High-pressure phase transformations and compressions of ilmenite and rutile, I. Experimental results

Details High-pressure phase transformations and compressions of ilmenite and rutile, I. Experimental results High-pressure phase transformations and compressions of ilmenite and rutile, I. Experimental results

Jun 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975pepi...10..167l&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 10, Issue 2, p. 167-176.

Physics

8

Scientific paper

Natural ilmenite (Fe,Mg)TiO3 has been found to transform to the perovskite structure and then to disproportionate into its component oxides, (Fe,Mg)O plus a cubic phase of TiO2, at loading pressures of 140 and 250 kbar respectively, and at temperatures of 1,400 to 1,800°C. Samples were compressed in a diamond-anvil press and heated by irradiation with a YAG laser. The lattice parameters of the perovskite phase of (Fe,Mg)TiO3 at room temperature and 1 bar are a0 = 4.471 +/- 0.004, b0 = 5.753 +/- 0.005, and c0 = 7.429 +/- 0.006 Å with 4 molecules per cell. The zero-pressure volume change is 8.0% for the ilmenite-perovskite transition, 13.3% for the perovskite-mixed-oxides transition, and 20.2% for the ilmenite-mixed-oxides transition. The cubic phase of TiO2 can be indexed on the basis of space group Fm3m with Z = 4 and a0 = 4.455 +/- 0.008 Å at room temperature and 1 bar, which corresponds to a decrease in zero-pressure volume of 29.2% for the rutile-cubic-phase transition. An isentropic bulk modulus at zero pressure of 5.75 +/- 0.30 Mbar and a pressure derivative greater than 8 were calculated for the high-pressure cubic phase. The calculated bulk modulus for the mixture of (Fe,Mg)O and cubic TiO2 is 2.48 +/- 0.25 Mbar. All the phase transformations, the calculated lattice parameters, and the bulk moduli observed in this study are in good agreement with published shock-Hugoniot data for ilmenite and rutile.

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