Showing papers on "Perovskite (structure) published in 1981"
TL;DR: In this article, a series of phases MICa2Nb3O10 (MI = Li, Na, K, Rb, Cs, NH4, Tl) has been prepared and characterized.
372 citations
TL;DR: The surface hydroxyl concentrations of BaTiO3, Sr TiO3 and LaCoO3 were determined by exchange with D2 as a function of the dehydroxylation temperature as mentioned in this paper.
162 citations
TL;DR: In this paper, it was shown that CaTiO3 (perovskite), SrTiOO3 and BaTiO 3 are as reactive as some silicate glasses below 100°C, but leach much more slowly than glasses above 100°c.
Abstract: Perovskite, a SYNROC host mineral for nuclear wastes, is thermodynamically unstable in natural waters and in association with common minerals. Leach experiments demonstrate that CaTiO3 (perovskite), SrTiO3 and BaTiO3 are as reactive as some silicate glasses below 100°C, but leach much more slowly than glasses above 100°C.
119 citations
01 Jan 1981
91 citations
TL;DR: In this article, the reducibility of La1-xSrxCoO3 (a perovskite-type mixed oxide) remarkably increased with the Sr2+ content, x, but the rate of re-oxidation of the reduced catalysts decreased with x.
Abstract: The reducibility of La1-xSrxCoO3 (a perovskite-type mixed oxide) remarkably increased with the Sr2+ content, x, but the rate of re-oxidation of the reduced catalysts decreased with x. These trends well explain the catalytic activity for oxidation on the basis of redox mechanism.
58 citations
TL;DR: LiNbO3 and LiTaO3 have been found to undergo ion exhange in certain aqueous solutions and hydrate melts, replacing some or all of the lithium with hydrogen.
Abstract: LiNbO3 and LiTaO3 have been found to undergo ion exhange in certain aqueous solutions and hydrate melts, replacing some or all of the lithium with hydrogen. Complete exchange results in a structural transformation from the LiNbO3 to the cubic perovskite structure. Properties of the exchanged phases and some applications of this process to optical waveguide fabrication are discussed.
54 citations
TL;DR: In this article, the luminescence properties of Cs3Bi2Br9 single crystals are reported, and the results are interpreted assuming detrapping and exciton migration.
Abstract: The luminescence properties of Cs3Bi2Br9 single crystals are reported. Cs3Bi2Br9 is an ordered perovskite, structurally and electronically related to the cesium lead halides. Emission and excitation spectra are measured at 4.2 K. The luminescence originates from the recombination of excitons bound to defects, except for a sharp line at 459.2 nm, which is ascribed to free exciton recombination. The band-gap transition takes place at about 2.7 eV and is found to be direct and allowed. The intensity of the emission bands and the decay times are measured as a function of temperature. The results are interpreted assuming detrapping and exciton migration.
45 citations
TL;DR: A phase analysis in pseudobinary (1−x)Pb(F 1/2Nb1/2)O3−x Pb(Mg 1/ 2W1/ 2) O3 system is conducted by measuring its dielectric properties, E −P hysteresis, and dc resistivity at x = 0.1 interval as discussed by the authors.
Abstract: A phase analysis in pseudobinary (1−x)Pb(F1/2Nb1/2)O3−xPb(Mg1/2W1/2)O3 system is conducted by measuring its dielectric properties, E‐P hysteresis, and dc resistivity at x = 0.1 interval. Lattice parameters and ordering of ions are analyzed by the x‐ray diffraction method, and the temperature‐composition phase diagram is determined. The system is found to form a solid solution of perovskite structure throughout the entire composition range, but the nature of its phase transitions changes from ferroelectric‐paraelectric for the composition range of 0.0⩽x⩽0.5 to antiferroelectric‐paraelectric for the composition range of 0.6⩽x⩽1.0. The ferroelectric‐paraelectric transition is relativity sharp for 0.0⩽x⩽0.1 and becomes diffuse for 0.2⩽x⩽0.5, and the antiferroelectric‐paraelectric is diffuse for 0.6⩽x⩽0.8 and becomes sharp for 0.9⩽x⩽1.0.
44 citations
TL;DR: In this article, the authors used thermochemical systematics to estimate the pressure for the transition from rocksalt to cesium chloride and from rock salt to nickel arsenide structures.
Abstract: Thermochemical systematics are used to estimate the pressure for the transition from rocksalt to cesium chloride and from rocksalt to nickel arsenide structures. For MgO, both transitions are predicted to occur at pressures greater than 3000 kbar, which implies that neither transition is likely for MgO in the lower mantle. For FeO, the transition to nickel arsenide is predicted to occur at much lower pressure (∼300 kbar) than that to cesium chloride (3000 kbar), and it is suggested that the transition observed by Jeanloz and Ahrens in shock experiments near 700 kbar may be to the nickel arsenide structure. If a (Mg, Fe) O solid solution with NiAs structure exists in the lower mantle as a minor phase, it will be strongly enriched in iron and other transition metals relative to a (Mg, Fe) SiO3 perovskite phase. This enrichment in the heavier elements, as well as the slightly higher density of nickel arsenide than rocksalt phases, would accentuate the density difference between MSiO3 and MO phases and enhance gravitational settling and lower mantle heterogeneity.
