Database (Denmark)

    Spitters, Bas

    2016-01-01

    Coquand's cubical set model for homotopy type theory provides the basis for a computational interpretation of the univalence axiom and some higher inductive types, as implemented in the cubical proof assistant. This paper contributes to the understanding of this model. We make three contributions...... show that it can also be a target for cubical realization by showing that Coquand's cubical sets classify the geometric theory of flat distributive lattices. As a side result, we obtain a simplicial realization of a cubical set. 2. Using the internal `interval' in the topos of cubical sets, we...... construct a Moore path model of identity types. 3. We construct a premodel structure internally in the cubical type theory and hence on the fibrant objects in cubical sets....

  15. A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.

    Science.gov (United States)

    Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

    2013-08-01

    In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.

  16. Temperature-Induced Phase Transition of In2O3 from a Rhombohedral Structure to a Body-Centered Cubic Structure

    Institute of Scientific and Technical Information of China (English)

    YANG Lin-Hong; DONG Hong-Xing; SUN Zheng; SUN Liao-Xin; SHEN Xue-Chu; CHEN Zhang-Hai

    2011-01-01

    @@ We report an experimental study on the temperature-induced phase transition of three-dimensional nanosheetbased flower-like microspheres(NBFMs)of In2O3.Using InOOH as precursor, rhombohedral-In2O3 NBFMs are fabricated.Temperature-induced phase transition of In2O3 NBFMs from a rhombohedral(rh) structure to a body-centered cubic(bcc) structure is examined by Raman spectroscopy and x-ray diffraction.The critical phase transition temperature is found to be about 500℃.Photoluminescence(PL)spectra of In2O3 are measured before annealing and after annealing at different temperatures.The PL spectral results provide further evidence for the phase transition, confirming the fabrication of bcc-In2O3 NBFMs via a simple annealing method.

  17. Ab initio density functional theory investigation of the structural, electronic and optical properties of Ca3Sb2 in hexagonal and cubic phases

    Science.gov (United States)

    Arghavani Nia, Borhan; Sedighi, Matin; Shahrokhi, Masoud; Moradian, Rostam

    2013-11-01

    A density functional theory study of structural, electronical and optical properties of Ca3Sb2 compound in hexagonal and cubic phases is presented. In the exchange-correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca3Sb2 has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated.

  18. Cubic modification crystal structure of cesium neodymium tetrametaphosphates,. beta. -CsNd(POsub(3))sub(4) (CsNdP/sub 4/O/sub 12/)

    Energy Technology Data Exchange (ETDEWEB)

    Palkina, K.K.; Maksimova, S.I.; Chibiskova, N.T. (AN SSSR, Moscow. Inst. Obshchej i Neorganicheskoj Khimii)

    1981-01-01

    A complete X-ray structural investigation into ..beta..-CsNd (PO/sub 3/)/sub 4/ crystallites is presented. ..beta..-CsNd (PO/sub 3/)/sub 4/ is crystallized in the cubic crystal system; space group is 143 d; the parameters of the elementary cell are a=15.233 (3)A; Z=12, V=3535 4A/sup 3/, dsub(roent)=3.34 g/cm/sup 3/. Interatomic distances and valent angles of crystals are presented. It is shown that ..beta..- CsNd(NO/sub 3/)/sub 4/ noncentrosymmetric crystals are isotropic, as they belong to cubic crystal structure and must obviously combine simultaneously luminescent, optic non-linear and piezoelectric properties.

  19. First-principles study of the electronic structure of PbF{sub 2} in the cubic, orthorhombic, and hexagonal phases

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Huitian [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Orlando, Roberto [Dipartimento di Scienze e Tecnologie Avanzate, Universita del Piemonte Orientale, C. so Borsalino 54, I-15100 Alessandria (Italy); Blanco, Miguel A [Departamento de QuImica Fisica y Analitica, Universidad de Oviedo, 33006-Oviedo (Spain); Pandey, Ravindra [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States)

    2004-05-12

    The results of electronic structure calculations for PbF{sub 2} in ambient and high-pressure phases are reported here. We employ the linear combination of atomic orbital-density functional theory approximation using the CRYSTAL program package whose capabilities were expanded to include the so-called soft-core pseudopotentials with higher-order components (e.g. d, f, and g) of the angular momentum terms for heavier atoms in the periodic table. The band structure and density of states of the cubic, orthorhombic, and hexagonal phases were calculated. A direct band gap at X is predicted for the cubic phase, whereas an indirect band gap is predicted for the high-pressure phases. The density of states reveals hybridization features involving Pb s and F p orbitals in the upper valence band of PbF{sub 2}.

  20. Fluorite transition metal hydride induced destabilization of the MgH2 system in MgH2/TMH2 multilayers ( TM=Sc , Ti, V, Cr, Y, Zr, Nb, La, Hf)

    Science.gov (United States)

    Tao, S. X.; Notten, P. H. L.; van Santen, R. A.; Jansen, A. P. J.

    2010-09-01

    The structural changes in MgH2 induced by contact with fluorite transition metal hydrides ( TMH2 , TM=Sc , Ti, V, Cr, Y, Zr, Nb, La, Hf) have been studied using density-functional theory calculations. Models of MgH2(rutile)/TiH2(fluorite) and MgH2(fluorite)/TiH2(fluorite) multilayers with different Mg:TM ratios have been designed. With a fixed thickness of the TMH2 layer, structure transformation of MgH2 from rutile to fluorite occurs with a decrease in thickness of the MgH2 layer. The hydrogen desorption energy from the fluorite MgH2 layer in the multilayers is significantly lower than that of the bulk rutile MgH2 . The structural deformation of the MgH2 layer due to the strain induced by TMH2 is found to be responsible for the destabilization of the Mg-H bond: the more structural deformation, the more destabilization of the Mg-H. Our results provide an important insight for the development of new hydrogen-storage materials with desirable thermodynamic properties.

  1. 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.

  2. Reply to “Structural and magnetic behavior of the cubic oxyfluoride SrFeO{sub 2}F studied by neutron diffraction”

    Energy Technology Data Exchange (ETDEWEB)

    Clemens, Oliver, E-mail: oliver.clemens@kit.edu [Technische Universität Darmstadt, Joint Research Laboratory Nanomaterials, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Berry, Frank J.; Wright, Adrian J. [School of Chemistry, The University of Birmingham, Birmingham B15 2TT (United Kingdom); Knight, Kevin S. [ISIS Facility, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX (United Kingdom); Perez-Mato, J.M.; Igartua, J.M. [Departamentos de Física de la Materia Condensada y Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao (Spain); Slater, Peter R. [School of Chemistry, The University of Birmingham, Birmingham B15 2TT (United Kingdom)

    2015-03-15

    In this article we comment on the results published by Thompson et al. (, J. Solid State Chem. 219 (2014) 173–178) on the crystal structure of SrFeO{sub 2}F, who claim the compound to crystallize in the cubic space group Pm-3m. We give a more detailed explanation of the determination of our previously reported structural model with Imma symmetry (Clemens et al., J. Solid State Chem. 206 (2013) 158–169), with addition of variable temperature XRD measurements with high counting time to provide unambiguous evidence for the Imma model being correct for our sample. - Graphical abstract: The crystal structure of SrFeO{sub 2}F is discussed with regards to previous reports. - Highlights: • SrFeO{sub 2}F was synthesized by polymer based fluorination of SrFeO{sub 3}. • Evaluation of the diffraction data shows a pseudocubic cell metric. • Superstructure reflections at low d-spacings indicate deviation from cubic symmetry. • The phase transition temperature from orthorhombic to cubic was determined using variable temperature X-ray diffraction. • Results published by Thompson et al. are critically discussed with respect to those observations.

  3. Fluid inclusion and cathodoluminescence studies on fluorite from the Kerio valley, Kenya

    Science.gov (United States)

    Ogola, J. S.; Behr, H. J.; van den Kerkhof, A. M.

    1994-04-01

    The Kerio valley lies between the Elgeyo escarpment and the Tugen hills which mark the western margin of the Kenya rift valley. The main fluorite deposits are located in the southern part of the valley at Kimwarer, Choff and Kamnaon. Three types of inclusion fillings were identified: Liquid+Vapour, Liquid+Daughter Minerals and Liquid. The L+V type is dominant. Inclusions occur as clusters, trails along the crystal growth zones and as isolated ones. Low salinities, apparently lower than the 5% wt. NaCl equivalent, were established. Homogenization temperatures suggest that fluorite mineralization took place at different stages and at temperatures between 120 and 180 °C. Isolated readings above 180°C may be referring to the original inclusions in limestone. These measurements and the absence of CO 2 in the inclusions, as well as the occurrence of vugs and crustifications with fluorite, suggest that mineralization took place at relatively shallow depths. Emission spectrum lines representing Eu 2+, Dy 3+, Tb 3+ and Sm 3+ in fluorite were identified. Sm 3+ was detected only in the pinkish luminescence of veined fluorite, whereas the pinkish zone in banded fluorite contains Tb 3+. Eu 2+ which gives the strongest emission lines in the blue part of the visible spectrum, apparently is responsible for the strong blue cathodoluminescence (CL) in fluorite. The dominance of Eu 2+ peaks further points to the fact that fluorite mineralization in the Kerio valley took place in an environment that was enriched in Lanthanide Rare Earth Elements (LREE). The presence of rare earths and radioactive elements in fluorite points towards their enrichment in the environment of fluorite mineralization. A juvenile origin of mineral forming solutions is proposed. Two generations of fluorite were established: allotriomorphic fluorite, forming the matrix, and the idiomorphic variety, occurring either in barite or in druzes in early fluorite. Barite in turn forms idiomorphic crystals in

  4. Influence of ions on two-dimensional and three-dimensional atomic force microscopy at fluorite-water interfaces

    Science.gov (United States)

    Miyazawa, K.; Watkins, M.; Shluger, A. L.; Fukuma, T.

    2017-06-01

    Recent advancement in liquid-environment atomic force microscopy (AFM) has enabled us to visualize three-dimensional (3D) hydration structures as well as two-dimensional (2D) surface structures with subnanometer-scale resolution at solid-water interfaces. However, the influence of ions present in solution on the 2D- and 3D-AFM measurements has not been well understood. In this study, we perform atomic-scale 2D- and 3D-AFM measurements at fluorite-water interfaces in pure water and a supersaturated solution of fluorite. The images obtained in these two environments are compared to understand the influence of the ions in solution on these measurements. In the 2D images, we found clear difference in the nanoscale structures but no significant difference in the atomic-scale contrasts. However, the 3D force images show clear difference in the subnanometer-scale contrasts. The force contrasts measured in pure water largely agree with those expected from the molecular dynamics simulation and the solvent tip approximation model. In the supersaturated solution, an additional force peak is observed over the negatively charged fluorine ion site. This location suggests that the observed force peak may originate from cations adsorbed on the fluorite surface. These results demonstrate that the ions can significantly alter the subnanometer-scale force contrasts in the 3D-AFM images.

  5. Preparation and properties of CeTe/sub 2/O/sub 6/ and ThTe/sub 2/O/sub 6/, compounds with a new superstructure of the fluorite type

    Energy Technology Data Exchange (ETDEWEB)

    Botto, I.L.; Baran, E.J. (La Plata Univ. Nacional (Argentina). Facultad de Ciencias Exactas)

    1982-01-01

    It is demonstrated that in the systems MO/sub 2//TeO/sub 2/ (with M = Ce, Th), treated in air and at 600 /sup 0/C, only phases of composition MTe/sub 2/O/sub 6/ are formed. They pertains to the cubic crystal system and constitutes a new type of fluorite-superstructure. Different aspects of its crystal chemistry are commented and also the infrared spectra are recorded and briefly discussed.

  6. [Assessment of Soil Fluorine Pollution in Jinhua Fluorite Ore Areas].

    Science.gov (United States)

    Ye, Qun-feng; Zhou, Xiao-ling

    2015-07-01

    The contents of. soil total fluorine (TF) and water-soluble fluorine (WF) were measured in fluorite ore areas located in Jinhua City. The single factor index, geoaccumulation index and health risk assessment were used to evaluate fluorine pollution in soil in four fluorite ore areas and one non-ore area, respectively. The results showed that the TF contents in soils were 28. 36-56 052. 39 mg.kg-1 with an arithmetic mean value of 8 325.90 mg.kg-1, a geometric mean of 1 555. 94 mg.kg-1, and a median of 812. 98 mg.kg-1. The variation coefficient of TF was 172. 07% . The soil WF contents ranged from 0. 83 to 74. 63 mg.kg-1 with an arithmetic mean value of 16. 94 mg.kg-1, a geometric mean of 10. 59 mg.kg-1, and a median of 10. 17 mg.kg-1. The variation coefficient of WF was 100. 10%. The soil TF and WF contents were far higher than the national average level of the local fluorine epidemic occurrence area. The fluoride pollution in soil was significantly affected by human factors. Soil fluorine pollution in Yangjia, Lengshuikeng and Huajie fluorite ore areas was the most serious, followed by Daren fluorite ore area, and in non-ore area there was almost no fluorine pollution. Oral ingestion of soils was the main exposure route. Sensitivity analysis of model parameters showed that children's weight exerted the largest influence over hazard quotient. Furthermore, a significant positive correlation was found among the three kinds of evaluation methods.

  7. Effect of Precursor Mechanism on CO-NO Catalytic Reaction on Body-Centred Cubic Structure: Monte Carlo Simulation

    Institute of Scientific and Technical Information of China (English)

    A. U. Qaisrani; M. Khalid; M. K.Khan

    2005-01-01

    @@ The CO-NO catalytic reaction on body-centred cubic (bcc) lattice is studied by Monte Carlo simulation. The simple Langmuir-Hinshelwood (LH) mechanism yields a steady reactive window, which is separated by continuous and discontinuous irreversible phase transitions. The effect of precursor mechanism on the phase diagram of the system is also studied. According to this mechanism, the precursor motion of CO molecules is considered only on the surface of bcc lattice. Some interesting observations are reported.

  8. The competitive growth of cubic domains in Ti(1-x)AlxN films studied by diffraction anomalous near-edge structure spectroscopy.

    Science.gov (United States)

    Pinot, Y; Tuilier, M-H; Pac, M-J; Rousselot, C; Thiaudière, D

    2015-11-01

    Titanium and aluminium nitride films deposited by magnetron sputtering generally grow as columnar domains made of oriented nanocrystallites with cubic or hexagonal symmetry depending on Al content, which are embedded in more disordered grain boundaries. The substitution of Al atoms for Ti in the cubic lattice of the films improves their resistance to wear and oxidation, allowing their use as protective coatings. Ti K-edge X-ray absorption spectroscopy, which probes both crystallized and more disordered grain boundaries, and X-ray diffraction anomalous fine structure, which is sensitive to short- and long-range order within a given crystallized domain, are carried out on a set of Ti(1-x)AlxN films deposited by magnetron sputtering on Si substrates. Attention is paid to the shape of the pre-edge region, which is sensitive to the symmetry of the site occupied by Ti atoms, either octahedral in face-centred-cubic Ti-rich (TiN, Ti0.54Al0.46N) samples or tetrahedral in hexagonal-close-packed Al-rich (Ti0.32Al0.68N) films. In order to obain information on the titanium environment in the well crystallized areas, subtraction of the smooth part of the energy-dependent structure factor for the Bragg reflections is applied to the pre-edge region of the diffraction anomalous data in order to restore their spectroscopic appearance. A flat pre-edge is related to the typical octahedral environment of Ti atoms for cubic reflections. The difference observed between pre-edge spectra associated with face-centred-cubic 200 and 111 Bragg reflections of Ti0.54Al0.46N is assigned to Ti enrichment of 111 large well ordered domains compared with the more disordered 200 ones. The sharp peak observed in the spectrum recorded from the hexagonal 002 peak of Ti0.32Al0.68N can be regarded as a standard for the pure tetrahedral Ti environment in hexagonal-close-packed nitride.

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

    Institute of Scientific and Technical Information of China (English)

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

    2010-01-01

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

  10. Anisotropic cubic curvature couplings

    CERN Document Server

    Bailey, Quentin G

    2016-01-01

    To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass dimension 8 coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the Weak Equivalence Principle for self-gravitating bodies. These coefficients can be measured in solar-system tests, while binary-pulsar systems and short-range gravity tests are particularly sensitive.

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

    Science.gov (United States)

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

    2016-12-01

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

  12. Average and equilibrium structures of methyl flouride studied by electron diffraction. A joint analysis with rotational constants and cubic force constants

    Science.gov (United States)

    Egawa, Toru; Yamamoto, Satoshi; Nakata, Munetaka; Kuchitsu, Kozo

    1987-02-01

    Electron diffraction intensity of methyl fluoride was measured and analyzed jointly with the rotational constants, Ao and Bo, of the normal species. The following structure was derived: rg(CF) = 1.391(1) Å, rg(CH) = 1.108(1) Å and β z(FCH) = 108.7(2)°, where the numbers in parentheses represent estimated limits of error. The effective anharmonic constants were derived using the rotational constants and the l-type doubling constants; the cubic force constants calculated by Kondo using a 6-311G** (MP2) basis set were also incorporated in the analysis. The following equilibrium structure was derived from the rz structure and the effective anharmonic constants: re(CF) = 1.383(1) Å, re(CH) = 1.086(2) Å and β e(FCH) = 108.8(3)°.

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

    Science.gov (United States)

    1992-06-01

    AD-A253 331 Semiannual Report Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication...Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using...34 substrates, such as using a graded AlxGal-xN solid solution as a buffer layer. E. Conclusion We have shown that in the use of our modified gas source MBE

  14. Symmetry-Guided Synthesis of Highly Porous Metal-Organic Frameworks with Fluorite Topology

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, MW; Chen, YP; Bosch, M; Gentle, T; Wang, KC; Feng, DW; Wang, ZYU; Zhou, HC

    2013-11-11

    Two stable, non-interpenetrated MOFs, PCN-521 and PCN-523, were synthesized by a symmetry-guided strategy. Augmentation of the 4-connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8-connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN-521 has the largest BET surface area (3411 m(2) g(-1)), pore size (20.5 x 20.5 x 37.4 angstrom) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non-interpenetrated MOFs with high porosity.

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

    Science.gov (United States)

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

    2016-11-01

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

  16. Optical, structural and fluorescence properties of nanocrystalline cubic or monoclinic Eu:Lu{sub 2}O{sub 3} films prepared by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Martinet, C. [Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS-Universite Lyon1, 10, rue Andre-Marie Ampere, 69622 Villeurbanne Cedex (France)]. E-mail: martinet@pcml.univ-lyon1.fr; Pillonnet, A. [Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS-Universite Lyon1, 10, rue Andre-Marie Ampere, 69622 Villeurbanne Cedex (France); Lancok, J. [Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 18221 Prague (Czech Republic); Garapon, C. [Laboratoire de Physico-Chimie des Materiaux Luminescents, CNRS-Universite Lyon1, 10, rue Andre-Marie Ampere, 69622 Villeurbanne Cedex (France)

    2007-10-15

    Eu{sup 3+}-doped lutetium oxide (Eu:Lu{sub 2}O{sub 3}) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 deg. C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu{sup 3+} fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band.

  17. Magnetic behaviors of a transverse spin-1/2 Ising cubic nanowire with core/shell structure

    Science.gov (United States)

    El Hamri, M.; Bouhou, S.; Essaoudi, I.; Ainane, A.; Ahuja, R.; Dujardin, F.

    2017-02-01

    The surface shell exchange coupling effect on the magnetic properties (surface shell, core, total longitudinal and total transverse magnetizations, susceptibility, phase diagram and hysteresis loops) of a transverse spin-1/2 Ising cubic nanowire is investigated, in the present work, by employing the effective-field theory based on the probability distribution technique with correlations, for both ferro- and antiferromagnetic cases. We have found that this parameter has a strong effect on the magnetic properties in both cases. In the ferromagnetic case, the total longitudinal magnetization curves display Q- and S-type behaviors and the hysteresis loop has just one loop, whereas in the antiferromagnetic case, the N-type behavior, in which one compensation temperature appears below the critical temperature, exists in the total longitudinal magnetization curve versus reduced temperature, and triple hysteresis loops are found. The effect of applied field is also investigated on the total longitudinal magnetization for the both cases, and we have found that a large applied field value can overcome the antiferromagnetic coupling leading to a ferromagnetic-like behavior.

  18. Cubic Subalgebras and Cubic Closed Ideals of B-algebras

    Directory of Open Access Journals (Sweden)

    Tapan Senapati

    2015-06-01

    Full Text Available In this paper, the concept of cubic set to subalgebras, ideals and closed ideals of B-algebras are introduced. Relations among cubic subalgebras with cubic ideals and cubic closed ideals of B-algebras investigated. The homomorphic image and inverse image of cubic subalgebras, ideals are studied and some related properties are investigated. Also, the product of cubic B-algebras are investigated.

  19. β-Mn-type Co(8+x)Zn(12-x) as a defect cubic Laves phase: site preferences, magnetism, and electronic structure.

    Science.gov (United States)

    Xie, Weiwei; Thimmaiah, Srinivasa; Lamsal, Jagat; Liu, Jing; Heitmann, Thomas W; Quirinale, Dante; Goldman, Alan I; Pecharsky, Vitalij; Miller, Gordon J

    2013-08-19

    The results of crystallographic analysis, magnetic characterization, and theoretical assessment of β-Mn-type Co-Zn intermetallics prepared using high-temperature methods are presented. These β-Mn Co-Zn phases crystallize in the space group P4(1)32 [Pearson symbol cP20; a = 6.3555(7)-6.3220(7)], and their stoichiometry may be expressed as Co(8+x)Zn(12-x) [1.7(2) phase with a Curie temperature of ∼420 K. Neutron powder diffraction and electronic structure calculations using the local spin density approximation indicate that the spontaneous magnetization of this phase arises exclusively from local moments at the Co atoms. Inspection of the atomic arrangements of Co(8+x)Zn(12-x) reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna ab initio simulation package (VASP) and starting from the undistorted, defect Laves phase structure achieved energy minimization at the observed β-Mn structure type, a result that offers greater insight into the β-Mn structure type and establishes a closer relationship with the corresponding α-Mn structure (cI58).

  20. Round Top Mountain rhyolite (Texas, USA), a massive, unique Y-bearing-fluorite-hosted heavy rare earth element (HREE) deposit

    Institute of Scientific and Technical Information of China (English)

    PINGITORE Nicholas; CLAGUE Juan; GORSKI Daniel

    2014-01-01

    Round Top Mountain in Hudspeth County, west Texas, USA is a surface-exposed rhyolite intrusion enriched in Y and heavy rare earth elements (HREEs), as well as Nb, Ta, Be, Li, F, Sn, Rb, Th, and U. The massive tonnage, estimated at well over 1 billion tons, of the deposit makes it a target for recovery of valuable yttrium and HREEs (YHREEs), and possibly other scarce ele-ments. Because of the extremely fine grain size of the mineralized rhyolite matrix, it has not been clear which minerals host the YHREEs and in what proportions. REE-bearing minerals reported in the deposit included bastnäsite-Ce, Y-bearing fluorite, xeno-time-Y, zircon, aeschynite-Ce, a Ca-Th-Pb fluoride, and possibly ancylite-La and cerianite-Ce. Extended X-ray absorption fine struc-ture (EXAFS) indicated that virtually all of the yttrium, a proxy for the HREEs, resided in a coordination in the fluorite-type crystal structure, rather than those in the structures of bastnäsite-Ce and xenotime-Y. The YREE grade of the Round Top deposit was just over 0.05%, with 72%of this consisting of YHREEs. This grade was in the range of the South China ionic clay deposits that supply essentially all of the world’s YHREEs. Because the host Y-bearing fluorite is soluble in dilute sulfuric acid at room temperature, a heap leaching of the deposit appeared feasible, aided by the fact that 90%-95%of the rock consists of unreactive and insoluble feld-spars and quartz. The absence of overburden, remarkable consistency of mineralization grade throughout the massive rhyolite, prox-imity (a few km) to a US interstate highway, major rail systems and gas and electricity, temperate climate, and stable political location in the world’s largest economy all enhanced the potential economic appeal of Round Top.

  1. First-principles calculations on the structural and electronic properties of cubic KCaF3 and NaCaF3 (001) surfaces

    Science.gov (United States)

    Yang, Kun; He, Yanqing; Cheng, Yi; Che, Li; Yao, Li

    2017-03-01

    First-principles density functional theory (DFT) calculations have been used to investigate the structural and electronic properties of the cubic KCaF3 and NaCaF3 (001) surfaces with MF (M = K or Na) and CaF2 terminations. For both KCaF3 and NaCaF3 (001) surfaces, the MF termination has stronger surface rumpling than the CaF2 termination. All the computed band gaps for the KCaF3 and NaCaF3 (001) surfaces are smaller than those of the bulks. Furthermore, separated bands that originate from surface layer F p states are introduced at the top of the valance band of MF-terminated surfaces, indicating the emergence of the surface states. The calculated surface energies show that the MF-terminated surface is energetically more favorable than the CaF2-terminated surface.

  2. Global Existence and Convergence of Solutions to a Cross-Diffusion Cubic Predator-Prey System with Stage Structure for the Prey

    Directory of Open Access Journals (Sweden)

    Shengmao Fu

    2010-01-01

    Full Text Available We study a cubic predator-prey system with stage structure for the prey. This system is a generalization of the two-species Lotka-Volterra predator-prey model. Firstly, we consider the asymptotical stability of equilibrium points to the system of ordinary differential equations type. Then, the global existence of solutions and the stability of equilibrium points to the system of weakly coupled reaction-diffusion type are discussed. Finally, the existence of nonnegative classical global solutions to the system of strongly coupled reaction-diffusion type is investigated when the space dimension is less than 6, and the global asymptotic stability of unique positive equilibrium point of the system is proved by constructing Lyapunov functions.

  3. Crystal structure and optical properties of the [Ag62S12(SBu(t))32](2+) nanocluster with a complete face-centered cubic kernel.

    Science.gov (United States)

    Jin, Shan; Wang, Shuxin; Song, Yongbo; Zhou, Meng; Zhong, Juan; Zhang, Jun; Xia, Andong; Pei, Yong; Chen, Man; Li, Peng; Zhu, Manzhou

    2014-11-05

    The crystal structure of the [Ag62S12(SBu(t))32](2+) nanocluster (denoted as NC-I) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag14 core structure with a Ag48(SBu(t))32 shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag62S13(SBu(t))32](4+) structure (denoted as NC-II for short) reported by Wang. Interestingly, NC-I exhibits prominent differences in the optical properties in comparison with the case of the NC-II nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in NC-I in comparison to that of NC-II is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of NC-I and NC-II. These findings offer a new insight into the structure and property evolution of silver cluster materials.

  4. Fluorite equilibria in thermal springs of the Snake River Basin, Idaho

    Science.gov (United States)

    Roberson, C.E.; Schoen, Robert

    1973-01-01

    Some thermal water sources of the Snake River basin, Idaho, are near saturation with respect to fluorite. That mineral was identified by X-ray diffraction in precipitates induced in three water samples by adding sodium fluoride. The derived solubility product (KS0) for zero ionic strength was close to that calculated from Latimer's thermodynamic data (10-9.7 7). The relative ease of precipitation of fluorite from these water samples indicates that equilibrium with respect to fluorite may occur in some ground-water systems.

  5. First-principles calculations of typical anisotropic cubic and hexagonal structures and homogenized moduli estimation based on the Y-parameter: Application to CaO, MgO, CH and Calcite CaCO3

    Science.gov (United States)

    Fu, Jia; Bernard, Fabrice; Kamali-Bernard, Siham

    2017-02-01

    X-ray method to test the material properties and to obtain elastic constants is commonly based on the Reuss model and Kroner model. Y parameter has been turned out to be an effective method to estimate elastic properties of polycrystalline material. Since Y-parameters of cubic polycrystalline material based on the certain uniform stress (Reuss model) has not been given, our work aims to complete this part of the theoretical analysis, which can effectively compare elastic constants measured by the X-ray diffraction method. The structural and the elastic properties of cubic structures (CaO and MgO) and hexagonal structures (CH and Calcite CaCO3) are investigated by the density functional theory method. And then the credibility of Y parameters for determing elastic moduli of cubic structures is proved and elastic properties in typical crystallographic planes of [100], [110] and [111] are also calculated. Meanwhile, Young's moduli of CH and Calcite structure are 58.08 GPa and 84.549 GPa, which are all close to references. Elastic properties of cubic and hexagonal structures under various pressures are calculated and the surface constructions of elastic moduli are drawn, showing the anisotropy at various directions. The crystal structure investigated in this work are typical of some primary or secondary components of Hardened Cements Pastes and their homogenized elastic properties are needed in a hierarchical multi-scale modeling, such as the one developed by some of the authors of this paper.

  6. Cubic Curves, Finite Geometry and Cryptography

    CERN Document Server

    Bruen, A A; Wehlau, D L

    2011-01-01

    Some geometry on non-singular cubic curves, mainly over finite fields, is surveyed. Such a curve has 9,3,1 or 0 points of inflexion, and cubic curves are classified accordingly. The group structure and the possible numbers of rational points are also surveyed. A possible strengthening of the security of elliptic curve cryptography is proposed using a `shared secret' related to the group law. Cubic curves are also used in a new way to construct sets of points having various combinatorial and geometric properties that are of particular interest in finite Desarguesian planes.

  7. In-depth investigation of EPR spectra of Mn(2+) ions in ZnS single crystals with pure cubic structure.

    Science.gov (United States)

    Nistor, S V; Stefan, M

    2009-04-01

    The X (9.8 GHz)-band electron paramagnetic resonance (EPR) properties of substitutional Mn(2+) ions in high quality cubic ZnS single crystals grown from PbCl(2) flux have been thoroughly investigated. Accurate spin Hamiltonian (SH) parameters: g = 2.002 25 ± 0.000 06; a = (7.987 ± 0.008) × 10(-4) cm(-1) and A = -(63.88 ± 0.02) × 10(-4) cm(-1) were obtained by simulation and fitting to the experimentally allowed transitions recorded for the magnetic field aligned within ± 0.25° along the main crystal axes. The normally forbidden hyperfine [Formula: see text], Δm = ± 1 transitions were also observed. Their position was found to be in agreement, within the experimental accuracy of ΔH = ± 0.01 mT, with calculations using the same SH parameters. The angular variation of the ratios of the intensities of the central forbidden to the allowed transitions could be accounted for only by including an additional constant contribution. The observed line broadening of the [Formula: see text] and [Formula: see text] fine structure transitions and their line width variation in a (110) plane have been quantitatively described by considering a random distribution of lattice strains at the Mn(2+) impurity ions. The influence of the forbidden transitions and line broadening on the EPR spectra line shape of the Mn(2+) ions in cubic ZnS crystalline powders is also examined.

  8. Crystal structure of monoclinic samarium and cubic europium sesquioxides and bound coherent neutron scattering lengths of the isotopes {sup 154}Sm and {sup 153}Eu

    Energy Technology Data Exchange (ETDEWEB)

    Kohlmann, Holger [Leipzig Univ. (Germany). Inst. of Inorganic Chemistry; Hein, Christina; Kautenburger, Ralf [Saarland Univ., Saarbruecken (Germany). Inorganic Solid State Chemistry; Hansen, Thomas C.; Ritter, Clemens [Institut Laue-Langevin, Grenoble (France); Doyle, Stephen [Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen (Germany). Inst. for Synchrotron Radiation (ISS)

    2016-11-01

    The crystal structures of monoclinic samarium and cubic europium sesquioxide, Sm{sub 2}O{sub 3} and Eu{sub 2}O{sub 3}, were reinvestigated by powder diffraction methods (laboratory X-ray, synchrotron, neutron). Rietveld analysis yields more precise structural parameters than previously known, especially for oxygen atoms. Interatomic distances d(Sm-O) in Sm{sub 2}O{sub 3} range from 226.3(4) to 275.9(2) pm [average 241.6(3) pm] for the monoclinic B type Sm{sub 2}O{sub 3} [space group C2/m, a = 1418.04(3) pm, b = 362.660(7) pm, c = 885.48(2) pm, β = 100.028(1) ], d(Eu-O) in Eu{sub 2}O{sub 3} from 229.9(2) to 238.8(2) pm for the cubic bixbyite (C) type [space group Ia anti 3, a = 1086.87(1) pm]. Neutron diffraction at 50 K and 2 K did not show any sign for magnetic ordering in Sm{sub 2}O{sub 3}. Isotopically enriched {sup 154}Sm{sub 2}O{sub 3} and {sup 153}Eu{sub 2}O{sub 3} were used for the neutron diffraction work because of the enormous absorption cross section of the natural isotopic mixtures for thermal neutrons. The isotopic purity was determined by inductively coupled plasma - mass spectrometry to be 98.9% for {sup 154}Sm and 99.8% for {sup 153}Eu. Advanced analysis of the neutron diffraction data suggest that the bound coherent scattering lengths of {sup 154}Sm and {sup 153}Eu need to be revised. We tentatively propose b{sub c}({sup 154}Sm) = 8.97(6) fm and b{sub c}({sup 153}Eu) = 8.85(3) fm for a neutron wavelength of 186.6 pm to be better values for these isotopes, showing up to 8% deviation from accepted literature values. It is shown that inaccurate scattering lengths may result in severe problems in crystal structure refinements causing erroneous structural details such as occupation parameters, which might be critically linked to physical properties like superconductivity in multinary oxides.

  9. Damage evolution of ion irradiated defected-fluorite La 2 Zr 2 O 7 epitaxial thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kaspar, Tiffany C.; Gigax, Jonathan G.; Shao, Lin; Bowden, Mark E.; Varga, Tamas; Shutthanandan, Vaithiyalingam; Spurgeon, Steven R.; Yan, Pengfei; Wang, Chongmin; Ramuhalli, Pradeep; Henager, Charles H.

    2017-05-01

    Pyrochlore-structure oxides, A2B2O7, may exhibit remarkable radiation tolerance due to the ease with which they can accommodate disorder by transitioning to a defected fluorite structure. The mechanism of defect formation was explored by evaluating the radiation damage behavior of high quality epitaxial La2Zr2O7 thin films with the defected fluorite structure, irradiated with 1 MeV Zr+ at doses up to 10 displacements per atom (dpa). The level of film damage was evaluated as a function of dose by Rutherford backscattering spectrometry in the channeling geometry (RBS/c) and scanning transmission electron microscopy (STEM). At lower doses, the surface of the La2Zr2O7 film amorphized, and the amorphous fraction as a function of dose fit well to a stimulated amorphization model. As the dose increased, the surface amorphization slowed, and amorphization appeared at the interface. Even at a dose of 10 dpa, the core of the film remained crystalline, despite the prediction of amorphization from the model. To inform future ab initio simulations of La2Zr2O7, the bandgap of a thick La2Zr2O7 film was measured to be indirect at 4.96 eV, with a direct transition at 5.60 eV.

  10. The body-centered cubic structure of methyllithium tetramer crystal: staggered methyl conformation by electrostatic stabilization via intratetramer multipolarization.

    Science.gov (United States)

    Ohta, Yusuke; Demura, Akimitsu; Okamoto, Takuya; Hitomi, Haruko; Nagaoka, Masataka

    2006-06-29

    The methyllithium tetramer (CH3Li)4 structure in the bcc crystal has been theoretically optimized with the use of density functional theory calculations under the periodic boundary condition. The X-ray structure shows that the methyl-group conformation in tetramer in crystal takes the staggered form rather than the eclipsed form that is taken in the isolated tetramer, i.e., the crystal packing effect, and this has been reproduced for the first time. It is concluded that the staggered form is advantageous in crystal, as a whole, due to the larger electrostatic stabilization via the induced intratetramer multipolarization, although it should cause, simultaneously, smaller destabilization in intratetramer electronic energy.

  11. Semisymmetric Cubic Graphs of Order 162

    Indian Academy of Sciences (India)

    Mehdi Alaeiyan; Hamid A Tavallaee; B N Onagh

    2010-02-01

    An undirected graph without isolated vertices is said to be semisymmetric if its full automorphism group acts transitively on its edge set but not on its vertex set. In this paper, we inquire the existence of connected semisymmetric cubic graphs of order 162. It is shown that for every odd prime , there exists a semisymmetric cubic graph of order 162 and its structure is explicitly specified by giving the corresponding voltage rules generating the covering projections.

  12. Einsteinian cubic gravity

    Science.gov (United States)

    Bueno, Pablo; Cano, Pablo A.

    2016-11-01

    We drastically simplify the problem of linearizing a general higher-order theory of gravity. We reduce it to the evaluation of its Lagrangian on a particular Riemann tensor depending on two parameters, and the computation of two derivatives with respect to one of those parameters. We use our method to construct a D -dimensional cubic theory of gravity which satisfies the following properties: (1) it shares the spectrum of Einstein gravity, i.e., it only propagates a transverse and massless graviton on a maximally symmetric background; (2) it is defined in the same way in general dimensions; (3) it is neither trivial nor topological in four dimensions. Up to cubic order in curvature, the only previously known theories satisfying the first two requirements are the Lovelock ones. We show that, up to cubic order, there exists only one additional theory satisfying requirements (1) and (2). Interestingly, this theory is, along with Einstein gravity, the only one which also satisfies (3).

  13. Synthesis, crystal structure, and bonding analysis of the hypoelectronic cubic phase Ca5Pd6Ge6.

    Science.gov (United States)

    Doverbratt, Isa; Ponou, Siméon; Wang, Fei; Lidin, Sven

    2015-09-21

    The title compound, Ca5Pd6Ge6, was obtained during a systematic investigation of the Ca-Pd-Ge ternary phase diagram. The crystal structure was determined and refined from single-crystal X-ray diffraction data. It crystallizes in a new structure variant of the Y4PdGa12-type structure (Im3̅m, a = 8.7764(4) Å) that features an arrangement of vertex-sharing body-centered cubes of calcium, Ca@Ca8, with a hierarchical bcc network, interpenetrating a second (Pd6Ge6) network consisting of Ge2 dumbbells surrounded by Pd in a strongly flattened octahedron with Pd(μ(2)-η(2),η(4)-Ge2)-like motifs. These octahedra are condensed through the Pd to form a 3D open fcc network. Theoretical band structure calculations suggested that the compound is hypoelectronic with predominantly multicenter-type interatomic interactions involving all three elements and essentially a Hume-Rothery-like regime of electronic stabilization. The similar electronegativity between germanium and palladium atoms has a decisive impact on the bonding picture of the system.

  14. Structure-property relationships in cubic cuprous iodide: A novel view on stability, chemical bonding, and electronic properties

    Science.gov (United States)

    Pishtshev, A.; Karazhanov, S. Zh.

    2017-02-01

    Based on the combination of density functional theory and theory-group methods, we performed systematic modeling of γ-CuI structural design at the atomistic level. Being started from the metallic copper lattice, we treated a crystal assembly as a stepwise iodination process characterized in terms of a sequence of intermediate lattice geometries. These geometries were selected and validated via screening of possible structural transformations. The genesis of chemical bonding was studied for three structural transformations by analyzing the relevant changes in the topology of valence electron densities. We determined structural trends driven by metal-ligand coupling. This allowed us to suggest the improved scenario of chemical bonding in γ-CuI. In particular, the unconventional effect of spatial separation of metallic and covalent interactions was found to be very important with respect to the preferred arrangements of valence electrons in the iodination process. We rigorously showed that useful electronic and optical properties of γ-CuI originate from the combination of two separated bonding patterns—strong covalency established in I-Cu tetrahedral connections and noncovalent interactions of copper cores is caused by the 3d10 closed-shell electron configurations. The other finding of ours is that the self-consistency of the GW calculations is crucial for correctly determining the dynamic electronic correlations in γ-CuI. Detail reinvestigation of the quasi-particle energy structure by means of the self-consistent GW approach allowed us to explain how p-type electrical conductivity can be engineered in the material.

  15. Structure-property relationships in cubic cuprous iodide: A novel view on stability, chemical bonding, and electronic properties.

    Science.gov (United States)

    Pishtshev, A; Karazhanov, S Zh

    2017-02-14

    Based on the combination of density functional theory and theory-group methods, we performed systematic modeling of γ-CuI structural design at the atomistic level. Being started from the metallic copper lattice, we treated a crystal assembly as a stepwise iodination process characterized in terms of a sequence of intermediate lattice geometries. These geometries were selected and validated via screening of possible structural transformations. The genesis of chemical bonding was studied for three structural transformations by analyzing the relevant changes in the topology of valence electron densities. We determined structural trends driven by metal-ligand coupling. This allowed us to suggest the improved scenario of chemical bonding in γ-CuI. In particular, the unconventional effect of spatial separation of metallic and covalent interactions was found to be very important with respect to the preferred arrangements of valence electrons in the iodination process. We rigorously showed that useful electronic and optical properties of γ-CuI originate from the combination of two separated bonding patterns-strong covalency established in I-Cu tetrahedral connections and noncovalent interactions of copper cores is caused by the 3d(10) closed-shell electron configurations. The other finding of ours is that the self-consistency of the GW calculations is crucial for correctly determining the dynamic electronic correlations in γ-CuI. Detail reinvestigation of the quasi-particle energy structure by means of the self-consistent GW approach allowed us to explain how p-type electrical conductivity can be engineered in the material.

  16. Near-edge x-ray absorption fine-structure study of ion-beam-induced phase transformation in Gd2(Ti1-yZry)2O7

    Science.gov (United States)

    Nachimuthu, P.; Thevuthasan, S.; Shutthanandan, V.; Adams, E. M.; Weber, W. J.; Begg, B. D.; Shuh, D. K.; Lindle, D. W.; Gullikson, E. M.; Perera, R. C. C.

    2005-02-01

    The structural and electronic properties of Gd2(Ti1-yZry)2O7 (y =0-1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation (˜5.0×1014Au2+/cm2) have been investigated by Ti2p and O1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd2(Ti1-yZry)2O7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd2(Ti1-yZry)2O7 with y ⩽0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with y ⩾0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr4+ in the irradiated Gd2(Ti1-yZry)2O7 with y ⩾0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y -ZrO2), thereby providing conclusive evidence for the phase transformation. The TiO6 octahedra present in Gd2(Ti1-yZry)2O7 are completely modified by ion-beam irradiation to TiOx polyhedra, and the Ti coordination is increased to eight with longer Ti -O bond distances. The similarity between cation sites and the degree of disorder in Gd2Zr2O7 facilitate the rearrangement and relaxation of Gd, Zr, and O ions/defects. This inhibits amorphization during the ion-beam-induced phase transition to the radiation-resistant defect fluorite structure, which is in contrast to the ordered Gd2Ti2O7.

  17. Guarded Cubical Type Theory

    DEFF Research Database (Denmark)

    Birkedal, Lars; Bizjak, Aleš; Clouston, Ranald;

    2016-01-01

    This paper improves the treatment of equality in guarded dependent type theory (GDTT), by combining it with cubical type theory (CTT). GDTT is an extensional type theory with guarded recursive types, which are useful for building models of program logics, and for programming and reasoning with co...

  18. Temperature dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-xSrxMnO3

    Energy Technology Data Exchange (ETDEWEB)

    Arenholz, Elke; Mannella, N.; Booth, C.H.; Rosenhahn, A.; Sell, B.C.; Nambu, A.; Marchesini, S.; Mun, B. S.; Yang, S.-H.; Watanabe, M.; Ibrahim, K.; Arenholz, E.; Young, A.; Guo, J.; Tomioka, Y.; Fadley, C.S.

    2007-12-06

    We have studied the temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La{sub 1-x}Sr{sub x}MnO{sub 3} (x= 0.3-0.4) with core and valence level photoemission (PE), x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS), extended x-ray absorption fine structure (EXAFS) spectroscopy and magnetometry. As the temperature is varied across the Curie temperature T{sub c}, our PE experiments reveal a dramatic change of the electronic structure involving an increase in the Mn spin moment from {approx} 3 {micro}B to {approx} 4 {micro}B, and a modification of the local chemical environment of the other constituent atoms indicative of electron localization on the Mn atom. These effects are reversible and exhibit a slow-timescale {approx}200 K-wide hysteresis centered at T{sub c}. Based upon the probing depths accessed in our PE measurements, these effects seem to survive for at least 35-50 {angstrom} inward from the surface, while other consistent signatures for this modification of the electronic structure are revealed by more bulk sensitive spectroscopies like XAS and XES/RIXS. We interpret these effects as spectroscopic fingerprints for polaron formation, consistent with the presence of local Jahn-Teller distortions of the MnO{sub 6} octahedra around the Mn atom, as revealed by the EXAFS data. Magnetic susceptibility measurements in addition show typical signatures of ferro-magnetic clusters formation well above the Curie temperature.

  19. Structural, electronic, optical and thermodynamic properties of cubic REGa{sub 3} (RE = Sc or Lu) compounds: Ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Laboratory, Department of Physics, Islamia College Peshawar (Pakistan); Gupta, S.K. [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Alahmed, Z.A. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Khachai, H. [Physics Department, Djillali Liabes University of Sidi Bel-Abbes (Algeria); Jha, P.K. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)

    2014-06-01

    Highlights: • REGa{sub 3} (RE = Sc or Lu) compounds are mechanical stabile. • Both ScGa{sub 3} and LuGa{sub 3} exhibit metallic behavior just like other REGa{sub 3} compounds. • Melting temperature T{sub m} (K) for ScGa{sub 3} and LuGa{sub 3} are 1244.2 and 1143.8. • High absorption observed in the visible energy region. • The present study would be helpful for future experimental/theoretical explorations. - Abstract: Structural, elastic, optoelectronic and thermodynamic properties of REGa{sub 3} (RE = Sc and Lu) compounds have been studied self consistently by employing state of the art full potential (FP) linearized (L) approach of augmented plane wave (APW) plus local orbitals method. Calculations were executed at the level of Perdew–Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA) for exchange correlation functional in addition to modified Becke–Johnson (mBJ) potential. Our obtained results of lattice parameters show reasonable agreement to the previously reported experimental and other theoretical studies. Analysis of the calculated band structure of ScGa{sub 3} and LuGa{sub 3} compounds demonstrates their metallic character. Moreover, a positive value of calculated Cauchy pressure, in addition to reflecting their ductile nature, endorses their metallic character as well. To understand optical behavior calculations related to the important optical parameters; real and imaginary parts of the dielectric function, reflectivity R(ω), refractive index n(ω) and electron energy-loss function L(ω) have also been performed. In the present work, thermodynamically properties are also investigated by employing lattice vibrations integrated in quasi harmonic Debye model. Obtained results of volume, heat capacity and Debye temperature as a function of temperature for both compounds, at different values of pressure, are found to be consistent. The calculated value of melting temperature for both compounds (ScGa{sub 3} and Lu

  20. Modified Ceria-Zirconia Fluorite-Like Catalysts for the Combustion of Methane

    Institute of Scientific and Technical Information of China (English)

    Tatiana Kuznetsova; Vladislav Sadykov; Lubsan Batuev; Ella Moroz; Elena Burgina; Vladimir Rogov; Vladimir Kriventsov; Dmitrii Kochubey

    2006-01-01

    For dispersed ceria-zirconia-based solid solutions prepared via the polymerized complex method and annealed at 700 ℃, effects of bulk doping by Ca, Mn, Co, Bi or Nb cations and surface modification by Mn and Pt on their structural features, surface/bulk oxygen reactivity and catalytic activity in methane combustion are considered. With up to 20 mol% doping, a structural type of homogeneous solid solutions of anion-deficient fluorite with disordered anion vacancies is formed. Doping by transition metal cations or Pt increases the mobility and reactivity of the surface/bulk oxygen. A broad variation in specific rates of methane combustion for the studied systems was observed, suggesting structural sensitivity of this reaction. In general, there is no universal relationship between the oxygen mobility, the reactivity and the catalytic activity in methane combustion, which is explained by the factor of specific methane activation on surface active sites. For the Pt-promoted samples, Pt efficiency in methane activation depends on the Pt-support interaction, and the most favorable ones being mixed Pt/MnOx and Pt/NbOx clusters on the surface of the supports that exhibit high lattice oxygen mobilities.

