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Cubic Perovskite Structure (cubic + perovskite_structure)
Selected AbstractsChemInform Abstract: Copper-Rich Framework Sulfides: A4Cu8Ge3S12 (A: K, Rb) with Cubic Perovskite Structure.CHEMINFORM, Issue 38 2010Ren-Chun Zhang Abstract The new title compounds (IV) are isotypic and crystallize in the cubic space group Fmc with Z = 2. [source] Structure and Dielectric Properties of Pb(Sc2/3W1/3)O3,Pb(Zr/Ti)O3 RelaxorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Pavol Juhás The structure and dielectric properties of (1,x)Pb(Sc2/3W1/3)O3,(x)Pb(Zr/Ti)O3 ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x, 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc2/3W1/3)O3 (PSW) can be described by a random-site model with one cation site occupied by Sc3+ and the other by a random distribution of (Sc1/33+W2/36+). The ordering is destabilized in solid solutions of PSW with PbZrO3 (PSW,PZ), but stabilized by PbTiO3 in the (1,x)PSW,(x)PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW,PZ the temperature of the permittivity maximum (T,,max) increases linearly with x; however, for PSW,PT T,,max decreases in the ordered region (up to x= 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW,(0.25)PT; when the order parameter was reduced from ,1.0 to ,0.65, T,,max increased by more than 60°C. [source] Barium Holmium Zirconate, A New Complex Perovskite Oxide: I, Synthesis, Characterization, and Potential Use as a Substrate for High-Critical-Temperature SuperconductorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Rajan Jose Barium holmium zirconate, a new complex perovskite ceramic oxide, has been synthesized through liquid-phase sintering for the first time. The conventional solid-state reaction method using constituent oxides and carbonates was found to be inadequate for the synthesis of Ba2HoZrO5.5 material. During high-temperature annealing, the development of stable BaZrO3 and BaHoO2.5 phases prevented the formation of Ba2HoZrO5.5 as a single-phase material, even at 1650°C. However, an addition of a small amount of CuO (1 wt%) in the reaction mixture has resulted in the formation of an ordered complex perovskite Ba2HoZrO5.5 phase during the heating process. The structure of Ba2HoZrO5.5 was studied by X-ray diffraction and found to have a cubic perovskite structure with a lattice constant of a= 8.482 Å. Dielectric constant and loss factor values of Ba2HoZrO5.5 are also in the range suitable for use as a substrate for microwave applications. The X-ray diffraction and resistivity measurements have shown that there is no detectable chemical reaction in YBa2Cu3O7,,,Ba2HoZrO5.5 and Bi(2212),Ba2HoZrO5.5 composites, even under extreme processing conditions. Dip-coated and melt-textured YBa2Cu3O7,, and Bi(2212) thick films developed on polycrystalline Ba2HoZrO5.5 gave zero-resistivity transition temperatures of Tc(0) = 92 and 85 K, respectively. [source] Investigation of the structure and phase transitions in the novel A-site substituted distorted perovskite compound Na0.5Bi0.5TiO3ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2002G. O. Jones Rietveld neutron powder profile analysis of the compound Na0.5Bi0.5TiO3 (NBT) is reported over the temperature range 5,873,K. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813,K), to one of tetragonal (673,773,K) and then rhombohedral structures (5,528,K) has been established. Coexisting tetragonal/cubic (773,813,K) and rhombohedral/tetragonal (with an upper temperature limit of 145,K between 528 and 673,K) phases have also been observed. Refinements have revealed that the rhombohedral phase, space group R3c, with aH = 5.4887,(2), cH = 13.5048,(8),Å, V = 352.33,(3),Å3, Z = 6 and Dx = 5.99,Mg,m,3, exhibits an antiphase, a,a,a, oxygen tilt system, , = 8.24,(4)°, with parallel cation displacements at room temperature. The tetragonal phase, space group P4bm, with aT = 5.5179,(2), cT = 3.9073,(2),Å, V = 118.96,(1),Å3, Z = 2 and Dx = 5.91,Mg,m,3, possesses an unusual combination of in-phase, a0a0c+ oxygen octahedra tilts, , = 3.06,(2)°, and antiparallel cation displacements along the polar axis. General trends of cation displacements and the various deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. An investigation of phase transition behaviour using second harmonic generation (SHG) to establish the centrosymmetric or non-centrosymmetric nature of the various phases is also reported. [source] | ||||||||||