Showing papers on "Perovskite (structure) published in 1980"
TL;DR: In this paper, X-ray powder diffraction is used to identify the strong superlattice reflections associated with the ordering of scandium and tantalum ions in the B-site, and to demonstrate quantitatively how the degree of ordering can be modified by suitable thermal treatment.
Abstract: Simple crystal-chemical arguments were used to suggest that in the ferroelectric perovskite lead-scanium-tantalate (PbSc0.5Ta0.5O3) the B-site cations in this simple ABO3 structure should be close to the boundary between order and disorder. Both polycrystal ceramic and single crystal materials of this composition have been grown. In this study X-ray powder diffraction is used to identify the strong superlattice reflections associated with the ordering of scandium and tantalum ions in the B-site, and to demonstrate quantitatively how the degree of ordering can be modified by suitable thermal treatment. Thermal changes associated with the ferroelectric Curie temperature have been measured by differential scanning calorimetry and show very clearly the manner in which the diffuse (broadened) transition in this crystal is sharpened by increase in the B-cation ordering.
410 citations
TL;DR: In this paper, the phase relationships in the ternary systems Cr Al C, V Al C and Ti Al C have been investigated, and the perovskite phase Ti3AlC has been found to be in equilibrium with Al4C3, Al(1), Al3V, V7Al8, V (solid solution with Al), V2C, V 2C, γ-VC1−x, and VC 1−x (including V8C7).
287 citations
TL;DR: In this paper, the systematics of the electronic structure of perovskite oxides, where the $B$ element scans the $3d$ transition-metal series from Ti to Co, are examined.
Abstract: The systematics of the electronic structure of $\mathrm{La}B{\mathrm{O}}_{3}$ perovskite oxides, where the $B$ element scans the $3d$ transition-metal series from Ti to Co, are examined. X-ray photoelectron spectra of valence bands and shallow core states are presented and compared with theoretical molecular cluster and free-ion multiplet models. Self-consistent ionic configurations are obtained from the embedded cluster calculations, which differ from the assumptions of crystal-field theory due to metal-oxygen covalency. The prospect for more rigorous many-electron models is discussed.
101 citations
TL;DR: In this article, the relation between local symmetry of solid surfaces and chemisorption and catalysis was discussed, and Maxima for Mn3+ and Co3+ were found.
Abstract: Catalytic activities for CO oxidation of a series of LaMeO3(Me3+=V3+, Cr3+, Mn3+, Fe3+, Co3+, Ni3+) perovskite-type oxides were measured. Maxima for Mn3+ and Co3+ were found. The relation between local symmetry of solid surfaces and chemisorption and catalysis is discussed.
86 citations
TL;DR: In this paper, two classes of phase transitions have been observed; order-disorder transitions of the rigid hydrocarbon chains and conformational transition of the chains, and typical examples of both classes are presented and their chain dynamics are discussed.
Abstract: Perovskite type layer-structure compounds of the formulas (Cn H2n+1 NH3)2·MCl4 and NH3 (CH2)n NH3MCl4 (M = Cd, Mn, Cu, Fe, n = 1–18) exhibit a variety of structural phase transitions which are connected with the dynamics of the alkyl-ammonium or alkylenediammonium chains respectively. Two classes of phase transitions have been observed; Order-disorder transitions of the rigid hydrocarbon chains and conformational transitions of the chains. Typical examples of both classes are presented and their chain dynamics are discussed.
86 citations
TL;DR: A new Ir(V) oxide LaLi 05 Ir 05 O 3 with an ordered orthorhombic perovskite structure has been prepared in this article, whose lattice parameters are a = 563, b = 558 and c = 787 A The possible space group is Pmm2Ir(V), with a low spin configuration t 4 2g e 0 g (3 T 1g ground term) and a large spin-orbit coupling constant (7485 ± 30 cm −1 )
60 citations
42 citations
TL;DR: In this article, the Rietveld method was used to refine the crystal structures of CeTaO 4, CeNbO 4, and NdTaO4 using neutron powder diffraction data collected at room temperature.
42 citations
41 citations
TL;DR: In this article, the electrostrictive coefficient of relaxation dielectrics was determined for BaZrO3 by measuring the hydrostatic pressure dependence of the dielectric permittivity.
Abstract: Polarization-related electrostrictive coefficients Qh have been determined for relaxation dielectrics 0.856Sr TiO3-0.144 Bi2/3 TiO3 and (K3/4Bi1/4) (Zn1/6Nb5/6)O3, and for a simple non-polar perovskite BaZrO3 by measuring the hydrostatic pressure dependence of the dielectric permittivity. Anomalous variation in the electrostrictive coefficient with temperature and frequency were observed in (K3/4Bi1/4) (Zn1/6Nb5/6)O3 in the relaxation-temperature region. This behavior can be explained qualitatively with a simple model based on potential barriers separating alternative cation sites. The empirical rule noted previously for ferroelectric perovskites, that the electrostrictive Q coefficient increases with cation order from disordered, through simple and then ordered perovskites is confirmed again in non-polar perovskites.
