Spin-state crossover and hyperfine interactions of ferric iron in MgSiO3 perovskite

Han Hsu, Peter Blaha, Matteo Cococcioni, Renata M. Wentzcovitch

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Abstract

Using density functional theory plus Hubbard U calculations, we show that the ground state of (Mg,Fe)(Si,Fe)O3 perovskite, the major mineral phase in Earth's lower mantle, has high-spin ferric iron (S=5/2) at both dodecahedral (A) and octahedral (B) sites. With increasing pressure, the B-site iron undergoes a spin-state crossover to the low-spin state (S=1/2) between 40 and 70 GPa, while the A-site iron remains in the high-spin state. This B-site spin-state crossover is accompanied by a noticeable volume reduction and an increase in quadrupole splitting, consistent with recent x-ray diffraction and Mössbauer spectroscopy measurements. The anomalous volume reduction leads to a significant softening in bulk modulus during the crossover, suggesting a possible source of seismic-velocity anomalies in the lower mantle.

Original languageEnglish
Article number118501
JournalPhysical Review Letters
Volume106
Issue number11
DOIs
StatePublished - 14 Mar 2011

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