Spectroscopy of low and intermediate Z elements at extreme conditions: in situ studies of Earth materials at pressure and temperature via X-ray Raman scattering

X-ray Raman scattering spectroscopy is an emerging method in the study of low and intermediate Z elements' core-electron excitations at extreme conditions in order to reveal information on local structure and electronic state of matter in situ. We discuss the capabilities of this method to address questions in Earth materials' science and demonstrate its sensitivity to detect changes in the oxidation state, electronic structure, coordination, and spin state. Examples are presented for the study of the oxygen K-, silicon L- and iron M-edges. We assess the application of both temperature and pressure in such investigations exploiting diamond anvil cells in combination with resistive or laser heating which is required to achieve realistic conditions of the Earth's crust, mantle, and core.KEYWORDS: X-ray Raman scattering, inelastic X-ray scattering, X-ray absorption, high pressure research, diamond anvil cell, minerals, glasses, melts, Earth materials, spin transition, bonding transition, coordination transformation, oxidation state, electronic structur