  1. KBi(2-x)Pbx (0 phase evolving from a distortion of the cubic Laves-phase structure.

    Science.gov (United States)

    Ponou, Siméon; Müller, Noémi; Fässler, Thomas F; Häussermann, Ulrich

    2005-10-17

    The quasibinary system KBi(2-x)Pbx has been investigated, both experimentally and theoretically. Phases with compositions 0 Laves-phase structure MgCu2 (space group Fdm), which contains a rigid framework of corner-condensed symmetry-equivalent tetrahedra formed by randomly distributed Bi and Pb atoms. For compositions x > or = 0.6, these tetrahedra become alternately elongated and contracted. The distortion of the framework lowers the space-group symmetry to F43m (KBi(1.2)Pb(0.8), F43m, Z = 8, a = 9.572(1) A). Magnetometer measurements show that KBi2 (x = 0) is metallic and goes through a superconducting transition below 3.5 K. First principles calculations reveal that the Fd3m --> F43m distortion is largest for KBiPb (x = 1.0), which at the same time turns into a semiconductor. Thus, F43m KBiPb corresponds to a proper charge-balanced Zintl phase, K+[BiPb]-, with separated polyanionic tetrahedra, (Bi2Pb2)2-. However, it was not possible to prepare F43m KBiPb. Syntheses attempting to increase the Pb content in KBi(2-x)Pbx above x = 0.8 yielded additional, not yet characterized, ternary phases.

  2. Phase stability, elastic anisotropy and electronic structure of cubic MAl2 (M = Mg, Ca, Sr and Ba) Laves phases from first-principles calculations

    Science.gov (United States)

    Kong, Yuanyuan; Duan, Yonghua; Ma, Lishi; Li, Runyue

    2016-10-01

    By performing first-principles calculations within the generalized gradient approximation, the phase stability, elastic constant and anisotropy, and density of states of cubic C15-type MAl2 (M = Mg, Ca, Sr and Ba) Laves phases have been investigated. Optimized equilibrium lattice parameters and formation enthalpies agree well with the available experimental data. Elastic constants C ij have been evaluated, and these C15-type MAl2 Laves phases are mechanically stable due to the meeting of C ij to the mechanical stability criteria. Polycrystalline elastic moduli have been deduced from elastic constants by Voigt-Reuss-Hill approximation. Plastic properties were characterized via values of B/G, Poisson’s ratio ν and Cauchy pressure (C 12-C 44). The elastic anisotropy has been considered by several anisotropy indexes (A U , A Z , A shear and A comp), anisotropy of shear modulus, and 3D surface constructions of bulk and Young’s moduli. Additionally, the sound velocity anisotropy and Debye temperature were predicted. Finally, electronic structures were carried out to reveal the underlying phase stability mechanism of these Laves phases.

  3. Structural, magnetic, and magneto-optical properties of nanocrystalline face centered cubic Co70Cr30/Pt multilayers with perpendicular magnetic anisotropy.

    Science.gov (United States)

    Papaioannou, E Th; Angelakeris, M; Poulopoulos, P; Tsiaoussis, I; Rüdt, C; Fumagalli, P; Flevaris, N K

    2007-12-01

    Co70Cr30 alloyed layers are combined with extremely thin Pt layers in order to produce novel face-centered-cubic multilayered films to be considered as a potential perpendicular magnetic recording medium. The films were grown on Si, glass and polyimide substrates by e-beam evaporation at a temperature slightly higher than room temperature. The multilayered structure of the films was verified by X-ray diffraction experiments. Plane-view transmission electron microscopy images have revealed the formation of very small grains in the range of 7-9 nm. Hysteresis loops as a function of temperature were recorded via the magneto-optic Kerr effect in the polar geometry configuration. The system exhibits perpendicular magnetic anisotropy, which enhances with decreasing temperature. Hysteresis loops with a squareness of 1 and a coercivity of 1.45 kOe were obtained at 10 K. Furthermore, complete magneto-optic spectra of the films are recorded, showing a strong magneto-optic enhancement in the ultraviolet region at around 4.5 eV.

  4. Body centered cubic magnesium niobium hydride with facile room temperature absorption and four weight percent reversible capacity.

    Science.gov (United States)

    Tan, XueHai; Wang, Liya; Holt, Chris M B; Zahiri, Beniamin; Eikerling, Michael H; Mitlin, David

    2012-08-21

    We have synthesized a new metastable metal hydride with promising hydrogen storage properties. Body centered cubic (bcc) magnesium niobium hydride (Mg(0.75)Nb(0.25))H(2) possesses 4.5 wt% hydrogen gravimetric density, with 4 wt% being reversible. Volumetric hydrogen absorption measurements yield an enthalpy of hydride formation of -53 kJ mol(-1) H(2), which indicates a significant thermodynamic destabilization relative to the baseline -77 kJ mol(-1) H(2) for rutile MgH(2). The hydrogenation cycling kinetics are remarkable. At room temperature and 1 bar hydrogen it takes 30 minutes to absorb a 1.5 μm thick film at sorption cycle 1, and 1 minute at cycle 5. Reversible desorption is achieved in about 60 minutes at 175 °C. Using ab initio calculations we have examined the thermodynamic stability of metallic alloys with hexagonal close packed (hcp) versus bcc crystal structure. Moreover we have analyzed the formation energies of the alloy hydrides that are bcc, rutile or fluorite.

  5. Guarded Cubical Type Theory

    DEFF Research Database (Denmark)

    Birkedal, Lars; Bizjak, Aleš; Clouston, Ranald;

    2016-01-01

    This paper improves the treatment of equality in guarded dependent type theory (GDTT), by combining it with cubical type theory (CTT). GDTT is an extensional type theory with guarded recursive types, which are useful for building models of program logics, and for programming and reasoning...... with coinductive types. We wish to implement GDTT with decidable type-checking, while still supporting non-trivial equality proofs that reason about the extensions of guarded recursive constructions. CTT is a variation of Martin-L\\"of type theory in which the identity type is replaced by abstract paths between...... terms. CTT provides a computational interpretation of functional extensionality, is conjectured to have decidable type checking, and has an implemented type-checker. Our new type theory, called guarded cubical type theory, provides a computational interpretation of extensionality for guarded recursive...

  6. Guarded Cubical Type Theory

    DEFF Research Database (Denmark)

    Birkedal, Lars; Bizjak, Aleš; Clouston, Ranald;

    2016-01-01

    This paper improves the treatment of equality in guarded dependent type theory (GDTT), by combining it with cubical type theory (CTT). GDTT is an extensional type theory with guarded recursive types, which are useful for building models of program logics, and for programming and reasoning...... with coinductive types. We wish to implement GDTT with decidable type checking, while still supporting non-trivial equality proofs that reason about the extensions of guarded recursive constructions. CTT is a variation of Martin-L\\"of type theory in which the identity type is replaced by abstract paths between...... terms. CTT provides a computational interpretation of functional extensionality, enjoys canonicity for the natural numbers type, and is conjectured to support decidable type-checking. Our new type theory, guarded cubical type theory (GCTT), provides a computational interpretation of extensionality...

  7. Synthesis of octahedral, truncated octahedral, and cubic Rh2Ni nanocrystals and their structure-activity relationship for the decomposition of hydrazine in aqueous solution to hydrogen

    Science.gov (United States)

    Li, Chun; Wang, Tao; Chu, Wei; Wu, Ping; Tong, Dong Ge

    2016-03-01

    We developed a co-reduction method to synthesize octahedral, truncated octahedral, and cubic Rh2Ni nanocrystals. The shape/size distribution, structural characteristics, and composition of the Rh2Ni nanocrystals are investigated, and their possible formation mechanism at high temperatures in margaric acid/1-aminoheptadecane solution in the presence of tetraethylgermanium and borane trimethylamine complexes is proposed. A preliminary probing of the structure-activity dependence of the surface ``clean'' Rh2Ni nanocrystals supported on carbon towards hydrazine (N2H4) in aqueous solution dehydrogenation revealed that the higher the percentage of {111} facets, the higher is the activity and H2 selectivity of the nanocrystals. This result was attributed to the {111} facets not only introducing more basic sites, but also weakening the interaction between the produced adspecies (including H2 and NHx) and surface metal atoms in comparison with those of {100} facets. Furthermore, the as-prepared Rh2Ni nanooctahedra exhibited 100% H2 selectivity and high activity at room temperature for H2 generation via N2H4 decomposition. The activation energy of the Rh2Ni nanooctahedra was 41.6 +/- 1.2 kJ mol-1. The Rh2Ni nanooctahedra were stable catalysts for the hydrolytic dehydrogenation of N2H4, providing 27 723 total turnovers in 30 h. Our work provides a new perspective concerning the possibility of constructing hydrogen-producing systems based on N2H4 and surface ``clean'' Rh2Ni nanocrystal catalysts with defined shapes supported on carbon that possess a competitive performance in comparison with NaBH4 and NH3BH3 hydrogen-producing systems for fuel cell applications.We developed a co-reduction method to synthesize octahedral, truncated octahedral, and cubic Rh2Ni nanocrystals. The shape/size distribution, structural characteristics, and composition of the Rh2Ni nanocrystals are investigated, and their possible formation mechanism at high temperatures in margaric acid/1

  8. Cubic spline symplectic algorithm for dynamic analysis of space truss structure%网架结构动力分析的三次样条辛算法

    Institute of Scientific and Technical Information of China (English)

    李纬华; 王堉; 罗恩

    2013-01-01

    According to the basic idea of dual-complementarity,the unconventional Hamilton-type variational principle in phase space for dynamic analysis of space truss structure was introduced,which can fully characterize this kind of dynamic initial-boundary-value problems.In addition,its Euler equation is of symplectic structure character.Based on this vairiational principle,a symplectic algorithm was presented,combining the finite element method in space domain with the time subdomain method,in which the cubic spline interpolation was applied as approximation.The results of numerical examples show that the method is a highly efficient method with better computational performance and superior ability of stability compared with Wilson-θ and Newmark-β methods.%根据对偶互补的思想,建立了网架结构动力学的相空间非传统Hamilton型变分原理.这种变分原理不仅能反映这种动力学初值-边值问题的全部特征,而且它的欧拉方程具有辛结构.基于该变分原理,空间域采用有限元法与时间子域采用三次样条函数插值的时间子域法相结合,构造了求解网架结构动力响应的一种辛算法,给出了逐步递推计算格式.数值算例结果表明,这种新方法的稳定性、计算精度和效率都明显高于Wilson-θ法和Newmark-β法.

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

    Science.gov (United States)

    Borah, Manjit; Mohanta, Dambarudhar

    2014-06-01

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

  10. Nano-crystals of cerium–hafnium binary oxide: Their size-dependent structure

    Energy Technology Data Exchange (ETDEWEB)

    Raitano, Joan M. [Department of Applied Physics and Applied Mathematics, Materials Science and Engineering Program, Columbia University, New York, NY 10027 (United States); Khalid, Syed [National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973 (United States); Marinkovic, Nebojsa [Chemical Engineering Department, Columbia University, 500 W 120th St, Mudd 801, New York, NY 10027 (United States); Chan, Siu-Wai, E-mail: sc174@columbia.edu [Department of Applied Physics and Applied Mathematics, Materials Science and Engineering Program, Columbia University, New York, NY 10027 (United States)

    2015-09-25

    Highlights: • (1 − x)CeO{sub 2}–xHfO{sub 2} was precipitated (0 < x < 1) and calcined in air. • For x ⩽ 0.14, crystallites ⩽140 nm in size exhibit only the fluorite structure. • This low hafnia solubility is attributable to no auto-reduction (Ce{sup 3+} = 0). • The low solubility is also due to the high temperature required for homogenization. • Coarsening is lessened as Hf{sup 4+} ions slow cation diffusion in these crystallites. - Abstract: Cerium oxide (CeO{sub 2}, “ceria”) and hafnium oxide (HfO{sub 2}, “hafnia”) were aqueously co-precipitated and subsequently calcined to allow for homogenization. The size of the (1−x)CeO{sub 2}–xHfO{sub 2} crystallites, determined by the Scherrer equation, varied from 140 nm for x = 0 to 15 nm for x = 0.73. For x ⩽ 0.14, only cubic structures are visible in X-ray diffractograms, and the lattice parameters are consistent with the values expected for structurally cubic solid solutions of hafnia in ceria. At x = 0.26, tetragonal and monoclinic phases nucleated with the former not being observed in the bulk phase diagram for ceria–hafnia. Therefore, the solubility limit of the cubic structure is between x = 0.14 and x = 0.26 for 40–61 nm crystallites, the sizes of these respective compositions. More specifically, for the 40 nm crystallites of x = 0.26 (1 − x)CeO{sub 2}–xHfO{sub 2}, 15% of the hafnia remains in a structurally cubic solid solution with ceria based on the observed cubic lattice parameter. The compositional domain for the cubic fluorite structure in this study is narrower than other nanostructured (1 − x)CeO{sub 2}–xHfO{sub 2} studies, especially studies with crystallite sizes less than 10 nm, but wider than observed in the bulk and helps to expand the size regime over which the relationship between crystallite size and phase stability is known. The extent of this cubic-structure domain is mainly attributable to the intermediate crystallite size and the roughly zero Ce{sup 3

  11. Key insights on the structural characterization of textured Er{sub 2}O{sub 3}-ZrO{sub 2} nano-oxides prepared by a surfactant-free solvothermal route

    Energy Technology Data Exchange (ETDEWEB)

    Julian-Lopez, Beatriz, E-mail: julian@qio.uji.es [Departamento de Quimica Inorganica y Organica, Universitat Jaume I, Avda. Vicente Sos Baynat s/n, 12071 Castellon (Spain); Luz, Veronica de la; Gonell, Francisco; Cordoncillo, Eloisa [Departamento de Quimica Inorganica y Organica, Universitat Jaume I, Avda. Vicente Sos Baynat s/n, 12071 Castellon (Spain); Lopez-Haro, Miguel; Calvino, Jose J. [Departamento de Ciencia de los Materiales e Ingenieria Metalurgica y Quimica Inorganica, Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, Puerto Real, 11510 Cadiz (Spain); Escribano, Purificacion [Departamento de Quimica Inorganica y Organica, Universitat Jaume I, Avda. Vicente Sos Baynat s/n, 12071 Castellon (Spain)

    2012-04-05

    Highlights: Black-Right-Pointing-Pointer Structural resolution of fluorite vs. pyrochlore in small nanocrystals. Black-Right-Pointing-Pointer Simple template-free solvothermal synthesis of Er{sub 2}O{sub 3}-ZrO{sub 2} nanooxides. Black-Right-Pointing-Pointer Good control over size, morphology and surface properties (280 m{sup 2} g{sup -1}). - Abstract: Zirconia-mixed oxides can exhibit cubic fluorite and pyrochlore structure. Their discrimination is not easy in nanooxides with a crystal size close to that of a few unit cells. In this work, high resolution transmission electron microscopy (HRTEM) has been employed to provide key insights on the structural characterization of a nanometric and porous mixed Er{sub 2}O{sub 3}-ZrO{sub 2} oxide. The material was prepared by a simple template-free solvothermal route that provided nanocrystalline powders at low temperature (170 Degree-Sign C) with spherical morphology, and high surface area ({approx}280 m{sup 2} g{sup -1}). The porosity was mainly originated from the assembling of organic complexing agents used in the synthesis to limit the crystal growth and to control hydrolysis and condensation reaction rates. The samples were characterized by thermal analysis, X-ray diffraction, scanning electron microscopy and N{sub 2} adsorption measurements. A detailed study by HRTEM was conducted on microtomed samples. It was observed that the material was made of nanocrystals packed into spherical agglomerates. HRTEM simulations indicated that it is not possible to identify the pyrochlore phase in nanoparticles with diameter below 2 nm. In our samples, the analysis of the HRTEM lattice images by means of fast Fourier transform (FFT) techniques revealed well defined spots that can be assigned to different planes of a cubic fluorite-type phase, even in the raw material. Raman spectroscopy was also a powerful technique to elucidate the crystalline phase of the materials with the smallest nanoparticles. HREM and Raman results evidenced

  12. Phase boundary between cubic B1 and rhombohedral structures in (Mg,Fe)O magnesiowüstite determined by in situ X-ray diffraction measurements

    Science.gov (United States)

    Dymshits, Anna M.; Litasov, Konstantin D.; Shatskiy, Anton; Chanyshev, Artem D.; Podborodnikov, Ivan V.; Higo, Yuji

    2017-06-01

    The phase relations and equation of state of (Mg0.08Fe0.92)O magnesiowüstite (Mw92) have been studied using the Kawai-type high-pressure apparatus coupled with synchrotron radiation. To determine the phase boundary between the NaCl-type cubic (B1) and rhombohedral (rB1) structures in Mw92, in situ X-ray observations were carried out at pressures of 0-35 GPa and temperatures of 300-1473 K. Au and MgO were used as the internal pressure markers and metallic Fe as oxygen fugacity buffer. The phase boundary between B1 and rB1 structures was described by a linear equation P (GPa) = 1.6 + 0.033 × T (K). The Clapeyron slope (dP/dT) determined in this study is close to that obtained at pressures above 70 GPa but steeper than that obtained for FeO. An addition of MgO to FeO structure expands the stability field of the rB1 phase to lower pressures and higher temperatures. Thus, the rB1 phase may be stabilized with respect to the B1 phase at a lower pressures. The pressure-volume-temperature equation of state of B1-Mw92 was determined up to 30 GPa and 1473 K. Fitting the hydrostatic compression data up to 30 GPa with the Birch-Murnaghan equation of state (EoS) yielded: unit cell volume (V 0,T0), 79.23 ± 4 Å3; bulk modulus (K 0,T0), 183 ± 4 GPa; its pressure derivative (K' T ), 4.1 ± 0.4; (∂K 0,T /∂T) = -0.029 ± 0.005 GPa K‒1; a = 3.70 ± 0.27 × 10-5 K-1 and b = 0.47 ± 0.49 × 10-8 K-2, where α0,T = a + bT is the volumetric thermal expansion coefficient. The obtained bulk modulus of Mw92 is very close to the value expected for stoichiometric iron-rich (Mg,Fe)O. This result confirms the idea that the bulk modulus of (Mg,Fe)O is greatly affected by the actual defect structure, caused by either Mg2+ or vacancies.

  13. Transparent polycrystalline cubic silicon nitride

    Science.gov (United States)

    Nishiyama, Norimasa; Ishikawa, Ryo; Ohfuji, Hiroaki; Marquardt, Hauke; Kurnosov, Alexander; Taniguchi, Takashi; Kim, Byung-Nam; Yoshida, Hidehiro; Masuno, Atsunobu; Bednarcik, Jozef; Kulik, Eleonora; Ikuhara, Yuichi; Wakai, Fumihiro; Irifune, Tetsuo

    2017-01-01

    Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties. It is known that polycrystalline ceramics with a spinel structure in compositions of MgAl2O4 and aluminum oxynitride (γ-AlON) show high optical transparency. Here we report the synthesis of the hardest transparent spinel ceramic, i.e. polycrystalline cubic silicon nitride (c-Si3N4). This material shows an intrinsic optical transparency over a wide range of wavelengths below its band-gap energy (258 nm) and is categorized as one of the third hardest materials next to diamond and cubic boron nitride (cBN). Since the high temperature metastability of c-Si3N4 in air is superior to those of diamond and cBN, the transparent c-Si3N4 ceramic can potentially be used as a window under extremely severe conditions. PMID:28303948

  14. REE Geochemistry of Fluorite from the Maoniuping REE Deposit, Sichuan Province, China: Implications for the Source of Ore-forming Fluids

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Fluorite is one of the main gangue minerals in the Maoniuping REE deposit, Sichuan Province, China. Fluorite with different colors occurs not only within various orebodies, but also in wallrocks of the orefield. Based on REE geochemistry, fluorite in the orefieid can be classified as the LREE-rich, LREE-flat and LREE-depleted types. The three types of fluorite formed at different stages from the same hydrothermal fluid source, with the LREE-rich fluorite forming at the relatively early stage, the LREE-flat fluorite in the middle, and the LREE-depleted fluorite at the latest stage. Various lines of evidence demonstrate that the variation of the REE contents of fluorite shows no relation to the color. The mineralization of the Maoniuping REE deposit is associated spatially and temporally with carbonatite-syenite magmatism and the ore-forming fluids are mainly derived from carbonatite and syenite melts.

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

    Science.gov (United States)

    1990-12-01

    Laboratories, Inc. 3. Structural Analysis Reflection high-energy electron diffraction performed during growth indicated that the BGaN film remained...was used (Hitachi H-800) to more closely examine the microstructural evolution of the BN/ BGaN /GaN epitaxial films. Cross-section TEM specimens were... BGaN layer to be a mixture of cubic and wurtzitic phases. This layer was heavily faulted. The latter phenomenon is to be expected given the high

  16. Exploiting the P L2,3 absorption edge for optics: spectroscopic and structural characterization of cubic boron phosphide thin films

    NARCIS (Netherlands)

    Huber, S.P.; Medvedev, V.V.; Meyer-Ilse, J.; Gullikson, E.; Padavala, B.; Edgar, J.H.; Sturm, J.M.; Kruijs, van de R.W.E.; Prendergast, D.; Bijkerk, F.

    2016-01-01

    The transmission of cubic boron phosphide (c-BP) thin films, prepared by chemical vapor deposition (CVD), was evaluated near the phosphorous L2,3 and boron K absorption edge. The c-BP films were analyzed with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray ab

  17. Fluid Origin of the Stratabound Fluorite and Celestite Deposits in Coahuila, Mexico.

    Science.gov (United States)

    Tritlla, J.; Gonzalez-Partida, E.; Banks, D.; Levresse, G.; Baca-Gasca, S.; Rodriguez-Santos, A.

    2004-12-01

    The Mesozoic units that outcrop north of Coahuila State in northern Mexico host numerous celestite, celestite-fluorite and fluorite deposits, mainly enclosed in the Cretaceous limestone units. Celestite and celestite-fluorite deposits are lens-shaped bodies, up to 2 m thick and a total length exceeding 500 meters, intercalated within the carbonates of the Cupido Formation (Aptian) or equivalents. Celestite-free fluorite bodies, mainly enclosed in the Aurora Formation (Albian-Cenomanian), appear as sub-concordant lenses with abundant evidences of hydraulic fracturing, usually near low-angle fractures. The celestite brine halogen composition on a Cl/Br vs Na/Br molar ratio plot on the trend defined by the evaporation of seawater, while in a ppm Cl vs Cl/Br plot away from the seawater evaporation line but parallel to it, indicating that the solution was mainly modified by dilution. The fluids involved in the genesis of the La Encantada fluorite deposit probably are evolved seawater that undergone some degree of evaporation. Mixing of fluids is clearly delineated by both microthemometric and halogen data, where salinities calculated are too low for the halogen ratios found, indicating a mixing with a low-salinity end-member. Hydrocarbon-bearing fluid inclusions repeatedly show the presence of solid bitumen trapped along with heavy oils, indicative of thermal degradation. Both, mixing and thermal degradation of hydrocarbon-rich fluids along with hydraulic fracture of the host rock points to an "in situ" organic matter maturation, due to the mixing of a saline, oxidant, sulphate and CaCl2-rich "bittern", which probably transported fluorite, with an organic-matter rich fluid present in the cretaceous carbonates. It is noteworthy that these previous results suggest that both celestite and fluorite-dominated deposits formed from brines from similar origin, showing the same halogen systematics. Strontium enrichment can be explained by leaching of Sr from the carbonate series

  18. Site distortions created by the stereoactive lone pair of Tin(II) in highly symmetric structures

    Science.gov (United States)

    Dénès, Georges; Madamba, M. Cecilia; Merazig, Hocine; Muntasar, Abdualhafed; Zhu, Zhimeng

    2016-10-01

    Several fluoride compounds containing divalent tin that have a fluorite (CaF2-type) unit cell have been prepared and studied. Some are stoichiometric compounds while others are solid solutions. The cubic symmetry of the unit-cell (no lattice distortion and no superstructure) and the unique metal ion site of the fluorite structure make it that tin and the other metal have to be disordered on the normal metal site of the fluorite unit-cell. However, that site has the m3m-Oh point symmetry, and the metal ion is located in the center of a cube having fluoride ions in all its corners. Therefore, the same coordination should apply to tin. However, tin(II) possesses a non-bonding pair of electrons called a "lone pair", and in order for tin(II) to have a cubic symmetry, its lone pair has to be located on the unhybridized 5s orbital, that is spherical and thus does not distort the coordination. In such a case, the lone pair is said to be "non-stereoactive". This would make tin present in the form of the Sn2+ stannous ion, and therefore Sn-F bonding must be ionic. However, tin(II) fluorides are known to be always covalent with a hybridized lone pair on tin, which has therefore a reduced coordination number and therefore a highly distorted polyhedron of coordination. Such a hybridized lone pair is said to be "stereoactive". Tin-119 Mössbauer spectroscopy was used to probe the bonding type and it showed that bonding is covalent, the lone pair is hybridized and the tin coordination is dramatically distorted. A model based on a double disorder was made that accounts for the apparent contradiction between the crystallographic and the Mössbauer results.

  19. THE COUPLING RELATIONSHIP BETWEEN FLUORITE MINE AND ORGANIC REEF-BANK OIL POOL OF ORDOVICIAN CARBONATES AND METALLOGENIC MODEL OF FLUORITE MINE IN TARIM BASIN%塔里木盆地奥陶系萤石矿和礁滩相油藏耦合关系与成矿模式

    Institute of Scientific and Technical Information of China (English)

    周刚; 郑荣才; 罗平; 张兴阳; 刘伟; 宋金民; 饶红娟

    2011-01-01

    metallogenic fluids were the unconformity and faults. Reef-bank and regional structure had playing an important controlling role in the aspects of layer,facies and position over the fluorite mine or oil pool.%塔里木盆地巴楚-柯坪野外露头区和塔中井区奥陶系萤石矿体呈串珠状或沿裂缝呈条带状分布,通过露头岩心、钻井岩心、普通薄片、电子探针、X衍射、阴极发光、流体包裹体和微量元素、稳定同位素分析等方法,对萤石矿及其围岩和油藏进行详细研究,探讨萤石矿和礁滩相油藏耦合关系与成矿模式.萤石矿体富集在礁、滩相灰岩为基岩的与断层相关的部分岩溶洞穴中,和萤石一起共生的矿物还有方解石、重晶石、硬石膏、石英及黑色沥青,萤石中含丰富的液态、气态烃包裹体、固态沥青包裹体和柱条状石膏子晶;萤石的K/Rb和Sr/Ba比值远小于正常海水值,富铕及轻稀土元素而贫重稀土元素,其礁滩相围岩碳、氧同位素具越靠近萤石脉体δ13C和δ18O值负偏移越明显特征,萤石相对其围岩具有更高的87Sr/86 Sr比值.研究表明塔里木盆地奥陶系萤石矿属于“被动型”密西西比层控矿床,成矿机理为礁滩型“油气藏”转化为“矿捕”作用,具先成藏后成矿、多期成藏多期成矿特点,成矿流体具有盆地油田卤水和深循环大气淡水双重特征的后期低温热液成因性质,成矿物质来源于下寒武统下部黑色硅质岩及磷块岩,不整合面和断层是热液流体及成矿流体运移通道,生物礁滩和区域断层对萤石矿或油藏具有极其重要的“层、相、位”控制作用.

  20. Low temperature formation of higher-k cubic phase HfO{sub 2} by atomic layer deposition on GeO{sub x}/Ge structures fabricated by in-situ thermal oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, R., E-mail: zhang@mosfet.t.u-tokyo.ac.jp [School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Department of Information Science and Electronic Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027 (China); Huang, P.-C.; Taoka, N.; Yokoyama, M.; Takenaka, M.; Takagi, S. [School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2016-02-01

    We have demonstrated a low temperature formation (300 °C) of higher-k HfO{sub 2} using atomic layer deposition (ALD) on an in-situ thermal oxidation GeO{sub x} interfacial layer. It is found that the cubic phase is dominant in the HfO{sub 2} film with an epitaxial-like growth behavior. The maximum permittivity of 42 is obtained for an ALD HfO{sub 2} film on a 1-nm-thick GeO{sub x} form by the in-situ thermal oxidation. It is suggested from physical analyses that the crystallization of cubic phase HfO{sub 2} can be induced by the formation of six-fold crystalline GeO{sub x} structures in the underlying GeO{sub x} interfacial layer.

  1. Effects of PEO-PPO diblock impurities on the cubic structure of aqueous PEO-PPO-PEO pluronics micelles: fcc and bcc ordered structures in F127

    DEFF Research Database (Denmark)

    Mortensen, Kell; Pedersen, Walther Batsberg; Hvidt, S.

    2008-01-01

    We report on structural properties of PEO-PPO-PEO type of triblock block copolymers (Pluronics F127) with special emphasis on the effect of diblock PEO-PPO impurities on the ordered gel phase. Commercial F127 polymers contain as received roughly 20% PEO-PPO diblock and 80% PEO-PPO-PEO triblock...... copolymers. Aqueous solutions of F127 copolymers used as received form fee ordered micellar structure. Copolymers depleted with respect to the diblock impurity, resulting in a pure PEO-PPO-PEO triblock copolymer system, form bcc ordered micelles within the major parts of the gel phase. However, close...

  2. Crystal Structure of Garnet-Related Li-Ion Conductor Li7–3x Ga x La3Zr2O12: Fast Li-Ion Conduction Caused by a Different Cubic Modification?

    OpenAIRE

    Wagner, Reinhard; Redhammer, Günther J.; Rettenwander, Daniel; Senyshyn, Anatoliy; Schmidt, Walter; Wilkening, Martin; Amthauer, Georg

    2016-01-01

    Li-oxide garnets such as Li7La3Zr2O12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next-generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia-3d, has to be stabilized with supervalent cations. LLZO stabilized with Ga3+ shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a comprehensive structural characteriz...

  3. Preparation of cubic Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} solid electrolyte using a nano-sized core–shell structured precursor

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yanhua; Cai, Jin [State Key Lab of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Chen, Fei, E-mail: chenfei027@gmail.com [State Key Lab of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Massachusetts Institute of Technology, 77 Massachusetts Avenue, W20-021 Cambridge, MA 02139-4307 (United States); Tu, Rong; Shen, Qiang; Zhang, Xulong [State Key Lab of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Zhang, Lianmeng [State Key Lab of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Massachusetts Institute of Technology, 77 Massachusetts Avenue, W20-021 Cambridge, MA 02139-4307 (United States)

    2015-09-25

    Highlights: • A core–shell nano-sized precursor was synthesized by a two-step precipitation. • Cubic LLZO dense body was obtained at low temperatures by the novel precursor. • The cubic LLZO sintered body showed an extremely high Li ionic conductivity. - Abstract: Nano-sized Al-doped Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} (LLZO) precursor is successfully synthesized by a novel two-step precipitation method. Microstructure and thermal behavior of the prepared LLZO precursor powders and properties of the sintered LLZO pellets are comprehensively investigated. Results show that the obtained precursor powders have a special core–shell structure that a coating of Li{sub 2}C{sub 2}O{sub 4} covers on the surface of the lanthanum and zirconium co-precipitate products. Pure cubic LLZO powders can be obtained at a low calcination temperature of 900 °C. Sample sintered by field assisted sintering technology at 1000 °C has a high relative density of 96.5% with a total ionic conductivity of as high as 3.32 × 10{sup −4} S cm{sup −1} (corresponding to the activation energy of 0.32 eV) at room temperature. The reported method provides a simple and low-temperature synthesis of high quality LLZO solid electrolytes.

  4. Study of genesis in Qahr-Abad fluorite deposit using fluid inclusion, southeast of Saqqez, the Kurdistan province

    Directory of Open Access Journals (Sweden)

    Mehrdad Barati

    2017-07-01

    Full Text Available Introduction The Qahr-abad fluorite deposit is located in the area of 36°10′ 3′′ N and 46°34′ 21′′E within the Sanandaj-Sirjan district east of the Kurdistan province , Iran and it is located ~57 km southeast of the city of Saqqez (Kholghi Khasraghi, 1999. This deposit is developed as scatter lenses, veins, and veinlets (stockwork structure within carbonate rocks of Elika formation and controlled by the regional NW–SE trending Zagross thrust nappe system. Fault trends in this area are perpendicular to fault trends in the Zagros zone. The fault dips are nearly vertical and mineralization has occurred in the brecciation fault zone (Talaii, 2010. The rough geological instruction of the deposit has indicated that it is similar to worldwide Epithermal deposits. The mineralization occurs as replacement (type I/ open-space (type II vein fillings and bodies within Mesozoic lime stones (mostly Upper Triassic and Lower Jurassic members of the Elika Formation, where they crop out to form horst structures. The mineralization is typically associated with post Pliocene disjunctive faults, which in part appear to have served as channel ways for the fluorite forming fluids that are representative of the geological setting of the mineralized area. Fluorite occurs in several color variations such as green, violet, blue, white or colorless, and is accompanied by quartz, barite and calcite (Moslehi, 2013. Materials and methods The minerals sampled for the fluid inclusion study include fluorite from mineralization stages. Samples covered all ore types. Micro thermometry analyses for 23 samples were performed after careful microscopic observation of 35 sections and 30 doubly polished sections. Micro thermometry was undertaken using a Linkam THS600 heating-freezing stage, with a measurable temperature range of between −196 and +600 °C (precision of freezing data and homogenization temperature of ±0.2 °C. Micro thermometry was undertaken in the

  5. Magnetism and electronic structure for RMn{sub 2} (R=Y and lanthanoids) with the cubic Laves phase (C15) structure

    Energy Technology Data Exchange (ETDEWEB)

    Terao, Kiyosi E-mail: terk005@gipac.shinshu-u.ac.jp; Yamada, Hideji

    2004-05-01

    Ab initio calculations for the electronic structure are carried out by means of LMTO-ASA with and without the GGA correction. The observed antiferromagnetic state with complicated spin configuration has slightly higher energy than that with the layered spin configuration near the observed volume and slightly lower than that for larger volume. In ferromagnetic configuration, Mn moment shows complicated dependence on volume and magnetic field.

  6. The modulated structure of Co3Al4Si2: incommensurability and Co-Co interactions in search of filled octadecets.

    Science.gov (United States)

    Fredrickson, Rie T; Fredrickson, Daniel C

    2013-03-18

    Incommensurate modulations are increasingly being recognized as a common phenomenon in solid-state compounds ranging from inorganic materials to molecular crystals. The origins of such modulations are often mysterious, but appear to be as diverse as the compounds in which they arise. In this Article, we describe the crystal structure and bonding of Co3Al4Si2, the δ phase of the Co-Si-Al system, whose modulated structure can be traced to a central concept of inorganic chemistry: the 18 electron rule. The structure is monoclinic, conforming to the 3 + 1D superspace group C/2m(0β0)s0. The basis of the crystal structure is a rod packing of columns of the fluorite (CaF2) type, a theme that is shared by the recently determined structure of Fe8Al(17.4)Si(7.6). The columns are arranged into sheets, within which the fluorite structure's primitive cubic network of Si/Al atoms continues uninterrupted from column to column. Between the sheets, layers of interstitial Si/Al atoms occur, some of which are arranged with a periodicity incommensurate with that of the fluorite-type columns. Strong modulations in the interstitial layers result. Electronic structure calculations, using a DFT-calibrated Hückel model on a commensurate approximate structure, reveal that the complex pattern of atoms within these interstitial layers serves to distribute Si/Al atoms around the Co atoms in order to reach 18 electron counts (filled octadecets). Central to this bonding scheme is the covalent sharing of electron pairs between Co atoms. The shared electron pairs occupy orbitals that are isolobal to classical Co-Co σ and π bonds, but whose stability is tied to multicenter character involving bridging Si/Al atoms. Through these features, Co3Al4Si2 expands the structural and electronic manifestations of the 18 electron rule in solid-state inorganic compounds.

  7. Crystal Structure of Garnet-Related Li-Ion Conductor Li7-3x Ga x La3Zr2O12: Fast Li-Ion Conduction Caused by a Different Cubic Modification?

    Science.gov (United States)

    Wagner, Reinhard; Redhammer, Günther J; Rettenwander, Daniel; Senyshyn, Anatoliy; Schmidt, Walter; Wilkening, Martin; Amthauer, Georg

    2016-03-22

    Li-oxide garnets such as Li7La3Zr2O12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next-generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia-3d, has to be stabilized with supervalent cations. LLZO stabilized with Ga(3+) shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a comprehensive structural characterization of Ga-stabilized LLZO is performed by means of single-crystal X-ray diffraction. Coarse-grained samples with crystal sizes of several hundred micrometers are obtained by solid-state reaction. Single-crystal X-ray diffraction results show that Li7-3x Ga x La3Zr2O12 with x > 0.07 crystallizes in the acentric cubic space group I-43d. This is the first definite record of this cubic modification for LLZO materials and might explain the superior electrochemical performance of Ga-stabilized LLZO compared to its Al-stabilized counterpart. The phase transition seems to be caused by the site preference of Ga(3+). (7)Li NMR spectroscopy indicates an additional Li-ion diffusion process for LLZO with space group I-43d compared to space group Ia-3d. Despite all efforts undertaken to reveal structure-property relationships for this class of materials, this study highlights the potential for new discoveries.

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

    Science.gov (United States)

    Francisco, E.; And Others

    1988-01-01

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

  9. Face-Centered-Cubic Nanostructured Polymer Foams

    Science.gov (United States)

    Cui, C.; Baughman, R. H.; Liu, L. M.; Zakhidov, A. A.; Khayrullin, I. I.

    1998-03-01

    Beautifully iridescent polymer foams having Fm-3m cubic symmetry and periodicities on the scale of the wavelength of light have been synthesized by the templating of porous synthetic opals. These fabrication processes involve the filling of porous SiO2 opals (with typical cubic lattice parameters of 250 nm) with either polymers or polymer precursors, polymerization of the precursors if necessary, and removal of the fcc array of SiO2 balls to provide an all-polymer structure. The structures of these foams are similar to periodic minimal surfaces, although the Gaussian curvature can have both positive and negative values. Depending upon whether the internal surfaces of the opal are polymer filled or polymer coated, the polymer replica has either one or two sets of independent channels. We fill these channels with semiconductors, metals, or superconductors to provide electronic and optical materials with novel properties dependent on the nanoscale periodicity.

  10. Crystal Structure of Garnet-Related Li-Ion Conductor Li7–3xGaxLa3Zr2O12: Fast Li-Ion Conduction Caused by a Different Cubic Modification?

    Science.gov (United States)

    2016-01-01

    Li-oxide garnets such as Li7La3Zr2O12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next-generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia-3d, has to be stabilized with supervalent cations. LLZO stabilized with Ga3+ shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a comprehensive structural characterization of Ga-stabilized LLZO is performed by means of single-crystal X-ray diffraction. Coarse-grained samples with crystal sizes of several hundred micrometers are obtained by solid-state reaction. Single-crystal X-ray diffraction results show that Li7–3xGaxLa3Zr2O12 with x > 0.07 crystallizes in the acentric cubic space group I-43d. This is the first definite record of this cubic modification for LLZO materials and might explain the superior electrochemical performance of Ga-stabilized LLZO compared to its Al-stabilized counterpart. The phase transition seems to be caused by the site preference of Ga3+. 7Li NMR spectroscopy indicates an additional Li-ion diffusion process for LLZO with space group I-43d compared to space group Ia-3d. Despite all efforts undertaken to reveal structure–property relationships for this class of materials, this study highlights the potential for new discoveries. PMID:27019548

  11. Raman micro-spectroscopy of UOX and MOX spent nuclear fuel characterization and oxidation resistance of the high burn-up structure

    Science.gov (United States)

    Jegou, C.; Gennisson, M.; Peuget, S.; Desgranges, L.; Guimbretière, G.; Magnin, M.; Talip, Z.; Simon, P.

    2015-03-01

    Raman micro-spectroscopy was applied to study the structure and oxidation resistance of UO2 (burnup 60 GWd/tHM) and MOX (burnup 47 GWd/tHM) irradiated fuels. The Raman technique, adapted to working under extreme conditions, enabled structural information to be obtained at the cubic micrometer scale in various zones of interest within irradiated fuel (central and zones like the Rim for UOX60, and the plutonium-enriched agglomerates for MOX47 characterized by a high burn-up structure), and the study of their oxidation resistance. As regards the structural information after irradiation, the spectra obtained make up a set of data consistent with the systematic presence of the T2g band characteristic of the fluorite structure, and of a triplet band located between 500 and 700 cm-1. The existence of this triplet can be attributed to the presence of defects originating in changes to the fuel chemistry occurring in the reactor (presence of fission products) and to the accumulation of irradiation damage. As concerns the oxidation resistance of the different zones of interest, Raman spectroscopy results confirmed the good stability of the restructured zones (plutonium-enriched agglomerates and Rim) rich in fission products compared to the non-restructured UO2 grains. A greater structural stability was noticed in the case of high plutonium content agglomerates, as this element favors the maintenance of the fluorite structure.

  12. A Cubic Tree Taper Model

    National Research Council Canada - National Science Library

    Goodwin, Adrian N

    2009-01-01

    A flexible tree taper model based on a cubic polynomial is described. It is algebraically invertible and integrable, and can be constrained by one or two diameters, neither of which need be diameter at breast height (DBH...

  13. Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

    Science.gov (United States)

    Solomon, Jonathan M.; Shamblin, Jacob; Lang, Maik; Navrotsky, Alexandra; Asta, Mark

    2016-12-01

    Fluorite-structured oxides find widespread use for applications spanning nuclear energy and waste containment, energy conversion, and sensing. In such applications the host tetravalent cation is often partially substituted by trivalent cations, with an associated formation of charge-compensating oxygen vacancies. The stability and properties of such materials are known to be influenced strongly by chemical ordering of the cations and vacancies, and the nature of such ordering and associated energetics are thus of considerable interest. Here we employ density-functional theory (DFT) calculations to study the structure and energetics of cation and oxygen-vacancy ordering in Ho2Zr2O7. In a recent neutron total scattering study, solid solutions in this system were reported to feature local chemical ordering based on the fluorite-derivative weberite structure. The calculations show a preferred chemical ordering qualitatively consistent with these findings, and yield values for the ordering energy of 9.5 kJ/mol-cation. Similar DFT calculations are applied to additional RE2Th2O7 fluorite compounds, spanning a range of values for the ratio of the tetravalent and trivalent (RE) cation radii. The results demonstrate that weberite-type order becomes destabilized with increasing values of this size ratio, consistent with an increasing energetic preference for the tetravalent cations to have higher oxygen coordination.

  14. The luminescence properties of rare-earth ions in natural fluorite

    Science.gov (United States)

    Czaja, M.; Bodył-Gajowska, S.; Lisiecki, R.; Meijerink, A.; Mazurak, Z.

    2012-09-01

    For the first time, the luminescence properties of Pr3+, Nd3+ and Tm3+ and Yb3+ ions in fluorite crystal have been obtained by steady-state measurements. In addition, the luminescence spectra of Ce3+, Sm2+, Sm3+, Dy3+, Er3+ and Yb3+ were measured. It was pointed out that λexc. = 415 nm is most suitable for measuring the Ho3+ emission beside the Er3+. The emission of trivalent holmium and erbium ions was measured independently using time-resolved measurements and tentative assignment of luminescence lines to C 3v and C 4v symmetry sites was proposed. Besides for natural fluorite crystal, the transitions between Stark energy levels of lanthanide ions were presented.

  15. Flotation of high-grade fluorite in a short column under negative bias regime

    OpenAIRE

    2006-01-01

    RESTRITO This paper presents flotation results carried out on fluorite ore using a relatively short column, operated under negative bias regime and without wash water. The term short column is used from a kinetic point of view from which collection zone comes out to be around 8 m tall (the relation height/diameter appears valid for industrial size columns). Negative bias was achieved making tailing flow smaller than feed flow. Hence, part of the water is carried up within bubbles wakes. No...

  16. Flocculation of fine fluorite particles with Corynebacterium xerosis and commercial long chain polymers

    Directory of Open Access Journals (Sweden)

    Rigo Lisandra N.

    2002-01-01

    Full Text Available This work aimed to study, comparatively, the flocculation of fluorite particles with Corynebacterium xerosis cells and three commercial long chain polymers. Best flocculation results were obtained with cells of C. xerosis and with an anionic polyacrylamide. Both were effective in solids removal and water clarification, although flocculation with C. xerosis cells requires a higher dosage of reagent per mass unit of processed ore.

  17. Fluorite's precipitation in KOH solutions in view of removing fluorides from wastewaters

    OpenAIRE

    Taraves, Raquel; Garcia, Daniel; Moutte, Jacques; Cameirão, Ana; Févotte, Gilles; Amaraggi, David; Morel, Bertrand

    2011-01-01

    International audience; The process under study aims at removing dissolved fluorides from effluent waters through the addition of calcium and the precipitation of fluorite in a fluidized bed. In the concept developed at COMURHEX, the effluent is a highly concentrated KOH solution and the calcium is provided as a suspension of portlandite with calcite as an impurity. COMURHEX's target is to achieve an efficient defluorination of KOH solutions prior to recycling and to control the growth of the...

  18. Electronic structure and magnetic properties of doped Al1- x Ti x N ( x = 0.03, 0.25) compositions based on cubic aluminum nitride from ab initio simulation data

    Science.gov (United States)

    Bannikov, V. V.; Beketov, A. R.; Baranov, M. V.; Elagin, A. A.; Kudyakova, V. S.; Shishkin, R. A.

    2016-05-01

    The phase stability, electronic structure, and magnetic properties of Al1- x Ti x N compositions based on the metastable aluminum nitride modification with the rock-salt structure at low ( x = 0.03) and high ( x = 0.25) concentrations of titanium in the system have been investigated using the results of ab initio band calculations. It has been shown that, at low values of x, the partial substitution is characterized by a positive enthalpy, which, however, changes sign with an increase in the titanium concentration. According to the results of the band structure calculations, the doped compositions have electronic conductivity. For x = 0.03, titanium impurity atoms have local magnetic moments (˜0.6 μB), and the electronic spectrum is characterized by a 100% spin polarization of near-Fermi states. Some of the specific features of the chemical bonding in Al1- x Ti x N cubic phases have been considered.

  19. Geometric structure, electronic structure and optical absorption properties of one-dimensional thiolate-protected gold clusters containing a quasi-face-centered-cubic (quasi-fcc) Au-core: a density-functional theoretical study.

