Perovskite Synthesis and Analysis Using Structure Prediction Diagnostic Software (2002)

The perovskite structure type accommodates most of the metallic ions in the periodic table and a significant number of different anions.This compositional diversity leads to a variety of physical properties.A software program, SPuDS (Structure Prediction Diagnostic Software) was developed to predict the crystal structures of perovskites, including those distorted by tilting of symmetric and Jahn-Teller distorted octahedra.Only the composition and oxidation states of the ions were required as user inputs.Rigid octahedra were maintained in electronically symmetric octahedra, while distortions of the octahedral bond lengths were utilized in Jahn-Teller distorted compositions.SPuDS calculates the optimal structure in Glazer tilt systems most often observed experimentally and for tilt systems with interesting multiple A-cation environments.Structure optimization occurs by distorting the structure to minimize the global instability index.Location of the A-site cation is chosen so as to maximize the symmetry of its coordination environment.SPuDS has been employed in a number of useful applications, including the use of predicted structural information to estimate physical properties of both hypothetical compositions and those materials for which accurate structural data is not available, as a guide for exploratory synthetic efforts, as a starting model for Rietveld refinements in the course of structurally characterizing new materials, and for extracting the effects of iii octahedral tilting distortions from other structural distortion mechanisms.Structural predictions were made for a variety of compositions with a single and multiple octahedral cations and compared with a number of previously determined structures to illustrate the accuracy of this approach.Synthesis and structural refinement from x-ray and neutron powder diffraction of Ca 2 MnMO 6 (M = Nb, Sb, Ru) and Sr 2 MnMO 6 (M=Nb, Sb) is reported.Various types of cooperative Jahn-Teller distortions (CJTD) that occur in ternary (AMX 3 ) and double (A 2 MMO 6 ) perovskites are reviewed.Interplay between CJTD's, octahedral tilting and cation order is systematically examined in A 2 MMO 6 perovskites, where M is an active Jahn-Teller (J-T) ion (Mn 3+ or Cu 2+ ) and M is an octahedrally symmetric cation.Perovskites with a + a + a + octahedral tilting and a single octahedral cation exhibit interesting dielectric properties.SPuDS was also used to examine the prospects for synthesizing new compounds in tilt systems with multiple A-cation coordination geometries.Perovskites with a specific type of octahedral tilting (a + a + a + ) coupled with Acation and rock-salt octahedral cation ordering were predicted to exist.A collaborative effort to perform high-pressure high-temperature synthesis resulted in the successful creation of four new dual A-site and octahedral cation ordered perovskites.Characterization of the structures and dielectric properties of CaCu 3 Ga 2 Sb 2 O 12 , CaCu 3 Cr 2 Sb 2 O 12 , CaCu 3 Ga 2 Nb 2 O 12 and CaCu 3 Ga 2 Ta 2 O 12 is reported.I thank Dr. Brett Hunter for collection of neutron powder diffraction at