High-pressure phase behavior of MnTiO_3: Decomposition of perovskite into MnO and MnTi_2O_5

摘要

The phase relations and compression behavior of MnTiO_3 perovskite were examined using a laser-heated diamond-anvil cell, X-ray diffraction, and analytical transmission electron microscopy. The results show that MnTiO_3 perovskite becomes unstable and decomposes into MnO and orthorhombic MnTi_2O_5 phases at above 38 GPa and high temperature. This is the first example of ABO_3 perovskite decomposing into AO + AB_2O_5 phases at high pressure. The compression behavior of volume, axes, and the tilting angle of TiO_6 octahedron of MnTiO_3 perovskite are consistent with those of other A~(2+)B~(4+)O_3 perovskites, although no such decomposition was observed in other perovskites. FeTiO_3 is also known to decompose into two phases, instead of transforming into the CaIrO_3-type post-perovskite phase and we argue that one of the reasons for the peculiar behavior of titanate is the weak covalency of the Ti-O chemical bonds.