    Science.gov (United States)

    Ma, Zhongyun; Wang, Pu; Pei, Yong

    2016-09-29

    Based on the recently reported atomic structures of thiolate-protected Au28(SR)20, Au36(SR)24, Au44(SR)28, and Au52(SR)32 clusters, a family of homogeneous, linear, thiolate-protected gold superstructures containing novel quasi-face-centered-cubic (quasi-fcc) Au-cores is theoretically envisioned, denoted as the Au20+8N(SR)16+4N cluster. By means of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, a unified view of the geometric structure, electronic structure, magic stable size and size-dependent NIR absorption properties of Au20+8N(SR)16+4N clusters is provided. We find that the Au20+8N(SR)16+4N clusters demonstrate oscillating transformation energies dependent on N. The odd-N clusters show more favorable (negative) reaction energies than the even-N clusters. The magic stability of recently reported Au28(SR)20, Au36(SR)24, Au44(SR)28, Au52(SR)32 and Au76(SR)44 clusters can be addressed from the relative reaction energies and geometric distortion of Au-cores. A novel 4N + 4 magic electron-number is suggested for the Au20+8N(SR)16+4N cluster. Using the polyhedral skeletal electron pair theory (PSEPT) and the extended Hückel molecular orbital (EHMO) calculations, we suggest that the magic 4N + 4 electron number is correlated with the quasi-fcc Au-cores, which can be viewed as double helical tetrahedron-Au4 chains. The size-dependent optical absorption properties of Au20+8N(SR)16+4N clusters are revealed based on TD-DFT calculations. We propose that these clusters are potential candidates for the experimental synthesis of atomically precise one-dimensional ligand protected gold superstructures with tunable NIR absorption properties.

  20. Coagulation of fines in fluorite froth flotation; Coagulacion de finos en la flotacion de la fluorita

    Energy Technology Data Exchange (ETDEWEB)

    Sarquis, P. E.; Gonzalez, M.; Moyano, A.; Bazan, V.

    2011-07-01

    Fluorite, a valuable mineral in the metallurgical industry, can be found together with silicates, carbonates and oxides in ore deposits. Commercial concentrates with more than 95 % of CaF{sub 2} are obtained processing the mineral in flotation plants and using oleic acid as fluorite collector. Depressor reagents such as sodium silicate, tannin and sodium carbonate are commonly employed to allow the oleic acid selective performance. These reagents cause a dispersant effect separating the solid-liquid solution on tailing plants. Fine particles in the recovered water enter the circuit and affect the flotation efficiency. The effect of coagulant ions was studied as a method to clarify the returned water. The problem of the presence of these ions is related to its reactions with the collector by the formation of compounds and possibly on the selectivity. Variable quantities of Al{sup 3}+, Fe{sup 3}+ and Ca{sup 2}+ ions were added to the flotation to evaluate its effect on the fluorite recovery, in the selectivity and in solids content in recirculation water. Results show that some ions fail to improve water quality and are detrimental to flotation. On the contrary, some ions contribute to reduce fine content in suspension. Therefore, although there is a recovery reduction, such effect can be counteracted increasing the collector consumption a little. (Author) 21 refs.

  1. Selective Separation of Fluorite, Barite and Calcite with Valonea Extract and Sodium Fluosilicate as Depressants

    Directory of Open Access Journals (Sweden)

    Zijie Ren

    2017-02-01

    Full Text Available Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that valonea extract displayed the strongest depression on calcite, while sodium fluosilicate displayed the strongest depression on barite. These two depressants allowed selective separation of the three minerals through sequential flotation. The flotation of mixed minerals showed that 94% of the calcite was successfully depressed by the valonea extract, and 95% recovery of the fluorite was achieved in the subsequent flotation with sodium fluosilicate depressing barite. The different depressant–mineral interactions were investigated via electro-kinetic studies and molecular dynamics (MD simulations using the Materials Studio 6.0 program. The valonea extract exhibited the strongest adsorption on the calcite surface, and sodium fluosilicate exhibited the strongest adsorption on the barite surface, which prevented oleate species from reacting with Ca2+ or Ba2+ surface sites. This study provides useful guidance for how to process fluorite, barite and calcite resources.

  2. Uranium exploration in the vicinity of abandoned fluorite mines, in northern Thailand, using cellulose nitrate films

    Energy Technology Data Exchange (ETDEWEB)

    Wattananikorn, K.; Asnachinda, P.; Lamphunphong, S. (Chiangmai Univ. (Thailand))

    1990-01-01

    Ground radon measurements using LR-115 type 2 as detectors were carried out covering an area of approx. 3.5 km{sup 2} in the vicinity of abandoned fluorite mines in northern Thailand. Each detector was enclosed in a PVC tube buried at a constant depth at each measuring station. Nine anomalies of {alpha}-track values were found covering an area of approx. 12000 m{sup 2}. Most of the anomalies were related closely to quartz veins, fluorite veins and faults. Three out of these nine anomalies showed corresponding distinct {gamma}-ray activities. The maximum {alpha}-track anomaly occurred at station P18, having a track density of 58685 t/cm{sup 2}.d. A small uranium-bearing quartz vein, about 10 cm wide and 2 m long, was subsequently discovered outcropping close to the station. The vein consists of quartz, fluorite and a secondary uranium mineral, torbernite. The maximum uranium content in the ore samples was found to be as much as 14%. (author).

  3. The influence of crystal structure on ion-irradiation tolerance in the Sm(x)Yb(2-x)TiO5 series

    Energy Technology Data Exchange (ETDEWEB)

    Aughterson, R. D.; Lumpkin, G. R.; de los Reyes, M.; Gault, B.; Baldo, P.; Ryan, E.; Whittle, K. R.; Smith, K. L.; Cairney, J. M.

    2016-04-01

    his ion-irradiation study covers the four major crystal structure types in the Ln(2)TiO(5) series (Ln = lanthanide), namely orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. This is the first systematic examination of the complete Ln(2)TiO(5) crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm(x)Yb(2-x)TiO5 (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr2+ ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation (D-c), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature (T-c), above which the sample cannot be rendered amorphous by ion irradiation. The structure type plus elements of bonding are correlated to ion-irradiation tolerance. The cubic phases, Yb2TiO5 and Sm0.6Yb1.4TiO5, were found to be the most radiation tolerant, with Tc values of 479 and 697 K respectively. The improved radiation tolerance with a change in symmetry to cubic is consistent with previous studies of similar compounds.

  4. A kinetic study of the replacement of calcite marble by fluorite

    Science.gov (United States)

    Trindade Pedrosa, Elisabete; Boeck, Lena; Putnis, Christine V.; Putnis, Andrew

    2016-04-01

    Replacement reactions are relevant in any situation that involves the reequilibration between a solid and an aqueous fluid phase and are commonly controlled by an interface-coupled dissolution-precipitation mechanism (Putnis and Putnis, 2007). These reactions control many large-scale Earth processes whenever aqueous fluids are available, such as during metamorphism, metasomatism, and weathering. An important consequence of coupled dissolution-precipitation is the generation of porosity in the product phase that then allows the infiltration of the fluid within the mineral being replaced. Understanding the mechanism and kinetics of the replacement of carbonates by fluorite has application in earth sciences and engineering. Fluorite (CaF2) occurs in all kinds of rocks (igneous, sedimentary, and metamorphic) and its origin is commonly associated with hydrothermal fluids. Moreover, calcium carbonate has been suggested as a successful seed material for the sequestration of fluoride from contaminated waters (Waghmare and Arfin, 2015). The aim of the present work is to investigate aspects of the replacement of calcium carbonate by fluorite to better understand the mechanism and kinetics of this reaction. Small cubes (˜ 3 × 3 × 3 mm) of Carrara marble (CaCO3 > 99 %) were cut and reacted with a 4 M ammonium fluoride (NH4F) solution for different times (1 to 48 hours) and temperatures (60, 80, 100, and 140 ° C). The microstructure of the product phases was analysed using SEM. The kinetics of replacement was monitored from the Rietveld analysis of X-ray powder diffraction patterns of the products as a function of temperature and reaction time. After reaction, all samples preserved their size and external morphology (a pseudomorphic replacement) and the product phase (fluorite) was highly porous. The activation energy Ea (kJ/mol) of the replacement reaction was empirically determined by both model-fitting and model-free methods. The isoconversional method yielded an

  5. Avalanche criticalities and elastic and calorimetric anomalies of the transition from cubic Cu-Al-Ni to a mixture of 18 R and 2 H structures

    Science.gov (United States)

    Vives, Eduard; Baró, Jordi; Gallardo, María Carmen; Martín-Olalla, José-María; Romero, Francisco Javier; Driver, Sarah L.; Carpenter, Michael A.; Salje, Ekhard K. H.; Stipcich, Marcelo; Romero, Ricardo; Planes, Antoni

    2016-07-01

    We studied the two-step martensitic transition of a Cu-Al-Ni shape-memory alloy by calorimetry, acoustic emission (AE), and resonant ultrasound spectroscopy (RUS) measurements. The transition occurs under cooling from the cubic (β , F m 3 m ) parent phase near 242 K to a mixture of orthorhombic 2 H and monoclinic 18 R phases. Heating leads first to the back transformation of small 18 R domains to β and/or 2 H near 255 K, and then to the transformation 2 H to β near 280 K. The total transformation enthalpy is Δ HT=328 ±10 J/mol and is observed as one large latent heat peak under cooling. The back-transformation entropy under heating breaks down into a large component 18 R to β at 255 K and a smaller, smeared component of the transformation 2 H to β near 280 K. The proportions inside the phase mixture depend on the thermal history of the sample. The elastic response of the sample is dominated by large elastic softening during cooling. The weakening of the elastic shear modulus shows a peak at 242 K, which is typical for the formation of complex microstructures. Cooling the sample further leads to additional changes of the microstructure and domain wall freezing, which is seen by gradual elastic hardening and increasing damping of the RUS signal. Heating from 220 K to room temperature leads to elastic anomalies due to the initial transformation, which is now shifted to high temperatures. The transition is smeared over a wider temperature interval and shows strong elastic damping. The shear modulus of the cubic phase is recovered at 280 K. The phase transformation leads to avalanches, which were recorded by AE and by time-resolved calorimetry. The cooling transition shows very extended avalanche signals in calorimetry with power-law distributions. Cooling and heating runs show AE signals over a large temperature interval above 260 K. Splitting the transformation into two martensite phases leads to power-law exponents ɛ ˜2 (β ↔ 18 R ) and ɛ ˜1.5 (β ↔ 2

  6. Crystal Structure-Ionic Conductivity Relationships in Doped Ceria Systems

    DEFF Research Database (Denmark)

    Omar, Shobit; Wachsman, Eric D.; Jones, Jacob L.;

    2009-01-01

    In the past, it has been suggested that the maximum ionic conductivity is achieved in ceria, when doped with an acceptor cation that causes minimum distortion in the cubic fluorite crystal lattice. In the present work, this hypothesis is tested by measuring both the ionic conductivity and elastic...

  7. Crystalline structure of ceria particles controlled by the oxygen partial pressure and STI CMP performances.

    Science.gov (United States)

    Kim, Ye-Hwan; Kim, Sang-Kyun; Kim, Namsoo; Park, Jea-Gun; Paik, Ungyu

    2008-09-01

    The effect of the crystalline structures of nano-sized ceria particles on shallow trench isolation (STI) chemical mechanical planarization (CMP) performance was investigated. The ceria particles were synthesized via a solid-state displacement reaction method, and their crystalline structure was controlled by regulating the oxygen partial pressure at the reaction site on the precursor. The crystalline structures of ceria particles were analyzed by the high-resolution TEM nano-beam diffraction pattern. In a calcination process with a high oxygen concentration, the synthesized ceria particles had a cubic fluorite structure (CeO(2)), because of the decarbonation of the cerium precursor. However, a low oxygen concentration results in a hexagonal phase cerium oxide (Ce(2)O(3)) rather than the cubic phase due to the insufficient oxidation of Ce(3+) to Ce(4+). In the STI CMP evaluation, the ceria slurry prepared with the cubic CeO(2) shows enhanced performances of the oxide-to-nitride removal selectivity.

  8. Aprotic synthesis and structural determination of the nanosized nonprotonated nu3-octahedral [Pt6Ni38(CO)48]6- hexaanion stabilized as a cubic solvated [NMe4]+ salt.

    Science.gov (United States)

    de Silva, Namal; Dahl, Lawrence F

    2006-10-30

    The nonprotonated member, 1 (n = 6), of the previously established nanosized nu3-octahedral [H(6-n)Pt6Ni38(CO)48]n- series (n = 3-6) has been isolated from an aprotic synthetic route and stabilized as the crystal-ordered cyclohexane/acetonitrile-solvated [NMe4]+ salt. A highly precise X-ray determination (cubic; Pa3; Z = 4 with 1 possessing -3 site symmetry) has allowed a comparative analysis of the nonprotonated pseudo-D3d structure of 1 with the monoprotonated structure of 2 (n = 5), which constitutes the only previously reported complete geometry of any member of this extraordinary Pt6-encapsulated nu3-octahedral Pt6Ni38 cluster series.

  9. Percolating hierarchical defect structures drive phase transformation in Ce1−xGdxO2−x/2: a total scattering study

    Directory of Open Access Journals (Sweden)

    Marco Scavini

    2015-09-01

    Full Text Available A new hierarchical approach is presented for elucidating the structural disorder in Ce1−xGdxO2−x/2 solid solutions on different scale lengths. The primary goal of this investigation is to shed light on the relations between the short-range and the average structure of these materials via an analysis of disorder on the mesocopic scale. Real-space (pair distribution function and reciprocal-space (Rietveld refinement and microstructure probing analysis of X-ray powder diffraction data and electron spin resonance (ESR investigations were carried out following this approach. On the local scale, Gd- and Ce-rich droplets (i.e. small regions a few ångströms wide form, exhibiting either a distorted fluorite (CeO2 or a C-type (Gd2O3 structure in the whole compositional range. These droplets can then form C-type nanodomains which, for Gd concentrations xGd ≤ 0.25, are embedded in the fluorite matrix. At the site percolation threshold pC for a cubic lattice (xGd = pC ≃ 0.311, C-type nanodomains percolate inside each crystallite and a structural phase transformation is observed. When this occurs, the peak-to-peak ESR line width ΔHpp shows a step-like behaviour, which can be associated with the increase in Gd–Gd dipolar interactions. A general crystallographic rationale is presented to explain the fluorite-to-C-type phase transformation. The approach shown here could be adopted more generally in the analysis of disorder in other highly doped materials.

  10. Ultrahard nanotwinned cubic boron nitride.

    Science.gov (United States)

    Tian, Yongjun; Xu, Bo; Yu, Dongli; Ma, Yanming; Wang, Yanbin; Jiang, Yingbing; Hu, Wentao; Tang, Chengchun; Gao, Yufei; Luo, Kun; Zhao, Zhisheng; Wang, Li-Min; Wen, Bin; He, Julong; Liu, Zhongyuan

    2013-01-17

    Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall-Petch effect--the tendency for hardness to increase with decreasing grain size. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m(1/2), well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m(1/2)). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall-Petch effect below a critical grain size or the twin thickness of ∼10-15 nm found in metals and alloys.

  11. Universal Reconfiguration of (Hyper-)cubic Robots

    OpenAIRE

    Abel, Zachary; Kominers, Scott D.

    2008-01-01

    We study a simple reconfigurable robot model which has not been previously examined: cubic robots comprised of three-dimensional cubic modules which can slide across each other and rotate about each others' edges. We demonstrate that the cubic robot model is universal, i.e., that an n-module cubic robot can reconfigure itself into any specified n-module configuration. Additionally, we provide an algorithm that efficiently plans and executes cubic robot motion. Our results directly extend to a...

  12. Electronic properties of cubic TaC{sub x}N{sub 1-x}: A comparative study using self-consistent cluster and ab initio band-structure calculations and X-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya. [Department of Physics, Don State Technical University, Gagarin Sq. 1, Rostov-on-Don (Russian Federation); Khyzhun, O.Yu. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, UA-03142 Kyiv (Ukraine)], E-mail: khyzhun@ipms.kiev.ua

    2009-03-20

    To investigate the influence of substitution of carbon atoms for nitrogen atoms in the cubic TaC{sub x}N{sub 1-x} carbonitrides, total and partial densities of states were calculated for TaC, TaC{sub 0.5}N{sub 0.5} and TaN compounds (NaCl structure) using the self-consistent cluster (with the FEFF8 code) and ab initio band-structure augmented plane wave + local orbitals (APW + LO) methods. In the present work a rather good agreement of the theoretical FEFF8 and APW + LO data for electronic properties of the TaC{sub x}N{sub 1-x} system under consideration was obtained. The results indicate that a strong hybridization of the Ta 5d- and C(N) 2p-like states is characteristic for the valence band of the TaC{sub x}N{sub 1-x} carbonitrides. When going from TaC to TaN through the TaC{sub 0.5}N{sub 0.5} carbonitride, the main maxima of curves representing total and partial Ta 5d densities of states shift in the direction opposite to the position of the Fermi level. In the above sequence of compounds, an increase of occupation of the near-Fermi sub-band formed by contributions of Ta 5d(t{sub 2g}) states has been detected. The theoretical FEFF8 and APW + LO results for the electronic structure of the TaC{sub x}N{sub 1-x} carbonitrides were found to be in excellent agreement with the experimental data derived in the present work employing X-ray photoelectron, emission and absorption spectroscopy methods for cubic TaC{sub 0.98}, TaC{sub 0.52}N{sub 0.49} and TaN{sub 0.97} compounds.

  13. Evaluation in situ of genotoxicity and stress in South American common toad Rhinella arenarum in environments related to fluorite mine.

    Science.gov (United States)

    Pollo, Favio E; Grenat, Pablo R; Salinas, Zulma A; Otero, Manuel A; Salas, Nancy E; Martino, Adolfo L

    2017-06-20

    Little attention has been paid to the impact of wastewater generated by mining activities on fluoride. In this study, we evaluated the hematology responses of common South American toad Rhinella arenarum inhabiting natural and artificial environments associated with a fluorite mine from central Argentina. We analyzed three sampling stations associated with the fluorite mine: (I) Los Cerros Negros stream (CN), which runs on granitic rock with a high fluorite content; (II) Los Vallecitos stream (LV), which runs on metamorphic rock with low fluorite content; and (III) artificial decantation ponds (DP) containing sediments produced by fluorite flotation process. We calculated frequencies of micronuclei, erythrocyte nuclear abnormalities, mitosis, and immature erythrocytes. In addition, we performed a differential leukocyte count and determined neutrophils/lymphocyte ratio as a stress response estimator. We found high micronucleus (MN) and erythrocyte nuclear abnormality (ENA) frequencies in DP and CN but low frequencies in LV. The neutrophil/lymphocyte ratio was different among sites, with a significant increase in individuals from DP. Values registered in DP could be caused by exposure to mixture of compounds registered in dams that hold wastewater, while high values registered in CN stream might be due to natural concentrations of fluoride. Our results suggest that blood is an effective and non-destructive sensitive indicator for monitoring genotoxic agents in freshwater ecosystems.

  14. Cubication of Conservative Nonlinear Oscillators

    Science.gov (United States)

    Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada

    2009-01-01

    A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…

  15. Cryptographic Analysis in Cubic Time

    DEFF Research Database (Denmark)

    Nielson, Flemming; Nielson, Hanne Riis; Seidl, H.

    2004-01-01

    The spi-calculus is a variant of the polyadic pi-calculus that admits symmetric cryptography and that admits expressing communication protocols in a precise though still abstract way. This paper shows that context-independent control flow analysis can be calculated in cubic time despite the fact ...

  16. The diagonalization of cubic matrices

    Science.gov (United States)

    Cocolicchio, D.; Viggiano, M.

    2000-08-01

    This paper is devoted to analysing the problem of the diagonalization of cubic matrices. We extend the familiar algebraic approach which is based on the Cardano formulae. We rewrite the complex roots of the associated resolvent secular equation in terms of transcendental functions and we derive the diagonalizing matrix.

  17. An Example of Body-Centered Cubic Crystal Structure: The Atomium in Brussels as an Educative Tool for Introductory Materials Chemistry

    Science.gov (United States)

    Pinto, Gabriel

    2012-01-01

    When students are introduced to the ways in which atoms are arranged in crystal structures, transposing the textbook illustrations into three-dimensional structures is difficult for some of them. To facilitate this transition, this article describes an approach to the study of the structure of solids through a well-known monument, the Atomium in…

  18. An Example of Body-Centered Cubic Crystal Structure: The Atomium in Brussels as an Educative Tool for Introductory Materials Chemistry

    Science.gov (United States)

    Pinto, Gabriel

    2012-01-01

    When students are introduced to the ways in which atoms are arranged in crystal structures, transposing the textbook illustrations into three-dimensional structures is difficult for some of them. To facilitate this transition, this article describes an approach to the study of the structure of solids through a well-known monument, the Atomium in…

  19. Coontail fluorite rhythmites of southern Illinois: evidence for episodic basin dewatering

    Energy Technology Data Exchange (ETDEWEB)

    Cowan, C.A.; Kelly, W.C.; Wilkinson, B.H.

    1985-01-01

    Stratiform coontail ore of the Cave-in-Rock fluorite district, southern Illinois, display conspicuous, rhythmic banded textures similar to those reported in many MVT deposits throughout the world (e.g., east Tennessee, USA; Silesian-Cracow Region, Poland; and northern Baffin Island, Canada). Banding is expressed by the rhythmic alteration of two types of layers: detrital layers of fluorite mottled with particulate gangue dolomite and quartz, and layers of clear, crystalline fluorspar. Both are now composed principally of fluorite but differ in color, fabric and outline. In the past, this rhythmic banding has generally been attributed to fine-scale replacement of a primary host rock stratification or to cyclic replacement of host carbonates by a fluid of oscillating chemistry. Detailed megascopic and microscopic studies of these ores and their carbonate host real that ore bands were not derived by fine-scale in situ limestone replacement. Detrital bands contain hydraulically transported, sorted and graded, allochthonous debris derived by dissolution and disaggregation of host limestone and overlying shale. The banded fabric thus represents a cyclic interplay of chemical and hydraulic processes active during hydrothermal ore mineralization. Coontail ore bodies evidently formed in a hydrothermal spelean system, whose laterally sinuous trace reflects localization of hydrothermal activity where feeder faults intersected relatively impermeable roof-rock shales. The banded nature of these ores testifies to the ability of Mississippi Valley-type hydrothermal solutions to both create and fill their own open spaces. Moreover, the rhythmic nature of coontail ores suggests a prolonged and pulsating mineralization best explained by episodic dewatering of the Illinois Basin.

  20. Ab initio study of the effect of pressure on the structural and electronic properties of cubic LaAlO{sub 3} by density function theory using GGA, LDA and PBEsol exchange correlation potentials

    Energy Technology Data Exchange (ETDEWEB)

    Benam, M.R., E-mail: m_benam@pnu.ac.ir [Department of Physics, Payame Noor University, P.O. BOX 19395-3697 (Iran, Islamic Republic of); Abdoshahi, N.; Majidiyan Sarmazdeh, M. [Department of Physics, Payame Noor University, P.O. BOX 19395-3697 (Iran, Islamic Republic of)

    2014-08-01

    In this paper the effect of pressure on the structural and electronic properties of cubic-LaAlO{sub 3} including the equilibrium lattice constant, bulk modulus, derivative of bulk modulus and band structure have been calculated by density functional theory (DFT) using GGA, LDA, and PBEsol exchange correlation potentials. It is found that the change of the lattice constant with pressure has an exponential behavior: with increasing pressure, the lattice constant decreases first sharply at low pressures, and then more slowly at high pressures. Furthermore, the lattice constant calculated by the PBEsol method and the bulk modulus calculated by LDA and PBEsol methods are closer to the available experimental values than those obtained using other exchange correlation potentials. Regarding the electronic properties, it is shown that an increase in pressure increases the band gap, the change being 0.26 eV at 34.00 GPa. The total density of state (t-DOS) calculations demonstrate that increasing pressure has a significant effect on the core and conduction band, but little effect on the valence band. The band structure calculations indicate that, in this material, the band gap changes from indirect to direct at a pressure of about 25 GPa. Also, increasing pressure produces a clear curvature in the band structure near the bottom of the conduction band, a behavior consistent with the strong pressure dependence of the transport properties.

  1. Ab initio study of the effect of pressure on the structural and electronic properties of cubic LaAlO3 by density function theory using GGA, LDA and PBEsol exchange correlation potentials

    Science.gov (United States)

    Benam, M. R.; Abdoshahi, N.; Majidiyan Sarmazdeh, M.

    2014-08-01

    In this paper the effect of pressure on the structural and electronic properties of cubic-LaAlO3 including the equilibrium lattice constant, bulk modulus, derivative of bulk modulus and band structure have been calculated by density functional theory (DFT) using GGA, LDA, and PBEsol exchange correlation potentials. It is found that the change of the lattice constant with pressure has an exponential behavior: with increasing pressure, the lattice constant decreases first sharply at low pressures, and then more slowly at high pressures. Furthermore, the lattice constant calculated by the PBEsol method and the bulk modulus calculated by LDA and PBEsol methods are closer to the available experimental values than those obtained using other exchange correlation potentials. Regarding the electronic properties, it is shown that an increase in pressure increases the band gap, the change being 0.26 eV at 34.00 GPa. The total density of state (t-DOS) calculations demonstrate that increasing pressure has a significant effect on the core and conduction band, but little effect on the valence band. The band structure calculations indicate that, in this material, the band gap changes from indirect to direct at a pressure of about 25 GPa. Also, increasing pressure produces a clear curvature in the band structure near the bottom of the conduction band, a behavior consistent with the strong pressure dependence of the transport properties.

  2. Optimization of cubic GaN/AlGaN quantum well-based structures for intersubband absorption in the infrared spectral range

    Science.gov (United States)

    Radosavljević, Ana; Radovanović, Jelena; Milanović, Vitomir

    2014-03-01

    A method is proposed for the optimization of structural parameters of GaN/AlGaN quantum wells and Bragg-confined structures, with respect to peak intersubband absorption from the ground to the first excited electronic state in the mid and near infrared spectral range. It is based on the application of the Genetic Algorithm and delivers globally optimal structures with a preset number of embedded layers. Simple rectangular quantum well profile is investigated for the maximal Stark effect and applications to tunable mid-infrared photodetectors. In case of Bragg-confined structures, an above the barrier bound state is used to extend the range of transition energies above the values available in conventional quantum wells. The effects of band nonparabolicity are taken into account.

  3. Cubication of conservative nonlinear oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Belendez, Augusto; Alvarez, Mariela L [Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Senal, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain); Fernandez, Elena; Pascual, Inmaculada [Departamento de Optica, FarmacologIa y Anatomia, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)], E-mail: a.belendez@ua.es

    2009-09-15

    A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear and cubic terms depend on the initial amplitude, A, while in a Taylor expansion of the restoring force these coefficients are independent of A. The replacement of the original nonlinear equation by an approximate Duffing equation allows us to obtain an approximate frequency-amplitude relation as a function of the complete elliptic integral of the first kind. Some conservative nonlinear oscillators are analysed to illustrate the usefulness and effectiveness of this scheme.

  4. Cubic Matrix, Nambu Mechanics and Beyond

    OpenAIRE

    Kawamura, Y

    2002-01-01

    We propose a generalization of cubic matrix mechanics by introducing a canonical triplet and study its relation to Nambu mechanics. The generalized cubic matrix mechanics we consider can be interpreted as a “quantum” generalization of Nambu mechanics.

  5. Numbers for reducible cubic scrolls

    Directory of Open Access Journals (Sweden)

    Israel Vainsencher

    2004-12-01

    Full Text Available We show how to compute the number of reducible cubic scrolls of codimension 2 in (math blackboard symbol Pn incident to the appropriate number of linear spaces.Mostramos como calcular o número de rolos cúbicos redutíveis de codimensão 2 em (math blackboard symbol Pn incidentes a espaços lineares apropriados.

  6. The Research Status of Fluorite Color%萤石颜色研究现状

    Institute of Scientific and Technical Information of China (English)

    郑惠; 李葆华; 罗英; 祝秀

    2015-01-01

    Fluoritehas a variety of colors, in addition to red which is rarely seen, other colors are very common. The color difference is caused by different genetic types, through the study on the color factors of fluorite, this pa⁃per discovered the fluorite color formation mechanism. The main causes of the color include the mixing of the im⁃purities, crystal defects and the mixing of organic matters.%萤石颜色多样,除红色少见外,其他颜色都很常见。不同成因类型造成的萤石颜色不同,本文通过对萤石致色因素的研究,揭示了萤石颜色的形成机理,其颜色形成的原因主要有杂质元素的混入、晶体缺陷以及有机质的混入。

  7. Electronic structure of cubic Hf{sub x}Ta{sub 1-x}C{sub y} carbides from X-ray spectroscopy studies and cluster self-consistent calculations

    Energy Technology Data Exchange (ETDEWEB)

    Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya. [Department of Physics, Don State Technical University, Gagarin Sq. 1, Rostov-on-Don (Russian Federation); Khyzhun, O.Yu. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Str., UA-03142 Kyiv (Ukraine)], E-mail: khyzhun@ipms.kiev.ua; Rehr, J.J. [Department of Physics, University of Washington, Seattle, WA 98195-1560 (United States)

    2008-08-25

    X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were employed in the present work to investigate the electronic structure of almost stoichiometric cubic (NaCl structure) Hf{sub x}Ta{sub 1-x}C{sub y} carbides. The XPS valence-band and core-level spectra, the XES bands reflecting energy distributions of mainly the Ta 5d- and C 2p-like states as well as the XAS Ta L{sub III} edges (unoccupied Ta d-like states) were derived and compared on a common energy scale for cubic HfC{sub 0.95}, Hf{sub 0.5}Ta{sub 0.5}C{sub 0.94} and TaC{sub 0.98} compounds. To investigate the influence of substitution of tantalum atoms for hafnium atoms in the Hf{sub x}Ta{sub 1-x}C{sub y} carbides, cluster self-consistent calculations of total and partial densities of states were carried out with the FEFF8 code for HfC, Hf{sub 0.5}Ta{sub 0.5}C and TaC compounds possessing the NaCl-type structure. In the present work a rather good agreement of the experimental and theoretical results for the electronic structure of the Hf{sub x}Ta{sub 1-x}C{sub y} system under study was obtained. The results indicate that a strong hybridization of the Hf(Ta) 5d- and C 2p-like states is characteristic for the Hf{sub x}Ta{sub 1-x}C{sub y} carbides. It has been established that, substitution of hafnium atoms by tantalum atoms in the Hf{sub x}Ta{sub 1-x}C{sub y} system reveals increasing the half-width of the XES C K{alpha} band. When going from HfC{sub 0.95} to TaC{sub 0.98} through the carbide of intermediate composition, the main maximum of the XPS valence-band spectrum shifts in the direction opposite to the position of the Fermi level. In the above sequence of compounds the asymmetry index of the C K{alpha} bands decreases significantly.

  8. First-principles calculations of the structural, electronic and optical properties of cubic B{sub x}Ga{sub 1-x}As alloys

    Energy Technology Data Exchange (ETDEWEB)

    Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, University Ibn Khaldoun of Tiaret, BP 78-Zaaroura, Tiaret 14000 (Algeria); Bouhafs, B. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Abdiche, A. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Al Douri, Y. [Institute of Nano Electronic Engineering, Universiti Malaysia Perlis, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)

    2012-04-15

    Density functional calculations are performed to study the structural, electronic and optical properties of technologically important B{sub x}Ga{sub 1-x}As ternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation potential, local density approximation (LDA) and the generalized gradient approximation (GGA) have been used. The structural properties, including lattice constants, bulk modulus and their pressure derivatives, are in very good agreement with the available experimental and theoretical data. The electronic band structure, density of states for the binary compounds and their ternary alloys are given. The dielectric function and the refractive index are also calculated using different models. The obtained results compare very well with previous calculations and experimental measurements.

  9. Cubic colloids : Synthesis, functionalization and applications

    NARCIS (Netherlands)

    Castillo, S.I.R.

    2015-01-01

    This thesis is a study on cubic colloids: micron-sized cubic particles with rounded corners (cubic superballs). Owing to their shape, particle packing for cubes is more efficient than for spheres and results in fascinating phase and packing behavior. For our cubes, the particle volume fraction when

  10. Cubic colloids : Synthesis, functionalization and applications

    NARCIS (Netherlands)

    Castillo, S.I.R.

    2015-01-01

    This thesis is a study on cubic colloids: micron-sized cubic particles with rounded corners (cubic superballs). Owing to their shape, particle packing for cubes is more efficient than for spheres and results in fascinating phase and packing behavior. For our cubes, the particle volume fraction when

  11. Solving Cubic Equations by Polynomial Decomposition

    Science.gov (United States)

    Kulkarni, Raghavendra G.

    2011-01-01

    Several mathematicians struggled to solve cubic equations, and in 1515 Scipione del Ferro reportedly solved the cubic while participating in a local mathematical contest, but did not bother to publish his method. Then it was Cardano (1539) who first published the solution to the general cubic equation in his book "The Great Art, or, The Rules of…

  12. Cubic Icosahedra? A Problem in Assigning Symmetry

    Science.gov (United States)

    Lloyd, D. R.

    2010-01-01

    There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…

  13. The 2:3:6 QPO structure in GRS 1915+105 and cubic subharmonics in the context of relativistic diskoseismology

    CERN Document Server

    Ortega-Rodr\\'\\iguez, Manuel; López-Barquero, Vanessa; Matamoros-Alvarado, Bryan; Venegas-Li, Ariadna

    2013-01-01

    We propose a simple toy model to explain the 2:3:6 QPO structure in GRS 1915+105 and, more generally, the 2:3 QPO structure in XTE J1550-564, GRO J1655-40, and H 1743-322. The model exploits the onset of subharmonics in the context of diskoseismology. The results include the prediction that, as better data become available, a QPO with a frequency of twice the higher twin frequency and a large quality factor will be observed in twin peak sources, as it might already have been observed in the especially active GRS 1915+105.

  14. Cubic metaplectic forms and theta functions

    CERN Document Server

    Proskurin, Nikolai

    1998-01-01

    The book is an introduction to the theory of cubic metaplectic forms on the 3-dimensional hyperbolic space and the author's research on cubic metaplectic forms on special linear and symplectic groups of rank 2. The topics include: Kubota and Bass-Milnor-Serre homomorphisms, cubic metaplectic Eisenstein series, cubic theta functions, Whittaker functions. A special method is developed and applied to find Fourier coefficients of the Eisenstein series and cubic theta functions. The book is intended for readers, with beginning graduate-level background, interested in further research in the theory of metaplectic forms and in possible applications.

  15. Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters

    Science.gov (United States)

    Souza, T. X. R.; Macedo, C. A.

    2016-01-01

    In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh’s conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653

  16. Structure characteristics of cubic and orthorhombic phases of high density scintillator PbF{sub 2} from 4.2--300 K

    Energy Technology Data Exchange (ETDEWEB)

    Shmyt`ko, I.; Savchenko, I.B.; Klassen, N.V.; Bagautdinov, B.S.; Emel`chenko, G.A.; Sinitzin, V.V. [Russian Academy of Sciences, Chernogolovka (Russian Federation). Inst. of Solid State Physics

    1994-12-31

    An anomaly of the temperature dependence of the unit cell parameter has been observed for {beta}-PbF{sub 2} single crystals at 200 K that is interpreted as a phase transition to a pseudocubic lattice. Such a pseudocubic phase is observable at room temperature after uniaxial plastic deformation of the bulk single crystals. The structural aspects of the {beta}{r_arrow}{alpha} transition have been established. The as-grown crystals of {alpha}-PbF{sub 2} phase are shown to undergo a phase transition at 100 K.

  17. Structural, electronic and optical properties of cubic SrTiO{sub 3} and KTaO{sub 3}: Ab initio and GW calculations

    Energy Technology Data Exchange (ETDEWEB)

    Benrekia, A.R., E-mail: benrekia.ahmed@yahoo.com [Faculty of Science and Technology, University of Medea (Algeria); Benkhettou, N. [Laboratoire des Materiaux Magnetiques, Faculte des Sciences, Universite Djillali Liabes de Sidi Bel Abbes (Algeria); Nassour, A. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France); Driz, M. [Applied Material Laboratory (AML), Electronics Department, University of Sidi bel Abbes (DZ 22000) (Algeria); Sahnoun, M. [Laboratoire de Physique Quantique de la Matiere et Modelisations Mathematique (LPQ3M), Faculty of Science and Technology,University of Mascara (Algeria); Lebegue, S. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France)

    2012-07-01

    We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO{sub 3} and KTaO{sub 3}. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO{sub 3} and KTaO{sub 3}.

  18. The Improvement Effect of Dispersant in Fluorite Flotation: Determination by the Analysis of XRD and FESEM-EDX

    Directory of Open Access Journals (Sweden)

    Y. J. Li

    2015-01-01

    Full Text Available Different dispersants were added in the dispersion process to improve the efficiency of fluorite flotation. The types and dosage of dispersant on the improvement of fluorite flotation were investigated; when the sodium polyacrylate (SPA was used as the dispersant and its addition is 0.5%, the concentrate grade of CaF2 increased from 90% to 98% and the fluorite recovery increased from 81% to 85%. Methods of X-ray powder diffraction (XRD, field emission scanning electron microscopy (FESEM, and Energy dispersive X-ray spectrometer (EDX were used to characterize the sample. According to the analysis of results, the optimal sample consisted of CaF2 and very little CaCO3 in the size range of 0–5 μm. It could be concluded that the mechanism of improvement for the concentrate grade and recovery of CaF2 was attributed to the change of potential energy barrier which caused the separation of particles with different charge. All results indicate that SPA has a great potential to be an efficient and cost-effective dispersant for the improvement of fluorite flotation.

  19. Synthesis, Characterization, and Electronic Structure Studies of Cubic Bi1.5ZnTa1.5O7 for Photocatalytic Applications

    Directory of Open Access Journals (Sweden)

    Ganchimeg Perenlei

    2015-01-01

    Full Text Available Bi1.5ZnTa1.5O7 (BZT has been synthesized using an alkoxide based sol-gel reaction route. The evolution of the phases produced from the alkoxide precursors and their properties have been characterized as function of temperature using a combination of thermogravimetric analysis (TGA coupled with mass spectrometry (MS, infrared emission spectrometry (IES, X-ray diffraction (XRD, ultraviolet and visible (UV-Vis spectroscopy, Raman spectroscopy, and N2 adsorption/desorption isotherms. The lowest sintering temperature (600°C to obtain phase pure BZT powders with high surface area (14.5 m2/g has been determined from the thermal decomposition and phase analyses. The photocatalytic activity of the BZT powders has been tested for the decolorization of organic azo-dye and found to be photoactive under UV irradiation. The electronic band structure of the BZT has been investigated using density functional theory (DFT calculations to determine the band gap energy (3.12 eV and to compare it with experimental band gap (3.02 eV at 800°C from optical absorption measurements. An excellent match is obtained for an assumption of Zn cation substitutions at specifically ordered sites in the BZT structure.

  20. First-Principle Study of the Structural, Electronic, and Optical Properties of Cubic InNxP1-x Ternary Alloys under Hydrostatic Pressure

    Science.gov (United States)

    Hattabi, I.; Abdiche, A.; Moussa, R.; Riane, R.; Hadji, K.; Soyalp, F.; Varshney, Dinesh; Syrotyuk, S. V.; Khenata, R.

    2016-09-01

    In this article, we present results of the first-principle study of the structural, electronic, and optical properties of the InN, InP binary compounds and their related ternary alloy InNxP1-x in the zinc-blend (ZB) phase within a nonrelativistic full potential linearised augmented plan wave (FP-LAPW) method using Wien2k code based on the density functional theory (DFT). Different approximations of exchange-correlation energy were used for the calculation of the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. Whereas the lattice constant decreases with increasing nitride composition x. Our results present a good agreement with theoretical and experimental data. The electronic band structures calculated using Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach present a direct band gap semiconductor character for InNxP1-x compounds at different x values. The electronic properties were also calculated under hydrostatic pressure for (P=0.00, 5.00, 10.0, 15.0, 20.0, 25.0 GPa) where it is found that the InP compound change from direct to indirect band gap at the pressure P≥7.80 GPa. Furthermore, the pressure effect on the dielectric function and the refractive index was carried out. Results obtained in our calculations present a good agreement with available theoretical reports and experimental data.

  1. First-principle study of the structural, electronic, and optical properties of cubic InN{sub x}P{sub 1-x} ternary alloys under hydrostatic pressure

    Energy Technology Data Exchange (ETDEWEB)

    Hattabi, I. [Ibn Khaldoun Univ. de Tiaret (Algeria). Lab. Synthese et Catalyse; Abdiche, A.; Riane, R. [Sidi-bel-Abbes Univ. (Algeria). Applied Materials Lab.; Moussa, R. [Sidi-bel-Abbes Univ. (Algeria). Physic Dept.; Hadji, K. [Ibn Khaldoun Univ. de Tiaret (Algeria). Science and Technology Dept.; Soyalp, F. [Yuezuencue Yil Univ., Van (Turkey). Dept. of Physics; Varshney, Dinesh [Devi Ahilya Univ., Indore (India). Materials Science Lab.; Syrotyuk, S.V. [National Univ. ' Lviv Polytechnic' , Lviv (Ukraine). Semiconductor Electronics Dept.; Khenata, R. [Mascara Univ. (Algeria). Lab. de Physique Quantique et de Modelisation Mathematique (LPQ3M)

    2016-07-01

    In this article, we present results of the first-principle study of the structural, electronic, and optical properties of the InN, InP binary compounds and their related ternary alloy InN{sub x}P{sub 1-x} in the zinc-blend (ZB) phase within a nonrelativistic full potential linearised augmented plan wave (FP-LAPW) method using Wien2k code based on the density functional theory (DFT). Different approximations of exchange-correlation energy were used for the calculation of the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. Whereas the lattice constant decreases with increasing nitride composition x. Our results present a good agreement with theoretical and experimental data. The electronic band structures calculated using Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach present a direct band gap semiconductor character for InN{sub x}P{sub 1-x} compounds at different x values. The electronic properties were also calculated under hydrostatic pressure for (P=0.00, 5.00, 10.0, 15.0, 20.0, 25.0 GPa) where it is found that the InP compound change from direct to indirect band gap at the pressure P≥7.80 GPa. Furthermore, the pressure effect on the dielectric function and the refractive index was carried out. Results obtained in our calculations present a good agreement with available theoretical reports and experimental data.

  2. Weighted cubic and biharmonic splines

    Science.gov (United States)

    Kvasov, Boris; Kim, Tae-Wan

    2017-01-01

    In this paper we discuss the design of algorithms for interpolating discrete data by using weighted cubic and biharmonic splines in such a way that the monotonicity and convexity of the data are preserved. We formulate the problem as a differential multipoint boundary value problem and consider its finite-difference approximation. Two algorithms for automatic selection of shape control parameters (weights) are presented. For weighted biharmonic splines the resulting system of linear equations can be efficiently solved by combining Gaussian elimination with successive over-relaxation method or finite-difference schemes in fractional steps. We consider basic computational aspects and illustrate main features of this original approach.

  3. Rheological properties of Cubic colloidal suspensions

    Science.gov (United States)

    Boromand, Arman; Maia, Joao

    2016-11-01

    Colloidal and non-colloidal suspensions are ubiquitous in many industrial application. There are numerous studies on these systems to understand and relate their complex rheological properties to their microstructural evolution under deformation. Although most of the experimental and simulation studies are centered on spherical particles, in most of the industrial applications the geometry of the colloidal particles deviate from the simple hard sphere and more complex geometries exist. Recent advances in microfabrication paved the way to fabricate colloidal particles with complex geometries for applications in different areas such as drug delivery where the fundamental understanding of their dynamics has remained unexplored. In this study, using dissipative particle dynamics, we investigate the rheological properties of cubic (superball) particles which are modeled as the cluster of core-modified DPD particles. Explicit representation of solvent particles in the DPD scheme will conserve the full hydrodynamic interactions between colloidal particles. Rheological properties of these cubic suspensions are investigated in the dilute and semi-dilute regimes. The Einstein and Huggins coefficients for these particles with different superball exponent will be calculate which represent the effect of single particle's geometry and multibody interactions on viscosity, respectively. The response of these suspensions is investigated under simple shear and oscillatory shear where it is shown that under oscillation these particles tend to form crystalline structure giving rise to stronger shear-thinning behavior recently measured experimentally.

  4. Local structural studies of the cubic Cd1–xCaxO system through Cd K-edge extended X-ray absorption spectroscopic studies

    Science.gov (United States)

    Srihari, Velaga; Sridharan, V.; Nomura, Masaharu; Sastry, V. Sankara; Sundar, C. S

    2012-01-01

    Cd K-edge extended X-ray absorption fine-structure spectroscopic studies were carried out on Cd1–xCaxO (0 ≤ x ≤0.9) solid solutions and the first and second nearest neighbour (NN) distances and their mean square relative displacement σ2 were estimated. The first NN distance, d Cd–O(x), was found to be smaller than its expected value, a(x)/2, obtained from the X-ray diffraction measurements. It increases monotonically and non-linearly with a negative curvature, comparable with that of the a(x) value variation. The variation σ2 of the 1NN with x is consistent with a disordered solid solution model. The 2NN distances d Cd–Cd(x) and d Cd–Ca(x) are found to follow the average values obtained by X-ray diffraction with d Cd–Ca(x) > d Cd–Cd(x). From detailed analysis it is argued that the solid solution exhibits a bimodal distribution of the 1NN distances, d Cd–O(x) and d Ca–O(x), and that the system belongs to a persistent type. PMID:22713887

  5. Comparison of Dust Lattice Waves in Three-Dimensional Cubic Configurations

    Institute of Scientific and Technical Information of China (English)

    B. Farokhi; A. Hameditabar

    2012-01-01

    A three-dimensional (3D) dusty plasma crystalline with cubic configurations is considered. We calculate the interaction between particles up to distance √2a, implying the second-neighbor interactions for the simple cubic structure, the third-neighbor interactions for the body-centered cubic structure, and the forth-neighbor interactions the for face-centered cubic structure. Longitudinal and transverse dispersion relations are derived in arbitrary directions. The dispersion relations are studied in special directions, I.e. (1,0,0), (l,l,0)/√2, and (1,1, l)/√3- Study of dispersion relations with more neighbor interactions show that in some cases the results change physically.%A three-dimensional (3D) dusty plasma crystalline with cubic configurations is considered.We calculate the interaction between particles up to distance (√2)a,implying the second-neighbor interactions for the simple cubic structure,the third-neighbor interactions for the body-centered cubic structure,and the forth-neighbor interactions the for face-centered cubic structure.Longitudinal and transverse dispersion relations are derived in arbitrary directions.The dispersion relations are studied in special directions,i.e.(1,0,0),(1,1,0)/(√2),and (1,1,1)/(√3).Study of dispersion relations with more neighbor interactions show that in some cases the results change physically.

