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 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 ~66.6 and ~33.3 wt% tausonite, which are consistent with formulae of approximately Sr2(NaLa)Ti3O9 and Sr(NaLa)2Ti3O9, respectively. The pseudo-cubic cell parameter apdecreases with increasing loparite content, while the  tilt angle F (F=0 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 (Na2/3Th1/3TiO3), which is unusual in that it contains a tetravalent cation at the A-site. This thorium titanium perovskite was synthesized in an attempt to determine its structure. Although power 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 (K2Cr2Ti6O16) and the n=3 member of the homologous series K2La2Ti3+nO10-2n, i.e., K2La2Ti6O16. This series is important in understanding the location and environment of the rare-earth cations in natural hollandite specimens and the capability of hollandite (i.e., SynRock) to immobilize large elements of varying charge and size. This pseudo-binary system is characterized by the presence of the following phases: hollandite [K1.54(Cr1.43Ti6.52)7.95O16]; perovskite-2 (LaCrO3); and perovskite-3 (La2Ti2O7). Complete solid-solution between the end-members of this system does not occur. The hollandites (space-group 14/m) have an A-site occupancy of approximately 75-82%, and exhibit no significant substitution of La3+ at any of the cation sites. Perovskite-1 is considered to be a non-stoichiometric A-site deficient perovskite. Potassium hexatitanate is the only main phase that is stoichiometric and contains no substitution of Cr3+ in any of the cation sites. All the Cr3+ excluded from the potassium hexatitanate structure is incorporated into perovskite-2.
A copy of the thesis can be downloaded here