COMPLETE FE-MG SOLID-SOLUTION IN LITHIUM-NIOBATE AND PEROVSKITE STRUCTURES IN TITANATES AT HIGH-PRESSURES AND TEMPERATURES

A new high-pressure MgTiO3 phase with the lithium niobate structure (R 3c) has been recovered from experiments at 21 GPa and 1200 degrees C. Phases with the lithium niobate structure were also synthesized for in termediate compositions between FeTiO3 and MgTiO3 and their lattice pa rameters determined. Previous thermodynamic calculations indicated the stable FeTiO3 phase at high pressure has the perovskite structure whi le the lithium niobate polymorph is a metastable quench phase. This su ggests that these magnesium-iron titanates with lithium niobate struct ures may also be metastable quench phases from perovskite. This exampl e of a complete solid solution between Fe and Mg in the lithium niobat e structure probably reveals a case of complete solid solution between Fe and Mg in the A sites of the perovskite structure.