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 (R3c) has been recovered from experiments at 21 GPa and 1200 °C. Phases with the lithium niobate structure were also synthesized for intermediate compositions between FeTiO₃ and MgTiO₃ and their lattice parameters determined. Previous thermodynamic calculations indicated the stable FeTiO₃ phase at high pressure has the perovskite structure while the lithium niobate polymorph is a metastable quench phase. This suggests that these magnesium-iron titanates with lithium niobate structures may also be metastable quench phases from perovskite. This example of a complete solid solution between Fe and Mg in the lithium niobate structure probably reveals a case of complete solid solution between Fe and Mg in the A sites of the perovskite structure.