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

    Science.gov (United States)

    1990-07-01

    that the BGaN film remained predominantly single crystal, but shows both a normal cubic [110] pattern and a second hexagonal pattern [0110]. By contrast...27 Transmission electron microscopy (iEM) was used (Hitachi H-800) to more closely examine the microstructural evolution of the BN/ BGaN /GaN epitaxial...area diffraction (SAD) also showed the BGaN layer to be a mixture of cubic and wurtzitic phases. This layer was heavily faulted. The latter phenomenon

  7. Autoradiography of geological fluorite samples for determination of uranium and thorium distribution using nuclear track methodology

    Energy Technology Data Exchange (ETDEWEB)

    Pi, T.; Sole, J. [Instituto de Geologia, UNAM, Cd. Universitaria, Coyoacan, 04510 Mexico DF (Mexico); Golzarri, J.I; Rickards, J.; Espinosa, G. [IFUNAM, AP 20-364, 01000 Mexico DF (Mexico)]. e-mail: espinosa@fisica.unam.mx

    2007-07-01

    In this paper we present the uranium and thorium distribution analysis of several samples of the 'La Azul' an epithermal fluorspar deposit in southern Mexico, using nuclear track methodology (NTM), in the alpha-autoradiography mode, by placing the mineral sample in contact with a polycarbonate detector. This constitutes a non-destructive analysis, with sufficient sensitivity to provide valuable information about textural and para genetic characteristics of the geological samples. The selected nuclear track detector was CR-39 (Landauer). The region of interest of the geological samples was polished and put in contact with the detector material surface for 45 days in a vacuum chamber (10-3 torr). After this period of time, the detectors were chemically etched, revealing the auto radiograph of the radioactive material. The results show a clear distribution of bands of uranium and thorium in the fluorite samples. This is valuable information for the genetic or geochronological studies of the ore deposits. (Author)

  8. Cubic surfaces and their invariants: Some memories of Raymond Stora

    Directory of Open Access Journals (Sweden)

    Michel Bauer

    2016-11-01

    I then turn to the study of the family of cubic surfaces. They depend on 20 parameters, and the action of the 15 parameter group SL4(C splits the family in orbits depending on 5 parameters. This takes us into the realm of (geometric invariant theory. I review briefly the classical theorems on the structure of the ring of polynomial invariants and illustrate its many facets by looking at a simple example, before turning to the already involved case of cubic surfaces. The invariant ring was described in the 19th century. I show how to retrieve this description via counting/generating functions and character formulae.

  9. An effective packing density of binary cubic crystals

    Science.gov (United States)

    Eremin, I. E.; Eremina, V. V.; Sychev, M. S.; Moiseenko, V. G.

    2015-04-01

    The methodology of effective macroscopic calculation of numerical values of internuclear distances in binary crystals of a cubic crystal system is based on the use of coefficients of the structural packing density of the crystal lattice. The possibility of combining the reference data on the main physicochemical parameters of the substance is implemented by synthesis of the corresponding mathematical models.

  10. Trapping of cubic ZnO nanocrystallites at ambient conditions

    DEFF Research Database (Denmark)

    Decremps, F.; Pellicer-Porres, J.; Datchi, F.

    2002-01-01

    Dense powder of nanocrystalline ZnO has been recovered at ambient conditions in the metastable cubic structure after a heat treatment at high pressure (15 GPa and 550 K). Combined x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) experiments have been performed to probe both long-ra...

  11. A new hypercube variant: Fractal Cubic Network Graph

    Directory of Open Access Journals (Sweden)

    Ali Karci

    2015-03-01

    Full Text Available Hypercube is a popular and more attractive interconnection networks. The attractive properties of hypercube caused the derivation of more variants of hypercube. In this paper, we have proposed two variants of hypercube which was called as “Fractal Cubic Network Graphs”, and we have investigated the Hamiltonian-like properties of Fractal Cubic Network Graphs FCNGr(n. Firstly, Fractal Cubic Network Graphs FCNGr(n are defined by a fractal structure. Further, we show the construction and characteristics analyses of FCNGr(n where r=1 or r=2. Therefore, FCNGr(n is a Hamiltonian graph which is obtained by using Gray Code for r=2 and FCNG1(n is not a Hamiltonian Graph. Furthermore, we have obtained a recursive algorithm which is used to label the nodes of FCNG2(n. Finally, we get routing algorithms on FCNG2(n by utilizing routing algorithms on the hypercubes.

  12. Tetragonal and cubic zirconia multilayered ceramic constructs created by EPD.

    Science.gov (United States)

    Mochales, Carolina; Frank, Stefan; Zehbe, Rolf; Traykova, Tania; Fleckenstein, Christine; Maerten, Anke; Fleck, Claudia; Mueller, Wolf-Dieter

    2013-02-14

    The interest in electrophoretic deposition (EPD) for nanomaterials and ceramics production has widely increased due to the versatility of this technique to effectively combine different materials in unique shapes and structures. We successfully established an EPD layering process with submicrometer sized powders of Y-TZP with different mol percentages of yttrium oxide (3 and 8%) and produced multilayers of alternating tetragonal and cubic phases with a clearly defined interface. The rationale behind the design of these multilayer constructs was to optimize the properties of the final ceramic by combining the high mechanical toughness of the tetragonal phase of zirconia together with the high ionic conductivity of its cubic phase. In this work, a preliminary study of the mechanical properties of these constructs proved the good mechanical integrity of the multilayered constructs obtained as well as crack deflection in the interface between tetragonal and cubic zirconia layers.

  13. Body-centered-cubic Ni and its magnetic properties.

    Science.gov (United States)

    Tian, C S; Qian, D; Wu, D; He, R H; Wu, Y Z; Tang, W X; Yin, L F; Shi, Y S; Dong, G S; Jin, X F; Jiang, X M; Liu, F Q; Qian, H J; Sun, K; Wang, L M; Rossi, G; Qiu, Z Q; Shi, J

    2005-04-08

    The body-centered-cubic (bcc) phase of Ni, which does not exist in nature, has been achieved as a thin film on GaAs(001) at 170 K via molecular beam epitaxy. The bcc Ni is ferromagnetic with a Curie temperature of 456 K and possesses a magnetic moment of 0.52+/-0.08 micro(B)/atom. The cubic magnetocrystalline anisotropy of bcc Ni is determined to be +4.0x10(5) ergs x cm(-3), as opposed to -5.7x10(4) ergs x cm(-3) for the naturally occurring face-centered-cubic (fcc) Ni. This sharp contrast in the magnetic anisotropy is attributed to the different electronic band structures between bcc Ni and fcc Ni, which are determined using angle-resolved photoemission with synchrotron radiation.

  14. Capturing dynamic cation hopping in cubic pyrochlores

    Science.gov (United States)

    Brooks Hinojosa, Beverly; Asthagiri, Aravind; Nino, Juan C.

    2011-08-01

    In direct contrast to recent reports, density functional theory predicts that the most stable structure of Bi2Ti2O7 pyrochlore is a cubic Fd3¯m space group by accounting for atomic displacements. The displaced Bi occupies the 96g(x,x,z) Wyckoff position with six equivalent sites, which create multiple local minima. Using nudged elastic band method, the transition states of Bi cation hopping between equivalent minima were investigated and an energy barrier between 0.11 and 0.21 eV was determined. Energy barriers associated with the motion of Bi between equivalent sites within the 96g Wyckoff position suggest the presence of dielectric relaxation in Bi2Ti2O7.

  15. Tame Kernels of Pure Cubic Fields

    Institute of Scientific and Technical Information of China (English)

    Xiao Yun CHENG

    2012-01-01

    In this paper,we study the p-rank of the tame kernels of pure cubic fields.In particular,we prove that for a fixed positive integer m,there exist infinitely many pure cubic fields whose 3-rank of the tame kernel equal to m.As an application,we determine the 3-rank of their tame kernels for some special pure cubic fields.

  16. Two-dimensional cubic convolution.

    Science.gov (United States)

    Reichenbach, Stephen E; Geng, Frank

    2003-01-01

    The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2] x [-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance.

  17. Cubic liquid crystalline nanoparticles: optimization and evaluation for ocular delivery of tropicamide.

    Science.gov (United States)

    Verma, Purnima; Ahuja, Munish

    2016-10-01

    The purpose of this study was to investigate the potential of cubic liquid crystalline nanoparticles for ocular delivery of tropicamide. Ultrasound-assisted fragmentation of cubic liquid crystalline bulk phases resulted in cubic liquid crystalline nanoparticles employing Pluronic F127 as dispersant. The effects of process variables such as sonication time, sonication amplitude, sonication depth, and pre-mixing time on particle size and polydispersity index was investigated using central composite design. The morphology of tropicamide-loaded nanoparticles was found to be nearly cubical in shape by transmission electron microscopy observation. Further, small angle X-ray scattering experiment confirmed the presence of D and P phase cubic structures in coexistence. The optimized tropicamide-loaded cubic nanoparticles showed in vitro corneal permeation of tropicamide across isolated porcine cornea comparable to its commercial preparation, Tropicacyl®. Ocular tolerance was evaluated by Hen's egg-chorioallantoic membrane test and histological studies. The results of in vivo mydriatic response study demonstrated a remarkably higher area under mydriatic response curve (AUC0→1440 min) values of cubic nanoparticles over Tropicacyl® indicating better therapeutic value of cubic nanoparticles. Furthermore, tropicamide-loaded cubic nanoparticles exhibited prolonged mydriatic effect on rabbits as compared to commercial conventional aqueous ophthalmic solution.

  18. Cubic surfaces and their invariants: Some memories of Raymond Stora

    Science.gov (United States)

    Bauer, Michel

    2016-11-01

    Cubic surfaces embedded in complex projective 3-space are a classical illustration of the use of old and new methods in algebraic geometry. Recently, they made their appearance in physics, and in particular aroused the interest of Raymond Stora, to the memory of whom these notes are dedicated, and to whom I'm very much indebted. Each smooth cubic surface has a rich geometric structure, which I review briefly, with emphasis on the 27 lines and the combinatorics of their intersections. Only elementary methods are used, relying on first order perturbation/deformation theory. I then turn to the study of the family of cubic surfaces. They depend on 20 parameters, and the action of the 15 parameter group SL4 (C) splits the family in orbits depending on 5 parameters. This takes us into the realm of (geometric) invariant theory. I review briefly the classical theorems on the structure of the ring of polynomial invariants and illustrate its many facets by looking at a simple example, before turning to the already involved case of cubic surfaces. The invariant ring was described in the 19th century. I show how to retrieve this description via counting/generating functions and character formulae.

  19. Cubical local partial orders on cubically subdivided spaces - Existence and construction

    DEFF Research Database (Denmark)

    Fajstrup, Lisbeth

    2006-01-01

    The geometric models of higher dimensional automata (HDA) and Dijkstra's PV-model are cubically subdivided topological spaces with a local partial order. If a cubicalization of a topological space is free of immersed cubic Möbius bands, then there are consistent choices of direction in all cubes...

  20. Cubical local partial orders on cubically subdivided spaces - existence and construction

    DEFF Research Database (Denmark)

    Fajstrup, Lisbeth

    The geometric models of Higher Dimensional Automata and Dijkstra's PV-model are cubically subdivided topological spaces with a local partial order. If a cubicalization of a topological space is free of immersed cubic Möbius bands, then there are consistent choices of direction in all cubes...

  1. Fluid-melt Inclusions in Fluorite of the Huanggangliang Skarn Iron-Tin Deposit and Their Significance to Mineralization

    Institute of Scientific and Technical Information of China (English)

    王莉娟; 王京彬; 王玉往; 毛骞

    2001-01-01

    For the first time, fluid-melt inclusions are found in fluorite of the Huanggangliang skarn iron-tin deposit (HSID). The fluorite was formed in the main stage of mineralization, named the hydro-skarnization stage. The inclusions contain various components such as Fe, Mg and Cr from deep sources. The melts of primary inclusions are mainly Ca- and F-rich and those of secondary inclusions tend to become Si-rich. During this evolution process, the melts and iron daughter minerals decreased and even vanished. These facts reveal that the evolution of the primary mineralizing fluids and the differentiation of the fluids and melts are the main factors leading to the deposition of Fe, Sn and other elements. This discovery confirms the magmatic genesis of the HSID and has filled in the gaps in the research of magmatogenic skarn deposits and furnished new methods for such research. Furthermore, it has enlarged the scope of the research on fluid inclusions.

  2. The x-ray reflection efficiencies of planes (III) in germanium silicon and fluorite analyzing crystals. Experimental data

    Energy Technology Data Exchange (ETDEWEB)

    Bermudez Polonio, J.

    1964-07-01

    Integrated and peak reflection efficiency curves relative to a LiF crystal are presented. K{sub {alpha}} fluorescent radiations between (22) Ti and (41) Nb were used for both germanium and silicon crystals: the interval was extended to CaK{sub {alpha}} radiation in the short wavelength region with the fluorite crystal. Reflection efficiency curves show sharp declines in the region around the K absorption edges of germanium and calcium. For CuK{sub {alpha}} radiation, the experimental reflection efficiencies at the peak for germanium, silicon and fluorite crystals are 52, 38.5 and 17 percent, whereas the integrated reflection efficiencies are 65.5, 38 and 14 percent respectively. The data were obtained from untreated crystals, using a standard Norelco non-focussing X-ray spectrometer. Experimental procedures are presented. Some considerations about the (222) missing reflections are made. (Author) 12 refs.

  3. Lipidic cubic phase injector facilitates membrane protein serial femtosecond crystallography.

    Science.gov (United States)

    Weierstall, Uwe; James, Daniel; Wang, Chong; White, Thomas A; Wang, Dingjie; Liu, Wei; Spence, John C H; Bruce Doak, R; Nelson, Garrett; Fromme, Petra; Fromme, Raimund; Grotjohann, Ingo; Kupitz, Christopher; Zatsepin, Nadia A; Liu, Haiguang; Basu, Shibom; Wacker, Daniel; Han, Gye Won; Katritch, Vsevolod; Boutet, Sébastien; Messerschmidt, Marc; Williams, Garth J; Koglin, Jason E; Marvin Seibert, M; Klinker, Markus; Gati, Cornelius; Shoeman, Robert L; Barty, Anton; Chapman, Henry N; Kirian, Richard A; Beyerlein, Kenneth R; Stevens, Raymond C; Li, Dianfan; Shah, Syed T A; Howe, Nicole; Caffrey, Martin; Cherezov, Vadim

    2014-01-01

    Lipidic cubic phase (LCP) crystallization has proven successful for high-resolution structure determination of challenging membrane proteins. Here we present a technique for extruding gel-like LCP with embedded membrane protein microcrystals, providing a continuously renewed source of material for serial femtosecond crystallography. Data collected from sub-10-μm-sized crystals produced with less than 0.5 mg of purified protein yield structural insights regarding cyclopamine binding to the Smoothened receptor.

  4. CLASSIFICATION OF CUBIC PARAMETERIZED HOMOGENEOUS VECTOR FIELDS

    Institute of Scientific and Technical Information of China (English)

    Karnal H.Yasir; TANG Yun

    2002-01-01

    In this paper the cubic homogeneous parameterized vector fields are studied.The classification of the phase portrait near the critical point is presented. This classification is an extension of the result given by Takens to the cubic homogeneous parameterized vector fields with six parameters.

  5. CLASSIFICATION OF CUBIC PARAMETERIZED HOMOGENEOUS VECTOR FIELDS

    Institute of Scientific and Technical Information of China (English)

    KamalH.Yasir; TNAGYun

    2002-01-01

    In this paper the cubic homogeneous parameterized vector fields are studied.The classification of the phase portrait near the critical point is presented.This classification is an extension of the result given by takens to the cubic homogeneous parameterized vector fields with six parameters.

  6. Structures and ionic conductivities in two fluorite type families: Pb{sub 5}Bi{sub 17}X{sub 5}O{sub 43} and Pb{sub 5}Bi{sub 18}X{sub 4}O{sub 42} (X = P, V and As)

    Energy Technology Data Exchange (ETDEWEB)

    Giraud, S.; Obbade, S.; Wignacourt, J.P. [Ecole Nationale Superieure de Chimie de Lille, Lab. de Cristallochimie et Physicochimie du Solide, CNRS UMR 8012, 59 - Villeneuve d' Ascq (France); Giraud, S. [University of Texas, Texas Materials Institute and Dept. of Chemical Engineering, Austin, TX (United States); Suard, E.; Steinfink, H. [Institut Laue-Langevin - ILL, 38 - Grenoble (France)

    2003-02-01

    The phases Pb{sub 5}Bi{sub 17}P{sub 5}O{sub 43} and Pb{sub 5}Bi{sub 18}P{sub 4}O{sub 42} are among many recent new oxy-phosphates discovered in the ternary system PbO-Bi{sub 2}O{sub 3}-P{sub 2}O{sub 5}. The syntheses of the vanadates and arsenates led to isostructural compounds. Both series display a distorted 3 x 3 x 3 superstructure of the tetragonal {delta}-Bi{sub 2}O{sub 3} polymorph. These types of phases display interesting anion conductivities and measurements were performed from 300 deg. C to 800 deg. C on the phosphates, arsenates and vanadates of the two families. The Pb{sub 5}Bi{sub 18}X{sub 4}O{sub 42} phases have higher conductivity values than those of Pb{sub 5}Bi{sub 17}X{sub 5}O{sub 43}. Of the three homologues the vanadates always have the highest conductivities, i.e., at 800 deg. C: 1.6 x 10{sup -2} Siemens.cm{sup -1} for Pb{sub 5}Bi{sub 18}V{sub 4}O{sub 42} and 1.6 x 10{sup -3} Siemens.cm{sup -1} for Pb{sub 5}Bi{sub 17}V{sub 5}O{sub 43}. An increase of the volume of the unit cell due to the increasing radius of the pentavalent cations from P, As to V, 0.34 Angstrom, 0.47 Angstrom, 0.59 Angstrom respectively, helps the anion migration through the structure. (authors)

  7. Stable isotope variations in the Quaternary epithermal calcite-fluorite deposit at Monte delle Fate near Cerveteri (Latium, central Italy)

    Science.gov (United States)

    Masi, U.; O'Neil, J.R.

    1980-01-01

    Carbon, oxygen and hydrogen isotope variations have been measured in samples from the epithermal fluorite vein deposit at Monte delle Fate, Latium. The ranges in ?? 13C and ??18O of calcite are -1.3 to 3.4 and 9.5 to 17.3, respectively. ??D values of water extracted from fluid inclusions are -49 to -39 for calcite and -41 to -34 for fluorite. Fluid inclusion filling temperatures (225??-240??C) and salinites (3.75) are nearly the same for both fluorite and sparry calcite. An elongated form of calcite, of minor abundance, precipitated at lower temperatures. The data indicate that (1) the CO2 involved in the mineralization was provided by the local marine limestones, (2) the waters were meteoric in origin and underwent an 18O shift of ??? 10 permil by exchange with marine country rocks, and (3) all geochemical features can be explained by the action of two hydrothermal fluids. Hot brines recently discovered in the Cesano geothermal area, 30 km to the east, have temperatures and some chemical characteristics similar to the hydrothermal fluids at Monte delle Fate. ?? 1980 Springer-Verlag.

  8. Nonlinear optical imaging of defects in cubic silicon carbide epilayers.

    Science.gov (United States)

    Hristu, Radu; Stanciu, Stefan G; Tranca, Denis E; Matei, Alecs; Stanciu, George A

    2014-06-11

    Silicon carbide is one of the most promising materials for power electronic devices capable of operating at extreme conditions. The widespread application of silicon carbide power devices is however limited by the presence of structural defects in silicon carbide epilayers. Our experiment demonstrates that optical second harmonic generation imaging represents a viable solution for characterizing structural defects such as stacking faults, dislocations and double positioning boundaries in cubic silicon carbide layers. X-ray diffraction and optical second harmonic rotational anisotropy were used to confirm the growth of the cubic polytype, atomic force microscopy was used to support the identification of silicon carbide defects based on their distinct shape, while second harmonic generation microscopy revealed the detailed structure of the defects. Our results show that this fast and noninvasive investigation method can identify defects which appear during the crystal growth and can be used to certify areas within the silicon carbide epilayer that have optimal quality.

  9. Influence of synthesis conditions on the crystal structure of the powder formed in the ZrO2 - Ce2O3/CeO2 system.

    Science.gov (United States)

    Popov, V. V.; Menushenkov, A. P.; Khubbutdinov, R. M.; Svetogorov, R. D.; Zubavichus, Ya V.; Sharapov, A. S.; Kurilkin, V. V.

    2016-09-01

    Influence of synthesis conditions (type of atmosphere, reduction and oxidation, annealing temperature) on the chemical composition and structure of the compounds formed in the “ZrO2 - Ce2O3 / CeO2” system has been investigated by X-ray absorption fine structure (XAFS) spectroscopy combined with X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It is revealed that isothermal annealing of precursor at temperatures less than 1000 °C in air leads to formation of Ce0.5Zr0.5O2 powders with cubic fluorite-type structure (Fm-3m). Further increase of annealing temperatures above 1000 °C causes decomposition of formed crystal structure into two phases: cubic and tetragonal. Annealing in reduction hydrogen atmosphere causes formation of Ce4 + 2xCe3 + 2-2xZr2O7 + x compounds with intermediate valency of cerium, where value of x depends on the reducing conditions and treatment parameters of precursor. Annealing in vacuum at 1400 °C strongly reduces the content of Ce4+ in a powder samples and leads to formation of pyrochlore structure (space group Fd-3m) with practically Ce3+ valence state.

  10. Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption.

    Science.gov (United States)

    Turner, Brett D; Binning, Philip; Stipp, S L S

    2005-12-15

    Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.

  11. The compressibility of cubic white and orthorhombic, rhombohedral, and simple cubic black phosphorus

    Energy Technology Data Exchange (ETDEWEB)

    Clark, Simon M; Zaug, Joseph

    2010-03-10

    The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The ?alpha phase was found to transform into the alpha' phase at 0.87 +- 0.04 GPa with a volume change of 0.1 +- 0.3 cc/mol. A fit of a second order Birch- Murnaghan equation to the data gave Vo = 16.94 ? 0.08 cc/mol and Ko = 6.7 +- 0.5 GPa for the alpha phase and Vo = 16.4 +- 0.1 cc/mol and Ko = 9.1 +- 0.3 GPa for the alpha' phase. The alpha' phase was found to transform to the A17 phase of black phosphorus at 2.68 +- 0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second order Birch-Murnaghan equation to our data combined with previous measurements gave Vo = 11.43 +- 0.05 cc/mol and Ko = 34.7 +- 0.5 GPa for the A17 phase, Vo = 9.62 +- 0.01 cc/mol and Ko = 65.0 +- 0.6 GPa for the A7 phase and , Vo = 9.23 +- 0.01 cc/mol and Ko = 72.5 +- 0.3 GPa for the simple cubic phase.

  12. Cubic III-nitrides: potential photonic materials

    Science.gov (United States)

    Onabe, K.; Sanorpim, S.; Kato, H.; Kakuda, M.; Nakamura, T.; Nakamura, K.; Kuboya, S.; Katayama, R.

    2011-01-01

    The growth and characterization of some cubic III-nitride films on suitable cubic substrates have been done, namely, c- GaN on GaAs by MOVPE, c-GaN and c-AlGaN on MgO by RF-MBE, and c-InN and c-InGaN (In-rich) on YSZ by RFMBE. This series of study has been much focused on the cubic-phase purity as dependent on the respective growth conditions and resulting electrical and optical properties. For c-GaN and c-InN films, a cubic-phase purity higher than 95% is attained in spite of the metastable nature of the cubic III-nitrides. However, for c-AlGaN and c-InGaN films, the cubic-phase purity is rapidly degraded with significant incorporation of the hexagonal phase through stacking faults on cubic {111} faces which may be exposed on the roughened growing or substrate surface. It has been shown that the electron mobilities in c-GaN and c-AlGaN films are much related to phase purity.

  13. Prediction of giant mechanocaloric effects in fluorite-structured superionic materials

    OpenAIRE

    Cazorla, Claudio; Errandonea, Daniel

    2016-01-01

    Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic s...

  14. Nanometric solid solutions of the fluorite and perovskite type crystal structures: Synthesis and properties

    Directory of Open Access Journals (Sweden)

    Snežana Bošković

    2012-09-01

    Full Text Available In this paper a short review of our results on the synthesis of nanosized CeO2, CaMnO3 and BaCeO3 solid solutions are presented. The nanopowders were prepared by two innovative methods: self propagating room temperature synthesis (SPRT and modified glycine/nitrate procedure (MGNP. Different types of solid solutions with rare earth dopants in concentrations ranging from 0–0.25 mol% were synthesized. The reactions forming solid solutions were studied. In addition, the characteristics of prepared nanopowders, phenomena during sintering and the properties of sintered samples are discussed.

  15. Generalized Vaidya spacetime for cubic gravity

    CERN Document Server

    Ruan, Shan-Ming

    2015-01-01

    We present a kind of generalized Vaidya solutions of a new cubic gravity in five dimensions whose field equations in spherically spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally we present the first law and second law hold in this gravity. Although all the results are analogue to those in Lovelock gravity, we in fact introduce the contribution of new cubic term in five dimensions where cubic Lovelock term is just zero.

  16. Cubical sets as a classifying topos

    DEFF Research Database (Denmark)

    Spitters, Bas

    Coquand’s cubical set model for homotopy type theory provides the basis for a computational interpretation of the univalence axiom and some higher inductive types, as implemented in the cubical proof assistant. We show that the underlying cube category is the opposite of the Lawvere theory of De...... Morgan algebras. The topos of cubical sets itself classifies the theory of ‘free De Morgan algebras’. This provides us with a topos with an internal ‘interval’. Using this interval we construct a model of type theory following van den Berg and Garner. We are currently investigating the precise relation...

  17. nanocomposites with body- centered cubic structure%一步法制备体心立方结构的介孔碳/氧化硅纳米复合材料

    Institute of Scientific and Technical Information of China (English)

    刘玉荣; 涂铭旌; 张进

    2012-01-01

    以酚醛树脂预聚体(Res01)为碳源前驱体,嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯(PEO-PPO-PEO,F127)和聚二甲基硅氧烷-聚氧乙烯(PDMS-PEO)为混合模板剂,采用溶剂挥发诱导自组装(EISA)方法制备了有序介孔碳-氧化硅纳米复合材料,并进一步采用小角X射线散射(SAXS)、透射电子显微镜(TEM)和氮气吸脱附分析对所制备样品的结构和组成进行表征.结果表明,所制备的介孔碳/氧化硅纳米复合材料具有体心立方Im3m结构,其BET比表面积、总孔容和孔径分别为l410m^2/g,1.12cm^3/g和5.4nm.%Mixed amphiphilic block copolymers of poly (ethylene oxide) - poly (propylene oxide) -poly (ethylene oxide) ( PEO - PPO - PEO) and polydimethylsiloxane poly ( ethylene oxide ) ( PDMS - PEO) have been successfully used as cotemplates to prepare ordered mesoporous carbon/silica nanocomposites by using phenolic resol polymer as a carbon precursor via the strategy of evaporation induced selfassembly (EISA). The structure and compositions of the samples have been characterized by smallangle X- ray scattering (SAXS), transmission electron microscopy (TEM) and nitrogen- sorption measurements. Experiments show that body - centered cubic ( space group lm'3m) mesoporous carbon/silica nanocomposite have been obtained. The BET surface areas, total pore sizes and pore volumes of mesoporous car- bon/silica nanocomposite are 1 410 m^2/g, 1. 12 cm^3/g and 5.4 nm,respectively.

  18. High-throughput continuous hydrothermal flow synthesis of Zn-Ce oxides: unprecedented solubility of Zn in the nanoparticle fluorite lattice.

    Science.gov (United States)

    Kellici, Suela; Gong, Kenan; Lin, Tian; Brown, Sonal; Clark, Robin J H; Vickers, Martin; Cockcroft, Jeremy K; Middelkoop, Vesna; Barnes, Paul; Perkins, James M; Tighe, Christopher J; Darr, Jawwad A

    2010-09-28

    High-throughput continuous hydrothermal flow synthesis has been used as a rapid and efficient synthetic route to produce a range of crystalline nanopowders in the Ce-Zn oxide binary system. High-resolution powder X-ray diffraction data were obtained for both as-prepared and heat-treated (850 degrees C for 10 h in air) samples using the new robotic beamline I11, located at Diamond Light Source. The influence of the sample composition on the crystal structure and on the optical and physical properties was studied. All the nanomaterials were characterized using Raman spectroscopy, UV-visible spectrophotometry, Brunauer-Emmett-Teller surface area and elemental analysis (via energy-dispersive X-ray spectroscopy). Initially, for 'as-prepared' Ce(1-x)Zn(x)O(y), a phase-pure cerium oxide (fluorite) structure was obtained for nominal values of x=0.1 and 0.2. Biphasic mixtures were obtained for nominal values of x in the range of 0.3-0.9 (inclusive). High-resolution transmission electron microscopy images revealed that the phase-pure nano-CeO(2) (x=0) consisted of ca 3.7 nm well-defined nanoparticles. The nanomaterials produced herein generally had high surface areas (greater than 150 m(2) g(-1)) and possessed combinations of particle properties (e.g. bandgap, crystallinity, size, etc.) that were unobtainable or difficult to achieve by other more conventional synthetic methods.

  19. A highly ordered cubic mesoporous silica/graphene nanocomposite

    Science.gov (United States)

    Lee, Chang-Wook; Roh, Kwang Chul; Kim, Kwang-Bum

    2013-09-01

    A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites.A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites. Electronic supplementary information (ESI) available: S1: TEM images of disordered mesoporous silica/graphene nanocomposite; S2: TEM images of KIT-6/GO nanocomposite; S3: Thermogravimetric analysis of KIT-6/GO and KG-400-700; S4: SEM and TEM images of KIT-6; S5: Low angle XRD, Raman spectra, N2 adsorption isotherms, pore size distribution and photographic images of the prepared samples; S6: TEM image and N2 adsorption isotherms of mesoporous carbon/graphene nanocomposite; S7: XPS C1s spectra of the prepared samples. See DOI: 10.1039/c3nr03108j

  20. Bicontinuous cubic liquid crystalline nanoparticles for oral delivery of Doxorubicin

    DEFF Research Database (Denmark)

    Swarnakar, Nitin K; Thanki, Kaushik; Jain, Sanyog

    2014-01-01

    PURPOSE: The present study explores the potential of bicontinous cubic liquid crystalline nanoparticles (LCNPs) for improving therapeutic potential of doxorubicin. METHODS: Phytantriol based Dox-LCNPs were prepared using hydrotrope method, optimized for various formulation components, process...... variables and lyophilized. Structural elucidation of the reconstituted formulation was performed using HR-TEM and SAXS analysis. The developed formulation was subjected to exhaustive cell culture experiments for delivery potential (Caco-2 cells) and efficacy (MCF-7 cells). Finally, in vivo pharmacokinetics...

  1. Epitaxial Growth of Cubic Crystalline Semiconductor Alloys on Basal Plane of Trigonal or Hexagonal Crystal

    Science.gov (United States)

    Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor)

    2011-01-01

    Hetero-epitaxial semiconductor materials comprising cubic crystalline semiconductor alloys grown on the basal plane of trigonal and hexagonal substrates, in which misfit dislocations are reduced by approximate lattice matching of the cubic crystal structure to underlying trigonal or hexagonal substrate structure, enabling the development of alloyed semiconductor layers of greater thickness, resulting in a new class of semiconductor materials and corresponding devices, including improved hetero-bipolar and high-electron mobility transistors, and high-mobility thermoelectric devices.

  2. The influence of crystal structure on ion-irradiation tolerance in the Sm{sub (x)}Yb{sub (2-x)}TiO{sub 5} series

    Energy Technology Data Exchange (ETDEWEB)

    Aughterson, R.D., E-mail: roa@ansto.gov.au [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234 (Australia); Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); Lumpkin, G.R.; Reyes, M. de los [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234 (Australia); Gault, B. [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Baldo, P.; Ryan, E. [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Whittle, K.R. [Centre for Materials and Structures, School of Engineering, The University of Liverpool, Liverpool L69 3GH UK (United Kingdom); Smith, K.L. [Government International and External Relations, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234 (Australia); Cairney, J.M. [Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia)

    2016-04-01

    This ion-irradiation study covers the four major crystal structure types in the Ln{sub 2}TiO{sub 5} series (Ln = lanthanide), namely orthorhombic Pnma, hexagonal P6{sub 3}/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. This is the first systematic examination of the complete Ln{sub 2}TiO{sub 5} crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm{sub (x)}Yb{sub (2-x)}TiO{sub 5} (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr{sup 2+} ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation (D{sub c}), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature (T{sub c}), above which the sample cannot be rendered amorphous by ion irradiation. The structure type plus elements of bonding are correlated to ion-irradiation tolerance. The cubic phases, Yb{sub 2}TiO{sub 5} and Sm{sub 0.6}Yb{sub 1.4}TiO{sub 5}, were found to be the most radiation tolerant, with T{sub c} values of 479 and 697 K respectively. The improved radiation tolerance with a change in symmetry to cubic is consistent with previous studies of similar compounds.

  3. MOVING SCREW DISLOCATION IN CUBIC QUASICRYSTAL

    Institute of Scientific and Technical Information of China (English)

    ZHOU Wang-min; SONG Yu-hai

    2005-01-01

    The elasticity theory of the dislocation of cubic quasicrystals is developed.The governing equations of anti-plane elasticity dynamics problem of the quasicrystals were reduced to a solution of wave equations by introducing displacement functions,and the analytical expressions of displacements, stresses and energies induced by a moving screw dislocation in the cubic quasicrystalline and the velocity limit of the dislocation were obtained. These provide important information for studying the plastic deformation of the new solid material.

  4. 2-rational Cubic Spline Involving Tension Parameters

    Indian Academy of Sciences (India)

    M Shrivastava; J Joseph

    2000-08-01

    In the present paper, 1-piecewise rational cubic spline function involving tension parameters is considered which produces a monotonic interpolant to a given monotonic data set. It is observed that under certain conditions the interpolant preserves the convexity property of the data set. The existence and uniqueness of a 2-rational cubic spline interpolant are established. The error analysis of the spline interpolant is also given.

  5. Cubical version of combinatorial differential forms

    DEFF Research Database (Denmark)

    Kock, Anders

    2010-01-01

    The theory of combinatorial differential forms is usually presented in simplicial terms. We present here a cubical version; it depends on the possibility of forming affine combinations of mutual neighbour points in a manifold, in the context of synthetic differential geometry.......The theory of combinatorial differential forms is usually presented in simplicial terms. We present here a cubical version; it depends on the possibility of forming affine combinations of mutual neighbour points in a manifold, in the context of synthetic differential geometry....

  6. Is inner core seismic anisotropy a marker of plastic flow of cubic iron?

    CERN Document Server

    Lincot, A; Cardin, Philippe

    2015-01-01

    This paper investigates whether observations of seismic anisotropy are compatible with a cubic structure of the inner core Fe alloy. We assume that anisotropy is the result of plastic deformation within a large scale flow induced by preferred growth at the inner core equator. Based on elastic moduli from the literature, bcc- or fcc-Fe produce seismic anisotropy well below seismic observations ($\\textless{}0.4\\%$). A Monte-Carlo approach allows us to generalize this result to any form of elastic anisotropy in a cubic system. Within our model, inner core global anisotropy is not compatible with a cubic structure of Fe alloy. Hence, if the inner core material is indeed cubic, large scale coherent anisotropic structures, incompatible with plastic deformation induced by large scale flow, must be present.

  7. Structural analysis of Bi{sub 3}TiNbO{sub 9} prepared by mechanical activation

    Energy Technology Data Exchange (ETDEWEB)

    Lara, Patricio; Serafini, Daniel; Romero, Rodrigo [Depto. de Fisica, Universidad de Santiago de Chile, Santiago (Chile); Avila, Ricardo E [Departamento de Materiales Nucleates, CCHEN, Cas. 188-D, Santiago (Chile); Cabrera, A L [Facultad de Fisica, Pontificia Universidad Catolica de Chile, Santiago (Chile)], E-mail: ravila@cchen.cl

    2008-11-01

    The synthesis by high energy mechanical activation and structural characterization of the phases of Bi{sub 3}TiNbO{sub 9} are described. A fluorite-like metastable phase was identified upon heating the activated powders in the temperature range of 593 to 823 K, followed by formation of the stable Aurivillius phase above 873 K. The crystallization temperature of the fluorite phase increases with milling time. From Rietveld analysis of X-ray diffraction patterns, the fluorite cell parameter is shown to decrease, while rutile TiO{sub 2} increases with milling time.

  8. U-Th/He ages of fluorite mineralizations of the Tangua alkaline intrusion; Idades U-Th/He das mineralizacoes de fluorita da intrusao alcalina de Tangua

    Energy Technology Data Exchange (ETDEWEB)

    Geraldes, M.C.; Vargas, T., E-mail: geraldes@uerj.br, E-mail: vargas@uerj.br [Universidade do Estado do Rio de Janeiro (UERJ), RJ (Brazil). Faculdade de Geologia; Evans, N., E-mail: Noreen.Evans@csiro.au [CSIRO and Curtin University for Technology, Western Australia (Australia); Nummer, A.R., E-mail: nummer@ufrrj.br [Universidade Federal Rural do Rio de Janeiro (DEGEOC/IA/UFRRJ), RJ (Brazil)

    2015-07-01

    The Tangua massif is part of a group of alkaline complexes that occurs in an extensive zone of faults and E-W lineaments and includes the Brazilian Southeastern Rift. This work presents U-He ages of the fluorite mineralization. The Tangua alkaline massif is emplaced in coarse-grained biotite gneiss (Oriental Domain, central portion of the Ribeira belt). Cataclastic gneiss with intense weathering are restricted to the intrusion contacts. The alkaline body is comprised of pulaskites and umptekites, nephelinesyenites, foiaites, and pseudoleucite foiaites and is cut by phonolite dykes, trachytes and alkaline lamprophyres. In the locality of Barbosao, veins of fluorite occur, accompanied by silica and pyrite within trachyte dykes. These veins are parallel to the gneiss foliation (N 50 - 70 E) with an average thickness of 30 cm and the fluorite contains limonite and manganese oxides inclusions. The U-He ages range from <2Ma to 73Ma. The older age is coherent with 80-65 ma range of K-Ar ages reported in the literature. The veins of fluorite crosscut the lithologies associated with shear zones, and are important to economic exploration in the region. The petrographic and U-Th/He sating studies indicate the fluorite formation coeval to alkaline intrusion and meteoric water fluid circulation recently. (author)

  9. Intervalence Charge Transfer Luminescence: Interplay between anomalous and 5d-4f emissions in Yb-doped fluorite-type crystals

    CERN Document Server

    Barandiaran, Zoila

    2014-01-01

    We report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorites associated with Yb2+-Yb3+ mixed valence pairs. We show that the very broad band, anomalous emission of Yb2+-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb2+-Yb3+ mixed valence pairs. It is very efficiently excited by a two-photon upconversion mechanism. The IVCT vertical transition leaves the pair moieties very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are substracted from the normal emission. The ab initio IVCT energy diagrams explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4f emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2; and the prese...

  10. Synthesis of Fluorite (CaF2 Crystal from Gypsum Waste of Phosphoric Acid Factory in Silica Gel

    Directory of Open Access Journals (Sweden)

    Mohammad Misbah Khunur

    2012-06-01

    Full Text Available This paper report the synthesis and characterization of fluorite single crystal prepared from gypsum waste of phosphoric acid production in silica gel. Instead of its high calcium, gypsum was used to recycle the waste which was massively produces in the phosphoric acid production. The gypsum waste, the raw material of CaCl2 supernatant, was dissolved in concentrated HCl and then precipitated as calcium oxalate (CaC2O4 by addition of ammonium oxalate. The CaCl2 was obtained by dissolving the CaC2O4 with HCl 3M. The crystals were grown at room temperature in silica gel and characterized by AAS, FTIR and powder XRD. The optimum crystal growth condition, which is pH of gel, CaCl2 concentration and growth time, were investigated. The result shows that at optimum condition of pH 5.80, CaCl2 concentrations of 1.2 M, and growth time of 144 hours, colorless crystals with the longest size of 3 mm, were obtained (72.57%. Characterization of the synthesized crystal by AAS indicates that the obtained crystal has high purity. Meanwhile, analysis by FTIR spectra shows a Ca–F peak at 775 cm-1, and powder-XRD analysis confirms that the obtained crystal was fluorite (CaF2. © 2012 BCREC UNDIP. All rights reservedReceived: 11st April 2012; Revised: 4th June 2012; Accepted: 13rd June 2012[How to Cite: M.M. Khunur, A. Risdianto, S. Mutrofin, Y.P. Prananto. (2012. Synthesis of Fluorite (CaF2 Crystal from Gypsum Waste of Phosphoric Acid Factory in Silica Gel. Bulletin of Chemical Reaction Engineering & Catalysis, 7 (1: 71-77.  doi:10.9767/bcrec.7.1.3171.71-77 ][How to Link / DOI: http://dx.doi.org/10.9767/bcrec.7.1.3171.71-77 ] | View in 

  11. Packing of nonoverlapping cubic particles: Computational algorithms and microstructural characteristics.

    Science.gov (United States)

    Malmir, Hessam; Sahimi, Muhammad; Tabar, M Reza Rahimi

    2016-12-01

    Packing of cubic particles arises in a variety of problems, ranging from biological materials to colloids and the fabrication of new types of porous materials with controlled morphology. The properties of such packings may also be relevant to problems involving suspensions of cubic zeolites, precipitation of salt crystals during CO_{2} sequestration in rock, and intrusion of fresh water in aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We present a detailed simulation and microstructural characterization of packings of nonoverlapping monodisperse cubic particles, following up on our preliminary results [H. Malmir et al., Sci. Rep. 6, 35024 (2016)2045-232210.1038/srep35024]. A modification of the random sequential addition (RSA) algorithm has been developed to generate such packings, and a variety of microstructural descriptors, including the radial distribution function, the face-normal correlation function, two-point probability and cluster functions, the lineal-path function, the pore-size distribution function, and surface-surface and surface-void correlation functions, have been computed, along with the specific surface and mean chord length of the packings. The results indicate the existence of both spatial and orientational long-range order as the the packing density increases. The maximum packing fraction achievable with the RSA method is about 0.57, which represents the limit for a structure similar to liquid crystals.

  12. Packing of nonoverlapping cubic particles: Computational algorithms and microstructural characteristics

    Science.gov (United States)

    Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi

    2016-12-01

    Packing of cubic particles arises in a variety of problems, ranging from biological materials to colloids and the fabrication of new types of porous materials with controlled morphology. The properties of such packings may also be relevant to problems involving suspensions of cubic zeolites, precipitation of salt crystals during CO2 sequestration in rock, and intrusion of fresh water in aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We present a detailed simulation and microstructural characterization of packings of nonoverlapping monodisperse cubic particles, following up on our preliminary results [H. Malmir et al., Sci. Rep. 6, 35024 (2016), 10.1038/srep35024]. A modification of the random sequential addition (RSA) algorithm has been developed to generate such packings, and a variety of microstructural descriptors, including the radial distribution function, the face-normal correlation function, two-point probability and cluster functions, the lineal-path function, the pore-size distribution function, and surface-surface and surface-void correlation functions, have been computed, along with the specific surface and mean chord length of the packings. The results indicate the existence of both spatial and orientational long-range order as the the packing density increases. The maximum packing fraction achievable with the RSA method is about 0.57, which represents the limit for a structure similar to liquid crystals.

  13. Cubic ideal ferromagnets at low temperature and weak magnetic field

    Science.gov (United States)

    Hofmann, Christoph P.

    2017-04-01

    The low-temperature series for the free energy density, pressure, magnetization and susceptibility of cubic ideal ferromagnets in weak external magnetic fields are discussed within the effective Lagrangian framework up to three loops. The structure of the simple, body-centered, and face-centered cubic lattice is taken into account explicitly. The expansion involves integer and half-integer powers of the temperature. The corresponding coefficients depend on the magnetic field and on low-energy effective constants that can be expressed in terms of microscopic quantities. Our formulas may also serve as efficiency or consistency check for other techniques like Green's function methods, where spurious terms in the low-temperature expansion have appeared. We explore the sign and magnitude of the spin-wave interaction in the pressure, magnetization and susceptibility, and emphasize that our effective field theory approach is fully systematic and rigorous.

  14. Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.

    Science.gov (United States)

    Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda

    2016-03-22

    Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials.

  15. Experimental core electron density of cubic boron nitride

    DEFF Research Database (Denmark)

    Wahlberg, Nanna; Bindzus, Niels; Bjerg, Lasse

    candidate because of its many similarities with diamond: bonding pattern in the extended network structure, hardness, and the quality of the crystallites.3 However, some degree ionic interaction is a part of the bonding in boron nitride, which is not present in diamond. By investigating the core density...... beyond multipolar modeling of the valence density. As was recently shown in a benchmark study of diamond by Bindzus et al.1 The next step is to investigate more complicated chemical bonding motives, to determine the effect of bonding on the core density. Cubic boron nitride2 lends itself as a perfect...... in boron nitride we may obtain a deeper understanding of the effect of bonding on the total density. We report here a thorough investigation of the charge density of cubic boron nitride with a detailed modelling of the inner atom charge density. By combining high resolution powder X-ray diffraction data...

  16. Mechanism of the body-centered cubic--hexagonal close-packed phase transition in iron.

    Science.gov (United States)

    Bassett, W A; Huang, E

    1987-11-06

    The transition from body-centered cubic to hexagonal close-packed phase in iron has been studied in a diamond anvil cell with synchrotron radiation. The hexagonal close-packed phase, when it first appears, has a ratio of lattice parameters that is significantly larger than normal. This is attributed to a displacive mechanism that causes a distortion of the hexagonal close-packed structure in a body-centered cubic matrix. The hexagonal close-packed phase adjacent to a boundary with the body-centered cubic phase is stretched in the c direction and compressed in the a direction when it first forms.

  17. Interpolation by two-dimensional cubic convolution

    Science.gov (United States)

    Shi, Jiazheng; Reichenbach, Stephen E.

    2003-08-01

    This paper presents results of image interpolation with an improved method for two-dimensional cubic convolution. Convolution with a piecewise cubic is one of the most popular methods for image reconstruction, but the traditional approach uses a separable two-dimensional convolution kernel that is based on a one-dimensional derivation. The traditional, separable method is sub-optimal for the usual case of non-separable images. The improved method in this paper implements the most general non-separable, two-dimensional, piecewise-cubic interpolator with constraints for symmetry, continuity, and smoothness. The improved method of two-dimensional cubic convolution has three parameters that can be tuned to yield maximal fidelity for specific scene ensembles characterized by autocorrelation or power-spectrum. This paper illustrates examples for several scene models (a circular disk of parametric size, a square pulse with parametric rotation, and a Markov random field with parametric spatial detail) and actual images -- presenting the optimal parameters and the resulting fidelity for each model. In these examples, improved two-dimensional cubic convolution is superior to several other popular small-kernel interpolation methods.

  18. High-pressure phase of the cubic spinel NiMn2O4

    DEFF Research Database (Denmark)

    Åsbrink, S.; Waskowska, A.; Olsen, J. Staun

    1998-01-01

    It has been observed that the fee spinel NiMn2O4 transforms to a tetragonal structure at about 12 GPa. The tetragonal phase does not revert to the cubic phase upon decompression and its unit-cell constants at ambient pressure are a(0)=8.65(8) and c(0)=7.88(15) Angstrom (distorted fee). Within thr......). The bulk modulus of the cubic phase is 206(4) GPa....

  19. Cubical Cohomology Ring of 3D Photographs

    CERN Document Server

    Gonzalez-Diaz, Rocio; Medrano, Belen; 10.1002/ima.20271

    2011-01-01

    Cohomology and cohomology ring of three-dimensional (3D) objects are topological invariants that characterize holes and their relations. Cohomology ring has been traditionally computed on simplicial complexes. Nevertheless, cubical complexes deal directly with the voxels in 3D images, no additional triangulation is necessary, facilitating efficient algorithms for the computation of topological invariants in the image context. In this paper, we present formulas to directly compute the cohomology ring of 3D cubical complexes without making use of any additional triangulation. Starting from a cubical complex $Q$ that represents a 3D binary-valued digital picture whose foreground has one connected component, we compute first the cohomological information on the boundary of the object, $\\partial Q$ by an incremental technique; then, using a face reduction algorithm, we compute it on the whole object; finally, applying the mentioned formulas, the cohomology ring is computed from such information.