43 citations
28 citations
TL;DR: In this paper, the two structural phase transitions in the perovskite type layer structure compound (C10H21NH3)2CuCl4 have been studied by single crystal 13C NMR.
Abstract: The two structural phase transitions in the perovskite type layer structure compound (C10H21NH3)2CuCl4 have been studied by single crystal 13C NMR. The paramagnetic shifts due to the Cu++ ions have been evaluated and subtracted from the experimental data to yield the 13C chemical shift tensors as a function of temperature. The results show in agreement with the DTA data that the transition from the low temperature to the intermediate temperature phase is connected with a partial melting of the alkylammonium chains and the vanishing of the average chain tilt, whereas the transition to the high temperature phase is accompanied by the onset of flipping of the polar heads and an associated rotation of the chains around the long axis. The two transitions are thus analogous to the ones found in lipid bilayer membranes and (C10H21NH3)2CdCl4 but the sequence of the two successive transitions is exchanged.
TL;DR: Two new phases with ordered anion vacancies, La 8 Mn 8 O 23 and La 4 Mn 4 O 11, both having the general formula A n B n O 3n·1, form during the reduction of perovskites of the type LaMnO 3.07.
TL;DR: In this paper, the local geometry of transition-metal-oxygen-vacancy defets is analyzed in a cubic SrTiO3 host and the authors show that the M ion moves by about 0.2A towards the vacancy site while the four oxygens in a plane perpendicular to the M-Vo axis are desplaced against the metal ion.
Abstract: The recent analysis of the local structure of transition-metal-oxygen-vacancy defets, M-Vo, trapped in a cubic SrTiO3 host (1), shows a distorsion of the local geometry. The M ion moves by about 0.2A towards the vacancy site while the four oxygens in a plane perpendicular to the M-Vo axis are desplaced against the metal ion by about 0.08A.
TL;DR: In this article, single crystals of perovskite type fluorides were grown from potassium fluoride and di-valent metal chloride solutions by a hydrothermal method under a temperature gradient, at maximum temperature 600° C and pressure 98 MPa.
Abstract: Single crystals of perovskite-type fluorides were grown from potassium fluoride and di-valent metal chloride solutions by a hydrothermal method under a temperature gradient, at maximum temperature 600° C and pressure 98 MPa. Single-crystal cubes of KMnF3, KFeF3, KCoF3 and KZnF3, of cube edge sizes ranging from 0.2 to 2.0 mm, were grown. Crystals of KNiF3 grew in rectangular prisms and those of KCdF3 in anhedral form. Single crystals of KCuF3 were grown in pure water from co-precipitated KCuF3 powder. KMgF3 crystals were not grown by this method.
TL;DR: In this article, the luminescence and photoconductivity of ordered perovskite Cs 3 Bi 2 Br 9 were investigated and the observed transitions in the excitation spectrum were explained using the band scheme which has been proposed for CsPbBr 3.
TL;DR: Oxygen-deficient perovskites of the system (CaxSr1−x)FeO3−y were prepared at high oxygen pressures up to 1900 atm (196 MPa) and measurements were made of their crystallographic and thermodynamic behavior as mentioned in this paper.
TL;DR: In this paper, an ion dynamics simulation study of the perfect NaMgF 3 structure was performed, which yields the correct lattice energy to 1% but which, unlike the case of CaF 2, shows no diffusion of either cationic or anionic species, even under strong superheating.
TL;DR: The spontaneous magnetic moment at 100 mK compares well with the value from the ground state doublet and is in disagreement with Mossbauer results as discussed by the authors, which is in agreement with certain features of a quasi one-dimensional Ising system.
TL;DR: In this article, the stability of AxByOz towards isothermal decomposition into a biphasic solid mixture is derived from the equilibrium condition ΔG∗ = 0 as functions of standard changes ΔH° and ΔS°.
TL;DR: In this paper, a set of interatomic potentials to describe the compound KMnF3 is developed, which are used to calculate point defect and migration energies for this compound.
Abstract: A set of interatomic potentials to describe the compound KMnF3 is developed. The near-neighbour cation—anion interactions are described by a conventional Born-Mayer potential; the second-neighbour anion-anion interactions use a more recent empirical potential developed for the alkali halides. These potentials are used to calculate point defect and migration energies for this compound. The results of the calculations indicate that the intrinsic disorder in KMnF3 should be Frenkel disorder on the anion sublattice; however, the isolated anion interstitial is not the most stable configuration—a dumb-bell configuration involving two interstitial anions and an anion vacancy aligned along the 〈100〉 direction is more likely.
TL;DR: In this paper, the concentration dependence and the influence of the coordination number of rare earth are reported, and the authors also present the photoluminescence of Trivalent Rare Earths in perovskite stacking polytypes Ba2La2−x REMgW2-O12, Ba6Y2−ex REW3-O18, and Sr8SrGd2-xREW4-O24.
