High-pressure experimental and computational XANES studies of (Mg,Fe)(Si,Al)O3 perovskite and (Mg,Fe)O ferropericlase as in the Earth's lower mantle

Seven iron-containing oxides and silicates including (Mg-0.88,Fe-0.12)SiO, (Mg-0.86,Fe-0.14)(Si-0.98,Al-0.02)O-3 perovskites, and (Mg-0.80,Fe-0.20) ferropericlase were studied using Fe K-edge x-ray absorption near edge spectroscopy under pressure up to 85 GPa at ambient temperature. First-principles calculations of Fe K-edges of (Mg-0.88,Fe-0.12)SiO perovskite and (Mg-0.80,Fe-0.20)O ferropericlase were performed using a spin-dependent method. The amount and quality of the data collected allows performance of a systematic study of the absorption edge features as a function of pressure in these geophysically important systems, providing direct experimental validation for band-structure calculations. The comparison between experiment and theory allows analyzing in detail the effect of Fe valence and spin state modifications on the spectra, allowing to confirm qualitatively the presence of a pressure induced spin pairing transition in (Mg,Fe)O ferropericlase and a high-spin intermediate spin crossover in (Mg,Fe)(Si,Al)O-3 perovskite.