39 citations
TL;DR: In this paper, it was shown that CO and C02 adsorb on surface O2 and give rise to IR bands at 1495, 1450, 1175, 1110, 1070 and 850 cm-1, attributed to bidentate carbonates.
Abstract: — 273 K, of 15 to 5 kJ mol~1 point to physisorption. Between 573 and 648 K, the isosteric heat was 49 kJ mol-1, and the entropy values show that the adsorbed species has translational mobility in two dimensions. Adsorption of CO at 673 and above caused reduction of the bulk. CO adsorption at 298 gives rise to IR bands at 1495, 1450, 1175, 1110, 1070 and 850cm-1, attributed to bidentate carbonates. CO adsorption at 298 on a surface with preadsorbed 02 was found to be practically equal to the adsorption measured on a clean surface. On the contrary, preadsorption of C02 decreased the subsequent adsorption of CO to 1.2 %. It is concluded that CO and C02 adsorb on surface O2
TL;DR: In this paper, a perovskite-type compound was studied for CO oxidation and its properties were found to correlate both with the electronic state and the binding energy of transition metal in accordance with a tolerance factor.
Abstract: CO oxidation was studied over perovskite-type compounds which were prepared by a conventional ceramic method. Catalytic activity strongly correlates both with the electronic state and the binding energy of transition metal in accordance with a tolerance factor of the perovskite structure.
TL;DR: In this article, the perovskite-gallium oxide mixture can be rationalized on the basis of a pseudobinary phase diagram for the Gd2O3-Ga2O 3 system.
TL;DR: In this paper, phase equilibria in the join of CaMgSi2O6-CaFeAlSiO6 -CaTiAl 2O3-CaTiN 2O6 have been determined in air at 1 atm by the ordinary quenching method.
Abstract: Phase equilibria in the join CaMgSi2O6-CaFeAlSiO6-CaTiAl2O6 have been determined in air at 1 atm by the ordinary quenching method. Clinopyroxeness, forsterite, perovskite, magnetitess, spinelss, hibonite and an unknown phase X are present at liquidus temperatures (ss: solid solution). At subsolidus temperatures the following phase assemblages were encountered; clinopyroxeness+perovskite, clinopyroxeness +perovskite+spinelss, clinopyroxeness +perovskite+melilite (+anorthite), clinopyroxeness +perovskite+melilite+spinelss+anorthite, clinopyroxeness +perovskite+anorthite+spinelss, and clinopyroxeness +perovskite+anorthite+hibonite. At subsolidus temperatures the single phase field of clinopyroxeness extends up to 19 wt.% CaTiAl2O6. Even in the field of clinopyroxeness+perovskite, the TiO2 content in clinopyroxeness continues to increase and attains 9.2 wt.% TiO2 with 24.8 wt.% Al2O3. An interesting fact is that unusual clinopyroxenes which contain more AlIV than SiIV are present in the CaFe-AlSiO6-rich region. The liquid coexisting with pyroxene is richer in Ti, Al, and Fe3+ than the coexisting pyroxene. The clinopyroxenesss coexisting with liquid contain less TiO2, Al2O3 and Fe2O3 than those crystallized at subsolidus temperatures. The petrological significance of the join and the crystallization of Ti- and Al-rich clinopyroxenes are discussed on the basis of the experimental results of the join.
TL;DR: In this paper, a synthetic perovskite (Mg, Fe) SiO3 prepared in a diamond anvil high pressure cell at 375 kbar and 1000°C has been examined in transmission electron microscopy and selected area diffraction.
Abstract: Synthetic perovskite (Mg, Fe) SiO3 prepared in a diamond anvil high pressure cell at 375 kbar and 1000°C has been examined in transmission electron microscopy and selected area diffraction. The crystals grow, probably by nucleation and growth, as small lozenge platelets on {111} planes of the pseudo cubic ideal cell. The diffraction patterns are compatible with a pseudo tetragonal cell with parameters twice as large as those previously determined by X-ray diffraction.
TL;DR: The perovskite lattice does not appear to stabilize CsEuCl3 in comparison with the binary chlorides CsCl and EuCl2 as mentioned in this paper.
TL;DR: The results obtained in the study of lead zirconate chosen as a convenient model perovskite oxide indicate that its non-stoichiometry is related primarily to extended defects (crystallographic shear planes) rather than to classical point defects as discussed by the authors.
Abstract: The results obtained in the study of lead zirconate chosen as a convenient model perovskite oxide indicate that its non-stoichiometry is related primarily to extended defects—crystallographic shear planes—rather than to classical point defects. The presence of crystallographic shear defects is of importance in interpreting the properties of ferroelectric perovskite oxides.
