Showing papers on "Perovskite (structure) published in 1969"

Structure Relations of Hexagonal Perovskite-Like Compounds ABX 3 at High Pressure

Abstract: Phase stability relations among four hexagonal perovskite-like structures as well as the cubic perovskite structure have been studied for several oxides (BaMnO 3 and SrMnO 3 ) and fluorides (CsMnF 3 , RbNiF 3 and TlNiF 3 ) at high pressure. A series of high pressure transformations are found to occur in the order of the packing sequence along the hexagonal c axis (or cubic 111 axis) of ( a b ), ( a b a b c b c a c ), ( a b a c ), ( a b c a c b ) and ( a b c ) with increasing pressure. This order is corresponding with the increasing order of the proportion of the cubic close-packed layers in the hexagonal close-packed structure. It is suggested that the tolerance factor of the perovskite structure and the Coulomb repulsive force play an important role in determining the crystal structure and its order in the series of phase transformations at high pressure.

Garnet-Like Structures of High-Pressure Cadmium Germanate and Calcium Germanate

Abstract: Crystals of CdGeO3 grown at a pressure of 65 kilobars are tetragonal and have an ordered, garnet-like crystal structure with cadmium occupying the dodecahedral and octahedral sites, and germanium the octahedral and tetrahedral sites. The crystal structure (a = 12.406 ± 1 angstroms, c = 12.256 ± 1 angstroms, and space group 14,/a) has been refined by least-squares analysis to an R (discrepancy index) of 0.073. Two high-pressure phases of CaGeO3 were synthesized, one isotypic with tetragonal CdGeO3 (a = 12.514 ± 3 angstroms, c = 12.358 ± 3 angstroms), and the other isotypic with perovskite.

Chemical and Magnetic Study of Layered Strontium Lanthanum Manganate Structures

Abstract: Previously published work describes the magnetic properties of the calcium manganate (IV) phases having tetragonal structures consisting of perovskite layers separated along the 001 direction by non‐magnetic layers. Anomalous magnetic behavior exhibited by these was attributed to a persistence of short‐range, two‐dimensional order above the Neel temperature. In the present study, phases having similar structures were prepared having the general composition SrO[(Sr1−xLaxMnx3+ Mn1−x4+)O3]y, where y = 1, 2, 3 corresponding to single, double, or triple perovskite layers. Magnetization measurements over the range 1.4°–300°K showed that ferromagnetism expected of the Mn3+‐O‐Mn4+ interaction was achieved. At low temperatures, remanent moments as high as 3.2 μB/MN ion were observed. With increasing temperatures, these decreased in an anomalous manner. At intermediate temperatures there was a sharp decrease‐like that expected at a Curie temperature. However, at its termination a significant moment remained. This behavior is thought to be related to the two‐dimensional nature of these layered structures and may depend upon a long spin‐correlation length which is expected of such structures.

Metamagnetism in the perovskite compound Gd2CoMnO6

Abstract: The compound Gd2CoMnO6 crystallizes with the orthorhombic perovskite structure and is isomorphous with GdFeO3. A crystal structure refinement shows that the Mn3+-O2−-Mn3+ bond angles are ∼ 145° and that the distortion from cubic symmetry is considerable. A spontaneous moment of 5 e.m.u./g develops below 115°K due to the exchange interactions between near neighbouring Mn3+ ions. Below 115°K a field induced metamagnetic transition to a state with a moment of 20 e.m.u./g is also observed and this transition is depressed in temperature by 1°c for 360 oe applied field. The metamagnetism is accounted for on the basis of a transition between an uncompensated anti-ferromagnetic and a ferromagnetic state which is observed in Gd2CoMnO6 due to a change in sign of the Mn3+-O2−-Mn3+ exchange interaction originating from Jahn-Teller electronic ordering in Mn3+ ions. This ordering is favoured at low temperatures and introduces a negative contribution to the exchange interaction.

Über CsHgF3, RbHgF3 und KHgF3††

Abstract: Neu dargestellt wurden CsHgF3 (kubisch, a = 4,57 A), RbHgF3 (kubisch, a = 4,47 A) und KHgF3 (orthorhombisch, a = 6,20; b = 6,28; c = 8,81 A), die zum Perowskit-Typ bzw. zur GdFeO3-Variante dieses Typs gehoren. Die farblosen Verbindungen sind gegen Feuchtigkeit auserordentlich empfindlich. New prepared are CsHgF3 (cubic, a = 4.57 A), RbHgF3 (cubic, a = 4.47 A) and KHgF3 (orthorhombic; a = 6.20; b = 6.28; c = 8.81 A), which belong to the perovskite type or the GdFeO3 variation of this type. The colourless compounds are extremly sensitive to moisture.

Synthesis of Barium Ferrates in Oxygen.

Abstract: Phase relations in the system BaO-Fe2O3-"FeO2" at 1 atm (1 atm = 1.013 × 105 N/m2) oxygen and between 800 to 1050 °C are shown in the vicinity (high Ba portion) of the 1:1 cation-cation ratio composition. A hexagonal BaTiO3-like phase, BaFeO3-X (a = 5.676A, c = 13.934A), exists below 960 °C. A perovskite-like phase BaFeO3-X' occurs between 960 and 1050 °C. Single-phase tetragonal perovskite can be obtained at room temperature by quenching compositions with Ba-Fe ratios of 67:66 (a = 3.985 A, c = 4.005 A, 1000 °C) and 27:26 (a = 3.988 A, c = 4.003 A, 1000 °C) from above 960 °C. At the 17:16 ratio, single phase cubic perovskite (a = 3.994 A, 1000 °C), can be synthesized. Influence of temperature, additions of barium, and use of Pt-containers on phase relations are discussed.

Magnetic Screening of 19F Nuclei in Perovskite KMgF3

Abstract: The present work cites the measurement data for the magnetic screening tensor of fluorine nuclei in KMgF3 and comparison results of 19F screening tensor components in this substance with the theoretical, based on the overlapping pattern of ion wave functions.

Microwave and optical properties of selected perovskite materials.

Abstract: : Single crystals of several perovskite materials including CsMnF3, alkali chloride-manganese chloride salts and Er3Fe5O12 have been prepared. The Faraday rotation of crystals of Er3Fe5O12 have been measured at 1.15 micrometers at room temperature and at liquid nitrogen temperature (i.e., below the compensation point). The use of this material as an optical memory is discussed. The optical properties of single crystals of several chloride salt of manganese have been measured. The results obtained for the fluorescence are compared with measurements on several fluoride salts. (Author)