THE HIGH-TEMPERATURE PHASE-TRANSITION IN PEROVSKITE

Perovskite (CaTiO3) is a model compound for the Earth's most abundant mineral, the perovskite (Mg, Fe)SiO3. High-temperature structural investigations using neutron powder diffraction reveal a phase transition to a highly disordered cubic phase. As one approaches this transition, the TiO6 octahedra become less distorted and their rotational disorder is reflected by the large atomic-displacement parameters of the oxygens in the (a, b)-plane, suggesting that the high-temperature transition to the cubic phase could be triggered by the onset of mobility in the oxygen sublattice. This would account for the fact that no intermediate tetragonal phase is observed.