Patent•
12 Aug 1980TL;DR: In this article, the perovskite-type ABO 3 crystal structure with from about 1 up to about 20 percent of the B cation sites occupied by rhodium ions and the remainder of B cations occupied by ions consisting essentially of cobalt and lanthanide ions of atomic number 57 to 71 and ions of at least 1 metal of Groups IA, IIA or IVA of the Periodic Table having ionic radii of about 0.9 A to 1.65 A.
Abstract: A catalyst of the perovskite-type ABO 3 crystal structure with from about 1 up to about 20 percent of the B cation sites occupied by rhodium ions and the remainder of the B cation sites occupied by ions consisting essentially of cobalt and the A cation sites occupied by lanthanide ions of atomic number 57 to 71 and ions of at least 1 metal of Groups IA, IIA or IVA of the Periodic Table having ionic radii of about 0.9 A to 1.65 A, and proportioned so that no more than 50 percent of the cobalt ions are tetravalent and the remaining cobalt ions are trivalent. The above-described catalyst on a refractory support. A method for producing hydrogen by reacting hydrocarbon in the presence of a catalyst as described above, either with or without a refractory support, by partial oxidation or steam reforming.
TL;DR: LaCoO3 is inactive for ethylene hydrogenation, but its activity sharply increases and goes through a maximum when the oxide, pretreated with hydrogen at temperatures between 300 and 490 °C, is reduced to different extents (up to 3 electrons/molecule).
Abstract: LaCoO3 is inactive for ethylene hydrogenation, but its activity sharply increases and goes through a maximum when the oxide, pretreated with hydrogen at temperatures between 300 and 490 °C, is reduced to different extents (up to 3 electrons/molecule).
TL;DR: In this paper, a crystal chemical study of the quaternary system LiNbO 3 − LiTaO3 − NaNb O 3 − NaTaO 3−NaTaO 4−NTaO 5−NBT 3−Niobium has been carried out and the obtained phase diagram depends on the temperature.
TL;DR: A series of ordered perovskite oxides of the type Ln2+0.25O3 has been synthesized and characterized by X-ray analysis and density measurements as mentioned in this paper.
TL;DR: In this article, two ordered perovskite-type fluorides, Rb2KNdF6 and Cs2KNDF6, have been synthesized and their luminescence properties investigated and their neodymium emission shows weak self-quenching.
01 Sep 1980
TL;DR: In this article, the La1-xSrx (La1-Srx) mnO3 (0.1 − 0.5) is used to define the La 1-Srix.
Abstract: ペロブスカイト型構造をとる (La1-xSrx)MnO3 (0.1≦x≦0.5) を合成し, この酸化物の電気抵抗 (R) を相対湿度 (H) 0-100%の範囲において調べた.試料を粉砕した後, アルミナ基板に塗布し, Arガス中, 800℃及び1000℃まで加熱した. この酸化物の電気抵抗を室温にて, 2端子法を用いて測定した. x=0.3の試料の電気抵抗は, 相対湿度の増加とともに, ほぼ直線的に増加することが分った. また焼成温度が高くなるにしたがって, ΔR(=R100%-R0%) は急激に減少することが分った. 水の吸着量が増すにしたがって電気抵抗が大きくなる現象は, 欠陥型吸着モデルを用いて説明できる.
TL;DR: The cubic perovskite Sr(Co1−xMnx)O3 has a maximum value of a-axis at x = 03 and a change of spin state of Co4+ ion from low to high as discussed by the authors.
TL;DR: The prototype structure of BaMF 4 type crystal is considered to be a structure composed of slabs of the perovskite, with the space group D 17 2 h.
Abstract: The prototype structure of BaMF 4 type crystal is considered to be a structure composed of slabs of the perovskite, with the space group D 17 2 h . Normal modes at the \(\varGamma\) point in the orthorhombic Brillouin zone of the hypothetical D 17 2 h phase and the C 12 2 v phase below the melting point were analyzed with a help of the group theory. The condensed modes to give the crystal structure at room temperature were assigned and discussed in comparison with the Sr 2 Ta 2 O 7 structure.
TL;DR: The stable polymorphs of MnGeO3 are orthopyroxene type (phase I), clinopyroxenetype (II), ilmenite type (III) and perovskite type(IV) in the order of pressure increase as mentioned in this paper.
Abstract: The stable polymorphs of MnGeO3 are orthopyroxene type (Phase I), clinopyroxenetype (II), ilmenite type (III) and perovskite type (IV) in the order of pressureincrease. The crystallographic data and crystal structures of the polymorphs aredescribed except for the perovskite type, the structure of which has not been accuratelydetermined. These structures areE compared with the structures of similargermanates and silicates of different metals rather than Mn and the characteristicsof the ilmenite type (III) of MnGeO3 are discussed.
TL;DR: In this paper, it has been shown that a very pronounced diffusion of phase transitions takes place in Ba(Ti x Sn 1− x )O 3 films and that the phase transition from the tetragonal to the regular phase increases with increasing concentration of tin in the films and also with decreasing film thickness.