High-pressure phase behaviors of ZnTiO3: ilmenite-perovskite transition, decomposition of perovskite into constituent oxides, and perovskite-lithium niobate transition

摘要

High-pressure high-temperature phase transitions of ZnTiO3 ilmenite were examined using multianvil apparatus up to 25.5 GPa and 1,500 A degrees C and diamond anvil cell to 26.5 GPa and about 2,000 A degrees C. Combined results of the multianvil quench experiments and in situ diamond anvil cell experiments indicated that at about 10 GPa and 1,200 A degrees C ZnTiO3 ilmenite transforms to orthorhombic perovskite which is converted to lithium niobate phase on release of pressure. The boundary of the ilmenite-provskite transition is expressed by P(GPa) = 15.9 - 0.005T (A degrees C). The high-pressure experiments also indicated that at 20-24 GPa and 1,000-1,400 A degrees C ZnTiO3 orthorhombic perovskite dissociates into rocksalt-type ZnO + baddeleyite-type TiO2 which are recovered, respectively, as wurtzite-type ZnO and alpha-PbO2-type TiO2 at 1 atm. The boundary of the perovskite dissociation is expressed by P(GPa) = 8.7 + 0.011T (A degrees C). Molar volume changes of ZnTiO3 at ambient conditions were estimated as -4.7 % for the ilmenite-perovskite transition and -3.5 % for the perovskite decomposition into the oxides. The absence of CaIrO3-type postperovskite in ZnTiO3 is consistent with that dissociation of ZnTiO3 perovskite into the oxides has the larger molar volume change than -1 to -2 % of the perovskite-postperovskite transition in various ABO(3) compounds and with previous data that ABO(3) perovskites with relatively ionic B-O bonds do not transform to the postperovskite. The transition behaviors of ZnTiO3 are similar to those of MnTiO3 and FeTiO3, but ZnTiO3 perovskite dissociates into the constituent oxides.