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

Abstract

High-pressure high-temperature phase transitions of ZnTiO3 ilmenite were examined using multianvil apparatus up to 25.5 GPa and 1,500 °C and diamond anvil cell to 26.5 GPa and about 2,000 °C. Combined results of the multianvil quench experiments and in situ diamond anvil cell experiments indicated that at about 10 GPa and 1,200 °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 (°C). The high-pressure experiments also indicated that at 20–24 GPa and 1,000–1,400 °C ZnTiO3 orthorhombic perovskite dissociates into rocksalt-type ZnO + baddeleyite-type TiO2 which are recovered, respectively, as wurtzite-type ZnO and α-PbO2-type TiO2 at 1 atm. The boundary of the perovskite dissociation is expressed by P(GPa) = 8.7 + 0.011T (°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 ABO3 compounds and with previous data that ABO3 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.