High pressure study on Mg2TiO4 and its implication for post-spinel phase
Abstract
Spinel-type phases are stable at transition zone pressures and transform to other dense structures in the deeper mantle. Several post-spinel structures have been suggested, but they vary with the compositions and synthesized pressure and temperature conditions. Our high-pressure and room-temperature study on Mg2TiO4 qandilite to 50 GPa using synchrotron X-ray diffraction and Raman spectroscopy shows that the cubic spinel phase transforms to a tetragonal (I41/amd) phase, rather than an orthorhombic structure. In addition, the spinel to tetragonal phase transition is sluggish. The appearance of the new phase was found at about 15 GPa and completed at about 23-24 GPa. Similar observations are also found for Zn2TiO4 but with a slightly higher transition pressure. Our results are consistent with previous study on MgCr2O4 and FeCr4O4 spinel, suggesting that the cations play an important role for determining the structure of the post-spinel phase.
The bulk modulus of the qandilite is determined to be 148(3) GPa and its pressure derivative is 6.6. For the tetragonal phase, the bulk modulus is 209(2) GPa when the K0' is fixed at 4. The volume change between the spinel and the tetragonal phase is about 9%.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR33C0135S
- Keywords:
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- 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction;
- MINERAL PHYSICSDE: 3612 Reactions and phase equilibria;
- MINERALOGY AND PETROLOGYDE: 3621 Mantle processes;
- MINERALOGY AND PETROLOGY