We propose to carry out a systematic spectroscopic study of the crystal chemistry of iron, including investigations of oxidation, reduction, disproportionation, and partitioning of iron in mantle and core materials at elevated pressures. The principal tools will be 57Fe Mossbauer and crystal-field spectroscopy, techniques that are ideally suited to studies of iron-bearing phases. The results will be correlated with vibrational spectra measured by Raman scattering and infrared absorption spectroscopy. The multi-anvil apparatus at SUNY Stony Brook, and diamond-anvil cell and piston-cylinder apparatus at the Geophysical Laboratory will be used for their complimentary pressure range and experimental conditions. Spectra will also be studied as a function of pressure in diamond-anvil cells. We shall map the P-T-fO2 conditions of the graphite/diamond buffer to lower mantle pressures with the piston-cylinder apparatus and the multi-anvil device and at ultrahigh pressure with the diamond-anvil cell. The results will be used to enlarge the existing thermodynamic database for iron-bearing mantle and core materials, which is crucial for modelling the mineralogy, chemical composition, and oxidation state of the deep interior.