  20. States of the Schottky defect in uranium dioxide and other fluorite type crystals: Molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Kovalenko, M.A., E-mail: akm_max@mail.ru; Kupryazhkin, A. Ya, E-mail: a.ya.kupryazhkin@urfu.ru

    2015-10-05

    Highlights: • We derived the degree of vacancy association in Schottky defects from temperature. • At high temperatures cation vacancy forms complexes with anion vacancies. • Point defects model in the presence of complexes was considered. • The presence of anion vacancies around cation vacancy lowers its migration energy. • The formation of nanovoids at high cation vacancy concentrations was shown. - Abstract: Mass transfer processes in fluorite-type systems are determined by the diffusion of cations via vacancies from Schottky defects. To predict diffusion coefficients of cations and other parameters based on it the Lidiard and Matzke approximation of the point defects model, namely the assumption of isolated vacancies, is widely used. States of the Schottky defect were studied with the high-speed molecular dynamics method in a wide temperature range, with six different interaction potentials. Schottky vacancies were dynamically detected during the simulation. It is shown that contrary to the Lidiard and Matzke model, the Schottky cation vacancy is always associated with anion vacancies. The degree of the Schottky defect association depends on the temperature, at high temperatures near the cation vacancy two or more anion vacancies are located. It is shown that the calculated formation energy of Schottky defects in the form of the trivacancy (5.8–7.4) eV for all potentials are close to the experimental value (6–7) eV, in contrast to the formation energy of Schottky defects in the form of isolated vacancies that exceeds 10 eV. Point defects model of the simulated system in the presence of an artificially created Schottky defect was constructed and compared with calculation results. According to our study the point defects model is applicable only at low temperatures less than half of the melting temperature. It is shown that the presence of anion vacancies near the cation vacancy reduces the migration energy of cations. However, for systems with

  1. Observation of Body-Centered Cubic Gold Nanocluster.

    Science.gov (United States)

    Liu, Chao; Li, Tao; Li, Gao; Nobusada, Katsuyuki; Zeng, Chenjie; Pang, Guangsheng; Rosi, Nathaniel L; Jin, Rongchao

    2015-08-17

    The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face-centered cubic (fcc) structure. Herein we report the first observation of a body-centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au38S2(SR)20], where R=C10H15) as revealed by single-crystal X-ray crystallography. This bcc structure is in striking contrast with the fcc structure of bulk gold and conventional Au nanoparticles, as well as the bi-icosahedral structure of [Au38(SCH2CH2Ph)24]. The bcc nanocluster has a distinct HOMO-LUMO gap of ca. 1.5 eV, much larger than the gap (0.9 eV) of the bi-icosahedral [Au38(SCH2CH2Ph)24]. The unique structure of the bcc gold nanocluster may be promising in catalytic applications.

  2. Purely cubic action for string field theory

    Science.gov (United States)

    Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.

    1986-01-01

    It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.

  3. Purely cubic action for string field theory

    Science.gov (United States)

    Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.

    1986-01-01

    It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.

  4. Polyol synthesis and characterizations of cubic ZrO{sub 2}:Eu{sup 3+} nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Meetei, S. Dhiren [Department of Physics, Manipur University, Canchipur-795 003, Imphal (India); Singh, Sh. Dorendrajit, E-mail: dorendrajit@yahoo.co.in [Department of Physics, Manipur University, Canchipur-795 003, Imphal (India); Sudarsan, V. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)

    2012-02-15

    Highlights: Black-Right-Pointing-Pointer By polyol route nanocrystalline cubic ZrO{sub 2}:Eu{sup 3+} can be synthesized. Black-Right-Pointing-Pointer Cubic phase is the most desirable phase of zirconia. Black-Right-Pointing-Pointer Distinguishing cubic from tetragonal phase is difficult. Black-Right-Pointing-Pointer Characterizations of the samples are done by XRD, TEM, FTIR and PL. Black-Right-Pointing-Pointer Eu{sup 3+} emission peaks vary as charge transfer state in ZrO{sub 2}:Eu{sup 3+}. - Abstract: Nanocrystalline ZrO{sub 2} and ZrO{sub 2}:Eu{sup 3+} were synthesized by polyol route. The x-ray diffraction (XRD) pattern of ZrO{sub 2} shows presence of both monoclinic and tetragonal phase of zirconia, while that of ZrO{sub 2}:Eu{sup 3+} show cubic structure. Cubic phase is the most desired phase of zirconia. However, it is difficult to distinguish between the tetragonal and cubic phases solely from XRD study. Therefore, the characterizations of cubic phase in the doped samples are substantiated by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and photoluminescence (PL) studies. Interplaner spacing, d{sub hkl} are calculated from the selected area electron diffraction (SAED) rings and they are found to be consistent with that of cubic zirconia. FT-IR spectra of doped and undoped samples are found to be different. This is attributed to the presence of both monoclinic and tetragonal phase in the undoped sample and only cubic phase in the doped samples. PL excitation and emission spectra of the samples are studied. The asymmetry ratio is found to be less than that of the reported tetragonal phase indicating that the present analyzing samples have higher symmetry than tetragonal phase. Variations of Eu{sup 3+} emission peaks are observed as that of charge transfer state (CTS).

  5. Optical and Electronic Analysis of the Two Fluorite-Related Phases in the Ga-In-Sn-O System

    Science.gov (United States)

    Dolgonos, Alex

    Optical transparency and electrical conductivity, traditionally mutually-exclusive materials properties, are both critical for the performance of electrode materials in applications such as flat-panel displays and organic photovoltaics (OPVs). Owing to their wide band gaps which are amenable to degenerate doping, transparent conducting oxides (TCOs) are widely utilized for organic optoelectronic applications. The two fluorite-related phases in the Ga-In-Sn-O (GITO) pseudo-ternary system---Ga,Sn co-substituted bixbyite 2O3 and the so-called "T-phase" Ga3--xIn5+xSn2O 16---have the potential to overcome the issues associated with Sn-doped 2O3 (ITO) by reducing the indium content, utilizing compositions that are more stable in acidic conditions, and offering work function levels that are in better alignment with adjacent layers in organic optoelectronic devices. In this work, the composition and processing effects on the optical and electronic properties of the bixbyite phase and the T-phase in the GITO system were determined. Electronic properties were analyzed by conductivity and Seebeck coefficient measurements, and the combination of these two properties revealed carrier characteristics for these two phases. The optical band gaps of the phases were determined from absorption data by methods developed in this work, which account for the band-altering effects of doping in TCOs. The optical characterization methods were experimentally confirmed through a combination of diffuse-reflectance and photoluminescence measurements of un-doped and Sn-doped In2O3. The bixbyite phase's conductivity, Seebeck coefficient, and optical band gap are dominated by the concentration of Sn-on-In substitution defects, as expected. Remarkably, Ga substition was found to have a negligible effect on the electronic properties. A conductivity of 3000 S/cm was achieved in bulk specimens containing a relatively small Sn content of 1 atomic percent and 4.5 atomic percent Ga. Ga behaves as an

  6. Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany

    Science.gov (United States)

    Majzlan, Juraj; Brey-Funke, Maria; Malz, Alexander; Donndorf, Stefan; Milovský, Rastislav

    2016-02-01

    Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24-27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O) point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo-Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies) can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines) could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was deposited as massive barite

  7. Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany

    Directory of Open Access Journals (Sweden)

    Majzlan Juraj

    2016-02-01

    Full Text Available Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24–27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo–Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was

  8. Unified treatment of coupled optical and acoustic phonons in piezoelectric cubic materials

    DEFF Research Database (Denmark)

    Willatzen, Morten; Wang, Zhong Lin

    2015-01-01

    A unified treatment of coupled optical and acoustic phonons in piezoelectric cubic materials is presented whereby the lattice displacement vector and the internal ionic displacement vector are found simultaneously. It is shown that phonon couplings exist in pairs only; either between the electric...... potential and the lattice displacement coordinate perpendicular to the phonon wave vector or between the two other lattice displacement components. The former leads to coupled acousto-optical phonons by virtue of the piezoelectric effect. We then establish three new conjectures that entirely stem from...... piezoelectricity in a cubic structured material slab. First, it is shown that isolated optical phonon modes generally cannot exist in piezoelectric cubic slabs. Second, we prove that confined acousto-optical phonon modes only exist for a discrete set of in-plane wave numbers in piezoelectric cubic slabs. Third...

  9. DEFICIENT CUBIC SPLINES WITH AVERAGE SLOPE MATCHING

    Institute of Scientific and Technical Information of China (English)

    V. B. Das; A. Kumar

    2005-01-01

    We obtain a deficient cubic spline function which matches the functions with certain area matching over a greater mesh intervals, and also provides a greater flexibility in replacing area matching as interpolation. We also study their convergence properties to the interpolating functions.

  10. Counting rational points on cubic curves

    Institute of Scientific and Technical Information of China (English)

    HEATH-BROWN; Roger; TESTA; Damiano

    2010-01-01

    We prove upper bounds for the number of rational points on non-singular cubic curves defined over the rationals.The bounds are uniform in the curve and involve the rank of the corresponding Jacobian.The method used in the proof is a combination of the "determinant method" with an m-descent on the curve.

  11. CONSTRAINED RATIONAL CUBIC SPLINE AND ITS APPLICATION

    Institute of Scientific and Technical Information of China (English)

    Qi Duan; Huan-ling Zhang; Xiang Lai; Nan Xie; Fu-hua (Frank) Cheng

    2001-01-01

    In this paper, a kind of rational cubic interpolation functionwith linear denominator is constructed. The constrained interpolation with constraint on shape of the interpolating curves and on the second-order derivative of the interpolating function is studied by using this interpolation, and as the consequent result, the convex interpolation conditions have been derived.

  12. Anisotropy of a cubic ferromagnet at criticality

    Science.gov (United States)

    Kudlis, A.; Sokolov, A. I.

    2016-10-01

    Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at Tc the universal value δ4*=2/v* 3 (u*+v*) where u* and v* are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ɛ expansion approach. The six-loop pseudo-ɛ expansions for u*, v*, and δ4* are derived for the arbitrary spin dimensionality n . For cubic crystals (n =3 ) higher-order coefficients of the pseudo-ɛ expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ɛ series for u*, v*, and δ4* leads to the estimate δ4*=0.079 ±0.006 , indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.

  13. Binomial Squares in Pure Cubic Number Fields

    CERN Document Server

    Lemmermeyer, Franz

    2011-01-01

    Let K = Q(\\omega) with \\omega^3 = m be a pure cubic number field. We show that the elements\\alpha \\in K^\\times whose squares have the form a - \\omega form a group isomorphic to the group of rational points on the elliptic curve E_m: y^2= x^3 - m.

  14. The cactus rank of cubic forms

    CERN Document Server

    Bernardi, Alessandra

    2011-01-01

    We prove that the smallest degree of an apolar 0-dimensional scheme to a general cubic form in $n+1$ variables is at most $2n+2$, when $n\\geq 8$, and therefore smaller than the rank of the form. When n=8 we show that the bound is sharp, i.e. the smallest degree of an apolar subscheme is 18.

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

    Directory of Open Access Journals (Sweden)

    Moulay N.

    2015-06-01

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

  16. Reversible hydrogen storage property and structural analysis for face-centered cubic hydride Mg0.82Zr0.18H2 prepared by gigapascal hydrogen pressure method.

    Science.gov (United States)

    Takasaki, Tomoaki; Kyoi, Daisuke; Kitamura, Naoyuki; Tanase, Shigeo; Sakai, Tetsuo

    2007-12-27

    The face-centered cubic (fcc) type magnesium-zirconium hydride (Mg0.82Zr0.18Hx) was synthesized by means of the ultrahigh pressure (UHP) technique, which could generate 8 GPa of hydrogen pressure. The differential scanning calorimeter (DSC) measurements indicated that the fcc phase exhibited reversible hydrogen releasing and restoring properties under 0.5 MPa of hydrogen pressure. On the pressure-composition isotherms, the released and restored hydrogen capacities were estimated to be 3 approximately 3.5 wt %. The Rietveld analysis for synchrotron X-ray diffraction (XRD) data showed that the fcc phase had around 70 wt % mass fraction and was preserved without decomposition during hydrogen releasing and restoring cycles.

  17. Vacancy-induced mechanical stabilization of cubic tungsten nitride

    Science.gov (United States)

    Balasubramanian, Karthik; Khare, Sanjay; Gall, Daniel

    2016-11-01

    First-principles methods are employed to determine the structural, mechanical, and thermodynamic reasons for the experimentally reported cubic WN phase. The defect-free rocksalt phase is both mechanically and thermodynamically unstable, with a negative single crystal shear modulus C44=-86 GPa and a positive enthalpy of formation per formula unit Hf=0.623 eV with respect to molecular nitrogen and metallic W. In contrast, WN in the NbO phase is stable, with C44=175 GPa and Hf=-0.839 eV . A charge distribution analysis reveals that the application of shear strain along [100] in rocksalt WN results in an increased overlap of the t2 g orbitals which causes electron migration from the expanded to the shortened W-W bond axes, yielding a negative shear modulus due to an energy reduction associated with new bonding states 8.1-8.7 eV below the Fermi level. A corresponding shear strain in WN in the NbO phase results in an energy increase and a positive shear modulus. The mechanical stability transition from the NaCl to the NbO phase is explored using supercell calculations of the NaCl structure containing Cv=0 %-25 % cation and anion vacancies, while keeping the N-to-W ratio constant at unity. The structure is mechanically unstable for Cvconcentration, the isotropic elastic modulus E of cubic WN is zero, but increases steeply to E =445 GPa for Cv=10 % , and then less steeply to E =561 GPa for Cv=25 % . Correspondingly, the hardness estimated using Tian's model increases from 0 to 15 to 26 GPa as Cv increases from 5% to 10% to 25%, indicating that a relatively small vacancy concentration stabilizes the cubic WN phase and that the large variations in reported mechanical properties of WN can be attributed to relatively small changes in Cv.

  18. The calculation of the energy curve of body-centered cubic structure of H+9 cluster with the simple oxygen wave functions%用类O原子波函数对H+9团簇的体心立方结构与能量的研究

    Institute of Scientific and Technical Information of China (English)

    朱俊; 曹乐千

    2001-01-01

    The simple oxygen wave functions are chosen as the electronic wave function of the H+9 cluster with one center spherical model approximation. The energy curve of the body-centered cubic structure of the H+9 cluster is calculated by means of variational method. The result of the calculation shows that the curve has a minimal energy -4.376 h0 at R=1.97a0 (a0=0.529 177×10-10 m, h0=27.2 eV). This means that the body-centered cubic structure of the H+9 cluster is stable and the cluster of H+9 may exist.%在单中心球模型近似下,选用类O原子解析函数,用变分法计算了H+9团簇体心立方结构与能量。结果表明当中心氢原子核到顶角氢原子核之间的距离R=1.97a0时,体系能量有一极小值E=-4.376 h0(a0=0.529 177×10-10m, h0=27.2 eV)。这表明H+9团簇的体心立方结构是稳定的结构,H+9团簇是存在的。

  19. Exotic Universal Solutions in Cubic Superstring Field Theory

    CERN Document Server

    Erler, Theodore

    2010-01-01

    We present a class of analytic solutions of cubic superstring field theory in the universal sector on a non-BPS D-brane. Computation of the action and gauge invariant overlap reveal that the solutions carry half the tension of a non-BPS D-brane. However, the solutions do not satisfy the reality condition. In fact, they display an intriguing topological structure: We find evidence that conjugation of the solutions is equivalent to a gauge transformation that cannot be continuously deformed to the identity.

  20. Structural characterization of nanosized CeO(2)-SiO(2), CeO(2)-TiO(2), and CeO(2)-ZrO(2) catalysts by XRD, Raman, and HREM techniques.

    Science.gov (United States)

    Reddy, Benjaram M; Khan, Ataullah; Lakshmanan, Pandian; Aouine, Mimoun; Loridant, Stéphane; Volta, Jean-Claude

    2005-03-03

    Structural characteristics of nanosized ceria-silica, ceria-titania, and ceria-zirconia mixed oxide catalysts have been investigated using X-ray diffraction (XRD), Raman spectroscopy, BET surface area, thermogravimetry, and high-resolution transmission electron microscopy (HREM). The effect of support oxides on the crystal modification of ceria cubic lattice was mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahighly dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO(2)-SiO(2) sample primarily consists of nanocrystalline CeO(2) on the amorphous SiO(2) surface. Both crystalline CeO(2) and TiO(2) anatase phases were noted in the case of CeO(2)-TiO(2) sample. Formation of cubic Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) (at 1073 K) were observed in the case of the CeO(2)-ZrO(2) sample. Raman measurements disclose the fluorite structure of ceria and the presence of oxygen vacancies/Ce(3+). The HREM results reveal well-dispersed CeO(2) nanocrystals over the amorphous SiO(2) matrix in the cases of CeO(2)-SiO(2), isolated CeO(2), and TiO(2) (anatase) nanocrystals, some overlapping regions in the case of CeO(2)-TiO(2), and nanosized CeO(2) and Ce-Zr oxides in the case of CeO(2)-ZrO(2) sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO(2) is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of the mixed oxide systems is more than that of pure CeO(2) and is system dependent.

  1. Deconvoluting the Effect of the Hydrophobic and Hydrophilic Domains of an Amphiphilic Integral Membrane Protein in Lipid Bicontinuous Cubic Mesophases.

    Science.gov (United States)

    van 't Hag, Leonie; Shen, Hsin-Hui; Lu, Jingxiong; Hawley, Adrian M; Gras, Sally L; Drummond, Calum J; Conn, Charlotte E

    2015-11-10

    Lipidic bicontinuous cubic mesophases with encapsulated amphiphilic proteins are widely used in a range of biological and biomedical applications, including in meso crystallization, as drug delivery vehicles for therapeutic proteins, and as biosensors and biofuel cells. However, the effect of amphiphilic protein encapsulation on the cubic phase nanostructure is not well-understood. In this study, we illustrate the effect of incorporating the bacterial amphiphilic membrane protein Ag43, and its individual hydrophobic β(43) and hydrophilic α(43) domains, in bicontinuous cubic mesophases. For the monoolein, monoalmitolein, and phytantriol cubic phases with and without 8% w/w cholesterol, the effect of the full length amphiphilic protein Ag43 on the cubic phase nanostructure was more significant than the sum of the individual hydrophobic β(43) and hydrophilic α(43) domains. Several factors were found to potentially influence the impact of the hydrophobic β(43) domain on the cubic phase internal nanostructure. These include the size of the hydrophobic β(43) domain relative to the thickness of the lipid bilayer, as well as its charge and diameter. The size of the hydrophilic α(43) domain relative to the water channel radius of the cubic mesophase was also found to be important. The secondary structure of the Ag43 proteins was affected by the hydrophobic thickness and physicochemical properties of the lipid bilayer and the water channel diameter of the cubic phase. Such structural changes may be small but could potentially affect membrane protein function.

  2. Cubic Phases, Cubosomes and Ethosomes for Cutaneous Application.

    Science.gov (United States)

    Esposito, Elisabetta; Drechsler, Markus; Nastruzzi, Claudio; Cortesi, Rita

    2016-01-01

    Cutaneous administration represents a good strategy to treat skin diseases, avoiding side effects related to systemic administration. Apart from conventional therapy, based on the use of semi-solid formulation such as gel, ointments and creams, recently the use of specialized delivery systems based on lipid has been taken hold. This review provides an overview about the use of cubic phases, cubosomes and ethosomes, as lipid systems recently proposed to treat skin pathologies. In addition in the final part of the review cubic phases, cubosomes and ethosomes are compared to solid lipid nanoparticles and lecithin organogel with respect to their potential as delivery systems for cutaneous application. It has been reported that lipid nanosystems are able to dissolve and deliver active molecules in a controlled fashion, thereby improving their bioavailability and reducing side-effects. Particularly lipid matrixes are characterized by skin affinity and biocompatibility allowing their application on skin. Indeed, after cutaneous administration, the lipid matrix of cubic phases and cubosomes coalesces with the lipids of the stratum comeum and leads to the formation of a lipid depot from which the drug associated to the nanosystem can be released in the deeper skin strata in a controlled manner. Ethosomes are characterized by a malleable structure that promotes their interaction with skin, improving their potential as skin delivery systems with respect to liposomes. Also in the case of solid lipid nanoparticles it has been suggested a deep interaction between lipid matrix and skin strata that endorses sustained and prolonged drug release. Concerning lecithin organogel, the peculiar structure of this system, where lecithin exerts a penetration enhancer role, allows a deep interaction with skin strata, promoting the transdermal absorption of the encapsulated drugs.

  3. Origin of birefringence in common silicate garnet: intergrowth of different cubic phases

    Science.gov (United States)

    Antao, S.; Klincker, A.; Round, S.

    2013-05-01

    Birefringence is unexpected in ideal high symmetry cubic minerals, such as common silicate garnets. Birefringence in cubic garnet was reported over a century ago, but the origin still remains questionable. Some grossular, spessartine, andradite, and uvarovite samples may show birefringence under cross-polarized light, which may indicate that they are not optically cubic. Several reasons were given as the cause of the birefringence, but the main one appears to be cation order that may cause symmetry reduction. The crystal structure of several birefringent garnet samples (grossular, spessartine, andradite, and uvarovite) were refined by the Rietveld method, space group Ia-3d, and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Electron-microprobe results indicate the samples are homogeneous or non-homogenous with two or three distinct compositions. Each birefringent sample contains an assemblage of cubic phases that have slightly different unit-cell parameters. The intergrowth of different phases causes strain-induced birefringence that arises from mismatch of different cubic unit-cell parameters. These results have many implications, including garnet phase transitions from cubic to lower symmetry in the mantle, which has important geophysical consequences.

  4. Accelerator-based analytical technique in the evaluation of some Nigeria's natural minerals: Fluorite, tourmaline and topaz

    Energy Technology Data Exchange (ETDEWEB)

    Olabanji, S.O. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy)]. E-mail: skayode2002@yahoo.co.uk; Ige, O.A. [Natural History Museum, Obafemi Awolowo University, Ile-Ife (Nigeria); Mazzoli, C. [Dipartimento di Mineralogia e Petrologia, Universita di Padova, 35100 Padova (Italy); Ceccato, D. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy); Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35100 Padova (Italy); Akintunde, J.A. [CERD, Obafemi Awolowo University, Ile-Ife (Nigeria); De Poli, M. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy); Moschini, G. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy); Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35100 Padova (Italy)

    2005-10-15

    For the first time, the complementary accelerator-based analytical technique of PIXE and electron microprobe analysis (EMPA) were employed for the characterization of some Nigeria's natural minerals namely fluorite, tourmaline and topaz. These minerals occur in different areas in Nigeria. The minerals are mainly used as gemstones and for other scientific and technological applications and therefore are very important. There is need to characterize them to know the quality of these gemstones and update the geochemical data on them geared towards useful applications. PIXE analysis was carried out using the 1.8 MeV collimated proton beam from the 2.5 MV AN 2000 Van de Graaff accelerator at INFN, LNL, Legnaro, Padova, Italy. The novel results which show many elements at different concentrations in these minerals are presented and discussed.

  5. Cubic Polynomials with Rational Roots and Critical Points

    Science.gov (United States)

    Gupta, Shiv K.; Szymanski, Waclaw

    2010-01-01

    If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.

  6. Shape preserving rational bi-cubic function

    Directory of Open Access Journals (Sweden)

    Malik Zawwar Hussain

    2012-11-01

    Full Text Available The study is dedicated to the development of shape preserving interpolation scheme for monotone and convex data. A rational bi-cubic function with parameters is used for interpolation. To preserve the shape of monotone and convex data, the simple data dependent constraints are developed on these parameters in each rectangular patch. The developed scheme of this paper is confined, cheap to run and produce smooth surfaces.

  7. Cubic Lienard Equations with Quadratic Damping (Ⅱ)

    Institute of Scientific and Technical Information of China (English)

    Yu-quan Wang; Zhu-jun Jing

    2002-01-01

    Applying Hopf bifurcation theory and qualitative theory, we show that the general cubic Lienard equations with quadratic damping have at most three limit cycles. This implies that the guess in which the system has at most two limit cycles is false. We give the sufficient conditions for the system has at most three limit cycles or two limit cycles. We present two examples with three limit cycles or two limit cycles by using numerical simulation.

  8. Method of synthesizing cubic system boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Yuzu, S.; Sumiya, H.; Degawa, J.

    1987-10-13

    A method is described for synthetically growing cubic system boron nitride crystals by using boron nitride sources, solvents for dissolving the boron nitride sources, and seed crystals under conditions of ultra-high pressure and high temperature for maintaining the cubic system boron nitride stable. The method comprises the following steps: preparing a synthesizing vessel having at least two chambers, arrayed in order in the synthesizing vessel so as to be heated according to a temperature gradient; placing the solvents having different eutectic temperatures in each chamber with respect to the boron nitride sources according to the temperature gradient; placing the boron nitride source in contact with a portion of each of the solvents heated at a relatively higher temperature and placing at least a seed crystal in a portion of each of the solvents heated at a relatively lower temperature; and growing at least one cubic system boron nitride crystal in each of the solvents in the chambers by heating the synthesizing vessel for establishing the temperature gradient while maintaining conditions of ultra-high pressure and high temperature.

  9. Lipidic cubic phase serial millisecond crystallography using synchrotron radiation

    Directory of Open Access Journals (Sweden)

    Przemyslaw Nogly

    2015-03-01

    Full Text Available Lipidic cubic phases (LCPs have emerged as successful matrixes for the crystallization of membrane proteins. Moreover, the viscous LCP also provides a highly effective delivery medium for serial femtosecond crystallography (SFX at X-ray free-electron lasers (XFELs. Here, the adaptation of this technology to perform serial millisecond crystallography (SMX at more widely available synchrotron microfocus beamlines is described. Compared with conventional microcrystallography, LCP-SMX eliminates the need for difficult handling of individual crystals and allows for data collection at room temperature. The technology is demonstrated by solving a structure of the light-driven proton-pump bacteriorhodopsin (bR at a resolution of 2.4 Å. The room-temperature structure of bR is very similar to previous cryogenic structures but shows small yet distinct differences in the retinal ligand and proton-transfer pathway.

  10. Novel Cubic Magnetite Nanoparticle Synthesis Using Room Temperature Ionic Liquid

    Directory of Open Access Journals (Sweden)

    M. Sundrarajan

    2012-01-01

    Full Text Available Room Temperature Ionic liquids are relatively more useful in the synthesis of inorganic nanostructured materials because of their unique properties. To synthesize the iron oxide nanoparticle in simple precipitation method, a novel ionic liquid was used as the greener medium and stabilizing agent namely “1-n-butyl-3-methylimidazolium trifluoromethane sulfonate [BMIM][TfO]”. The crystallinity, chemical structure, morphology and magnetic properties of the synthesized magnetite nanoparticles have been characterized by using X-ray diffraction (XRD, Fourier Transform Infrared (FT-IR, Scanning electron microscopy (SEM, Atomic force microscopy(AFM, Transmission electron microscopy (TEM and Vibrating sample magnetometer (VSM studies. The XRD study is divulge that the synthesized magnetite nanoparticles have inverse spinel face centered cubic structure. The FT-IR vibration peaks show the formation of Fe3O4 nanoparticles, where the vibration peak for Fe-O is deliberately presence at 584 cm-1. The average particle size of the synthesized nanoparticles is found to be 35 nm. Homogeneously dispersed cubic shape with superstructure is found through SEM, AFM and TEM examination studies. The synthesized iron oxide nanoparticles have a high saturation magnetization value of 25 emu/g, which is very much useful for biomedical applications.

  11. A novel cubic phase of medium chain lipid origin for the delivery of poorly water soluble drugs.

    Science.gov (United States)

    Kossena, Greg A; Charman, William N; Boyd, Ben J; Porter, Christopher J H

    2004-09-30

    The existence of a novel cubic liquid crystalline phase is described within the pseudo-ternary system comprising lauric acid, monolaurin, and simulated endogenous intestinal fluid (SEIF). This phase behaviour has been characterized using cross-polarizing light microscopy (CPLM), and the structure of the cubic phase identified by small angle X-ray scattering (SAXS). The presence of the cubic phase was found to be temperature sensitive within the 20-37 degrees C range making it putative material for in situ gelation purposes. The cubic phase was shown to have a high capacity to solubilise a model poorly water-soluble drug, cinnarizine, and initial in vitro release data highlight the potential of this phase to provide sustained release. Absorption of cinnarizine from the cubic phase was studied in an unconscious rat model via duodenal administration and blood sampling via the carotid artery. The rate of absorption was significantly reduced when compared to a simple suspension formulation, a likely combination of retarded erosion of the cubic phase together with hindered drug release from the cubic matrix. The results of this study suggest that this cubic phase may potentially be of benefit in the delivery of poorly water-soluble compounds due to its high loading capacity and potential for sustained release. The ability to manipulate this system using temperature may warrant further interest in delivery applications via other routes of administration.

  12. Préparation et caractérisation d'oxynitrures Ln2W(O, N) 6- x à structure fluorine déficitaire

    Science.gov (United States)

    Marchand, R.; Antoine, P.; Laurent, Y.

    1993-11-01

    L'action de l'ammoniac sur les tungstates de lanthanides Ln2 WO 6 à 800°C permet de préparer une nouvelle famille d'oxynitrures à structure fluorine déficitaire, de formule Ln2W(O, N) 6- x ( Ln = Nd → Yb, Y). Leur composition générale de type A4X6.6 est intermédiaire entre la stoechiométrie de la fluorine CaF 2( A4X8) et celle de la bixbyite Mn 2O 3( A4X6) qui en dérive. La maille cristalline est cubique avec un paramètre, fonction de la taille du lanthanide, compris entre 5,16 et 5,39 Å. L'étude cristallochimique démontre que les atomes de lanthanide et de tungstène occupent une même position cristallographique. New oxynitrides corresponding to the general formulation Ln2 W(O,N) 6- x ( Ln = Nd → Yb, Y) have been prepared by reaction at 800°C between ammonia and Ln2 WO 6 tungstates, and characterized as defect fluorite type compounds. Their general composition A4X6.6 is intermediate between the Ca F 2( A4X8) fluorite and Mn 2O 3( A4X6) bixbyite stoichiometries. The parameter of the cubic unit cell, comprised between 5.16 and 5.39 Å, depends on the size of the lanthanide. Ln and W atoms occupy a same crystallographic position.

  13. Optical properties of GaAs 2D hexagonal and cubic photonic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Arab, F., E-mail: farab@CDTA.DZ; Assali, A.; Grain, R.; Kanouni, F. [Centre for Development of Advanced Technologies (CDTA) Research Unit in Optics and Photonics (UROP), University of Setif 1, El Bez, 19000 Setif (Algeria)

    2015-03-30

    In this paper we present our theoretical study of 2D hexagonal and cubic rods GaAs in air, with plan wave expansion (PWE) and finite difference time domain (FDTD) by using BandSOLVE and FullWAVE of Rsoft photonic CAD package. In order to investigate the effect of symmetry and radius, we performed calculations of the band structures for both TM and TE polarization, contour and electromagnetic propagation and transmission spectra. Our calculations show that the hexagonal structure gives a largest band gaps compare to cubic one for a same filling factor.

  14. Cubic Copper Hexacyanoferrates Nanoparticles: Facile Template-Free Deposition and Electrocatalytic Sensing Towards Hydrazine

    Directory of Open Access Journals (Sweden)

    Xingxing Wang

    2011-01-01

    Full Text Available Cubic copper hexacyanoferrate (CuHCF nanoparticles prepared via electrolytic deposition are presented with their morphology and crystalline structure characterized with SEM and XRD. The advantage of this methodology is that it allows the fabrication of uniform cubic nanoparticles with permeable structures onto the desired underlying electrode substrate. It was observed that the CuHCF film acts as a permeable membrane for cations such as K+, Na+, Li+, and NH4+ with a selection order of K+> Li+>NH4+> Na+. Furthermore, the analytical utility of these cubic-like CuHCF morphologies supported on a glassy carbon electrode was evaluated towards the electrochemical oxidation of hydrazine which was found to exhibit a linear response over the range 66 M to 17 mM with a detection limit corresponding to 16.5 M.

  15. Pressure-induced phase transformations in cubic Gd[subscript 2]O[subscript 3

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Ligang; Liu, Jing; Li, Xiaodong; Jiang, Sheng; Xiao, Wansheng; Li, Yanchun; Tang, Lingyun; Zhang, Yufeng; Zhang, Dechun; (Chinese Aca. Sci.)

    2009-10-21

    High-pressure transformation and compression behavior of Gd{sub 2}O{sub 3} were investigated using synchrotron radiation x-ray diffraction in a diamond anvil cell up to 44 GPa at room temperature. The structural transformation from a cubic to a monoclinic phase occurred during the sample precompression process. Phase transitions from both the cubic and the monoclinic polymorphs to a hexagonal structure were observed. The hexagonal phase was stable up to the highest pressure in this study and was not quenchable and transformed to a monoclinic phase after pressure release. The bulk moduli of Gd{sub 2}O{sub 3} for the cubic, monoclinic, and hexagonal phases were obtained by fitting the compression data to the Birch-Murnaghan equation of state. Moreover, an anomaly of the hexagonal type Gd{sub 2}O{sub 3} was observed.

  16. Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography

    Science.gov (United States)

    Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent

    2015-11-01

    Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase.

  17. Estimate of radiation doses to workers in underground mines of coal and fluorite in the Brazilian state of Santa Catarina and considerations on the optimisation of radiation protection

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Carlos Eduardo Lima dos; Vignol, Maria Lidia; Conceicao, Rommulo Vieira [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Inst. de Geociencias], e-mail: carlos.lima@ufrgs.br; Xavier, Ana Maria; Gouvea, Vandir; Macacini, Jose Flavio [Comissao Nacional de Energia Nuclear (CNEN/RJ), Rio de Janeiro, RJ (Brazil)], e-mail: axavier@cnen.gov.br

    2009-07-01

    The inhalation of radon present in underground mines can imply in the deposition of its descendants in the lungs, which may cause harm to the lungs tissues and induce cancer. Concentrations of radon in the environment of underground mines above 1000 - 1500 Bq/m{sup 3} are internationally considered to require protective measures for the miners. The objectives of the present work were to determine the concentrations of radon in air, as well as the resulting doses due to the presence of this radionuclide in three underground mines of fluorite and three underground mines of coal in the State of Santa Catarina. The concentration of radon was measured employing two types of detectors of nuclear tracks (SSNTD), the LEXAN and the CR-39. This detection method consisted in counting, with the help of a microscope, tracks resulting from the interaction of alpha particles with the film, due to the penetration of Rn-222 in the interior of the detector chamber and its decaying process. The average dose to the workers of the coal mines was estimated as 0.7 mSv/a, value inferior to the limit of 1 mSv/a established by the Brazilian Nuclear Energy Commission (CNEN) for members of the public. On the other hand, the fluorite mines showed much higher concentrations of radon and superior to 1000 Bq/m{sup 3}. The inefficiency of the ventilation system and the liberation of radon during the various explosions may have contributed to the high concentrations of radon in these mines since the concentration of radium in the rocks (normal and weathered granites) and in the minerals (green and purple fluorides) that compose the mining environment are not high. The modification of the ventilation system of one of the fluorite mines was sufficient to reduce the radon concentration to levels of the order of 500 Bq/m{sup 3}. The weathered granite contributes more significantly to the increase of the concentration of Rn-222 in the air than the other rocks here studied, i.e. normal granite as well as

  18. Structure and Properties of Some Layered U2O5 Phases: A Density Functional Theory Study

    OpenAIRE

    Molinari, Marco; Brincat, Nicholas A.; Allen, Geoffrey C.; Parker, Stephen C.

    2017-01-01

    U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we ...

  19. THERMODYNAMIC PARAMETERS OF LEAD SULFIDE CRYSTALS IN THE CUBIC PHASE

    Directory of Open Access Journals (Sweden)

    T. O. Parashchuk

    2016-07-01

    Full Text Available Geometric and thermodynamic parameters of cubic PbS crystals were obtained using the computer calculations of the thermodynamic parameters within density functional theory method DFT. Cluster models for the calculation based on the analysis of the crystal and electronic structure. Temperature dependence of energy ΔE and enthalpy ΔH, Gibbs free energy ΔG, heat capacity at constant pressure CP and constant volume CV, entropy ΔS were determined on the basis of ab initio calculations of the crystal structure of molecular clusters. Analytical expressions of temperature dependences of thermodynamic parameters which were approximated with quantum-chemical calculation points have been presented. Experimental results compared with theoretically calculated data.

  20. 掺氧化钙及相变对高压下立方氧化锆电子结构和光吸收的影响%Effects of CaO-doping and the phase transition in cubic zirconia on its electronic structure and optical-absortption property at high pressure

    Institute of Scientific and Technical Information of China (English)

    高敏; 曾鸣凤; 尹君; 叶强; 何林

    2015-01-01

    研究表明,立方氧化锆可作为冲击波实验中的窗口材料。为了使得该材料在常态下保持结构稳定,需添加稳定剂———氧化钙。然而,掺杂会导致其在29 GPa的冲击压力下从立方转变为斜方II结构相。因此,该材料在冲击压缩下的电子结构和光学吸收性质以及作为光学窗口的适用压力范围是值得研究的重要问题。本文运用第一性原理的方法,分别计算了在100 GPa范围内两种结构氧化锆的电子结构和光学吸收性质。结果表明:(1)在立方结构相区,冲击压力将导致其吸收边蓝移,而在斜方II结构相区,却使得其吸收边红移;(2)在立方结构相区,掺杂将引起能隙变窄(吸收边红移),但对于斜方II相区,却导致能隙变宽(吸收边蓝移);(3)冲击结构相变使得能隙变窄,吸收边红移。本文数据建议,掺氧化钙的立方氧化锆在95 GPa的冲击压力范围内可作为光学窗口材料。%It is shown that cubic zirconia can be used as a window material in shock wave experiments .A stabi-lizer, calcium oxide, is needed to be added into this material to maintain its structural stability at ambient condi-tions.However, CaO-doping may cause a cubic-to-orthorhombic II phase transition in Zirconia occurring in a shock pressure of 29 GPa.Therefore, the electronic structure and optical -absorption property of CaO -ZrO2 un-der shock compression as well as the shock -pressure range as the optical window are some important issues . Here, electronic structure and optical -absorption property of pure and CaO -doped Zirconia with two crystal structures within 100 GPa were calculated using first -principles methods , respectively .The results show that:(1) the shock pressure leads to the blue-shift of the absorption edge in the cubic -phase region but its red-shift in orthorhombic II phase region;(2) the doping causes a band-gap decrease in the cubic -phase

  1. Cherenkov and Scintillation Properties of Cubic Zirconium

    Science.gov (United States)

    Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.

    2008-01-01

    Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed

  2. Tachyon Vacuum in Cubic Superstring Field Theory

    CERN Document Server

    Erler, Theodore

    2008-01-01

    In this paper we give an exact analytic solution for tachyon condensation in the modified (picture 0) cubic superstring field theory. We prove the absence of cohomology and, crucially, reproduce the correct value for the D-brane tension. The solution is surprising for two reasons: First, the existence of a tachyon vacuum in this theory has not been definitively established in the level expansion. Second, the solution {\\it vanishes} in the GSO$(-)$ sector, implying a ``tachyon vacuum'' solution exists even for a {\\it BPS} D-brane.

  3. Generalized fairing algorithm of parametric cubic splines

    Institute of Scientific and Technical Information of China (English)

    WANG Yuan-jun; CAO Yuan

    2006-01-01

    Kjellander has reported an algorithm for fairing uniform parametric cubic splines. Poliakoff extended Kjellander's algorithm to non-uniform case. However, they merely changed the bad point's position, and neglected the smoothing of tangent at bad point. In this paper, we present a fairing algorithm that both changed point's position and its corresponding tangent vector. The new algorithm possesses the minimum property of energy. We also proved Poliakoff's fairing algorithm is a deduction of our fairing algorithm. Several fairing examples are given in this paper.

  4. Fractal Symmetries: Ungauging the Cubic Code

    CERN Document Server

    Williamson, Dominic J

    2016-01-01

    Gauging is a ubiquitous tool in many-body physics. It allows one to construct highly entangled topological phases of matter from relatively simple phases and to relate certain characteristics of the two. Here we develop a gauging procedure for general submanifold symmetries of Pauli Hamiltonians, including symmetries of fractal type. We show a relation between the pre- and post- gauging models and use this to construct short range entangled phases with fractal like symmetries, one of which is mapped to the cubic code by the gauging.

  5. The Exact Limit of Some Cubic Towers

    DEFF Research Database (Denmark)

    Anbar Meidl, Nurdagül; Beelen, Peter; Nguyen, Nhut

    2016-01-01

    Recently, a new explicit tower of function fields was introduced by Bassa, Beelen, Garcia and Stichtenoth (BBGS). This resulted in currently the best known lower bound for Ihara’s constant in the case of non-prime finite fields. In particular over cubic fields, the tower’s limit is at least as good...... as Zink’s bound; i.e. λ(BBGS/Fq3 ) ≥ 2(q2 - 1)/(q + 2). In this paper, the exact value of λ(BBGS/Fq3 ) is computed. We also settle a question stated by Ihara....

  6. Investigation on synthesis, structure, morphology, spectroscopic and electrochemical studies of praseodymium-doped ceria nanoparticles by combustion method

    Energy Technology Data Exchange (ETDEWEB)

    Esther Jeyanthi, C., E-mail: esther.jeyanthi@yahoo.com [Research and Development Centre, Bharathiar University, Coimbatore 641046 (India); Department of Physics, Panimalar Engineering College, Chennai 600123, TN (India); Siddheswaran, R. [New Technologies Research Centre, University of West Bohemia in Pilsen, Plzeň 30614 (Czech Republic); Kumar, Pushpendra [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Karl Chinnu, M. [Department of Applied Physics, Tunghai University, Taichung City, 40740, Taiwan (China); Rajarajan, K. [Department of Physics, Rajeswari Vedachalam Govt. Arts College, Chengalpet 603001, TN (India); Jayavel, R. [Centre for Nanoscience and Technology, Anna University, Chennai 600025 (India)

    2015-02-01

    The investigation deals with the synthesis and characterization of praseodymium doped ceria (PDC) nanoparticles by citrate nitrate auto-combustion method. The as prepared PDC powders were calcined at 700 °C, and then dense cylindrical electrolyte bodies were fabricated by uni-axial compression followed by sintering at 1200 °C. The PDC nanocrystals and compacts were subjected to characterization studies such as X-ray diffraction, scanning and transmission electron microscopy, elemental analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and electrochemical analyses. The crystal structure of PDC was found to be a cubic fluorite system by X-ray diffraction analysis (XRD). The surface morphologies and the grain distributions of the calcined nanoparticles and sintered bodies were studied by scanning electron microscopy (SEM). The grain size of the sintered material was found to be in the range from 100 nm to 500 nm. Transmission electron microscopic (TEM) images revealed the presence of polyhedral, sphere-like shape of the nanoparticles with a size range 10–25 nm. The symmetric stretching mode of the Ce–O was obtained at 555 cm{sup −1} in the FTIR spectrum. The Raman active mode for the PDC was obtained at 457 cm{sup −1}. The presence of oxygen vacancies was confirmed from the weaker absorption band observed at 560 cm{sup −1} in the Raman spectrum. The change in current density with increasing sweep scan potential was studied by cyclic voltammetry (CV) analysis. The specific capacitance range of the PDC was calculated as 20–72.4 Fg{sup −1}. - Highlights: • Praseodymium doped Ceria was synthesized by citrate nitrate auto-combustion method. • XRD revealed that they crystallize as single-phase cubic fluorite structure. • FTIR and RAMAN studies were carried to analyze the existence of functional groups. • The morphology of the particles and compacts were analyzed by SEM and TEM. • Cyclic voltammetry (CV) for the

  7. Cubic phase nanoparticles for sustained release of ibuprofen formulation characterization and enhanced bioavailability study

    Directory of Open Access Journals (Sweden)

    Dian L

    2013-02-01

    Full Text Available Linghui Dian,1,2,* Zhiwen Yang,3,* Feng Li,1 Zhouhua Wang,1 Xin Pan,1 Xinsheng Peng,2 Xintian Huang,1 Zhefei Guo,1 Guilan Quan,1 Xuan Shi,1 Bao Chen,1 Ge Li,4 Chuanbin Wu1,41School of Pharmaceutical Sciences, Sun Yat-Sen University, University Town, Guangzhou, People’s Republic of China; 2School of Pharmaceutical Sciences, Guangdong Medical College, Dongguan, People’s Republic of China; 3Department of Gastroenterology, Songjiang Branch of the Affiliated First People’s Hospital of Shanghai Jiaotong University, Shanghai, People’s Republic of China; 4Guangdong Research Center for Drug Delivery Systems, Guangzhou, People’s Republic of China*These authors contributed equally to this workAbstract: In order to improve the oral bioavailability of ibuprofen, ibuprofen-loaded cubic nanoparticles were prepared as a delivery system for aqueous formulations. The cubic inner structure was verified by cryogenic transmission electron microscopy. With an encapsulation efficiency greater than 85%, the ibuprofen-loaded cubic nanoparticles had a narrow size distribution around a mean size of 238 nm. Differential scanning calorimetry and X-ray diffraction determined that ibuprofen was in an amorphous and molecular form within the lipid matrix. The in vitro release of ibuprofen from cubic nanoparticles was greater than 80% at 24 hours, showing sustained characteristics. The pharmacokinetic study in beagle dogs showed improved absorption of ibuprofen from cubic nanoparticles compared to that of pure ibuprofen, with evidence of a longer half-life and a relative oral bioavailability of 222% (P < 0.05. The ibuprofen-loaded cubic nanoparticles provide a promising carrier candidate with an efficient drug delivery for therapeutic treatment.Keywords: ibuprofen, cubic nanoparticles, oral drug delivery, bioavailability

  8. Direct reading spectrochemical determination of aluminium, iron and silicon in fluorite; Determinacion espectroquimica de lectura directa de aluminio, hierro y silicio en fluorita

    Energy Technology Data Exchange (ETDEWEB)

    Roca, M.

    1966-07-01

    A quantitative spectrochemical method for the determination of Al, Fe and Si in fluorite has been worked out. The sample was supported in a graphite electrode with crater of 5 mm. in diameter, 2,5 mm deep, and burned by a d.c. are in a direct reading spectrometer. The excitation of samples has been studied without dilution as well as using graphite powder as diluent in the ratios 1:1, 1:4, and 1:9; the latter factor was chosen. Ag, Ca, Co, Cr, Mo and Sn were tested as internal standards. It has not been found any significant inter element effect. It is necessary to use natural fluorite as base material for the standards. (Author) 5 refs.

  9. Fluid Inclusion Studies and Geochemistry of Rare Earth Elements of Hydrothermal Fluorites from P?hrenk, Kir?ehir, Central Turkey

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Fluorite mineralization occurs along fractures and cracks of Middle Eocene and Pliocene limestones and marls in the north and northeast of the P?hrenk region (?i?ekdagi, Kirsehir). Tb/Ca ( Tb/La and Y/Ho ratios were obtained from REE contents of fluorites which have revealed that mineralization is of hydrothermal type. Negative Ce anomalies and positive Eu anomalies reflect that hydrothermal solutions once had high oxygen fugacity. Fluid inclusion studies indicate that homogenization temperatures of mineralization varied between 90oC and 200oC, and hydrothermal solutions are composed of NaCl + KCl + MgCl2 + H2O. In addition, salinity measurements show that hydrothermal solutions were mixed with meteoric or rock formation water. Geologic setting, REE geochemistry and fluid inclusion studies suggest that mineralization was deposited from a solution generated by mixing of magmatic and meteoric water under epithermal conditions.

