Japan Geoscience Union Meeting 2014

Presentation information

Poster

Symbol S (Solid Earth Sciences) » S-GC Geochemistry

[S-GC56_30PO1] Solid Earth Geochemistry, Cosmochemistry

Wed. Apr 30, 2014 6:15 PM - 7:30 PM Poster (3F)

Convener:*Shimoda Gen(Geological Survey of Japan, AIST), Katsuhiko Suzuki(Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology), Katsuyuki Yamashita Katsuyuki(Graduate School of Natural Science and Technology, Okayama University)

6:15 PM - 7:30 PM

[SGC56-P05] High-pressure high-temperature phase transitions in ZnTiO3

*Kohei ABE1, Hiroshi KOJITANI1, Masaki AKAOGI1 (1.Department of Chemistry, Gakushuin University)

Keywords:ZnTiO3, Perovskite, LiNbO3, High pressure

It is widely accepted that perovskite-type MgSiO3 is the most abundant mineral in Earth’s lower mantle. Ilmenite-type MgSiO3 transforms to perovskite at 23 GPa and 1600 ℃. It was reported that ilmenite-type ZnTiO3, an analogue to ilmenite-type MgSiO3, decomposes into ZnO and TiO2 at about 20-25 GPa (Ito and Matsui, 1979). However, phase relations in ZnTiO3 have not been studied yet in detail. Therefore, we investigated the phase relations in ZnTiO3 by high-pressure high-temperature experiments. A starting material of ilmenite-type ZnTiO3 was synthesized by heating a mixture of ZnO and TiO2 with 1:1 mol ratio at 800 ℃ for 32 hours in air. High-pressure phase relation experiments were made by using a Kawai-type 6-8 multi-anvil apparatus in the pressure and temperature ranges of 13-35 GPa and 1000-1400 ℃, respectively. After keeping the starting sample at desired conditions for 1-2 hours, the samples were quenched, and then decompressed to ambient pressure. Recovered samples were identified by using the powder X-ray diffraction method. We found that the recovered samples which were compressed between 15 and 20 GPa at 1000-1400 ℃ had the LiNbO3-type (LNO) structure. The ilmenite-LNO phase boundary was determined as P(GPa)=19.9-0.0038T(℃). FeTiO3 ilmenite which is an analogue to ilmenite-type MgSiO3 transforms to perovskite above 15 GPa, and the perovskite transforms to the LNO-type structure during decompression (Ming et al., 2006). The ilmenite-perovskite phase boundary in FeTiO3 has a negative slope which is caused by a positive entropy change for the transition due to increase of coordination number of divalent cation from 6 to 8. If the LNO-type ZnTiO3 is a stable phase, the slope of the boundary should be positive because of no change in the coordination number of the divalent cation. Therefore, the negative slope of the boundary implies that the recovered LNO-type ZnTiO3 was originally perovskite-type at 15-20 GPa.The recovered samples synthesized above 20 GPa were identified to be an assembly of wurtzite-type ZnO and α-PbO2-type TiO2. The post-perovskite phase boundary in ZnTiO3 is determined as P(GPa)=9.5-0.010T(℃). Wurtzite-type ZnO transforms to NaCl-type at about 6 GPa (Kusaba et al., 1999). Also, α-PbO2-type TiO2 transforms to baddeleyite-type at about 17 GPa (Tang and Endo, 1993). Therefore, we suggest that the phase assembly of NaCl-type ZnO and baddeleyite-type TiO2 is stable above 20 GPa.