Complete Fe-Mg solid solution in lithium niobate and perovskite structures in titanates at high pressures and temperatures

Abstract

A new high-pressure MgTiO3 phase with the lithium niobate structure (R3c) has been recovered from experiments at 21 GPa and 1200 8C. 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.