HIGH-PRESSURE TRANSFORMATIONS IN SILICATES, GERMANATES, AND TITANATES WITH ABO3 STOICHIOMETRY

High-pressure phase transformations were investigated for two silicates, MgSiO3 and ZnSiO3; six germanates, MGeO3 and six titanates, MTiO3 (M=Ni, Mg, Co, Zn, Fe, and Mn) at about 1,000°C and pressures up to ca. 30 GPa. CoGeO3 was found to assume the ilmenite form. The ilmenite phases were confirmed to transform in the following schemes: to perovskite in MgSiO3 and MnGeO3, to corundum in MgGeO3 and ZnGeO3, to rocksalt plus rutile in ZnSiO3 and CoGeO3 and to rocksalt plus TiO2 (possibly of some denser structure) in NiTiO3, MgTiO3, CoTiO3, ZnTiO3 and FeTiO3. In the case of FeTiO3, the corundum form appeared as an intermediate phase. The possibility that the corundum type MnTiO3 might transform to some denser modification could not be excluded. The compound NiGeO3 was nonexistent throughout the pressure range studied. High-pressure phases of ABO3 (A=Ni, Mg, Co, Zn, Fe, and Mn; B=Si, Ge and Ti) are summarized, and those stabilized at pressures higher than 20 GPa are discussed. © 1979 Springer-Verlag.