An X-ray diffraction study of ilmenite (FeTiO3) under high pressures and temperatures using large-volume pressure and synchrotron radiation

L.C. Ming,1; Y.H. Kim,2; Y.Wang, T. Uchida, S. Sutton, and M. Rivers3

1Univ. of Hawaii;
2Geongsang National Univ. , Korea;
3GSE-CARS, The Univ. of Chicago

APS GSECARS

Two natural samples of ilmenite (FeTiO3) were studied in a large volume press with T-CUP apparatus to 19.6 GPa and 800 oC. In situ X-ray diffraction measurements were carried using synchrotron radiation from the GSECARS beamline 13-BMD at the Advanced Photon Source (APS). As the sample was pressurized at room temperature to 19.6 GPa and heated to 700°C, we observed a direct phase transforms from the ilmenite phase to the perovskite at ~ 20 GPa and 600°C. The perovskite phase persists when quenched to room temperature, suggesting the perovskite phase is the stable high-pressure phase for FeTiO3. As we decrease pressure, the perovskite phase gradually converts to the LiNbO3 phase at ~ 15 GPa, in accord with previous observation that LiNbO3 phase transforms to the perovskite phase at 16 GPa at room temperature [1]. The LiNbO3 phase was converted to the ilmenite phase when temperature was increased to 300°C at ~ 14 GPa but the reverse transition from ilmenite back to the LiNbO3 phase was not observed during cooling cycle. It is therefore concluded that LiNbO3 is a metastable phase with no stability field in the P-T space. These results are in line with the general crystal structural behavior for the ABO3 compounds under high pressures. By cycling the pressure up and down at a given high temperature, the perovskite (pv)-ilmenite (il) transformation could be observed in both directions, and thus the transition pressure could be bracketed. However, the results thus determined for the two samples appear to be different with one another, and also different from that reported previously [2], suggesting phase boundary of the pv-il transition may be sensitive to the chemical composition of the starting materials. Ilmenite (FeTiO3) is a common accessory mineral in igneous and metamorphic rocks. It usually forms a solid solution with hematite (Fe2O3) and geikilite (MgTiO3). A systematic phase transformation study on the solid solutions of the FeTiO3-MgTiO3-Fe2O3 system under high P/T conditions would be valuable for petrological applications.

References:

  1. Leinenweber, K, W. Utsumi, T. Tsuchida, T. Yagi, and K. Kurita (1991), Phys. Chem. Minerals 18:244-250.
  2. Syono, Y. H. Yamauchi, A. Ito, Y. Someya, E. Ito, Y. Matsui, M. Akaogi (1980), in Ferrite: Proceeding of the International Conference, Japan, 192-195.