Abstract: Rhomboedrische 12 L-Stapelvarianten Ba2La2−xSEMgW2□O12 zeigen mit SE3+ = Pr, Sm, Eu, Tb, Dy, Ho, Er, Tm; die rhomboedrischen 18 L-Stapelvarianten Ba6Y2−xSEW3□O18 sowie die polymorphen Perowskite Sr8SrGd2−xSEW4□O24 mit SE3+ = Sm, Eu, Dy, Ho, Er Photolumineszenz im Sichtbaren Gebiet. Uber die Konzentrationsabhangigkeit und den Einflus der Koordinationszahl des Seltenen Erds wird berichtet.
Photoluminescence of Trivalent Rare Earths in Perovskite Stacking Polytypes Ba2La2−x REMgW2□O12, Ba6Y2−x REW3□O18, and Sr8SrGd2−xREW4□O24
Rhombohedral 12 L stacking polytypes Ba2La2−xREMgW2□O12 show with RE3+ = Pr, Sm, Eu, Tb, Dy, Ho, Er, Tm; the 18 L stacking polytypes Ba6Y2−xREW3□O18 and the polymorphic perovskites Sr8SrGd2−xREW4□O24 with RE3+ = Sm, Eu, Dy, Ho, Er visible photoluminescence. The concentration dependence and the influence of the coordination number of the rare earth are reported.
TL;DR: In this article, a superconducting thin oxide of perovskite-type oxide of BaPb1-xBixO3 (x=0.95Sr0.05 Pb0.75Bi0.25O3) was prepared by sputtering under sufficiently high oxygen partial pressure.
Abstract: Superconducting thin films of perovskite-type oxide of BaPb1-xBixO3 (x=0.2, 0.25, 0.3, 0.4) and Ba0.95Sr0.05 Pb0.75Bi0.25O3 were prepared by rf sputtering with their superconducting transition onsets of about 8 K. The films tended to lack Pb and Bi and this tendency could be reduced by sputtering under sufficiently high oxygen partial pressure. The transition temperature becomes reduced in both cases of low (x=0.2) and high (x=0.4) Bi content. The strontium substitution aiming at sharp transitions was not so effective as in the bulk materials and resulted in high resistive thin films.
TL;DR: In this article, the phase diagrams of the pseudo-binary systems PbOPb(Fe 1 2 Nb 1 2 )O3 (PbO(Mn 1 2 nb 1 1 2 ).
01 Jan 1981
TL;DR: In this paper, molecular cluster predictions for electronic structures of cubic, tetragonal and orthorhombic NbO67-clusters, obtained within the self-consistent field X alpha framework, are related to the electronic and optical properties of KNbO3 crystals in the cubic, Tetragonal, and OrthorHombic phases.
Abstract: Molecular cluster predictions for electronic structures of cubic, tetragonal and orthorhombic NbO67- clusters, obtained within the self-consistent-field X alpha framework, are related to the electronic and optical properties of KNbO3 crystals in the cubic, tetragonal and orthorhombic phases. Distortions in electronic state levels and electronic populations induced by atomic displacements from the cubic perovskite positions are examined. Ground state electronic distributions are used to determine the inequivalent populations of oxygen ligands inside the valence band, pictured by local densities of states of O 2p-type. X alpha -cluster ionic charges allow the theoretical determination of the spontaneous polarisation, Ps in ferroelectric phases, and comparison with experimental data shows a rather correct estimation of Ps from cluster computations. The band gap anisotropy and the band edge polarisation potentials are obtained using transition-state calculations. A rough estimation of the anisotropy of the imaginary part of the dielectric constant is obtained from the energies of dipolar-allowed transitions. X alpha results are discussed according to different choices of atomic sphere radii.
TL;DR: In this article, it was shown that under the same conditions tetrachlorocadmate salts (RNH3)2CdCl4(R = CH2CHCH2- and CHCCH2)- do not react.
Abstract: U.v. and X-ray irradiation causes polymerization of amino-diacetylene cations R1NH3+ and H3NR2NH32+ where R1= ClCH2CC–CCCH2– and R2=(–CH2CO2CH2CC–)2 in the solid salts (R1NH3)2CdCl4 and (H3NR2NH3)CdCl4 with he layer perovskite structure; under the same conditions tetrachlorocadmate salts (RNH3)2CdCl4(R = CH2CHCH2– and CHCCH2–) do not react.
TL;DR: In this paper, two approaches were tried and found to be effective to synthesize catalysts that were active for the partial oxidation of propane, and a model system with controllable defects was studied.
Abstract: Two approaches were tried and found to be effective to synthesize catalysts that were active for the partial oxidation of propane. A model system with controllable defects was studied. A series of perovskites were found to be active if both bismuth atoms and vacancies were present simultaneously on the “A” site. Second, we found that substitution and stabilization of vanadium (+IV) into ternary rutile related structures provided a means of producing catalytically active phases. The activity decreased from 500 to 350°C. The selectivity was somewhat different for the perovskite and trirutile catalysts; the selectivity changes with decreasing temperature. The perovskites showed activity that was similar to scheelites containing Bi and vacancies on the high coordinate site. The vanadium catalysts were more active in producing partially oxidized products with less than three carbons. An unexpected increase in activity was seen between 425 and 400°C.