  10. Impact of lanthanum on the modification of HfO2 films structure

    Institute of Scientific and Technical Information of China (English)

    T. P. Smirnova; L.V. Yakovkina; V.O. Borisov

    2015-01-01

    LaxHf1–xOy thin films with various concentrations of La, homogeneous and nonhomogeneous distributions of elements throughout the films thickness was purposefully grown by CVD. The composition of the films and their chemical structures were characterized throughout the films thickness by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectrometry (EDXA). A full picture of the film crystallinity was provided by the combination of grazing incidence X-ray diffraction (GIXRD) synchrotron radiation (SR) and high resolution transmission electron microscopy (HR TEM). It was shown that La acted as “molar volume modulator” and stabilized the nonequilibrium atT≤1300 °C cubic phases. The samples with La content in range of 7 at.%fluorite-type (Fm-3m) structure. The pyrochlore phase formation was observed at ~18 at.% La content. The correlation between the La-doped content and the films microstructure was revealed.

  11. Key parameters governing the densification of cubic-Li7La3Zr2O12 Li+ conductors

    Science.gov (United States)

    Yi, Eongyu; Wang, Weimin; Kieffer, John; Laine, Richard M.

    2017-06-01

    Cubic-Li7La3Zr2O12 (LLZO) is regarded as one of the most promising solid electrolytes for the construction of inherently safe, next generation all-solid-state Li batteries. Unfortunately, sintering these materials to full density with controlled grain sizes, mechanical and electrochemical properties relies on energy and equipment intensive processes. In this work, we elucidate key parameters dictating LLZO densification by tracing the compositional and structural changes during processing calcined and ball-milled Al3+ doped LLZO powders. We find that the powders undergo ion (Li+/H+) exchange during room temperature processing, such that on heating, the protonated LLZO lattice collapses and crystallizes to its constituent oxides, leading to reaction driven densification at sizes and protonation cannot be decoupled, and actually aid densification. We conclude that using fully decomposed nanoparticle mixtures, as obtained by liquid-feed flame spray pyrolysis, provides an ideal approach to use high surface and reaction energy to drive densification, resulting in pressureless sintering of Ga3+ doped LLZO thin films (25 μm) at 1130 °C/0.3 h to ideal microstructures (95 ± 1% density, 1.2 ± 0.2 μm average grain size) normally accessible only by pressure-assisted sintering. Such films offer both high ionic conductivity (1.3 ± 0.1 mS cm-1) and record low ionic area specific resistance (2 Ω cm2).

  12. Quantification of fluorite mass-content in powdered ores using a Laser-Induced Breakdown Spectroscopy method based on the detection of minor elements and CaF molecular bands

    Energy Technology Data Exchange (ETDEWEB)

    Álvarez, C.; Pisonero, J., E-mail: pisonerojorge@uniovi.es; Bordel, N., E-mail: bordel@uniovi.es

    2014-10-01

    Laser Induced Breakdown Spectroscopy (LIBS) is investigated as a fast and robust method to determine the fluorite (CaF{sub 2}) mass-content of powdered ore samples. Calibrating samples covering a wide CaF{sub 2} concentration range (from 2.3 to 97.6%) are employed. LIBS operating conditions are optimized for the analysis of elemental emission lines and molecular bands, respectively. In particular, LIBS emission intensities from different CaF molecular bands are evaluated to calibrate the fluorite concentration as an alternative to the use of atomic fluorine F I emission lines. Furthermore, the determination of LIBS emission signals from minor elements (e.g. Si I and Mg I) is studied to further improve the accuracy and precision of pure fluorite sample analyses (e.g. [CaF{sub 2}] > 75%). The proposed LIBS method avoids the tedious dissolution processes that are required by other analytical methods employed in mining industry for the quantitative analysis of fluorite. - Highlights: • Fluorite ore mass-content is determined using a LIBS system. • F I emission line at 685.60 nm is used to calibrate the fluorite mass-content. • CaF emission bands are used to quantify samples with low CaF2 concentrations. • Minor elements are used to quantify samples with high CaF2 concentrations.

  13. Test Research on Beneficiation of Calcite Type Fluorite Ore in Hu'nan%湖南某方解石型萤石选矿试验研究

    Institute of Scientific and Technical Information of China (English)

    胡瑞彪; 吉红; 陈典助; 荆正强

    2013-01-01

    The CaF 2 grade of calcite type fluorite ore from Hu'nan is reaching up to 56 .72%,regard as high-grades fluorite ore .According to the mineralogical characteristic of the ore ,the fluorite was studied,Using sodium carbonate as pH adjusting agent ,sodium silicate and starch as depressant ,so-dium oleate as collector , closed -circuit test were carried out in the condition that the roughing grinding fineness was -0 .074 mm 65%.The grade and recovery of the fluorite concentrate were 97.16%and 80.38%respectively,and the content of SiO2 and CaCO3 meet the national standards . The results showed that concentrate were obtained by swept one rougher -five cleaners-one scav-enging and coarse concentrate regrinding closed -circuit process .%湖南某方解石型萤石矿原矿含CaF256.72%,属高品位萤石矿。结合该矿石的工艺矿物学特性,采用碳酸钠为pH调整剂、水玻璃+淀粉为抑制剂、油酸钠为捕收剂进行浮选试验研究。闭路试验在粗选磨矿细度-0.074 mm占65%的情况下,通过一粗五精一扫-粗精矿再磨的工艺流程,可以获得品位97.16%、回收率80.38%的萤石精矿,且萤石精矿中含SiO21.20%、CaCO30.65%,达到国家萤石粉F97C的质量标准。

  14. Characterizations of Cubic ZnMgO Films Grown on Si(111) at Low Substrate Temperature

    Institute of Scientific and Technical Information of China (English)

    邱东江; 吴惠桢; 陈乃波; 徐天宁

    2003-01-01

    Cubic ZnMgO thin films in the (100) orientation were grown on Si (111) substrates by reactive electron beamevaporation at low substrate temperature. X-ray photoelectron spectroscopy (XPS) analyses show that Mgcontent as high as 75 at.% in the cubic ZnMgO film can be obtained. Secondary ion mass spectroscopy (SIMS)measurement indicates the evidence of Mg richness in the interface between the ZnMgO film and the Si substrate,and it is probably the primary reason to form the MgO-like cubic ZnMgO structures rather than the wurtziteone. The optical band gap of cubic ZnMgO is estimated to be 5.76eV, which was measured by the transmissionspectrum of the cubic ZnMgO film grown on the sapphire substrate under the same growth condition with thaton Si (111). The band gap is of 2.39eV blueshifted compared with that of ZnO (3.37eV), which should renderapplications in the fabrication of ZnMgO-related heterostructures.

  15. Recurrence approach and higher rank cubic algebras for the N-dimensional superintegrable systems

    Science.gov (United States)

    Fazlul Hoque, Md; Marquette, Ian; Zhang, Yao-Zhong

    2016-03-01

    By applying the recurrence approach and coupling constant metamorphosis, we construct higher order integrals of motion for the Stackel equivalents of the N-dimensional superintegrable Kepler-Coulomb model with non-central terms and the double singular oscillators of type (n,N-n). We show how the integrals of motion generate higher rank cubic algebra C(3)\\oplus {L}1\\oplus {L}2 with structure constants involving Casimir operators of the Lie algebras L 1 and L 2. The realizations of the cubic algebras in terms of deformed oscillators enable us to construct finite dimensional unitary representations and derive the degenerate energy spectra of the corresponding superintegrable systems.

  16. Industrial growth of yttria-stabilized cubic zirconia crystals by skull melting process

    Institute of Scientific and Technical Information of China (English)

    徐家跃; 雷秀云; 蒋新; 何庆波; 房永征; 张道标; 何雪梅

    2009-01-01

    We reported the development of a Ф100 cm growth apparatus for skull melting growth of yttria-stabilized cubic zirconia(YSZ) crystals and more than 1000 kg crystals have been grown in the furnace each time.The growth conditions were optimized and the structure of the as-grown crystals was characterized by X-ray diffraction.The transmittance of 15 mol.% yttria-stabilized cubic zirconia crystal was nearly 80% in the range of 400-1600 nm.The refractive indices were measured and fitted the Sellmeier equation whi...

  17. Slanted stacking faults and persistent face centered cubic crystal growth in sedimentary colloidal hard sphere crystals

    NARCIS (Netherlands)

    Hilhorst, J.; Wolters, J. R.; Petukhov, A.V.

    2010-01-01

    Hard sphere crystal growth is a delicate interplay between kinetics and thermodynamics, where the former is commonly thought to favour a random hexagonal close packed structure and the latter leads to a face centered cubic crystal. In this article, we discuss the influence of slanted stacking faults

  18. THE UNIQUENESS OF LIMIT CYCLE AND CRITICAL POINT FOR A CLASS OF CUBIC SYSTEM

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In this paper,we consider an accompany system concerning some class of cubic system. We then prove that the system has at most one limit cycle. Finally,we obtain the topological structure of both the critical points at infinity and the singular points lying on invariant lines.

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

    DEFF Research Database (Denmark)

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

    2012-01-01

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

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

    DEFF Research Database (Denmark)

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

    2014-01-01

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

  1. Effect of pressure on itinerant magnetism and spin disorder in cubic FeGe.

    Science.gov (United States)

    Pulikkotil, J J; Auluck, S; Rout, P K; Budhani, R C

    2012-03-01

    The results of ab initio calculations of the pressure dependence of Fe magnetism in cubic FeGe are presented. We find that when the pressure-volume scale is set by means of generalized gradient approximation total energies and magnetism is described by means of the local density approximation, the critical pressure at which the magnetic phase transition occurs is estimated at ≈18 GPa, which is in good agreement with experiments. Using the disordered local moment method we find a localized to itinerant model cross-over of Fe magnetism in cubic FeGe, as a function of volume. Moreover, our calculations also suggest subtle signatures of longitudinal spin fluctuations in cubic FeGe, and that the stiffness parameter softens with increasing pressure. We associate the retention of metallicity in FeGe under pressure with the spin-disorder scattering. The effect of spin-orbit coupling on the electronic structure is also discussed.

  2. Phase de-locking in cubic 3k-antiferromagnets. [USb; UIn[sub 3

    Energy Technology Data Exchange (ETDEWEB)

    Asch, L. (Physik Dept., Technische Univ. Muenchen, Garching (Germany)); Kalvius, G.M. (Physik Dept., Technische Univ. Muenchen, Garching (Germany)); Kratzer, A. (Physik Dept., Technische Univ. Muenchen, Garching (Germany)); Litterst, F.J. (Inst. fuer Metallphysik, Technische Univ. Braunschweig (Germany))

    1994-07-01

    It is shown that the temperature dependence of [mu]SR spectra of some simple cubic (NaCl, CsCl, AuCu[sub 3] structures) compounds involving rare earths and actinides differs for a 1k when compared to a a 3k spin structure. This allows their distinction. In the 3 k structure magnetic pseudo excitations resulting from phase de-locking diffuse slowly (1-5 MHz). (orig.)

  3. All unitary cubic curvature gravities in D dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Sisman, Tahsin Cagri; Guellue, Ibrahim; Tekin, Bayram, E-mail: sisman@metu.edu.tr, E-mail: e075555@metu.edu.tr, E-mail: btekin@metu.edu.tr [Department of Physics, Middle East Technical University, 06531 Ankara (Turkey)

    2011-10-07

    We construct all the unitary cubic curvature gravity theories built on the contractions of the Riemann tensor in D-dimensional (anti)-de Sitter spacetimes. Our construction is based on finding the equivalent quadratic action for the general cubic curvature theory and imposing ghost and tachyon freedom, which greatly simplifies the highly complicated problem of finding the propagator of cubic curvature theories in constant curvature backgrounds. To carry out the procedure we have also classified all the unitary quadratic models. We use our general results to study the recently found cubic curvature theories using different techniques and the string generated cubic curvature gravity model. We also study the scattering in critical gravity and give its cubic curvature extensions.

  4. Gauge Fixing of Modified Cubic Open Superstring Field Theory

    CERN Document Server

    Kohriki, Maiko; Kunitomo, Hiroshi

    2011-01-01

    The gauge-fixing problem of modified cubic open superstring field theory is discussed in detail both for the Ramond and Neveu-Schwarz sectors in the Batalin-Vilkovisky (BV) framework. We prove for the first time that the same form of action as the classical gauge-invariant one with the ghost-number constraint on the string field relaxed gives the master action satisfying the BV master equation. This is achieved by identifying independent component fields based on the analysis of the kernel structure of the inverse picture changing operator. The explicit gauge-fixing conditions for the component fields are discussed. In a kind of $b_0=0$ gauge, we explicitly obtain the NS propagator which has poles at the zeros of the Virasoro operator $L_0$.

  5. Enhanced initial protein adsorption on an engineered nanostructured cubic zirconia

    CERN Document Server

    Sabirianov, R F; Namavar, F

    2010-01-01

    Motivated by experimentally observed biocompatibility enhancement of nanoengineered cubic zirconia ZrO2 coatings to mesenchymal stromal cells, we have carried out computational analysis of the initial immobilization of one of known structural fragment of the adhesive protein (fibronectin) on the corresponding surface. We constructed an atomistic model of the zirconia nano-hillock of 3-fold symmetry based on AFM and TEM images. First-principle quantum-mechanical calculations show a substantial variation of electrostatic potential at the hillock due to the presence of surface features such as edges and vertexes. Using an implemented Monte Carlo simulated annealing method we found the orientation of the immobilized protein on the zirconia surface (both flat and nanostructured) and contribution of the each amino acid residue from the protein sequence to the adsorption energy. Accounting for the variation of the dielectric permittivity at the protein-implant interface we use a model distance-dependent dielectric f...

  6. Cubic Derivative Interactions and Asymptotic Dynamics of the Galileon Vacuum

    CERN Document Server

    De Arcia, Roberto; León, Genly; Nucamendi, Ulises; Quiros, Israel

    2015-01-01

    In this paper we apply the tools of the dynamical systems theory in order to uncover the whole asymptotic structure of the vacuum interactions of a galileon model with a cubic derivative interaction term. It is shown that, contrary to what occurs in the presence of background matter, the galileon interactions of vacuum appreciably modify the late-time cosmic dynamics. In particular, a local late-time attractor representing phantom behavior arises which is inevitably associated with a big rip singularity. It seems that the gravitational interactions of the background matter with the galileon screen the effects of the gravitational self-interactions of the galileon, thus erasing any potential modification of the late-time dynamics by the galileon vacuum processes. Unlike other galileon models inspired in the DGP scenario, self-accelerating solutions do not arise in this model.

  7. Quantum corrections for the cubic Galileon in the covariant language

    Science.gov (United States)

    Saltas, Ippocratis D.; Vitagliano, Vincenzo

    2017-05-01

    We present for the first time an explicit exposition of quantum corrections within the cubic Galileon theory including the effect of quantum gravity, in a background- and gauge-invariant manner, employing the field-reparametrisation approach of the covariant effective action at 1-loop. We show that the consideration of gravitational effects in combination with the non-linear derivative structure of the theory reveals new interactions at the perturbative level, which manifest themselves as higher-operators in the associated effective action, which' relevance is controlled by appropriate ratios of the cosmological vacuum and the Galileon mass scale. The significance and concept of the covariant approach in this context is discussed, while all calculations are explicitly presented.

  8. Hairy black holes in cubic quasi-topological gravity

    Science.gov (United States)

    Dykaar, Hannah; Hennigar, Robie A.; Mann, Robert B.

    2017-05-01

    We construct a class of five dimensional black hole solutions to cubic quasi-topological gravity with conformal scalar hair and study their thermodynamics. We find these black holes provide the second example of black hole λ-lines: a line of second order (continuous) phase transitions, akin to the fluid/superfluid transition of 4He. Examples of isolated critical points are found for spherical black holes, marking the first in the literature to date. We also find various novel and interesting phase structures, including an isolated critical point occurring in conjunction with a double reentrant phase transition. The AdS vacua of the theory are studied, finding ghost-free configurations where the scalar field takes on a non-zero constant value, in notable contrast to the five dimensional Lovelock case.

  9. Formation and properties of silicon/fluorite heterostructures. Final report, June 1, 1994--May 31, 1997

    Energy Technology Data Exchange (ETDEWEB)

    Olmstead, M.A.

    1997-10-01

    Our primary goal during the previous support periods was to determine the interrelationship among the structure of the CaF{sub 2}/Si interface, the growth kinetics, the structure and morphology of the overlying film, and the intrinsic dielectric properties of the interface itself. The experiments were designed (i) to determine the CaF{sub 2} overlayer structure and morphology as a function of kinetic conditions [Den93a, Den93b, Won93, Den95, Hes95], (ii) to develop and test models explaining the observed structures [Den95, Hes95], (iii) to investigate the stability of the interface structure [Les97] and (iv) to determine and interpret the photoelectron kinetic energy distributions as a function of the emitting atom location [Rot93, Rot94, Rot96]. As summarized below, we were successful in accomplishing these experiments and in largely fulfilling our original goal.

  10. Cubic meter volume optical coherence tomography

    Science.gov (United States)

    WANG, ZHAO; POTSAID, BENJAMIN; CHEN, LONG; DOERR, CHRIS; LEE, HSIANG-CHIEH; NIELSON, TORBEN; JAYARAMAN, VIJAYSEKHAR; CABLE, ALEX E.; SWANSON, ERIC; FUJIMOTO, JAMES G.

    2017-01-01

    Optical coherence tomography (OCT) is a powerful three-dimensional (3D) imaging modality with micrometer-scale axial resolution and up to multi-GigaVoxel/s imaging speed. However, the imaging range of high-speed OCT has been limited. Here, we report 3D OCT over cubic meter volumes using a long coherence length, 1310 nm vertical-cavity surface-emitting laser and silicon photonic integrated circuit dual-quadrature receiver technology combined with enhanced signal processing. We achieved 15 µm depth resolution for tomographic imaging at a 100 kHz axial scan rate over a 1.5 m range. We show 3D macroscopic imaging examples of a human mannequin, bicycle, machine shop gauge blocks, and a human skull/brain model. High-bandwidth, meter-range OCT demonstrates new capabilities that promise to enable a wide range of biomedical, scientific, industrial, and research applications. PMID:28239628

  11. Black holes in Einsteinian cubic gravity

    CERN Document Server

    Hennigar, Robie A

    2016-01-01

    Using numerical and perturbative methods, we construct the first examples of black hole solutions in Einsteinian cubic gravity and study their thermodynamics. Focusing first on four dimensional solutions, we show that these black holes have a novel equation of state in which the pressure is a quadratic function of the temperature. Despite this, they undergo a first order phase transition with associated van der Waals behaviour. We then construct perturbative solutions for general $D \\ge 5$ and study the properties of these solutions for $D=5$ and $D=6$ in particular. We find novel examples of zeroth order phase transitions and find super-entropic behaviour over a large portion of the parameter space. We analyse the specific heat, determining that the black holes are thermodynamically stable over large regions of parameter space.

  12. Triangulation of cubic panorama for view synthesis.

    Science.gov (United States)

    Zhang, Chunxiao; Zhao, Yan; Wu, Falin

    2011-08-01

    An unstructured triangulation approach, new to our knowledge, is proposed to apply triangular meshes for representing and rendering a scene on a cubic panorama (CP). It sophisticatedly converts a complicated three-dimensional triangulation into a simple three-step triangulation. First, a two-dimensional Delaunay triangulation is individually carried out on each face. Second, an improved polygonal triangulation is implemented in the intermediate regions of each of two faces. Third, a cobweblike triangulation is designed for the remaining intermediate regions after unfolding four faces to the top/bottom face. Since the last two steps well solve the boundary problem arising from cube edges, the triangulation with irregular-distribution feature points is implemented in a CP as a whole. The triangular meshes can be warped from multiple reference CPs onto an arbitrary viewpoint by face-to-face homography transformations. The experiments indicate that the proposed triangulation approach provides a good modeling for the scene with photorealistic rendered CPs.

  13. Black holes in a cubic Galileon universe

    CERN Document Server

    Babichev, Eugeny; Lehébel, Antoine; Moskalets, Tetiana

    2016-01-01

    We find and study the properties of black hole solutions for a subclass of Horndeski theory including the cubic Galileon term. The theory under study has shift symmetry but not reflection symmetry for the scalar field. The Galileon is assumed to have linear time dependence characterized by a velocity parameter. We give analytic 3-dimensional solutions that are akin to the BTZ solutions but with a non-trivial scalar field that modifies the effective cosmological constant. We then study the 4-dimensional asymptotically flat and de Sitter solutions. The latter present three different branches according to their effective cosmological constant. For two of these branches, we find families of black hole solutions, parametrized by the velocity of the scalar field. These spherically symmetric solutions, obtained numerically, are different from GR solutions close to the black hole event horizon, while they have the same de-Sitter asymptotic behavior. The velocity parameter represents black hole primary hair.

  14. Finite element differential forms on cubical meshes

    CERN Document Server

    Arnold, Douglas N

    2012-01-01

    We develop a family of finite element spaces of differential forms defined on cubical meshes in any number of dimensions. The family contains elements of all polynomial degrees and all form degrees. In two dimensions, these include the serendipity finite elements and the rectangular BDM elements. In three dimensions they include a recent generalization of the serendipity spaces, and new H(curl) and H(div) finite element spaces. Spaces in the family can be combined to give finite element subcomplexes of the de Rham complex which satisfy the basic hypotheses of the finite element exterior calculus, and hence can be used for stable discretization of a variety of problems. The construction and properties of the spaces are established in a uniform manner using finite element exterior calculus.

  15. On the plane-wave cubic vertex

    CERN Document Server

    Lucietti, J; Sinha, A K; Lucietti, James; Schäfer-Nameki, Sakura; Sinha, Aninda

    2004-01-01

    The exact bosonic Neumann matrices of the cubic vertex in plane-wave light-cone string field theory are derived using the contour integration techniques developed in our earlier paper. This simplifies the original derivation of the vertex. In particular, the Neumann matrices are written in terms of \\mu-deformed Gamma-functions, thus casting them into a form that elegantly generalizes the well-known flat-space solution. The asymptotics of the \\mu-deformed Gamma-functions allow one to determine the large-\\mu behaviour of the Neumann matrices including exponential corrections. We provide an explicit expression for the first exponential correction and make a conjecture for the subsequent exponential correction terms.

  16. Polarization conversion in cubic Raman crystals

    Science.gov (United States)

    McKay, Aaron; Sabella, Alexander; Mildren, Richard P.

    2017-01-01

    Nonlinear conversion of unpolarized beams to lower frequencies is generally inefficient in c(2) materials, as it is challenging to achieve phase-matching for input ordinary and extraordinary beams simultaneously in the normal dispersion regime. Here, we show that cubic Raman crystals having doubly and triply degenerate (E and F type) modes provide a method for efficient nonlinear frequency downconversion of an unpolarized beam and yield a linearly polarized output state. Using Mueller calculus, optimal crystal directions for such polarization conversion are determined. Using diamond, an example of an F-class Raman crystal, we have verified that such conversion is possible with near quantum-defect-limited slope efficiency and a linear polarization contrast of more than 23.9 dB. PMID:28169327

  17. On the Stability of Cubic Galileon Accretion

    CERN Document Server

    Bergliaffa, Santiago P E

    2016-01-01

    We examine the stability of steady-state galileon accretion for the case of a Schwarzshild black hole. Considering the galileon action up to the cubic term in a static and spherically symmetric background we obtain the general solution for the equation of motion which is divided in two branches. By perturbing this solution we define an effective metric which determines the propagation of fluctuations. In this general picture we establish the position of the sonic horizon together with the matching condition of the two branches on it. Restricting to the case of a Schwarzschild background, we show, via the analysis of the energy of the perturbations and its time derivative, that the accreting field is linearly stable.

  18. Improved sinterability and conductivity enhancement of 10-mol% calcium-doped ceria using different fuel-aided combustion reactions and its structural characterisation

    Energy Technology Data Exchange (ETDEWEB)

    Ong, P.S., E-mail: pohshing@gmail.com [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Tan, Y.P., E-mail: yptan@science.upm.edu.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Putra Laboratory for Catalysis Science and Technology, Department Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Taufiq-Yap, Y.H., E-mail: yap@science.upm.edu.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Putra Laboratory for Catalysis Science and Technology, Department Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Zainal, Z., E-mail: zulkar@science.upm.edu.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Putra Laboratory for Catalysis Science and Technology, Department Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia)

    2014-07-01

    Highlights: • The analysis of the combustion parameters for different fuel-aided combustion syntheses of Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} is investigated. • The influence of fuel and its direct correlation with calculated thermochemistry is studied. • A complex reaction equation based on stoichiometric mole of fuels to propellant chemistry concept is created. • The influence of fuel utilised on the combustion process and on physiochemical properties is examined. • Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} ceramic from citric acid-aided combustion synthesis showed the highest conductivity (σ{sub 800°c} = 0.017 S cm{sup −1}). - Abstract: Cubic fluorite structure of ceria doped with 10-mol% calcium, Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9}, was prepared using fuel-aided combustion techniques, utilising glycine, urea and citric acid as fuels along with metal nitrates as the oxidiser. The influence of fuel utilised on the combustion process and on physiochemical properties was thoroughly studied. The results of X-ray diffraction showed that all powders calcined at 400 °C were of single phase with cubic fluorite structure. Conductivity optimisation was achieved via ceramic sintering at various temperatures within 1000–1200 °C. The results showed that Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} ceramic prepared using citric acid-aided combustion synthesis had higher ionic conductivity, σ{sub 800°c} = 0.017 S cm{sup −1}, and lower activation energy, E{sub a} = 0.84 eV, compared to Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} ceramics prepared using glycine and urea. The scanning electron microscopy (SEM) results showed that pellets sintered at 1200 °C were dense, and the relative densities of these pellets were over 95%, determined using the Archimedes method.

  19. Ultrafast synthesis of yolk-shell and cubic NiO Nanopowders and application in lithium ion batteries.

    Science.gov (United States)

    Choi, Seung Ho; Kang, Yun Chan

    2014-02-26

    A continuous one-pot method was employed to synthesize yolk-shell and single-crystalline cubic NiO powders in a few seconds. Submicrometer-sized NiO yolk-shell particles were prepared by spray pyrolysis at 900 °C. Single-crystalline cubic NiO nanopowders were prepared by one-pot flame spray pyrolysis from NiO vapors. Particle surface areas of the yolk-shell and single-crystalline cubic NiO powders as obtained using the Brunauer-Emmett-Teller method were 8 and 5 m(2) g(-1), respectively. The mean crystallite sizes of the yolk-shell-structured and cubic NiO powders were 50 and 80 nm, respectively. The yolk-shell and single-crystalline cubic NiO powders delivered discharge capacities of 951 and 416 mA h g(-1), respectively, after 150 cycles, and the corresponding capacity retentions measured after the first cycle were 106 and 66%, respectively. The yolk-shell-structured NiO powders showed rate performance better than that of the single-crystalline cubic NiO nanopowders. Even at a high current density of 1 A g(-1), the discharge capacity of the yolk-shell-structured NiO powders was as high as 824 mA h g(-1) after 50 cycles, in which the current densities were increased stepwise.

  20. Low pressure growth of cubic boron nitride films

    Science.gov (United States)

    Ong, Tiong P. (Inventor); Shing, Yuh-Han (Inventor)

    1997-01-01

    A method for forming thin films of cubic boron nitride on substrates at low pressures and temperatures. A substrate is first coated with polycrystalline diamond to provide a uniform surface upon which cubic boron nitride can be deposited by chemical vapor deposition. The cubic boron nitride film is useful as a substitute for diamond coatings for a variety of applications in which diamond is not suitable. any tetragonal or hexagonal boron nitride. The cubic boron nitride produced in accordance with the preceding example is particularly well-suited for use as a coating for ultra hard tool bits and abrasives, especially those intended to use in cutting or otherwise fabricating iron.

  1. Shape preserving rational cubic spline for positive and convex data

    Directory of Open Access Journals (Sweden)

    Malik Zawwar Hussain

    2011-11-01

    Full Text Available In this paper, the problem of shape preserving C2 rational cubic spline has been proposed. The shapes of the positive and convex data are under discussion of the proposed spline solutions. A C2 rational cubic function with two families of free parameters has been introduced to attain the C2 positive curves from positive data and C2 convex curves from convex data. Simple data dependent constraints are derived on free parameters in the description of rational cubic function to obtain the desired shape of the data. The rational cubic schemes have unique representations.

  2. Leucas aspera mediated multifunctional CeO2 nanoparticles: Structural, photoluminescent, photocatalytic and antibacterial properties.

    Science.gov (United States)

    Malleshappa, J; Nagabhushana, H; Sharma, S C; Vidya, Y S; Anantharaju, K S; Prashantha, S C; Daruka Prasad, B; Raja Naika, H; Lingaraju, K; Surendra, B S

    2015-01-01

    Spherical shaped cerium dioxide (CeO2) nanoparticles (NPs) were synthesized via bio mediated route using Leucas aspera (LA) leaf extract. The NPs were characterized by PXRD, SEM, UV-Visible techniques. Photoluminescence (PL), photocatalysis and antibacterial properties of NPs were studied. PXRD patterns and Rietveld analysis confirm cubic fluorite structure with space group Fm-3m. SEM results evident that morphology of the NPs was greatly influenced by the concentration of LA leaf extract in the reaction mixture. The band gap energy of the NPs was found to be in the range of 2.98-3.4 eV. The photocatalytic activity of NPs was evaluated by decolorization of Rhodamine-B (RhB) under UVA and Sun light irradiation. CeO2 NPs show intense blue emission with CIE coordinates (0.14, 0.22) and average color coordinated temperature value ∼148,953 K. Therefore the present NPs quite useful for cool LEDs. The superior photocatalytic activity was observed for CeO2 NPs with 20 ml LA under both UVA and Sunlight irradiation. The enhanced photocatalytic activity and photoluminescent properties were attributed to defect induced band gap engineered CeO2 NPs. Further, CeO2 with 20 ml LA exhibit significant antibacterial activity against Escherichia coli (EC) and Staphylococcus aureus (SA). These findings show great promise of CeO2 NPs as multifunctional material for various applications.

  3. CRACK PROBLEM UNDER SHEAR LOADING IN CUBIC QUASICRYSTAL

    Institute of Scientific and Technical Information of China (English)

    周旺民; 范天佑; 尹姝媛

    2003-01-01

    The axisymmetric elasticity problem of cubic quasicrystal is reduced to a single higher-order partial differential equation by introducing a displacement function. Based on the work, the analytic solutions of elastic field of cubic quasicrystal with a penny-shaped crack under the shear loading are found, and the stress intensity factor and strain energy release rate are determined.

  4. Cubic Polynomials with Real or Complex Coefficients: The Full Picture

    Science.gov (United States)

    Bardell, Nicholas S.

    2016-01-01

    The cubic polynomial with real coefficients has a rich and interesting history primarily associated with the endeavours of great mathematicians like del Ferro, Tartaglia, Cardano or Vieta who sought a solution for the roots (Katz, 1998; see Chapter 12.3: The Solution of the Cubic Equation). Suffice it to say that since the times of renaissance…

  5. An application of Cubical Cohomology to Adinkras and Supersymmetry Representations

    CERN Document Server

    Doran, Charles; Landweber, Greg

    2012-01-01

    An Adinkra is a class of graphs with certain signs marking its vertices and edges, which encodes off-shell representations of the super Poincar\\'e algebra. The markings on the vertices and edges of an Adinkra are cochains for cubical cohomology. This article explores the cubical cohomology of Adinkras, treating these markings analogously to characteristic classes on smooth manifolds.

  6. Rational Cubics and Conics Representation: A Practical Approach

    Directory of Open Access Journals (Sweden)

    M. Sarfraz

    2012-08-01

    Full Text Available A rational cubic spline, with one family of shape parameters, has been discussed with the view to its application in Computer Graphics. It incorporates both conic sections and parametric cubic curves as special cases. The parameters (weights, in the description of the spline curve can be used to modify the shape of the curve, locally and globally, at the knot intervals. The rational cubic spline attains parametric   smoothness whereas the stitching of the conic segments preserves visually reasonable smoothness at the neighboring knots. The curve scheme is interpolatory and can plot parabolic, hyperbolic, elliptic, and circular splines independently as well as bits and pieces of a rational cubic spline.Key Words: Computer Graphics, Interpolation, Spline, Conic, Rational Cubic

  7. On cubic equations over $P-$adic field

    CERN Document Server

    Mukhamedov, Farrukh; Saburov, Mansoor

    2012-01-01

    We provide a solvability criteria for a depressed cubic equation in domains $\\bz_p^{*},\\bz_p,\\bq_p$. We show that, in principal, the Cardano method is not always applicable for such equations. Moreover, the numbers of solutions of the depressed cubic equation in domains $\\bz_p^{*},\\bz_p,\\bq_p$ are provided. Since $\\bbf_p\\subset\\bq_p,$ we generalize J.-P. Serre's \\cite{JPSJ} and Z.H.Sun's \\cite{ZHS1,ZHS3} results concerning with depressed cubic equations over the finite field $\\bbf_p$. Finally, all depressed cubic equations, for which the Cardano method could be applied, are described and the $p-$adic Cardano formula is provided for those cubic equations.

  8. Bubble Formation and Lattice Parameter Changes Resulting from He Irradiation of Defect-Fluorite Gd2Zr2O7

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Caitlin A.; Patel, Maulik K.; Aguiar, Jeffery A.; Zhang, Yanwen; Crespillo, Miguel L.; Wen, Juan; Xue, Haizhou; Wang, Yongqiang; Weber, William J.

    2016-08-15

    Pyrochlores have long been considered as potential candidates for advanced ceramic waste-forms for the immobilization of radioactive waste nuclides. This work provides evidence that Gd2Zr2O7, often considered the most radiation tolerant pyrochlore, could be susceptible to radiation damage in the form of bubble nucleation at the highest He doses expected over geological time. Ion irradiations were utilized to experimentally simulate the radiation damage and He accumulation produced by ..alpha..-decay. Samples were pre-damaged using 7 MeV Au3+ to induce the pyrochlore to defect-fluorite phase transformation, which would occur due to ..alpha..-recoil damage within several hundred years of storage in a Gd2Zr2O7 waste-form. These samples were then implanted to various He concentrations in order to study the long-term effects of He accumulation. Helium bubbles 1-3 nm in diameter were observed in TEM at a concentration of 4.6 at.% He. Some bubbles remained isolated, while others formed chains 10-30 nm in length parallel to the surface. GIXRD measurements showed lattice swelling after irradiating pristine Gd2Zr2O7 with 7 MeV Au3+ to a fluence of 2.2 x 1015 Au/cm2. An increase in lattice swelling was also measured after 2.2 x 1015 Au/cm2 + 2 x 1015 He/cm2 and 2.2 x 1015 Au/cm2 + 2 x 1016 He/cm2. A decrease in lattice swelling was measured after irradiation with 2.2 x 1015 Au/cm2 + 2 x 1017 He/cm2, the fluence where bubbles and bubble chains were observed in TEM. Bubble chains are thought to form in order to reduce lattice strain normal to the surface, which is produced by the Au and He irradiation damage.

  9. The Body Center Cubic Quark Lattice Model

    CERN Document Server

    Lin Xu, Jiao

    2004-01-01

    The Standard Model while successful in many ways is incomplete; many questions remain. The origin of quark masses and hadronization of quarks are awaiting an answer. From the Dirac sea concept, we infer that two kinds of elementary quarks (u(0) and d(0)) constitute a body center cubic (BCC) quark lattice with a lattice constant a < $10^{-18}$m in the vacuum. Using energy band theory and the BCC quark lattice, we can deduce the rest masses and the intrinsic quantum numbers (I, S, C, b and Q) of quarks. With the quark spectrum, we deduce a baryon spectrum. The theoretical spectrum is in agreement well with the experimental results. Not only will this paper provide a physical basis for the Quark Model, but also it will open a door to study the more fundamental nature at distance scales <$10^{-18}$m. This paper predicts some new quarks $u_{c}$(6490) and d$_{b}$(9950), and new baryons $\\Lambda_{c}^{+}$(6500), $\\Lambda_{b}^{0}$(9960).

  10. Observation of the structural, optical and magnetic properties during the transformation from hexagonal NiS nano-compounds to cubic NiO nanostructures due to thermal oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Linganiso, E.C., E-mail: elinganiso@csir.co.za [National Centre for Nano-Structured Materials, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001 (South Africa); DST/NRF Centre of Excellence in Strong Materials, Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, Johannesburg, Wits 2050 (South Africa); Mwakikunga, B.W., E-mail: bmwakikunga@csir.co.za [National Centre for Nano-Structured Materials, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001 (South Africa); Coville, N.J. [DST/NRF Centre of Excellence in Strong Materials, Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, Johannesburg, Wits 2050 (South Africa); Mhlanga, S.D. [Department of Applied Chemistry, University of Johannesburg, PO Box 17011, Doornfontein, 2028 Johannesburg (South Africa)

    2015-04-25

    Graphical abstract: The transition temperature of 350 °C for the formation of c-NiO from h-NiS oxidation was obtained from structural and optical property studies and by calculating the number of spins obtained from the EPR data. Vibrating sample magnetometry (VSM) shows that this pure NiS has both ferromagnetic ordering and paramagnetic domains. Further, the transition temperature of −9 °C of the pure α-NiS nano-alloys was confirmed by performing electrical measurements on the as-synthesized material. - Highlights: • Single hexagonal phase NiS obtained by microwave assisted hydrothermal synthesis. • NiS nanoalloys show both ferromagnetic and paramagnetic domains by VSM. • Structural evolution of annealed NiS and temperature dependent NiS oxidation presented. • Phase transition from NiS to NiO studied and correlated to the EPR spin population data and crystallite size. • Ferromagnetic and paramagnetic ordering observed for the raw NiS nanostructures. - Abstract: Single phase α-NiS nano-compounds with uniformly distributed hierarchical networks were synthesized by a microwave-assisted hydrothermal technique. The materials were evaluated for thermal stability under an oxidative environment and at temperatures between 150 °C and 600 °C. NiS materials showed stability at 300 °C and NiO formation was observed from 350 °C to 600 °C. The annealing effect on the crystalline size and IR absorption of the annealed samples is reported by XRD and FTIR studied. The EPR properties of the annealed materials were studied and compared to the oxidized materials. The transition temperature of 350 °C for the formation of NiO from NiS oxidation was confirmed by calculating the number of spins obtained from the EPR data. Vibrating sample magnetometry (VSM) shows that this pure NiS has both ferromagnetic ordering and paramagnetic domains. Further, the transition temperature of −9 °C of the pure α-NiS nano-compounds was confirmed by performing electrical

  11. Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium

    Science.gov (United States)

    Zaoui, A.; Belabbes, A.; Ahuja, R.; Ferhat, M.

    2011-04-01

    Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (α=86°) and hR2 (α=97.9°) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.

  12. Photocatalytic water splitting for hydrogen generation on cubic, orthorhombic, and tetragonal KNbO3 microcubes

    Science.gov (United States)

    Zhang, Tingting; Zhao, Kun; Yu, Jiaguo; Jin, Jian; Qi, Yang; Li, Huiquan; Hou, Xinjuan; Liu, Gang

    2013-08-01

    Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was

  13. Local structural studies of the cubic Cd{sub 1-x}Ca{sub x}O system through Cd K-edge extended X-ray absorption spectroscopic studies

    Energy Technology Data Exchange (ETDEWEB)

    Srihari, Velaga [Saha Institute of Nuclear Physics, Kolkata (India). Surface Physics Div.; Sridharan, V.; Sankara Sastry, V.; Sundar, C.S. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India). Materials Science Group; Nomura, Masaharu [High Energy Accelerator Research Organization, Tsukuba (Japan). Photon Factory

    2012-07-15

    Cd K-edge extended X-ray absorption fine-structure spectroscopic studies were carried out on Cd{sub 1-x}Ca{sub x}O (0 {<=} x {<=} 0.9) solid solutions and the first and second nearest neighbour (NN) distances and their mean square relative displacement {sigma}{sup 2} were estimated. The first NN distance, d{sub Cd-O}(x), was found to be smaller than its expected value, a(x)/2, obtained from the X-ray diffraction measurements. It increases monotonically and non-linearly with a negative curvature, comparable with that of the a(x) value variation. The variation {sigma}{sup 2} of the 1NN with x is consistent with a disordered solid solution model. The 2NN distances d{sub Cd-Cd}(x) and d{sub Cd-Ca}(x) are found to follow the average values obtained by X-ray diffraction with d{sub Cd-Ca}(x) > d{sub Cd-Cd}(x). From detailed analysis it is argued that the solid solution exhibits a bimodal distribution of the 1NN distances, d{sub Cd-O}(x) and d{sub Ca-O}(x), and that the system belongs to a persistent type. (orig.)

  14. Mineral chemistry of monazite-(Nd, xenotime-(Y, apatite, fluorite and zircon hosting in lamprophyre dyke in Abu Rusheid area, South Eastern Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Mohamed A. Ali

    2012-06-01

    Full Text Available The studied mineralized lamprophyre dyke in Abu Rusheid area is trending NNW-SSE, and occurs withinAbu Rusheid mineralized shear zone, measuring 0.2 - 1.0 m in width and 0.5 - 1.0 km in length. It was emplacedparallel with the Abu Rusheid shear zone. The dyke is mainly composed of plagioclases, amphiboles, mica (musco-vite and biotite, relics of pyroxenes with K-feldspars and quartz derived from surrounding country rocks asphenocrysts embedded in fine-grained groundmass. The lamprophyre dyke hosts REE-minerals monazite-(Nd,xenotime-(Y, and REE-bearing minerals apatite, fluorite, zircon-(Hf, rutile with inclusions of xenotime and ironoxides. The emplacement of lamprophyre dyke caused heating in the mineralized shear zone of Abu Rusheid area.The lamprophyre dyke was subsequently affected by hydrothermal alterations (e.g. chlorite-carbonate, muscovitization,fluoritization.The REE were remobilized from the mineralized shear zones by hydrothermal solutionsand re-precipitatedas REE-minerals xenotime-(Y and monazite-(Nd around flourapatite, fluorite, zircon andrutile. The solid solutions between monazite-(Nd and xenotime-(Y were formed as a product precipitation fromhydrothermal solutions. Also, the apatite mineral in the lamprophyre dyke was subjected to the heating duringthe emplacement, which lead to its alteration and breakdown with concominant precipitation of xenotime-(Yand monazite-(Nd. The chemistry of monazite-(Nd and xenotime-(Y obtained by scanning electron microscopy(SEM, and electron probe microanalysis (EPMA, showed that these minerals are enriched in U and Th. Themonazite-(Nd associated with fluorapatite in the studied dyke is poor in Th (0.02 ≤ Th ≤ 0.81 wt%, but usuallyrich in U (0.92 ≤ U ≤ 2.91 wt%, which indicates that monazite formed as a result of flourapatite metasomatism.

  15. Spectroscopic and computer modelling studies of mixed-cation superionic fluorites

    CSIR Research Space (South Africa)

    Netshisaulu, TT

    2005-10-19

    Full Text Available -heating furnace with beryllium windows. 2.2. Experimental procedure EXAFS measurements around the Cd-K edge (26.716 keV) and the Pb-L3 edge (13.036 keV) were carried out using the Science and Engineering Research Council?s SynchrotronRadiation Source... solutions such as RbBiF4,werealso observed by Catlow and co-workers [1]. Table 3 gives the structural parameters (radial distances and 2sigma 2)determined from the first peaks of the FTs for both Cd-K and Pb-L3 edges in CdF2(xPbF2).Inspection of the table...

  16. Phonon softening induced cubic-to-tetragonal phase transition in ReO3

    Science.gov (United States)

    Liu, Yaming; Zhang, Niu; Jia, Yu; Sun, Qiang; Chao, Mingju

    2015-10-01

    Within density functional theory, the structural, electronic and lattice dynamical properties of ReO3 in cubic Pm-3m and tetragonal P4/mbm phases are studied by using quasiharmonic approximation. The enthalpy-pressure curves show that a phase transition may take place at 5.0 kbar and the nonexistence of imaginary frequency in phonon dispersions demonstrates the two phases are dynamically stable under proper conditions. With the increase of pressure, an obvious softening of M3 mode at M point appears in cubic phase, and a cubic-to-tetragonal phase transition is accompanied with the presence of negative frequency in M3 mode at 5.0 kbar. In detail, one type of O atoms displaced from x = 0.2500 to x = 0.2401, which corresponds to the softening of M3 mode, are responsible for the phase transition. Our theoretical results show that ReO3 can exist in the tetragonal P4/mbm phase, and a cubic-to-tetragonal phase transition will appear at around 5.0 kbar.

  17. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively.

    Science.gov (United States)

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-04-25

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50-15000 μmoL L(-1) (cubic SiC NWs) and 5-8000 μmoL L(-1) (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L(-1) respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility.

  18. In Situ Diffraction from Levitated Solids Under Extreme Conditions-Structure and Thermal Expansion in the Eu 2 O 3 -ZrO 2 System

    Energy Technology Data Exchange (ETDEWEB)

    Maram, Pardha S. [Peter A. Rock Thermochemistry Laboratory and Neat ORU, University of California, Davis, One Shields Avenue 4415 Chemistry Annex Davis California 95616; Ushakov, Sergey V. [Peter A. Rock Thermochemistry Laboratory and Neat ORU, University of California, Davis, One Shields Avenue 4415 Chemistry Annex Davis California 95616; Weber, Richard J. K. [Materials Development, Inc., 3090 Daniels Court Arlington Heights Illinois 60004; X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue Lemont Illinois 60439; Benmore, Chris J. [X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue Lemont Illinois 60439; Navrotsky, Alexandra [Peter A. Rock Thermochemistry Laboratory and Neat ORU, University of California, Davis, One Shields Avenue 4415 Chemistry Annex Davis California 95616; Raveau, B.

    2014-12-31

    The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500 degrees C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200 degrees C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu2O3-ZrO2 binary system were investigated, including the high-temperature order-disorder transformation in Eu2Zr2O7. The disordered fluorite phase is found to be stable above 1900 degrees C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu2Zr2O7 show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6-12.0x10(-6)C(-1). These studies open new vistas for in situ exploration of complex structural changes in high-temperature materials.

  19. Hydrothermal synthesis and crystal structure analysis of two new cadmium bismuthates, CdBi2O6 and Cd0.37Bi0.63O1.79

    Directory of Open Access Journals (Sweden)

    N. Kumada

    2015-09-01

    Full Text Available Two new cadmium bismuthates, CdBi2O6 and Cd0.37Bi0.63O1.79, were prepared by hydrothermal reaction using NaBiO3·nH2O as one of the starting compounds. The crystal structures of these compounds were refined by using synchrotron X-ray powder diffraction data. The former bismuthate has a MnSb2O6-type structure with a hexagonal cell (space group: P321; the cell parameters were a = 9.3641(7 and c = 4.9523(3 Å, and the final R-factors were Rwp = 4.59% and Rp = 3.04%. The latter bismuthate has a fluorite-type structure with a cubic cell (space group: Fm3¯m of a = 5.4110(4 Å, and the final R-factors were Rwp = 4.79% and Rp = 3.57%. These new bismuthates exhibit no photocatalytic activity under visible light.

