High-Pressure and Variable Temperatures Studies of Minerals
Magnetic-Electronic Properties of Selected Mineral Assemblages at High-Pressure and Variable Temperatures
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High pressure and variable temperature studies of synthetic FeS and Fe7S8 as well as natural FeTiO3 have been carried out in a diamond anvil cell. FeS in the low-pressure less than ~7 GPa has thermally activated charge carriers and a high-spin electronic configuration, whereas monoclinic-FeS above ~7 GPa adopts a magnetically quenched low-spin state and non-metallic behaviour associated with the filled valence band. By contrast Fe7S8 is magnetic and metallic below ~5 GPa and diamagnetic metallic above this pressure. The Fe3+/Fe2+ ratio in natural ilmenite samples shows rapid increase under pre...
High pressure and variable temperature studies of synthetic FeS and Fe7S8 as well as natural FeTiO3 have been carried out in a diamond anvil cell. FeS in the low-pressure less than ~7 GPa has thermally activated charge carriers and a high-spin electronic configuration, whereas monoclinic-FeS above ~7 GPa adopts a magnetically quenched low-spin state and non-metallic behaviour associated with the filled valence band. By contrast Fe7S8 is magnetic and metallic below ~5 GPa and diamagnetic metallic above this pressure. The Fe3+/Fe2+ ratio in natural ilmenite samples shows rapid increase under pressure from ambient up to ~2 GPa, as deduced from 57Fe Mössbauer pressure studies. Pressure induced intervalence charge transfer away from the ferrous sites, conceivably across regions of octahedra, to the empty 3d manifold of the Ti4+ cation in an adjacent face-sharing layer along the c-axis may account for the change in the Fe3+/Fe2+ ratio. This is the first heteronuclear intervalence charge transfer observed by high-pressure Mössbauer study.
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