HIGH PRESSURE-HIGH TEMPERATURE ELASTICITY OF IRON HYDRIDE FROM NUCLEAR RESONANT INELASTIC X-RAY SCATTERING AND X-RAY DIFFRACTION

As major constituents of the Earth’s core, Fe and its alloys have long been of great interest to geophysicists. Information on their high-pressure, vibrational dynamic behavior is essential for interpreting seismic observations and for theoretical modeling of the Earth’s deep interior. Hydrogen has been suggested as possible lower atomic weight components in the Earth’s core. Hydrogen in the core would have profound implications on the H budget within the Earth and our understanding of the physics and chemistry of the core. X-ray diffraction (XRD) experiments show that stoichiometric FeH is formed at 3 GPa from the reaction of Fe and fluid hydrogen, and this compound is stable to at least 62 GPa. With the limitation of XRD alone, however, important geophysical and crystal chemical information about FeH is still lacking. We have conducted nuclear resonant inelastic scattering (NRIXS) experiments on FeH to over 50 GPa in a diamond anvil cell at ambient temperature and at high temperature using laser-heating. The collected NRIXS spectra have been summed, and converted to a partial (Fe related) phonon density of state for final analysis. The initial slope coupled with hydrostatic equation of state data yields VP and VS for comparison to seismic observations for insight into core chemistry and physics.