  20. Assembly of body-centered cubic crystals in hard spheres.

    Science.gov (United States)

    Xu, W-S; Sun, Z-Y; An, L-J

    2011-05-01

    We investigate the crystallization of monodisperse hard spheres confined by two square patterned substrates (possessing the basic character of the body-centered cubic (bcc) crystal structure) at varying substrate separations via molecular dynamics simulation. Through slowly increasing the density of the system, we find that crystallization under the influence of square patterned substrates can set in at lower densities compared with the homogeneous crystallization. As the substrate separation decreases, the density, where crystallization occurs (i.e., pressure drops), becomes small. Moreover, two distinct regimes are identified in the plane of bcc particle fraction and density for the separation range investigated. For large substrate separations, the bcc particle fraction displays a local maximum as the density is increased, and the resulting formed crystals have a polycrystalline structure. However, and more importantly, another situation emerges for small substrate separations: the capillary effects (stemming from the presence of two substrates) overwhelm the bulk driving forces (stemming from the spontaneous thermal fluctuations in the bulk) during the densification, eventually resulting in the formation of a defect-free bcc crystal (unstable with respect to the bulk hard-sphere crystals) by using two square patterned substrates.

  1. Structure and properties of the Mn doped CeO{sub 2} thin film grown on LaAlO{sub 3} (0 0 1) via a modified sol–gel spin-coating technique

    Energy Technology Data Exchange (ETDEWEB)

    Mahmoud, Waleed E., E-mail: w_e_mahmoud@yahoo.com [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Suez Canal University, Faculty of Science, Department of Physics, Ismailia (Egypt); Al-Ghamdi, A.A. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Al-Agel, F.A. [Hail University, College of Science, Department of Physics, Hail (Saudi Arabia); Al-Arfaj, E. [Umm Alqura University, Department of Physics, Makkah (Saudi Arabia); Qaseem University, Physics Department, Qaseem (Saudi Arabia); Shokr, F.S. [King Abdulaziz University, Faculty of Science & Arts, Department of Physics, Rabigh (Saudi Arabia); Al-Gahtany, S.A. [King Abdulaziz University, Faculty of Science for Girls, Department of Physics, Jeddah (Saudi Arabia); Alshahrie, Ahmed [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Hafez, M. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Suez Canal University, Faculty of Science, Department of Physics, Ismailia (Egypt); Bronstein, L.M. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Indiana University, Department of Chemistry, Bloomington, IN 47405 (United States); Beall, Gary W. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Texas State University-San Marcos, Department of Chemistry and Biochemistry, 601 University Dr., San Marcos, TX 78666 (United States)

    2015-08-15

    Highlights: • Mn doped CeO{sub 2} was grown on LaAlO{sub 3} (0 0 1) via sol–gel technique. • The concentration of the Mn ions was varied from 1 to 13 at.%. • The incorporation of 7 at.% of Mn ions was found to provide formation of exceptionally smooth films. • This amount demonstrated the highest saturation magnetization of 1.75 μ{sub B}/Mn and coercive field of 487 Gauss. - Abstract: Here we report Mn doped cerium oxide films prepared on the LaAlO{sub 3} (0 0 1) substrate via an ethylene glycol modified sol–gel spin coating technique and evaluation of their properties as diluted magnetic semiconductors. Cerium oxide was selected because of its high dielectric constant and fluorite cubic structure, matching the silicon and lanthanum aluminate based electronic devices. The concentration of the Mn ions was varied from 1 to 13 at.% and the influence of this concentration on the structure, surface morphology, optical and magnetic properties of these films was studied using scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, ellipsometric spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and magnetic measurements. The incorporation of 7 at.% of Mn ions was found to provide formation of exceptionally smooth films, demonstrating the highest saturation magnetization of 1.75 μ{sub B}/Mn and the coercive field of 487 Gauss. These properties are assigned to the conversion of Ce{sup 4+} to Ce{sup 3+} upon incorporation of Mn ions into the CeO{sub 2} structure and the oxidation of Mn{sup 2+} to Mn{sup 4+}, creating two oxygen vacancies to preserve the cubic structure of cerium oxide and promoting ferromagnetism.

  2. Ab initio LSDA and LSDA+U study of pure and Cd-doped cubic lanthanide sesquioxides

    DEFF Research Database (Denmark)

    Richard, D.; Muñoz, E.L.; Rentería, M.

    2013-01-01

    The electronic, structural, and hyperfine properties of pure and Cd-doped lanthanide (Ln) sesquioxides with the cubic bixbyite structure (Ln2O3, Ln ranging from La to Lu) have been studied using the full-potential augmented plane wave plus local orbital (APW+lo) method within the local spin density...

  3. Cubic B-spline curve approximation by curve unclamping

    OpenAIRE

    Chen, Xiao-Diao; Ma, Weiyin; Paul, Jean-Claude

    2010-01-01

    International audience; A new approach for cubic B-spline curve approximation is presented. The method produces an approximation cubic B-spline curve tangent to a given curve at a set of selected positions, called tangent points, in a piecewise manner starting from a seed segment. A heuristic method is provided to select the tangent points. The first segment of the approximation cubic B-spline curve can be obtained using an inner point interpolation method, least-squares method or geometric H...

  4. On q-power cycles in cubic graphs

    DEFF Research Database (Denmark)

    Bensmail, Julien

    2017-01-01

    In the context of a conjecture of Erdos and Gyárfás, we consider, for any q ≥ 2, the existence of q-power cycles (i.e. with length a power of q) in cubic graphs. We exhibit constructions showing that, for every q ≥ 3, there exist arbitrarily large cubic graphs with no q-power cycles. Concerning...... the remaining case q = 2 (which corresponds to the conjecture of Erdos and Gyárfás), we show that there exist arbitrarily large cubic graphs whose only 2-power cycles have length 4 only, or 8 only....

  5. On q-power cycles in cubic graphs

    DEFF Research Database (Denmark)

    Bensmail, Julien

    2016-01-01

    In the context of a conjecture of Erdos and Gyárfás, we consider, for any q ≥ 2, the existence of q-power cycles (i.e. with length a power of q) in cubic graphs. We exhibit constructions showing that, for every q ≥ 3, there exist arbitrarily large cubic graphs with no q-power cycles. Concerning...... the remaining case q = 2 (which corresponds to the conjecture of Erdos and Gyárfás), we show that there exist arbitrarily large cubic graphs whose only 2-power cycles have length 4 only, or 8 only....

  6. Natural oxidation of InN quantum dots: the role of cubic InN

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, David; Lozano, Juan G.; Herrera, Miriam; Garcia, Rafael [Departamento de Ciencia de los Materiales e Ingenieria Metalurgica y Quimica Inorganica, Universidad de Cadiz, Apdo. 40, E-11510 Puerto Real (Cadiz) (Spain); Browning, Nigel D. [Department of Chemical Engineering and Materials Science, University of California-Davis, One Shields Ave, Davis, CA 95616 (United States); Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Ruffenach, Sandra; Briot, Olivier

    2010-01-15

    The natural aging process occured in indium nitride quantum dots (QDs) heterostructures as a consequence of exposure to the atmosphere has been studied by means of transmission electron microscopy and electron beam related techniques. The comparison between GaN-capped and uncapped InN QDs kept at room conditions during 36 months indicates the structural changes that take place. While the capping layer seems to act in a protective way avoiding any change in the QDs, the uncapped structures suffer a series of phase transformations, where the original wurtzite structure is replaced by a layer of cubic phases. The main constituent of this layer is shown to be bcc-In{sub 2}O{sub 3} formed by the substitution of the nitrogen atoms by oxygen from the atmosphere. This supposes a transformation from a hexagonal to a cubic structure, explained by the existence of an oxygen-rich cubic InN acting as an intermediate phase. The difference in the formation enthalpy between the original and the final product, together with the good match between the crystals would explain this transformation that shows the high instability of InN at environmental conditions. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Electrochemical synthesis and characterization of cubic magnetite nanoparticle in aqueous ferrous perchlorate medium

    Directory of Open Access Journals (Sweden)

    D. Gopi

    2016-09-01

    Full Text Available Electrochemical synthesis of cubic magnetite nanoparticle (MNP in ferrous perchlorate aqueous medium and its spectral investigations have been carried out. The structural property of MNP is evidenced by X-ray diffraction pattern shows the characteristic peaks. Further the vibrational frequencies of MNP are evaluated using FT-IR and Raman spectroscopic techniques. UV–visible spectroscopic studies show the possibility of surface plasmon resonance effect. The cubic structure of MNP has been confirmed by transmission electron microscope (TEM technique and it is also evidenced by scanning electron microscope (SEM. The as-synthesized MNP shows superparamagnetic property which is confirmed by the vibrating sample magnetometer, hence it could be useful for synthesis of very ultra superparamagnetic iron oxide solution (VUSPIO for cancer treatment.

  8. Metastable cubic tin sulfide: A novel phonon-stable chiral semiconductor

    Directory of Open Access Journals (Sweden)

    Jonathan M. Skelton

    2017-03-01

    Full Text Available SnS is a semiconductor of interest for next-generation thin-film photovoltaic devices. The ground-state phase is layered with an orthorhombic (Pnma crystal structure. Anisotropy in the electrical properties has been linked to the low performance of SnS solar cells. These factors make a new cubic phase (π-SnS of immense practical interest. We report the properties of the recently solved crystal structure (P213 of cubic SnS from first-principles. π-SnS is phonon stable, in contrast to the zincblende phase, and lies 2.2 kJ/mol above the ground state. It features an electronic bandgap of 1.7 eV with a chiral modulation of the band-edge states.

  9. Structural, mechanical and thermodynamic properties of AuIn{sub 2} crystal under pressure: A first-principles density functional theory calculation

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Ching-Feng [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Cheng, Hsien-Chie, E-mail: hccheng@fcu.edu.tw [Department of Aerospace and Systems Engineering, Feng Chia University, Taichung 40724, Taiwan (China); Chen, Wen-Hwa, E-mail: whchen@pme.nthu.edu.tw [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

    2015-01-15

    Highlights: • The mechanical and thermodynamic properties of AuIn{sub 2} are reported for the first time. • The calculated lattice constants and elastic properties of AuIn{sub 2} are consistent with the literature data. • The results reveal that AuIn{sub 2} demonstrates low elastic anisotropy, low hardness and high ductility. • It is worth to note that the anisotropic AuIn{sub 2} tends to become elastically isotropic as hydrostatic pressure increases. - Abstract: The structural, mechanical and thermodynamic properties of cubic AuIn{sub 2} crystal in the cubic fluorite structure, and also their temperature, hydrostatic pressure and direction dependences are investigated using first-principles calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized lattice constants of AuIn{sub 2} single crystal are first evaluated, by which its hydrostatic pressure-dependent elastic constants are also derived. Then, the hydrostatic pressure-dependent mechanical characteristics of the single crystal, including ductile/brittle behavior and elastic anisotropy, are explored according to the characterized angular character of atomic bonding, Zener anisotropy factor and directional Young’s modulus. Moreover, the polycrystalline elastic properties of AuIn{sub 2}, such as bulk modulus, shear modulus and Young’s modulus, and its ductile/brittle and microhardness characteristics are assessed versus hydrostatic pressure. Finally, the temperature-dependent Debye temperature and heat capacity of AuIn{sub 2} single crystal are investigated by quasi-harmonic Debye modeling. The present results reveal that AuIn{sub 2} crystal demonstrates low elastic anisotropy, low hardness and high ductility. Furthermore, its heat capacity strictly follows the Debye T{sup 3}-law at temperatures below the Debye temperature, and reaches the Dulong–Petit limit at temperatures far above the Debye temperature.

  10. The Boolean Algebra of Cubical Areas as a Tensor Product in the Category of Semilattices with Zero

    Directory of Open Access Journals (Sweden)

    Nicolas Ninin

    2014-10-01

    Full Text Available In this paper we describe a model of concurrency together with an algebraic structure reflecting the parallel composition. For the sake of simplicity we restrict to linear concurrent programs i.e. the ones with no loops nor branching. Such programs are given a semantics using cubical areas. Such a semantics is said to be geometric. The collection of all these cubical areas enjoys a structure of tensor product in the category of semi-lattice with zero. These results naturally extend to fully fledged concurrent programs up to some technical tricks.

  11. Symmetry transition in the cubic phase of a ternary surfactant system

    OpenAIRE

    Radiman, S.; Toprakcioglu, C.; Faruqi, A.R.

    1990-01-01

    We report a small-angle X-ray and neutron scattering investigation in the cubic phase of the ternary system water/didodecyldimethyl ammonium bromide (DDAB)/octane. We have observed a systematic variation in the lattice parameter as a function of water content, which can be related to the change in interfacial area per unit cell with the aqueous volume fraction. Our results are consistent with a bicontinuous periodic constant mean curvature structure, and show a transition from diamond to body...

  12. Effect of shear on cubic phases in gels of a diblock copolymer

    DEFF Research Database (Denmark)

    Hamley, I.W.; Pople, J.A.; Fairclough, J.P.A.;

    1998-01-01

    The effect of shear on the orientation of cubic micellar phases formed by a poly(oxyethylene)poly(oxybutylene) diblock copolymer in aqueous solution has been investigated using small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS was performed on samples oriented in...... to form a macroscopically oriented domain. Shear only homogenized the sample, producing a powder SAXS pattern from a fcc structure....

  13. Global infinite energy solutions for the cubic wave equation

    OpenAIRE

    Burq, N.; L. Thomann; Tzvetkov, N.

    2012-01-01

    International audience; We prove the existence of infinite energy global solutions of the cubic wave equation in dimension greater than 3. The data is a typical element on the support of suitable probability measures.

  14. Spinning solitons in cubic-quintic nonlinear media

    Indian Academy of Sciences (India)

    Lucian-Cornel Crasovan; Boris A Malomed; Dumitru Mihalache

    2001-11-01

    We review recent theoretical results concerning the existence, stability and unique features of families of bright vortex solitons (doughnuts, or ‘spinning’ solitons) in both conservative and dissipative cubic-quintic nonlinear media.

  15. Stress Intensity of Antiplane Conjugate Cracks in Cubic Quasicrystal

    Institute of Scientific and Technical Information of China (English)

    ZHANG Lei

    2008-01-01

    Based on the theory of Muskhelishvili, the general solutions for stress and strain of conjugate cracks in cubic quasicrystal are obtained, with which the stress intensity factors of cubic quasicrystal at crack tips and the stress distribution functions of phonon and phason fields are given. The results show that though phason field is coupled with phonon field by constitutive equations, the stress intensity factors are not coupled with any other factors.

  16. Direct observation of covalency between O and disordered Pb in cubic PbZrO sub 3

    CERN Document Server

    Aoyagi, S; Sawada, A; Tanaka, H; Harada, J; Nishibori, E; Takata, M; Sakata, M

    2002-01-01

    In cubic PbZrO sub 3 , which undergoes an antiferroelectric phase transition, the distinct disorder of Pb at twelve sites toward the neighboring O is detected for the first time by analyzing high-energy X-ray powder diffraction data. In the charge density distributions, the covalent nature of the Pb-O bond is also revealed, which proves the existence of electron hybridization between O and disordered Pb in cubic PbZrO sub 3. None of these structural characteristics of PbZrO sub 3 were found in the previously studied cubic PbTiO sub 3 structure [Y. Kuroiwa et al.: Phys. Rev. Lett. 87 (2001) 217601], which undergoes a ferroelectric phase transition. This may be a clue to understanding why PbTiO sub 3 and PbZrO sub 3 respectively show ferroelectric and antiferroelectric phase transitions.

  17. Effects of thickness on cubic GaN nucleation layers on GaAs(001) substrates

    Institute of Scientific and Technical Information of China (English)

    X.H.Zheng; X.M.Jiang; 等

    2001-01-01

    The effects of growth time on the structure and morphology of cubic GaN nucleation layers on GaAs(001)substrates by metalorganic chemical vapor deposition (MOCVD) have been investigated using a synchrotron X-ray diffraction(XRD).The XRD results show that the GaN 111 reflections at 54.75° inχ are a measurable component,however the 002 reflections parallel to GaAs(001) surface are not detected.The XRD Φ scans and pole figures give a convincing proof that the GaN nucleation latyers show exactly the cubic symmetrical structure.The coherence lengths along the close-packed direction estuimated from the 111 peak are nanometer order of magnitude,The optimal photoluminescence (PL) spectrum was obtained from the cubic GaN epilayer deposited on the nucleation layer for 60sec.

  18. Serial femtosecond crystallography of soluble proteins in lipidic cubic phase

    Directory of Open Access Journals (Sweden)

    Raimund Fromme

    2015-09-01

    Full Text Available Serial femtosecond crystallography (SFX at X-ray free-electron lasers (XFELs enables high-resolution protein structure determination using micrometre-sized crystals at room temperature with minimal effects from radiation damage. SFX requires a steady supply of microcrystals intersecting the XFEL beam at random orientations. An LCP–SFX method has recently been introduced in which microcrystals of membrane proteins are grown and delivered for SFX data collection inside a gel-like membrane-mimetic matrix, known as lipidic cubic phase (LCP, using a special LCP microextrusion injector. Here, it is demonstrated that LCP can also be used as a suitable carrier medium for microcrystals of soluble proteins, enabling a dramatic reduction in the amount of crystallized protein required for data collection compared with crystals delivered by liquid injectors. High-quality LCP–SFX data sets were collected for two soluble proteins, lysozyme and phycocyanin, using less than 0.1 mg of each protein.

  19. HfO_2and ZrO2 : Comparison of Structures and Thermodynamic and Electronic Properties Based on Ab Initio Calculations and Experiment

    Science.gov (United States)

    Demkov, Alexander A.; Navrotsky, Alexandra

    2001-03-01

    The International Technology Roadmap for Semiconductors (ITRS) predicts that the strategy of scaling complementary metal-oxide-semiconductor (CMOS) devices will come to an abrupt end around the year 2012. The main reason for this will be the unacceptably high leakage current through the silicon dioxide gate with a thickness below 20 ÅFinding a gate insulator alternative to SiO2 has proven to be far from trivial. Hafnium and zirconium dioxides and silicates have been recently considered as gate dielectrics with intermediate dielectric constants. Hafnia and ziconia are important ceramic materials as well, and their phase relations are rather well studied. There is also interest in hafnia as a constituent of ceramic waste forms for plutonium, based on its refractory nature and high neutron absorption cross section. We use a combination of the ab-initio calculations and calorimetry to investigate thermodynamic and electronic properties of hafnia and zirconia. We describe the cubic to tetragonal phase transition in the fluorite structure by computing the total energy surface for zone-edge distortions correct to fourth order in the soft-mode displacement with the strain coupling renormalization included. We compare the two materials using some simple chemical concepts.

  20. Intervalence charge transfer luminescence: Interplay between anomalous and 5d − 4f emissions in Yb-doped fluorite-type crystals

    Energy Technology Data Exchange (ETDEWEB)

    Barandiarán, Zoila, E-mail: zoila.barandiaran@uam.es; Seijo, Luis [Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid (Spain); Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid (Spain)

    2014-12-21

    In this paper, we report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorite-type crystals associated with Yb{sup 2+}–Yb{sup 3+} mixed valence pairs. By means of embedded cluster, wave function theory ab initio calculations, we show that the widely studied, very broad band, anomalous emission of Yb{sup 2+}-doped CaF{sub 2} and SrF{sub 2}, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb{sup 2+}–Yb{sup 3+} mixed valence pairs. The IVCT luminescence is very efficiently excited by a two-photon upconversion mechanism where each photon provokes the same strong 4f{sup 14}–1A{sub 1g}→ 4f{sup 13}({sup 2}F{sub 7/2})5de{sub g}–1T{sub 1u} absorption in the Yb{sup 2+} part of the pair: the first one, from the pair ground state; the second one, from an excited state of the pair whose Yb{sup 3+} moiety is in the higher 4f{sup 13}({sup 2}F{sub 5/2}) multiplet. The Yb{sup 2+}–Yb{sup 3+} → Yb{sup 3+}–Yb{sup 2+} IVCT emission consists of an Yb{sup 2+} 5de{sub g} → Yb{sup 3+} 4f{sub 7/2} charge transfer accompanied by a 4f{sub 7/2} → 4f{sub 5/2} deexcitation within the Yb{sup 2+} 4f{sup 13} subshell: [{sup 2}F{sub 5/2}5de{sub g},{sup 2}F{sub 7/2}] → [{sup 2}F{sub 7/2},4f{sup 14}]. The IVCT vertical transition leaves the oxidized and reduced moieties of the pair after electron transfer very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are subtracted from the normal emission. The IVCT energy diagrams resulting from the quantum mechanical calculations explain the different luminescent properties of Yb-doped CaF{sub 2}, SrF{sub 2}, BaF{sub 2}, and SrCl{sub 2}: the presence of IVCT luminescence in Yb-doped CaF{sub 2} and SrF{sub 2}; its coexistence with regular 5d-4f emission in SrF{sub 2}; its absence in BaF{sub 2} and SrCl{sub 2}; the quenching of

  1. Spinor bose gases in cubic optical lattice

    Energy Technology Data Exchange (ETDEWEB)

    Mobarak, Mohamed Saidan Sayed Mohamed

    2014-01-27

    In recent years the quantum simulation of condensed-matter physics problems has resulted from exciting experimental progress in the realm of ultracold atoms and molecules in optical lattices. In this thesis we analyze theoretically a spinor Bose gas loaded into a three-dimensional cubic optical lattice. In order to account for different superfluid phases of spin-1 bosons with a linear Zeeman effect, we work out a Ginzburg-Landau theory for the underlying spin-1 Bose-Hubbard model. To this end we add artificial symmetry-breaking currents to the spin-1 Bose-Hubbard Hamiltonian in order to break the global U (1) symmetry. With this we determine a diagrammatic expansion of the grand-canonical free energy up to fourth order in the symmetry-breaking currents and up to the leading non-trivial order in the hopping strength which is of first order. As a cross-check we demonstrate that the resulting grand-canonical free energy allows to recover the mean-field theory. Applying a Legendre transformation to the grand-canonical free energy, where the symmetry-breaking currents are transformed to order parameters, we obtain the effective Ginzburg-Landau action. With this we calculate in detail at zero temperature the Mott insulator-superfluid quantum phase boundary as well as condensate and particle number density in the superfluid phase. We find that both mean-field and Ginzburg-Landau theory yield the same quantum phase transition between the Mott insulator and superfluid phases, but the range of validity of the mean-field theory turns out to be smaller than that of the Ginzburg-Landau theory. Due to this finding we expect that the Ginzburg-Landau theory gives better results for the superfluid phase and, thus, we restrict ourselves to extremize only the effective Ginzburg-Landau action with respect to the order parameters. Without external magnetic field the superfluid phase is a polar (ferromagnetic) state for anti-ferromagnetic (ferromagnetic) interactions, i.e. only the

  2. Pharmacokinetics and enhanced oral bioavailability in beagle dogs of cyclosporine A encapsulated in glyceryl monooleate/poloxamer 407 cubic nanoparticles

    Directory of Open Access Journals (Sweden)

    Jie Lai

    2009-12-01

    Full Text Available Jie Lai1,2, Yi Lu1, Zongning Yin2, Fuqiang Hu3, Wei Wu11School of Pharmacy, Fudan University, Shanghai, China, 2West China School of Pharmacy, Sichuan University, Chengdu, China, 3School of Pharmacy, Zhejiang University, Hangzhou, ChinaAbstract: Efforts to improve the oral bioavailability of cyclosporine A (CyA remains a challenge in the field of drug delivery. In this study, glyceryl monooleate (GMO/poloxamer 407 cubic nanoparticles were evaluated as potential vehicles to improve the oral bioavailability of CyA. Cubic nanoparticles were prepared via the fragmentation of a bulk GMO/poloxamer 407 cubic phase gel by sonication and homogenization. The cubic inner structure formed was verified using Cryo-TEM. The mean diameters of the nanoparticles were about 180 nm, and the entrapment efficiency of these particles for CyA was over 85%. The in vitro release of CyA from these nanoparticles was less than 5% at 12 h. The results of a pharmacokinetic study in beagle dogs showed improved absorption of CyA from cubic nanoparticles as compared to microemulsion-based Neoral®; higher Cmax (1371.18 ± 37.34 vs 969.68 ± 176.3 ng mL-1, higher AUC0–t (7757.21 ± 1093.64 vs 4739.52 ± 806.30 ng h mL-1 and AUC0–∞ (9004.77 ± 1090.38 vs 5462.31 ± 930.76 ng h mL-1. The relative oral bioavailability of CyA cubic nanoparticles calculated on the basis of AUC0–∞ was about 178% as compared to Neoral®. The enhanced bioavailability of CyA is likely due to facilitated absorption by cubic nanoparticles rather than improved release.Keywords: nanoparticles, cubosomes, cyclosporine A, glyceryl monooleate, oral drug delivery, bioavailability, beagle dogs

  3. Modèles d'arrangements anioniques locaux dans les solutions solides à structure fluorine stabilisée par dopage Na 0.5- xY 0.5+ xF 2+2 x

    Science.gov (United States)

    Pontonnier, L.; Patrat, G.; Aléonard, S.

    1990-07-01

    Electron, X-ray, and neutron diffuse scattering measurements have been performed on single crystals of the Na 0.5- xY 0.5+ xF 2+2 x solid-solutions having a doped stabilized fluorite structure. The localization and the shape of the diffuse scattering agree with a description of the local structure using a tridimensional arrangement of microdomains. A model of the fluorine local order agreeing with the refinements of the average structure is proposed. It assumes that all the interstitial atoms are trapped in thermally stable [NaY 3F 12] 2- clusters diluted in a fluorite matrix. The high inelastic contribution to the diffuse scattering indicates that the fluorine sublattice of the fluorite structure is strongly affected by anharmonic vibrations.

  4. MBE growth of cubic AlN on 3C-SiC substrate

    Energy Technology Data Exchange (ETDEWEB)

    Schupp, Thorsten; Lischka, Klaus; As, Donat Josef [Department of Physics, University of Paderborn, Warburger Str. 100, 33095 Paderborn (Germany); Rossbach, Georg; Schley, Pascal; Goldhahn, Ruediger [Institut fuer Physik, Technische Universitaet Ilmenau, PF 100565, 98684 Ilmenau (Germany); Roeppischer, Marcus; Esser, Norbert; Cobet, Christoph [Department Berlin, ISAS - Institute for Analytical Sciences, Albert-Einstein-Str. 9, 12489 Berlin (Germany)

    2010-06-15

    We present our recent results on the growth of cubic AlN (001) layers by plasma assisted molecular beam epitaxy (PAMBE) using freestanding 3C-SiC (001) substrate. For high-quality c-AlN layers reflection high-electron energy diffraction (RHEED) patterns in all azimuths show RHEED patterns of the cubic lattice, hexagonal reflections are absent. High-resolution X-ray diffraction (HRXRD) measurements confirm the cubic structure of the c-AlN layers with a lattice parameter of 4.373A. Atomic force microscopy (AFM) scans show an atomically smooth surface with a roughness of 0.2 nm RMS. Ellipsometry studies yield the dielectric function (DF) of c-AlN from 1 to 10 eV. The direct gap is determined with 5.93 eV at room temperature, while the indirect one is below 5.3 eV (onset of adsorption). The high-energy part of the DF is dominated by two transitions at 7.20 and 7.95 eV attributed to critical points of the band structure. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  5. Docosapentaenoic acid (DPA) is a critical determinant of cubic membrane formation in amoeba Chaos mitochondria.

    Science.gov (United States)

    Deng, Yuru; Almsherqi, Zakaria A; Shui, Guanghou; Wenk, Markus R; Kohlwein, Sepp D

    2009-09-01

    Very long-chain polyunsaturated fatty acids (VLC-PUFAs), such as docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA), have recently made it to the realm of "magical molecules" based on their multiple presumably beneficial effects in biological systems, making these PUFAs particularly interesting in biomedicine. Their specific biological functions, however, remain enigmatic. Here we provide evidence derived from studies in the amoeba Chaos that indicates a structural role for omega-6 DPA in cell membrane organization, which may help to explain the multiple diverse effects of VLC-PUFA in healthy and diseased states. Amoeba Chaos mitochondria undergo a remarkable and reversible morphological transition into cubic morphology on starvation. This morphological transition is reflected in major changes in fatty acid and lipid composition, as determined by gas liquid chromatography and mass spectrometry, in particular by a drastic increase in C22:5 modified phosphatidylcholine plasmalogen, phosphatidylethanolamine plasmalogen, and phosphatidylinositol species. Liposomes produced in vitro from lipids of starved amoeba cells show a high propensity to form hexagonal tubular and cubic morphologies. Addition of omega-6 DPA, but not of omega-3 DPA, to the cell culture also induced mitochondrial membrane transformation into cubic morphology in fed cells, demonstrating for the first time an important structural role of omega-6 DPA-containing lipids in cell membrane organization.

  6. Cubic Gallium Nitride on Micropatterned Si (001) for Longer Wavelength LEDs

    Energy Technology Data Exchange (ETDEWEB)

    Durniak, Mark T. [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Materials Science and Engineering; Chaudhuri, Anabil [Univ. of New Mexico, Albuquerque, NM (United States). Center for High Technology Materials; Smith, Michael L. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Advanced Material Sciences; Allerman, Andrew A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Advanced Material Sciences; Lee, S. C. [Univ. of New Mexico, Albuquerque, NM (United States). Center for High Technology Materials; Brueck, S. R. J. [Univ. of New Mexico, Albuquerque, NM (United States). Center for High Technology Materials; Wetzel, Christian [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Physics, Applied Physics, and Astronomy and Dept. of Materials Science and Engineering

    2016-03-01

    GaInN/GaN heterostructures of cubic phase have the potential to overcome the limitations of wurtzite structures commonly used for light emitting and laser diodes. Wurtzite GaInN suffers from large internal polarization fields, which force design compromises ( 0001 ) towards ultra-narrow quantum wells and reduce recombination volume and efficiency. Cubic GaInN microstripes grown at Rensselaer Polytechnic Institute by metal organic vapor phase epitaxy on micropatterned Si , with {111} v-grooves oriented along Si ( 001 ) , offer a system free of internal polarization fields, wider quantum wells, and smaller <00$\\bar1$> bandgap energy. We prepared 6 and 9 nm Ga x In 1-x N/GaN single quantum well structures with peak wavelength ranges from 520 to 570 nm with photons predominately polarized perpendicular to the grooves. We estimate a cubic InN composition range of 0 < x < 0.5 and an upper limit of the internal quantum efficiency of 50%. Stripe geometry and polarization may be suitable for mode confinement and reduced threshold stimulated emission.

  7. The influence of coordinated defects on inhomogeneous broadening in cubic lattices

    Science.gov (United States)

    Matheson, P. L.; Sullivan, Francis P.; Evenson, William E.

    2016-12-01

    The joint probability distribution function (JPDF) of electric field gradient (EFG) tensor components in cubic materials is dominated by coordinated pairings of defects in shells near probe nuclei. The contributions from these inner shell combinations and their surrounding structures contain the essential physics that determine the PAC-relevant quantities derived from them. The JPDF can be used to predict the nature of inhomogeneous broadening (IHB) in perturbed angular correlation (PAC) experiments by modeling the G 2 spectrum and finding expectation values for V zz and η. The ease with which this can be done depends upon the representation of the JPDF. Expanding on an earlier work by Czjzek et al. (Hyperfine Interact. 14, 189-194, 1983), Evenson et al. (Hyperfine Interact. 237, 119, 2016) provide a set of coordinates constructed from the EFG tensor invariants they named W 1 and W 2. Using this parameterization, the JPDF in cubic structures was constructed using a point charge model in which a single trapped defect (TD) is the nearest neighbor to a probe nucleus. Individual defects on nearby lattice sites pair with the TD to provide a locus of points in the W 1- W 2 plane around which an amorphous-like distribution of probability density grows. Interestingly, however, marginal, separable PDFs appear adequate to model IHB relevant cases. We present cases from simulations in cubic materials illustrating the importance of these near-shell coordinations.

  8. Cubic Single Crystal Representations in Classical and Size-dependent Couple Stress Elasticity

    CERN Document Server

    Bansal, Dipanshu; Aref, Amjad J; Hadjesfandiari, Ali R

    2015-01-01

    Beginning with Cosserat theory in the early 20th century, there have been several different formulations for size-dependent elastic response. In this paper, we concentrate on the application of classical Cauchy theory and the recent parsimonious consistent couple stress theory to model a homogeneous linear elastic solid, exemplified by a pure single crystal with cubic structure. The focus is on an examination of elastodynamic response based upon wave velocities from ultrasonic excitation and phonon dispersion curves, along with adiabatic bulk moduli measurements. In particular, we consider in detail elastic parameter estimation within classical elasticity and consistent couple stress theory for four different cubic single crystals (NaCl, KCl, Cu, CuZn). The classical theory requires the estimation of three independent material parameters, while only one additional parameter relating skew-symmetric mean curvature to skew-symmetric couple-stress is needed for the size-dependent consistent couple stress theory. ...

  9. The Electric Field of a Uniformly Charged Non-Conducting Cubic Surface

    CERN Document Server

    McCreery, Kaitlin

    2016-01-01

    As an integrative and insightful example for undergraduates learning about electrostatics, we discuss how to use symmetry, Coulomb's Law, superposition, Gauss's law, and visualization to understand the electric field produced by a non-conducting cubic surface that is covered with a uniform surface charge density. We first discuss how to deduce qualitatively, using only elementary physics, the surprising fact that the electric field inside the cubic surface is nonzero and has a complex structure, pointing inwards towards the cube center from the midface of each cube and pointing outwards towards each edge and corner. We then discuss how to understand the quantitative features of the electric field by plotting an analytical expression for E along symmetry lines and on symmetry surfaces. This example would be a good choice for group problem solving in a recitation or flipped classroom.

  10. PVTx measurements of the N-methylpyrrolidone/methanol mixed solvent: cubic and SAFT EOS analyses.

    Science.gov (United States)

    Aparicio, Santiago; García, Begoña; Alcalde, Rafael; Davila, María J; Leal, José M

    2006-04-06

    The PVTx behavior for the x N-methylpyrrolidone (NMP) + (1 - x) methanol compressed liquid solvent is reported over the full composition range and within wide pressure and temperature ranges. The derived excess properties were analyzed in terms of structural effects and intermolecular interactions and revealed strong H-bonding heteroassociations between the two components. The cubic equations of state by Soave (SRK), Peng-Robinson (PR), Patel-Teja (PT), and Sako-Wu-Prausnitz (SWP), and the statistical associating fluid theory (SAFT) equation of state, combined with a number of selected mixing rules, were used to correlate and predict the behavior of both the pure components and mixed solvent. While the classical cubic equations of state were not successful in describing the properties of this system, the SWP equation of state and the SAFT yielded reasonably good results.

  11. Nanosize stabilization of cubic and tetragonal phases in reactive plasma synthesized zirconia powders

    Energy Technology Data Exchange (ETDEWEB)

    Jayakumar, S., E-mail: sjayakumar.physics@gmail.com [Research and Development Centre, Bharathiar University, Coimbatore 641 014 (India); Department of Physics, Pollachi Institute of Engineering and Technology, Pollachi 642 205 (India); Ananthapadmanabhan, P.V.; Thiyagarajan, T.K. [Laser and Plasma Technology Division, BARC, Trombay, Mumbai 400 085 (India); Perumal, K. [Vision for Wisdom, Temple of Consciousness, Aliyar 642 101 (India); Mishra, S.C. [Department of Metallurgical and Materials Engg, National Institute of Technology, Rourkela 769 008 (India); Suresh, G. [Department of Physics, Park College of Engineering and Technology, Coimbatore 641 659 (India); Su, L.T.; Tok, A.I.Y. [School of Materials Science and Engg, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639 798 (Singapore)

    2013-06-15

    Pure zirconium oxide powders with particle size 2–33 nm are synthesized by reactive plasma processing. Transmission electron microscopy investigation of these particles revealed size dependent behavior for their phase stabilization. The monoclinic phase is found to be stable when particle size is ≥20 nm; Tetragonal is found to be stabilized in the range of 7–20 nm and as the particle size decreases to 6 nm and less, the cubic phase is stabilized. - Highlights: ► Direct conversion of micron-sized zirconium hydride powder to single crystal ZrO{sub 2} nanopowder. ► Size dependent stabilization of cubic, tetragonal and monoclinic phases in the reactive plasma synthesized ZrO{sub 2} nanopowder. ► Transmission electron microscopic investigation to identify particles of different sizes and their corresponding phase structure.

  12. Low energy radiation stability of nano-crystalline cubic Zirconia films

    Science.gov (United States)

    Kalita, Parswajit; Ghosh, Santanu; Avasthi, Devesh K.

    2016-07-01

    The radiation stability of nano-crystalline cubic Zirconia films was investigated under 41 keV He ion irradiation. These ions were chosen to simulate alpha particles (produced during fission events) because of the similar electronic energy loss in Zirconia. The ZrO2 films, with an average grain size of 8 nm, were grown on Si (1 0 0) substrates by electron beam assisted thermal evaporation. Although the cubic structure was retained upon irradiation, a slight reduction in crystallinity in the irradiated films was detected as compared to the as-deposited film. No bulk amorphization was however observed for any of the fluences and hence these films are radiation tolerant to alpha particles.

  13. Performance evaluation of a micro ultrasonic motor using a one-cubic-millimeter stator.

    Science.gov (United States)

    Mashimo, Tomoaki

    2015-10-01

    A piezoelectric ultrasonic motor has two significant advantages, high energy density and simple structure, and these advantages can help in the miniaturization of the motor. We build a prototype micro ultrasonic motor using a stator with a volume of approximately 1 cubic millimeter. To evaluate its representative performance values (torque, angular velocity, and energy efficiency), we built an experimental setup and operated the prototype motor by varying experimental conditions, such as the preload between the stator and rotor and the amplitude of voltages applied to motor. The performance values obtained at the millimeter to sub-millimeter scale are discussed analytically using the macro scale models of ultrasonic motors. Experimentally, the prototype motor has generated a torque of more than 10 μNm with a 1-cubic-millimeter stator. The motor described herein is now the smallest micro ultrasonic motor with a practical torque, although its efficiency is still low.

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

    Institute of Scientific and Technical Information of China (English)

    何卫中; 方志杰

    2012-01-01

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

  15. Synthesis of Gold Nanoparticle-Embedded Silver Cubic Mesh Nanostructures Using AgCl Nanocubes for Plasmonic Photocatalysis.

    Science.gov (United States)

    Joo, Jang Ho; Kim, Byung-Ho; Lee, Jae-Seung

    2017-09-13

    A novel room-temperature aqueous synthesis for gold nanoparticle-embedded silver cubic mesh nanostructures using AgCl templates via a template-assisted coreduction method is developed. The cubic AgCl templates are coreduced in the presence of AuCl4(-) and Ag(+) , resulting in the reduction of AuCl4(-) into gold nanoparticles on the outer region of AgCl templates, followed by the reduction of AgCl and Ag(+) into silver cubic mesh nanostructures. Removal of the template clearly demonstrates the delicately designed silver mesh nanostructures embedded with gold nanoparticles. The synthetic mechanism, structural properties, and surface functionalization are spectroscopically investigated. The plasmonic photocatalysis of the cubic mesh nanostructures for the degradation of organic pollutants and removal of highly toxic metal ions is investigated; the photocatalytic activity of the cubic mesh nanostructures is superior to those of conventional TiO2 catalysts and they are catalytically functional even in natural water, owing to their high surface area and excellent chemical stability. The synthetic development presented in this study can be exploited for the highly elaborate, yet, facile design of nanomaterials with outstanding properties. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Cubic wavefunction deformation of compressed atoms

    CERN Document Server

    Portela, Pedro Calvo

    2015-01-01

    We hypothesize that in a non-metallic crystalline structure under extreme pressures, atomic wavefunctions deform to adopt a reduced rotational symmetry consistent with minimizing interstitial space in the crystal. We exemplify with a simple numeric variational calculation that yields the energy cost of this deformation for Helium to 25%. Balancing this with the free energy gained by tighter packing we obtain the pressures required to effect such deformation. The consequent modification of the structure suggests a decrease in the resistance to tangential stress, and an associated decrease of the crystal's shear modulus. The atomic form factor is also modified. We also compare with neutron matter in the interior of compact stars.

  17. The phase space of the focused cubic Schroedinger equation: A numerical study

    Energy Technology Data Exchange (ETDEWEB)

    Burlakov, Yuri O. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    1998-05-01

    distinctly different components. They point out the interesting fact that the phase space into distinctly different components. They point out the interesting fact that the phase transition type behavior of the discretized cubic Schroedinger equation can be observed in a discretization with as few as 2 points. The refinement of the discretization does not change the global picture qualitatively. The authors vary two parameters in the canonical ensemble of the cubic Schroedinger equation: the first parameter is the temperature, the second one is a certain constraint on the function space. They demonstrate that at a fixed low temperature, as the constraint varies, the canonical ensemble of the cubic Schroedinger equation undergoes a bifurcation which is manifested both in the change in the shape of the typical function and in a corresponding change of the structure of the phase space.

  18. Low temperature synthesis of fluorite-type Ce-based oxides of composition Ln₂Ce₂O₇ (Ln = Pr, Nd and Eu): photodegradation and Luminescence studies

    Indian Academy of Sciences (India)

    M MALATHI; K SREENU; GUNDEBOINA RAVI; P VIJAYA KUMAR; CH SUDHAKAR REDDY; RAVINDER GUJE; RADHA VELCHURI; M VITHAL

    2017-08-01

    In this work, we have studied the structural behavior of Fluortie-type (F-type) Ce-based oxides of compositions Ln₂Ce₂O₇ (Ln = Pr, Nd and Eu). F-type oxides can be considered as multi-functional materials due to the deficiency of anions. Pr₂Ce₂O₇ (PCO), Nd₂Ce₂O₇ (NCO) and Eu₂Ce₂O₇ (ECO) were prepared by ethylene glycol-assisted sol–gel method. The structural investigation of these oxides was carried out by Powder XRD and Rietveld refinement. All the materials were found to crystallize in the cubic lattice with space group $Fm\\bar{3}m$. Raman spectra of these materials are reliable with their XRD data. The morphology and bandgap energy of all the samples were obtained from SEM and KM plot, respectively. The visible light photocatalytic performance of these oxides was examined against the degradation of methylene blue under ambient conditions. The photoluminescence property of the rare earth ionswas also studied, and the color coordinates were calculated using CIE 1931 chromaticity.

  19. Modelling term structure of interest rate in T-bill market based on negative exponential cubic smooth L1-spline%国债市场利率期限结构建模——负指数立方L1平滑样条

    Institute of Scientific and Technical Information of China (English)

    吴泽福

    2012-01-01

    Based on the comparision of basic static estimate methods of term structure of interest rate (TSIR), we improved B-spline function estimate method, which involved optimization on estimation programmes, node numbers choice, and node placement design. To overcome the subjective effect of B-spline node distribution and C2 smoothness condition of discount function, we introduced negative exponential smoothness cubic Li-spline optimization technology with minimum constraint function of estimation error from quadratic sum to absolute value and minimum volatility of discount function, to increase the estimation reliability and prediction ability of short-term interest rate's volatility structure mutation, improve the advantage on depicting the long-term interest rate volatility trend, and reduce the excessive volatility of discount function.%通过对比国内外利率期限结构静态估计模型的优劣,分析节点数目变化和定位改进B样条函数对利率期限结构静态估计的误差,构建最小化定价误差的节点组合布局搜索程序,并引入负指数平滑立方L1样条优化模型,将误差函数最小化结构从平方和最小化转化为误差距离最小化,权衡拟合误差绝对距离最小化与贴现函数波动性约束,克服B样条函数对节点数目与定位的人工干预和放宽对贴现函数的二阶平滑要求,保留B样条函数刻画中长期利率波动趋势的优势,增强对短期利率波动结构突变的估计和预测能力,提高定价精确度和缓解利率期限结构曲线的过度波动问题.

  20. Cluster-assembled cubic zirconia films with tunable and stable nanoscale morphology against thermal annealing

    Energy Technology Data Exchange (ETDEWEB)

    Borghi, F.; Lenardi, C.; Podestà, A.; Milani, P., E-mail: pmilani@mi.infn.it [CIMAINA and Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano (Italy); Sogne, E. [CIMAINA and Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano (Italy); European School of Molecular Medicine (SEMM), IFOM-IEO, Milano (Italy); Merlini, M. [Dipartimento di Scienze della Terra “Ardito Desio”, Università degli Studi di Milano, via Mangiagalli 32, 20133 Milano (Italy); Ducati, C. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2016-08-07

    Nanostructured zirconium dioxide (zirconia) films are very promising for catalysis and biotechnological applications: a precise control of the interfacial properties of the material at different length scales and, in particular, at the nanoscale, is therefore necessary. Here, we present the characterization of cluster-assembled zirconia films produced by supersonic cluster beam deposition possessing cubic structure at room temperature and controlled nanoscale morphology. We characterized the effect of thermal annealing in reducing and oxidizing conditions on the crystalline structure, grain dimensions, and topography. We highlight the mechanisms of film growth and phase transitions, which determine the observed interfacial morphological properties and their resilience against thermal treatments.

  1. First-principles comparison of the cubic and tetragonal phases of Mo 3Sb7

    KAUST Repository

    Nazir, Safdar

    2011-03-01

    Using ab initio density functional based methods, we study the normal metal state properties of the ∼3 K Mo3Sb7 superconductor, in its high temperature cubic and low temperature tetragonal structures. Although the density of states at the Fermi energy is reasonably high in both structures, our calculations unequivocally show that there exists no long range magnetic ordering in this system. We also address the optical properties of the compound. The magnetism in Mo3Sb7 is studied by fixed spin moment calculations, which yield a shallow non-magnetic minimum, thus inferring propensity to a magnetic instability. © 2011 Elsevier B.V. All rights reserved.

  2. Cluster-assembled cubic zirconia films with tunable and stable nanoscale morphology against thermal annealing

    KAUST Repository

    Borghi, F.

    2016-08-05

    Nanostructured zirconium dioxide (zirconia) films are very promising for catalysis and biotechnological applications: a precise control of the interfacial properties of the material at different length scales and, in particular, at the nanoscale, is therefore necessary. Here, we present the characterization of cluster-assembled zirconia films produced by supersonic cluster beam deposition possessing cubic structure at room temperature and controlled nanoscale morphology. We characterized the effect of thermal annealing in reducing and oxidizing conditions on the crystalline structure, grain dimensions, and topography. We highlight the mechanisms of film growth and phase transitions, which determine the observed interfacial morphological properties and their resilience against thermal treatments. Published by AIP Publishing.

  3. Molecular dynamics simulation of kink in 《100》 edge dislocation in body centred cubic iron

    Institute of Scientific and Technical Information of China (English)

    CHEN LiQun; WANG ChongYu; YU Tao

    2007-01-01

    Using the molecular dynamics method, we have constructed two kink models corresponding to the {010} and {011} edge dislocations (EDs) in body centred cubic (bcc) Fe.It is found that the geometric structure of a kink depends on the type of edge dislocation and the structural energies of the atoms sites in the dislocation core region.The formation energies, migration energies and widths of the kinks in different types of EDs are calculated.The results show that formation and migration of the kink in the {010} edge dislocation are difficult.The {011} edge dislocation moves primarily through kink nucleation, rather than kink migration.

