First-principles investigation on high-pressure structural evolution of MnTiO3

First-principle calculations using density-functional theory with linearized augmented plane wave method and projector-augmented method have been performed for the high-pressure MnTiO3 polymorphs and their possible dissociation products. Theoretical results demonstrate that ilmenite-type MnTiO3 transforms into perovskite phase at 27 GPa and 0 K. The lithium niobate phase of MnTiO3 is confirmed to be metastable according to its higher Gibbs free energy compared with that of ilmenite at ambient conditions. In ilmenite and lithium niobate phases, MnO6 octahedra become more distorted while TiO6 octahedra become more regular with increasing pressure. In orthorhombic perovskite phase, the structural distortion deviated from the ideal cubic perovskite is enhanced at higher pressure. Based on the non-spin-polarized calculations, perovskite phase MnTiO3 is predicted to dissociate into Fm3̄m-MnO+P21/c-MnTi2O5 at 29 GPa.