Characteristics of perovskite-related materials

Oxides with perovskite structure show characteristic features of their physical behaviour that can be relevant for the understanding of the mantle m aterial (MgFe)SiO3. Perovskites distort locally, and four different mechanisms have been found: tilt of octahedral complexes, off-centring of the octahedrally coordinated cation, distortion of the octahedral cage and off-centring of the 12-fold coordinated site. These deformations usually lead to structural instabilities related to phase transitions, extremely sluggish kinetic behaviour even leading to pseudo-glasses and polaronic transport. All these properties depend sensitively on the oxygen fugacities, defect densities and the rheology of the system. There is some evidence that the predicted structural phase transitions and glass states occur in CaSiO3 whereas no structural instability has yet been reported in MgSiO3.