Crystallographic studies of selected perovskite-group compounds

This study investigates the tausonite-loparite solid solution series. Members of this series are important in some alkaline complexes, thus making studies of their crystallography essential. Rietveld refinement of the crystal structures of the tausonite-loparite solid solution series, using X-ray diffraction powder patterns, indicates that there is a reduction in symmetry from cubic (Pm3m) to orthorhombic (Pnma), by way of an intermediate tetragonal (P4/mbm) modification. The symmetry changes appear to occur at about {dollar}sim{dollar}66.6 and {dollar}sim{dollar}33.3 wt% tausonite, which are consistent with formulae of approximately {dollar}rm Srsb2(NaLa)Tisb3Osb9{dollar} and {dollar}rm Sr(NaLa)sb2Tisb3Osb9,{dollar} respectively. The pseudo-cubic cell parameter {dollar}{lcub}bf a{rcub}rmsb{lcub}p{rcub}{dollar}, decreases with increasing loparite content, while the (111) tilt angle {dollar}Phi(Phi = 0{dollar} in Pm3m) on inception at 50 wt% loparite achieves a maximum and decreases thereafter with increasing loparite content. Rietveld refinements indicate that no ordering at the A-site exists throughout the solid solution series.; This study also investigates a titanium perovskite {dollar}rm(Nasb{lcub}2/3{rcub}Thsb{lcub}1/3{rcub}TiOsb3),{dollar} which is unusual in that it contains a tetravalent cation at the A-site. This thorium titanium perovskite was synthesised in an attempt to determine its structure. Although powder diffractometry suggests an Fm3m space-group, attempts at Rietveld refinement of the structure show the actual space-group must be of reduced symmetry.; This study also provides data on the pseudo-binary system between hollandite {dollar}rm(Ksb2Crsb2Tisb6Osb{lcub}16{rcub}){dollar} and the {dollar}n = 3{dollar} member of the homologous series {dollar}rm Ksb2Lasb2Tisb{lcub}3+n{rcub}Osb{lcub}10+2n{rcub},{dollar} i.e., {dollar}rm Ksb 2Lasb2Tisb6Osb{lcub}16{rcub}.{dollar} (Abstract shortened by UMI.)...