  4. Superconductivity in cubic noncentrosymmetric PdBiSe Crystal

    Science.gov (United States)

    Joshi, B.; Thamizhavel, A.; Ramakrishnan, S.

    2015-03-01

    Mixing of spin singlet and spin triplet superconducting pairing state is expected in noncentrosymmetric superconductors (NCS) due to the inherent presence of Rashba-type antisymmetric spin-orbit coupling. Unlike low symmetry (tetragonal or monoclinic) NCS, parity is isotropicaly broken in space for cubic NCS and can additionally lead to the coexistence of magnetic and superconducting state under certain conditions. Motivated with such enriched possibility of unconventional superconducting phases in cubic NCS we are reporting successful formation of single crystalline cubic noncentrosymmetric PdBiSe with lattice parameter a = 6.4316 Å and space group P21 3 (space group no. 198) which undergoes to superconducting transition state below 1.8 K as measured by electrical transport and AC susceptibility measurements. Significant strength of Rashba-type antisymmetric spin-orbit coupling can be expected for PdBiSe due to the presence of high Z (atomic number) elements consequently making it potential candidate for unconventional superconductivity.

  5. Cubic interactions of Maxwell-like higher spins

    CERN Document Server

    Francia, Dario; Mkrtchyan, Karapet

    2016-01-01

    We study the cubic vertices for Maxwell-like higher-spins in flat space. Reducibility of their free spectra implies that a single cubic vertex involving any three fields subsumes a number of couplings among different particles of various spins. The resulting vertices do not involve traces of the fields and in this sense are simpler than their Fronsdal counterparts. We propose an extension of both the free theory and of its cubic deformation to a more general class of partially reducible systems, that one can obtain from the original theory upon imposing trace constraints of various orders. The key to our results is a version of the Noether procedure allowing to systematically account for the deformations of the transversality conditions to be imposed on the gauge parameters at the free level.

  6. Extended temperature dependence of elastic constants in cubic crystals.

    Science.gov (United States)

    Telichko, A V; Sorokin, B P

    2015-08-01

    To extend the theory of the temperature dependence of the elastic constants in cubic crystals beyond the second- and third-order elastic constants, the fourth-order elastic constants, as well as the non-linearity in the thermal expansion temperature dependence, have been taken into account. Theoretical results were represented as temperature functions of the effective elastic constants and compared with experimental data for a number of cubic crystals, such as alkali metal halides, and elements gold and silver. The relations obtained give a more accurate description of the experimental temperature dependences of second-order elastic constants for a number of cubic crystals, including deviations from linear behavior. A good agreement between theoretical estimates and experimental data has been observed.

  7. Hardness and thermal stability of cubic silicon nitride

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Kragh, Flemming; Frost, D. J.

    2001-01-01

    The hardness and thermal stability of cubic spinel silicon nitride (c-Si3N4), synthesized under high-pressure and high-temperature conditions, have been studied by microindentation measurements, and x-ray powder diffraction and scanning electron microscopy, respectively The phase at ambient...... temperature has an average hardness of 35.31 GPa, slightly larger than SiO2 stishovite, which is often referred to as the third hardest material after diamond and cubic boron nitride. The cubic phase is stable up to 1673 K in air. At 1873 K, alpha -and beta -Si3N4 phases are observed, indicating a phase...... transformation sequence of c-to-alpha -to-beta -Si3N4 phases....

  8. Image interpolation by two-dimensional parametric cubic convolution.

    Science.gov (United States)

    Shi, Jiazheng; Reichenbach, Stephen E

    2006-07-01

    Cubic convolution is a popular method for image interpolation. Traditionally, the piecewise-cubic kernel has been derived in one dimension with one parameter and applied to two-dimensional (2-D) images in a separable fashion. However, images typically are statistically nonseparable, which motivates this investigation of nonseparable cubic convolution. This paper derives two new nonseparable, 2-D cubic-convolution kernels. The first kernel, with three parameters (designated 2D-3PCC), is the most general 2-D, piecewise-cubic interpolator defined on [-2, 2] x [-2, 2] with constraints for biaxial symmetry, diagonal (or 90 degrees rotational) symmetry, continuity, and smoothness. The second kernel, with five parameters (designated 2D-5PCC), relaxes the constraint of diagonal symmetry, based on the observation that many images have rotationally asymmetric statistical properties. This paper also develops a closed-form solution for determining the optimal parameter values for parametric cubic-convolution kernels with respect to ensembles of scenes characterized by autocorrelation (or power spectrum). This solution establishes a practical foundation for adaptive interpolation based on local autocorrelation estimates. Quantitative fidelity analyses and visual experiments indicate that these new methods can outperform several popular interpolation methods. An analysis of the error budgets for reconstruction error associated with blurring and aliasing illustrates that the methods improve interpolation fidelity for images with aliased components. For images with little or no aliasing, the methods yield results similar to other popular methods. Both 2D-3PCC and 2D-5PCC are low-order polynomials with small spatial support and so are easy to implement and efficient to apply.

  9. Synthesis and characterization of cubic mesoporous bridged polysilsesquioxane for removing organic pollutants from water.

    Science.gov (United States)

    Lin, Derong; Zhao, Qing; Hu, Lijiang; Xing, Baoshan

    2014-05-01

    Hexane, octane, phenyl, and biphenyl-bridged bis(triethoxysilyl) precursors were used in synthesizing cubic mesoporous bridged polysilsesquioxane (BPS) copolymers. Structural characterization was carried out by FTIR, small angle XRD, Brunauer-Emmett-Teller-N2 sorption, (1)H NMR, and TEM. We successfully synthesized both "rigid" and "soft" 3D cubic mesoporous BPS with high surface area and pore volume, as attested by the comprehensive characterization data. Adsorption of pyrene, phenanthrene, nitrobenzene, and 2,4-dichlorophenol on BPS was greatly affected by adsorbate properties, i.e., Kow, solvation properties and molecular size. Hydrophobic interaction dominantly controlled organic pollutants' sorption on BPS. Other interactions, e.g., π-π and H-bond interactions, also have effects on sorption as indicated by Kow normalized sorption isotherms. Rigid aromatic BPS (phenyl and biphenyl) showed a higher sorption capacity than soft aliphatic BPS (hexane and octane). A conceptual model was proposed to further explain the phenomena. This study suggests a promising application of cubic mesoporous BPS in wastewater treatment.

  10. Dielectric properties and microstructural characterization of cubic pyrochlored bismuth magnesium niobates

    KAUST Repository

    Zhang, Yuan

    2013-08-06

    Cubic bismuth pyrochlores in the Bi2O3 Bi 2O3-MgO-Nb2O5 Nb2O 5 system have been investigated as promising dielectric materials due to their high dielectric constant and low dielectric loss. Here, we report on the dielectric properties and microstructures of cubic pyrochlored Bi 1.5 MgNb 1.5 O 7 Bi1.5MgNb1.5O7 (BMN) ceramic samples synthesized via solid-state reactions. The dielectric constant (measured at 1 MHz) was measured to be ∼ 120 ∼120 at room temperature, and the dielectric loss was as low as 0.001. X-ray diffraction patterns demonstrated that the BMN samples had a cubic pyrochlored structure, which was also confirmed by selected area electron diffraction (SAED) patterns. Raman spectrum revealed more than six vibrational models predicted for the ideal pyrochlore structure, indicating additional atomic displacements of the A and O′ O\\' sites from the ideal atomic positions in the BMN samples. Structural modulations of the pyrochlore structure along the [110] and [121] directions were observed in SAED patterns and high-resolution transmission electron microscopy (HR-TEM) images. In addition, HR-TEM images also revealed that the grain boundaries (GBs) in the BMN samples were much clean, and no segregation or impure phase was observed forming at GBs. The high dielectric constants in the BMN samples were ascribed to the long-range ordered pyrochlore structures since the electric dipoles formed at the superstructural direction could be enhanced. The low dielectric loss was attributed to the existence of noncontaminated GBs in the BMN ceramics. © 2013 Springer-Verlag Berlin Heidelberg.

  11. Higher-spin Interactions from CFT: The Complete Cubic Couplings

    CERN Document Server

    Sleight, Charlotte

    2016-01-01

    In this letter we provide a complete holographic reconstruction of the cubic couplings in the minimal bosonic higher-spin theory in AdS$_{d+1}$. For this purpose we also determine the OPE coefficients of all single-trace conserved currents in the $d$-dimensional free scalar $O\\left(N\\right)$ vector model, and compute the tree-level three-point Witten diagram amplitudes for a generic cubic interaction of higher-spin gauge fields in the metric-like formulation.

  12. Classifying Cubic Edge-Transitive Graphs of Order 8

    Indian Academy of Sciences (India)

    Mehdi Alaeiyan; M K Hosseinipoor

    2009-11-01

    A simple undirected graph is said to be semisymmetric if it is regular and edge-transitive but not vertex-transitive. Let be a prime. It was shown by Folkman (J. Combin. Theory 3(1967) 215--232) that a regular edge-transitive graph of order 2 or 22 is necessarily vertex-transitive. In this paper, an extension of his result in the case of cubic graphs is given. It is proved that, every cubic edge-transitive graph of order 8 is symmetric, and then all such graphs are classified.

  13. Possible form of multi-polar interaction in cubic lattice

    Energy Technology Data Exchange (ETDEWEB)

    Sakai, Osamu; Shiina, Ryousuke; Shiba, Hiroyuki

    2003-05-01

    The invariant form of interaction between multi-poles, including the octupole, is studied for the simple cubic (SC), body centered and face centered cubic lattices. The coupling terms can be arranged in a way similar to that of the hopping matrix between the LCAO's. A table for SC by Shiina et al. (J. Phys. Soc. Japan 66 (1997) 1741) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is thereby analyzed. The development of the ferromagnetic moment below the anti-ferromagnetic transition under the anti-ferro quadrupolar order phase is discussed in this connection.

  14. Possible form of multi-polar interaction in cubic lattice

    Science.gov (United States)

    Sakai, Osamu; Shiina, Ryousuke; Shiba, Hiroyuki

    2003-05-01

    The invariant form of interaction between multi-poles, including the octupole, is studied for the simple cubic (SC), body centered and face centered cubic lattices. The coupling terms can be arranged in a way similar to that of the hopping matrix between the LCAO's. A table for SC by Shiina et al. (J. Phys. Soc. Japan 66 (1997) 1741) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is thereby analyzed. The development of the ferromagnetic moment below the anti-ferromagnetic transition under the anti-ferro quadrupolar order phase is discussed in this connection.

  15. Counting perfect matchings of cubic graphs in the geometric dual

    CERN Document Server

    Jiménez, Andrea

    2010-01-01

    Lov\\'asz and Plummer conjectured, in the mid 1970's, that every cubic graph G with no cutedge has an exponential in |V(G)| number of perfect matchings. In this work we show that every cubic planar graph G whose geometric dual graph is a stack triangulation has at least 3 times the golden ratio to |V(G)|/72 distinct perfect matchings. Our work builds on a novel approach relating Lov\\'asz and Plummer's conjecture and the number of so called groundstates of the widely studied Ising model from statistical physics.

  16. Elastic interaction of point defects in crystals with cubic symmetry

    Science.gov (United States)

    Kuz'michev, S. V.; Kukushkin, S. A.; Osipov, A. V.

    2013-07-01

    The energy of elastic mechanical interaction between point defects in cubic crystals is analyzed numerically. The finite-element complex ANSYS is used to investigate the character of interaction between point defects depending on their location along the crystallographic directions , , and on the distance from the free boundary of the crystal. The numerical results are compared with the results of analytic computations of the energy of interaction between two point defects in an infinite anisotropic medium with cubic symmetry. The interaction between compressible and incompressible defects of general type is studied. Conditions for onset of elastic attraction between the defects, which leads to general relaxation of the crystal elastic energy, are obtained.

  17. Incorporation of the dopamine D2L receptor and bacteriorhodopsin within bicontinuous cubic lipid phases. 2. Relevance to in meso crystallization of integral membrane proteins in novel lipid systems

    Energy Technology Data Exchange (ETDEWEB)

    Conn, Charlotte E.; Darmanin, Connie; Sagnella, Sharon M.; Mulet, Xavier; Greaves, Tamar L.; Varghese, Joseph N.; Drummond, Calum J.

    2014-09-24

    The dopamine D2 long (D2L) receptor and bacteriorhodopsin (bR), which are integral membraneproteins, have been incorporated within bicontinuous cubic mesophases formed by the lipids anandamide and H-farnesoyl monoethanolamide, which have been specifically investigated by us for use as in mesocrystallization media. We show that the incorporated membraneprotein affects the structure of the cubic phases with the particular effect observed dependent on the geometry of the underlying cubic phase. The results are complementary to those obtained in Part 1 of this series, where we demonstrated that the structural effects observed depend on the structure of the membraneprotein. Importantly protein concentrations commonly used for crystallization can destroy the cubic phase matrix, particularly where there is a large discrepancy between the hydrophilic and the hydrophobic spans of the membraneprotein, and the hydrophilic and hydrophobic domain sizes of the cubic phase.

  18. Distinguishing cubic and hexagonal phases within InGaN/GaN microstructures using electron energy loss spectroscopy.

    Science.gov (United States)

    Griffiths, I J; Cherns, D; Albert, S; Bengoechea-Encabo, A; Angel Sanchez, M; Calleja, E; Schimpke, T; Strassburg, M

    2016-05-01

    3D InGaN/GaN microstructures grown by metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) have been extensively studied using a range of electron microscopy techniques. The growth of material by MBE has led to the growth of cubic GaN material. The changes in these crystal phases has been investigated by Electron Energy Loss Spectroscopy, where the variations in the fine structure of the N K-edge shows a clear difference allowing the mapping of the phases to take place. GaN layers grown for light emitting devices sometimes have cubic inclusions in the normally hexagonal wurtzite structures, which can influence the device electronic properties. Differences in the fine structure of the N K-edge between cubic and hexagonal material in electron energy loss spectra are used to map cubic and hexagonal regions in a GaN/InGaN microcolumnar device. The method of mapping is explained, and the factors limiting spatial resolution are discussed.

  19. Distinguishing cubic and hexagonal phases within InGaN/GaN microstructures using electron energy loss spectroscopy

    Science.gov (United States)

    CHERNS, D; ALBERT, S.; BENGOECHEA‐ENCABO, A.; ANGEL SANCHEZ, M.; CALLEJA, E.; SCHIMPKE, T.; STRASSBURG, M.

    2015-01-01

    Summary 3D InGaN/GaN microstructures grown by metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) have been extensively studied using a range of electron microscopy techniques. The growth of material by MBE has led to the growth of cubic GaN material. The changes in these crystal phases has been investigated by Electron Energy Loss Spectroscopy, where the variations in the fine structure of the N K‐edge shows a clear difference allowing the mapping of the phases to take place. GaN layers grown for light emitting devices sometimes have cubic inclusions in the normally hexagonal wurtzite structures, which can influence the device electronic properties. Differences in the fine structure of the N K‐edge between cubic and hexagonal material in electron energy loss spectra are used to map cubic and hexagonal regions in a GaN/InGaN microcolumnar device. The method of mapping is explained, and the factors limiting spatial resolution are discussed. PMID:26366483

  20. Sr2(Nd, Ce)2MCu2O9, M=Al, Co, Ga. A new layered copper oxide structure type

    NARCIS (Netherlands)

    Cava, R.J.; Zandbergen, H.W.; Krajewski, J.J.; Peck Jr., W.F.; Hessen, B.; Dover, R.B. Van; Cheong, S.-W.

    1992-01-01

    A new layered copper oxide structure type is reported based on the ordered interleaving of AlO4, CoO4 or GaO4 tetrahedra between the apices of copper oxide pyramids, and an (Nd, Ce)2O2 fluorite layer between the bases of the pyramids. Despite the structural similarities to the recently reported Sr2(

  1. Phase diagrams and synthesis of cubic boron nitride

    CERN Document Server

    Turkevich, V Z

    2002-01-01

    On the basis of phase equilibria, the lowest temperatures, T sub m sub i sub n , above which at high pressures cubic boron nitride crystallization from melt solution is allowable in terms of thermodynamics have been found for a number of systems that include boron nitride.

  2. Interaction of dispersed cubic phases with blood components

    DEFF Research Database (Denmark)

    Bode, J C; Kuntsche, Judith; Funari, S S;

    2013-01-01

    The interaction of aqueous nanoparticle dispersions, e.g. based on monoolein/poloxamer 407, with blood components is an important topic concerning especially the parenteral way of administration. Therefore, the influence of human and porcine plasma on dispersed cubic phases was investigated...

  3. Exact solutions for the cubic-quintic nonlinear Schroedinger equation

    Energy Technology Data Exchange (ETDEWEB)

    Zhu Jiamin [Department of Physics, Zhejiang Lishui University, Lishui 323000 (China)]. E-mail: zjm64@163.com; Ma Zhengyi [Department of Physics, Zhejiang Lishui University, Lishui 323000 (China); Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072 (China)

    2007-08-15

    In this paper, the cubic-quintic nonlinear Schroedinger equation is solved through the extended elliptic sub-equation method. As a consequence, many types of exact travelling wave solutions are obtained which including bell and kink profile solitary wave solutions, triangular periodic wave solutions and singular solutions.

  4. Combinatorics on Words in Symbolic Dynamics: the Antisymmetric Cubic Map

    Institute of Scientific and Technical Information of China (English)

    Wan Ji DAI; Kebo L(U); Jun WANG

    2008-01-01

    This paper is contributed to the combinatorial properties of the periodic kneading words of antisymmetric cubic maps defined on a interval.The least words of given lengths,the adjacency relations on the words of given lengths and the parity-alternative property in some sets of such words are established.

  5. A Unified Approach to Teaching Quadratic and Cubic Equations.

    Science.gov (United States)

    Ward, A. J. B.

    2003-01-01

    Presents a simple method for teaching the algebraic solution of cubic equations via completion of the cube. Shows that this method is readily accepted by students already familiar with completion of the square as a method for quadratic equations. (Author/KHR)

  6. Orientational phase transition in cubic liquid crystals with positional order

    OpenAIRE

    Pokrovsky, V.L.; Saidachmetov, P.A.

    1988-01-01

    An electric field can give rise to a shear deformation of a cubic liquid crystal with long-range positional order fixed by two plates. The critical value of the field does not depend on the size of the system and depends crucially on the orientation.

  7. Specific heat of the simple-cubic Ising model

    NARCIS (Netherlands)

    Feng, X.; Blöte, H.W.J.

    2010-01-01

    We provide an expression quantitatively describing the specific heat of the Ising model on the simple-cubic lattice in the critical region. This expression is based on finite-size scaling of numerical results obtained by means of a Monte Carlo method. It agrees satisfactorily with series expansions

  8. Connecting the Dots Parametrically: An Alternative to Cubic Splines.

    Science.gov (United States)

    Hildebrand, Wilbur J.

    1990-01-01

    Discusses a method of cubic splines to determine a curve through a series of points and a second method for obtaining parametric equations for a smooth curve that passes through a sequence of points. Procedures for determining the curves and results of each of the methods are compared. (YP)

  9. Cubic spline approximation techniques for parameter estimation in distributed systems

    Science.gov (United States)

    Banks, H. T.; Crowley, J. M.; Kunisch, K.

    1983-01-01

    Approximation schemes employing cubic splines in the context of a linear semigroup framework are developed for both parabolic and hyperbolic second-order partial differential equation parameter estimation problems. Convergence results are established for problems with linear and nonlinear systems, and a summary of numerical experiments with the techniques proposed is given.

  10. Rheology of cubic particles suspended in a Newtonian fluid.

    Science.gov (United States)

    Cwalina, Colin D; Harrison, Kelsey J; Wagner, Norman J

    2016-05-18

    Many real-world industrial processes involve non-spherical particles suspended in a fluid medium. Knowledge of the flow behavior of these suspensions is essential for optimizing their transport properties and designing processing equipment. In the present work, we explore and report on the rheology of concentrated suspensions of cubic-shaped colloidal particles under steady and dynamic shear flow. These suspensions exhibit a rich non-Newtonian rheology that includes shear thickening and normal stress differences at high shear stresses. Scalings are proposed to connect the material properties of these suspensions of cubic particle to those measured for suspensions of spherical particles. Negative first normal stress differences indicate that lubrication hydrodynamic forces dominate the stress in the shear-thickened state. Accounting for the increased lubrication hydrodynamic interactions between the flat surfaces of the cubic particles allows for a quantitative comparison of the deviatoric stress in the shear-thickened state to that of spherical particles. New semi-empirical models for the viscosity and normal stress difference coefficients are presented for the shear-thickened state. The results of this study indicate that cubic particles offer new and unique opportunities to formulate colloidal dispersions for field-responsive materials.

  11. Infinite Face Centered Cubic Network of Identical Resistors

    CERN Document Server

    Asad, J H

    2012-01-01

    The equivalent resistance between the origin and any other lattice site, in an infinite Face Centered Cubic network consisting from identical resistors, has been expressed rationally in terms of the known value and . The asymptotic behavior is investigated, and some calculated values for the equivalent resistance are presented.

  12. Trace spaces in a pre-cubical complex

    DEFF Research Database (Denmark)

    Raussen, Martin

    In directed algebraic topology, (spaces of) directed irreversible (d)-paths are studied from a topological and from a categorical point of view. Motivated by models for concurrent computation, we study in this paper spaces of d-paths in a pre-cubical complex. Such paths are equipped with a natural...

  13. Morphosynthesis of cubic silver cages on monolithic activated carbon.

    Science.gov (United States)

    Wang, Fei; Zhao, Hong; Lai, Yijian; Liu, Siyu; Zhao, Binyuan; Ning, Yuesheng; Hu, Xiaobin

    2013-11-14

    Cubic silver cages were prepared on monolithic activated carbon (MAC) pre-absorbed with Cl(-), SO4(2-), or PO4(3-) anions. Silver insoluble salts served as templates for the morphosynthesis of silver cages. The silver ions were reduced by reductive functional groups on MAC micropores through a galvanic cell reaction mechanism.

  14. SUPERCONVERGENCE ANALYSIS FOR CUBIC TRIANGULAR ELEMENT OF THE FINITE ELEMENT

    Institute of Scientific and Technical Information of China (English)

    Qi-ding Zhu

    2000-01-01

    In this paper, we construct a projection interpolation for cubic triangular ele- ment by using othogonal expansion triangular method. We show two fundamental formulas of estimation on a special partion and obtain a superconvergence result of 1 -e order higher for the placement function and its tangential derivative on the third order Lobatto points and Gauss points on each edge of triangular element.

  15. Integrability of Lotka-Volterra Planar Complex Cubic Systems

    Science.gov (United States)

    Dukarić, Maša; Giné, Jaume

    In this paper, we study the Lotka-Volterra complex cubic systems. We obtain necessary conditions of integrability for these systems with some restriction on the parameters. The sufficiency is proved for all conditions, except one which remains open, using different methods.

  16. Global Well-Posedness for Cubic NLS with Nonlinear Damping

    KAUST Repository

    Antonelli, Paolo

    2010-11-04

    We study the Cauchy problem for the cubic nonlinear Schrödinger equation, perturbed by (higher order) dissipative nonlinearities. We prove global in-time existence of solutions for general initial data in the energy space. In particular we treat the energy-critical case of a quintic dissipation in three space dimensions. © Taylor & Francis Group, LLC.

  17. Synthesis of cubic Ia-3d mesoporous silica in anionic surfactant templating system with the aid of acetate.

    Science.gov (United States)

    Deng, Shao-Xin; Xu, Xue-Yan; He, Wen-Chao; Wang, Jin-Gui; Chen, Tie-Hong

    2014-08-01

    Mesoporous silica with three-dimensional (3D) bicontinuous cubic Ia-3d structure and fascinating caterpillar-like morphology was synthesized by using anionic surfactant N-lauroylsarcosine sodium (Sar-Na) as the template and 3-amionpropyltrimethoxysilane (APS) as the co-structure-directing agent (CSDA) with the aid of acetate. A phase transformation from high interfacial curvature 2D hexagonal to low interfacial curvature 3D cubic Ia-3d occurred in the presence of a proper amount of acetate. Other species of salts (excluding acetate) had the ability to induce the caterpillar-like morphology, but failed to induce the cubic Ia-3d mesostructure. Furthermore, [3-(2-aminoethyl)-aminopropyl]trimethoxysilane (DAPS) was also used as the CSDA to synthesize Ia-3d mesostructured silica under the aid of sodium acetate. After extraction of the anionic surfactants, amino and di-amine functionalized 3D bicontinuous cubic Ia-3d mesoporous silicas were obtained and used as supports to immobilize Pd nanoparticles for supported catalysts. The catalytic activity of the catalysts was tested by catalytic hydrogenation of allyl alcohol.

  18. Synthesis, characterization and processing of cubic iron pyrite nanocrystals in a photovoltaic cell

    Energy Technology Data Exchange (ETDEWEB)

    Alam Khan, M., E-mail: alamkhan77@gmail.com; Sarker, J.C.; Lee, Seunyong; Mangham, Scott C.; Manasreh, M.O.

    2014-12-15

    Cubic iron pyrite (fool's gold) nanocrystals with an average diameter of ∼60 nm were grown in an oleylamine ligand which acts as a solvent and surfactant without the utilization of alkyl phosphine and phosphonic acids at 230 °C in a Schlenk flask. For the first time photoluminescence properties of such cubic nanocrystals were analyzed at 77 K, showing band gaps of 1.71 eV. However, UV–Vis spectra shows a band gap of 1.41 eV for the same nanocrystals, close to the direct band gap (1.38 eV) of reported pyrite materials. The discrepancy of 0.3 eV in absorption (UV–Vis) and emission spectra (PL) are attributed to the phonon coupling (stokes shift). The prepared cubic nanocrystals were well suited for an inexpensive thin film solar cells and further processed and spin casted with a synthesized CdSe quantum dots in chloroform solvent as a bulk-heterojunction (BHJ) solar cell in order to get photovoltaic responses in real devices. We successfully report here an efficiency of 0.5% with the J{sub SC} of 3.7 mA/cm{sup −2} and V{sub OC} of 0.16 mV with a cell structure of ITO/PEDOT:PSS/FeS{sub 2}:CdSe/Au. The morphology and optoelectronic properties are elucidated by SEM, TEM, TEM-EDS, XRD, micro-Raman spectra, IV curve and micro-PL techniques. - Highlights: • Excellent cubic iron pyrite nanocrystals are synthesized by using an oleylamine ligand. • First time PL spectra were used to measure band gaps of such colloidal cubic nanocrytsals. • Pyrite ink was made in suitable solvent to fabricate practical devices. • A successful 0.5% efficiency is reported in bulk-heterojunction cell with CdSe QDs.

  19. Clues on chemical mechanisms from renormalizability: The example of a noisy cubic autocatalytic model

    Science.gov (United States)

    Gagnon, Jean-Sébastien; Pérez-Mercader, Juan

    2017-08-01

    We study the effect of external power-law noise on the renormalizability of a specific reaction-diffusion system of equations describing a cubic autocatalytic chemical reaction. We show that changing the noise exponent modifies the divergence structure of loop integrals and thus the renormalizability of the model. The effects of noise-generated higher order interactions are discussed. We show how noise induces new interaction terms that can be interpreted as a manifestation of some (internal) ;chemical mechanism;. We also show how ideas of effective field theory can be applied to construct a more fundamental chemical model for this system.

  20. Dual Effect of the Cubic Ag₃PO₄ Crystal on Pseudomonas syringae Growth and Plant Immunity

    Directory of Open Access Journals (Sweden)

    Mi Kyung Kim

    2016-04-01

    Full Text Available We previously found that the antibacterial activity of silver phosphate crystals on Escherichia coli depends on their structure. We here show that the cubic form of silver phosphate crystal (SPC can also be applied to inhibit the growth of a plant-pathogenic Pseudomonas syringae bacterium. SPC pretreatment resulted in reduced in planta multiplication of P. syringae. Induced expression of a plant defense marker gene PR1 by SPC alone is suggestive of its additional plant immunity-stimulating activity. Since SPC can simultaneously inhibit P. syringae growth and induce plant defense responses, it might be used as a more effective plant disease-controlling agent.

  1. Phonon-magnon interactions in body centered cubic iron: A combined molecular and spin dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Perera, Dilina, E-mail: dilinanp@physast.uga.edu; Landau, David P. [Center for Simulational Physics, The University of Georgia, Georgia 30602 (United States); Nicholson, Don M.; Malcolm Stocks, G.; Eisenbach, Markus; Yin, Junqi [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Brown, Gregory [Florida State University, Tallahassee, Florida 32306 (United States)

    2014-05-07

    Combining an atomistic many-body potential with a classical spin Hamiltonian parameterized by first principles calculations, molecular-spin dynamics computer simulations were performed to investigate phonon-magnon interactions in body centered cubic iron. Results obtained for spin-spin and density-density dynamic structure factors show that noticeable softening and damping of magnon modes occur due to the presence of lattice vibrations. Furthermore, as a result of the phonon-magnon coupling, additional longitudinal spin wave excitations are observed, with the same frequencies as the longitudinal phonon modes.

  2. Elastic and magnetic properties of cubic Fe$_{4}$C from first-principles

    OpenAIRE

    Rahman, Gul; Jan, Haseen Ullah

    2014-01-01

    First-principles based on density functional theory is used to study the phase stability, elastic, magnetic, and electronic properties of cubic (c)-Fe$_4$C. Our results show that c-Fe$_{4}$C has a ferromagnetic (FM) ground state structure compared with antiferromagnetic (AFM) and nonmagnetic (NM)states. To study the phase stability of c-Fe$_4$C, BCC Fe$_4$C, FCC Fe$_4$C, and BCC Fe$_{16}$C, where C is considered at tetrahedral and octahedral interstitial sites, are also considered. Although, ...

  3. Self-oriented Ag-based polycrystalline cubic nanostructures through polymer stabilization

    Science.gov (United States)

    Alonso, Amanda; Vigués, Núria; Rodríguez-Rodríguez, Rosalía; Borrisé, Xavier; Muñoz, María; Muraviev, Dmitri N.; Mas, Jordi; Muñoz-Berbel, Xavier

    2016-10-01

    This paper presents the study of the dynamics of the formation of polymer-assisted highly-orientated polycrystalline cubic structures (CS) by a fractal-mediated mechanism. This mechanism involves the formation of seed Ag@Co nanoparticles by InterMatrix Synthesis and subsequent overgrowth after incubation at a low temperature in chloride and phosphate solutions. These ions promote the dissolution and recrystallization in an ordered configuration of pre-synthetized nanoparticles initially embedded in negatively-charged polymeric matrices. During recrystallization, silver ions aggregate in AgCl@Co fractal-like structures, then evolve into regular polycrystalline solid nanostructures (e.g. CS) in a single crystallization step on specific regions of the ion exchange resin (IER) which maintain the integrity of polycrystalline nanocubes. Here, we study the essential role of the IER in the formation of these CS for the maintenance of their integrity and stability. Thus, this synthesis protocol may be easily expanded to the composition of other nanoparticles providing an interesting, cheap and simple alternative for cubic structure formation and isolation.

  4. Hydrothermal Synthesis and Tunable Multicolor Upconversion Emission of Cubic Phase Y2O3 Nanoparticles

    Directory of Open Access Journals (Sweden)

    Haibo Wang

    2013-01-01

    Full Text Available Highly crystalline body-centered cubic structure Y2O3 with lanthanide (Ln codopants (Ln = Yb3+/Er3+ and Yb3+/Ho3+ has been synthesized via a moderate hydrothermal method in combination with a subsequent calcination. The structure and morphology of Y(OH3 precursors and Y2O3 nanoparticles were characterized by X-ray diffraction and transmission electron microscopy. The results reveal that the Y2O3 nanoparticles possess cubic phase and form the quasispherical structure. The upconversion luminescence properties of Y2O3 nanoparticles doped with different Ln3+ (Yb3+/ Er3+ and Yb3+/ Ho3+ ions were well investigated under the 980 nm excitation. The results show that the Yb3+/Er3+ and Yb3+/Ho3+ codoped Y2O3 nanoparticles exhibit strong red and light yellow upconversion emissions, respectively. It is expected that these Y2O3 nanoparticles with tunable multicolor output and intense red upconversion emission may have potential application in color displays and biolabels.

  5. BDA: A novel method for identifying defects in body-centered cubic crystals.

    Science.gov (United States)

    Möller, Johannes J; Bitzek, Erik

    2016-01-01

    The accurate and fast identification of crystallographic defects plays a key role for the analysis of atomistic simulation output data. For face-centered cubic (fcc) metals, most existing structure analysis tools allow for the direct distinction of common defects, such as stacking faults or certain low-index surfaces. For body-centered cubic (bcc) metals, on the other hand, a robust way to identify such defects is currently not easily available. We therefore introduce a new method for analyzing atomistic configurations of bcc metals, the BCC Defect Analysis (BDA). It uses existing structure analysis algorithms and combines their results to uniquely distinguish between typical defects in bcc metals. In essence, the BDA method offers the following features:•Identification of typical defect structures in bcc metals.•Reduction of erroneously identified defects by iterative comparison to the defects in the atom's neighborhood.•Availability as ready-to-use Python script for the widespread visualization tool OVITO [http://ovito.org].

  6. Formation and properties of reverse micellar cubic liquid crystals and derived emulsions.

    Science.gov (United States)

    Rodríguez-Abreu, Carlos; Shrestha, Lok Kumar; Varade, Dharmesh; Aramaki, Kenji; Maestro, Alicia; Quintela, Arturo López; Solans, Conxita

    2007-10-23

    The structure of the reverse micellar cubic (I2) liquid crystal and the adjacent micellar phase in amphiphilic block copolymer/water/oil systems has been studied by small-angle X-ray scattering (SAXS), rheometry, and differential scanning calorimetry (DSC). Upon addition of water to the copolymer/oil mixture, spherical micelles are formed and grow in size until a disorder-order transition takes place, which is related to a sudden increase in the viscosity and shear modulus. The transition is driven by the packing of the spherical micelles into a Fd3m cubic lattice. The single-phase I2 liquid crystals show gel-like behavior and elastic moduli higher than 104 Pa, as determined by oscillatory measurements. Further addition of water induces phase separation, and it is found that reverse water-in-oil emulsions with high internal phase ratio and stabilized by I2 liquid crystals can be prepared in the two-phase region. Contrary to liquid-liquid emulsions, both the elastic modulus and the viscosity decrease with the fraction of dispersed water, due to a decrease in the crystalline fraction in the sample, although the reverse emulsions remain gel-like even at high volume fractions of the dispersed phase. A temperature induced order-disorder transition can be detected by calorimetry and rheometry. Upon heating the I2 liquid crystals, two thermal events associated with small enthalpy values were detected: one endothermic, related to the "melting" of the liquid crystal, and the other exothermic, attributed to phase separation. The melting of the liquid crystal is associated with a sudden drop in viscosity and shear moduli. Results are relevant for understanding the formation of cubic-phase-based reverse emulsions and for their application as templates for the synthesis of structured materials.

  7. Determination of the cubic to hexagonal fraction in GaN nucleation layers using grazing incidence x-ray scattering

    Energy Technology Data Exchange (ETDEWEB)

    Munkholm, A.; Thompson, C.; Foster, C.M.; Eastman, J.A.; Auciello, O.; Stephenson, G.B. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Fini, P.; DenBaars, S.P.; Speck, J.S. [Department of Materials, University of California, Santa Barbara, California 93106 (United States)

    1998-06-01

    Recent electron diffraction and microscopy studies of GaN nucleation layers have shown that faults in the stacking of the close-packed planes result in the coexistence of cubic and hexagonal phases within the layers. Using grazing incidence x-ray scattering, we have quantified the proportion of the cubic and hexagonal phases throughout the nucleation layer. We compare the structure of a 20 nm nucleation layer grown on sapphire by atmospheric pressure metal-organic chemical vapor deposition at 525thinsp{degree}C to that of an identical layer heated to 1060thinsp{degree}C. The fractions of cubic and hexagonal phases in the layers are determined by a comparison of the scattering data with a Hendricks{endash}Teller model. High temperature exposure results in a decrease of the cubic fraction from 0.56 to 0.17. The good agreement with the Hendricks{endash}Teller model indicates that the positions of the stacking faults are uncorrelated. {copyright} {ital 1998 American Institute of Physics.}

  8. Counting real cubics with passage/tangency conditions

    CERN Document Server

    Lanzat, Sergei

    2010-01-01

    We study the following question: given a set of seven points and an immersed curve in the real plane R^2, all in general position, how many real rational nodal plane cubics pass through these points and are tangent to this curve. We count each such cubic with a certain sign, and present an explicit formula for their algebraic number. This number is preserved under small regular homotopies of the curve, but jumps (in a well-controlled way) when in the process of homotopy we pass a certain singular discriminant. We discuss the relation of such enumerative problems with finite type invariants. Our approach is based on maps of configuration spaces and the intersection theory in the spirit of classical algebraic topology.

  9. The Piecewise Cubic Method (PCM) for computational fluid dynamics

    Science.gov (United States)

    Lee, Dongwook; Faller, Hugues; Reyes, Adam

    2017-07-01

    We present a new high-order finite volume reconstruction method for hyperbolic conservation laws. The method is based on a piecewise cubic polynomial which provides its solutions a fifth-order accuracy in space. The spatially reconstructed solutions are evolved in time with a fourth-order accuracy by tracing the characteristics of the cubic polynomials. As a result, our temporal update scheme provides a significantly simpler and computationally more efficient approach in achieving fourth order accuracy in time, relative to the comparable fourth-order Runge-Kutta method. We demonstrate that the solutions of PCM converges at fifth-order in solving 1D smooth flows described by hyperbolic conservation laws. We test the new scheme on a range of numerical experiments, including both gas dynamics and magnetohydrodynamics applications in multiple spatial dimensions.

  10. The Piecewise Cubic Method (PCM) for Computational Fluid Dynamics

    CERN Document Server

    Lee, Dongwook; Reyes, Adam

    2016-01-01

    We present a new high-order finite volume reconstruction method for hyperbolic conservation laws. The method is based on a piecewise cubic polynomial which provides its solutions a fifth-order accuracy in space. The spatially reconstructed solutions are evolved in time with a fourth-order accuracy by tracing the characteristics of the cubic polynomials. As a result, our temporal update scheme provides a significantly simpler and computationally more efficient approach in achieving fourth order accuracy in time, relative to the comparable fourth-order Runge-Kutta method. We demonstrate that the solutions of PCM converges in fifth-order in solving 1D smooth flows described by hyperbolic conservation laws. We test the new scheme in a range of numerical experiments, including both gas dynamics and magnetohydrodynamics applications in multiple spatial dimensions.

  11. Cubic Composite Sensor with Photodiodes for Tracking Solar Orientation

    Directory of Open Access Journals (Sweden)

    Yong-Nong Chang

    2013-01-01

    Full Text Available A cubic composite solar sensor with photo diode is proposed for tracking the relative solar orientation. The proposed solar sensor composes of five photodiode detectors which are placed on the front, rear, left, right, and horizontal facets in a cubic body, respectively. The solar detectors placed on five facets can detect solar power of different facets. Based on the geometric coordinate transformation principle, the relationship equations of solar light orientation between measured powers with respect to various facets can be conducted. As a result, the solar orientation can be precisely achieved without needing any assistance of electronic compass and extra orientation angle corrector. Eventually, the relative solar light orientation, the elevation angle, and azimuth angle of the solar light can be measured precisely.

  12. Global Sufficient Optimality Conditions for a Special Cubic Minimization Problem

    Directory of Open Access Journals (Sweden)

    Xiaomei Zhang

    2012-01-01

    Full Text Available We present some sufficient global optimality conditions for a special cubic minimization problem with box constraints or binary constraints by extending the global subdifferential approach proposed by V. Jeyakumar et al. (2006. The present conditions generalize the results developed in the work of V. Jeyakumar et al. where a quadratic minimization problem with box constraints or binary constraints was considered. In addition, a special diagonal matrix is constructed, which is used to provide a convenient method for justifying the proposed sufficient conditions. Then, the reformulation of the sufficient conditions follows. It is worth noting that this reformulation is also applicable to the quadratic minimization problem with box or binary constraints considered in the works of V. Jeyakumar et al. (2006 and Y. Wang et al. (2010. Finally some examples demonstrate that our optimality conditions can effectively be used for identifying global minimizers of the certain nonconvex cubic minimization problem.

  13. Plasma simulation with the Differential Algebraic Cubic Interpolated Propagation scheme

    Energy Technology Data Exchange (ETDEWEB)

    Utsumi, Takayuki [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1998-03-01

    A computer code based on the Differential Algebraic Cubic Interpolated Propagation scheme has been developed for the numerical solution of the Boltzmann equation for a one-dimensional plasma with immobile ions. The scheme advects the distribution function and its first derivatives in the phase space for one time step by using a numerical integration method for ordinary differential equations, and reconstructs the profile in phase space by using a cubic polynomial within a grid cell. The method gives stable and accurate results, and is efficient. It is successfully applied to a number of equations; the Vlasov equation, the Boltzmann equation with the Fokker-Planck or the Bhatnagar-Gross-Krook (BGK) collision term and the relativistic Vlasov equation. The method can be generalized in a straightforward way to treat cases such as problems with nonperiodic boundary conditions and higher dimensional problems. (author)

  14. Quantum spectra and classical periodic orbit in the cubic billiard

    Institute of Scientific and Technical Information of China (English)

    Dehua Wang; Yongjiang Yu; Shenglu Lin

    2006-01-01

    Quantum billiards have attracted much interest in many fields. People have made a lot of researches on the two-dimensional (2D) billiard systems. Contrary to the 2D billiard, due to the complication of its classical periodic orbits, no one has studied the correspondence between the quantum spectra and the classical orbits of the three-dimensional (3D) billiards. Taking the cubic billiard as an example, using the periodic orbit theory, we find the periodic orbit of the cubic billiard and study the correspondence between the quantum spectra and the length of the classical orbits in 3D system. The Fourier transformed spectrum of this system has allowed direct comparison between peaks in such plot and the length of the periodic orbits, which verifies the correctness of the periodic orbit theory. This is another example showing that semiclassical method provides a bridge between quantum and classical mechanics.

  15. Quantum Phase Transitions in Anti-ferromagnetic Planar Cubic Lattices

    CERN Document Server

    Wellard, C J; Wellard, Cameron; Orus, Roman

    2004-01-01

    Motivated by its relation to an NP-hard problem we analyze the ground state properties of anti-ferromagnetic Ising-spin networks in planar cubic lattices under the action of homogeneous transverse and longitudinal magnetic fields. We consider different instances of the cubic geometry and find a set of quantum phase transitions for each one of the systems, which we characterize by means of entanglement behavior and majorization theory. Entanglement scaling at the critical region is in agreement with results arising from conformal symmetry, therefore even the simplest planar systems can display very large amounts of quantum correlation. No conclusion can be made as to the scaling behavior of the minimum energy gap, with the data allowing equally good fits to exponential and power law decays. Analysis of entanglement and especially of majorization instead of the energy spectrum proves to be a good way of detecting quantum phase transitions in highly frustrated configurations.

  16. Higher-Order Approximation of Cubic-Quintic Duffing Model

    DEFF Research Database (Denmark)

    Ganji, S. S.; Barari, Amin; Babazadeh, H.

    2011-01-01

    We apply an Artificial Parameter Lindstedt-Poincaré Method (APL-PM) to find improved approximate solutions for strongly nonlinear Duffing oscillations with cubic-quintic nonlinear restoring force. This approach yields simple linear algebraic equations instead of nonlinear algebraic equations...... without analytical solution which makes it a unique solution. It is demonstrated that this method works very well for the whole range of parameters in the case of the cubic-quintic oscillator, and excellent agreement of the approximate frequencies with the exact one has been observed and discussed....... Moreover, it is not limited to the small parameter such as in the classical perturbation method. Interestingly, this study revealed that the relative error percentage in the second-order approximate analytical period is less than 0.042% for the whole parameter values. In addition, we compared...

  17. 3D Medical Image Interpolation Based on Parametric Cubic Convolution

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In the process of display, manipulation and analysis of biomedical image data, they usually need to be converted to data of isotropic discretization through the process of interpolation, while the cubic convolution interpolation is widely used due to its good tradeoff between computational cost and accuracy. In this paper, we present a whole concept for the 3D medical image interpolation based on cubic convolution, and the six methods, with the different sharp control parameter, which are formulated in details. Furthermore, we also give an objective comparison for these methods using data sets with the different slice spacing. Each slice in these data sets is estimated by each interpolation method and compared with the original slice using three measures: mean-squared difference, number of sites of disagreement, and largest difference. According to the experimental results, we present a recommendation for 3D medical images under the different situations in the end.

  18. Beneficiation Study on a Low Grade Fluorite Ore%某低品位萤石矿选矿工艺研究

    Institute of Scientific and Technical Information of China (English)

    程建国; 廖乾; 周韫; 李淮湘; 解振朝

    2014-01-01

    某低品位萤石矿含CaF2为25.20%,在磨矿细度-0.075 mm含量70%的条件下,采用碳酸钠为pH调整剂、常规水玻璃和酸化水玻璃为抑制剂、油酸为捕收剂,经过一次粗选—粗精矿一次精选脱泥—五次精选,可获得产率为15.93%、CaF2品位98.27%、回收率为62.37%的高品质酸级萤石精矿产品1;中矿集中处理,经过三次精选,可以获得产率为6.20%、CaF2品位82.73%、回收率为20.44%的冶金级萤石精矿产品2,萤石总回收率达到82.81%。精选添加酸化水玻璃,有助于提升萤石精矿的品级。%A low grade fluorite ore of which the CaF 2 grade was 25.20%, flotation tests were con-ducted under the condition of grinding fineness -0 .075 mm 70%, using sodium carbonate as pH adjusting agent , sodium silicate and acidified sodium silicate as depressant and oleic acid as collec-tor .After a roughing and a cleaning flotation , the rough concentrate was deslimed and moved to an-other five cleaning flotation .A high quality concentrate assaying 98.27%CaF2 was obtained with a yield of 15.93%and recovery of 62.37%.The middling products of flowsheet were handled together by three cleaning flotation and another concentrate product was obtained with assaying 82 .81%CaF2 ,the quality of which reached to metallurgical level .The yield was 6.20% and recovery rate was 20 .44%.This fluorite concentrate was upgraded by using acidified sodium silicate .

  19. Quadratic and Cubic Nonlinear Oscillators with Damping and Their Applications

    Science.gov (United States)

    Li, Jibin; Feng, Zhaosheng

    We apply the qualitative theory of dynamical systems to study exact solutions and the dynamics of quadratic and cubic nonlinear oscillators with damping. Under certain parametric conditions, we also consider the van der Waals normal form, Chaffee-Infante equation, compound Burgers-KdV equation and Burgers-KdV equation for explicit representations of kink-profile wave solutions and unbounded traveling wave solutions.

  20. The Number of Real Roots of a Cubic Equation

    Science.gov (United States)

    Kavinoky, Richard; Thoo, John B.

    2008-01-01

    To find the number of distinct real roots of the cubic equation (1) x[caret]3 + bx[caret]2 + cx + d = 0, we could attempt to solve the equation. Fortunately, it is easy to tell the number of distinct real roots of (1) without having to solve the equation. The key is the discriminant. The discriminant of (1) appears in Cardan's (or Cardano's) cubic…