Iron spin state in silicate perovskite at conditions of the Earth's deep interior

Abstract

We present a review of our recent work concerning the spin state of Fe²⁺ and Fe³⁺ in iron magnesium aluminium silicate perovskite, the most abundant phase in the Earth's interior. Experimental results obtained using Mössbauer spectroscopy (with a radioactive source and a Synchrotron Mössbauer Source) and nuclear forward scattering for a range of different sample compositions in both externally heated and laser-heated diamond anvil cells show clear trends in the variation of hyperfine parameters with pressure and temperature. These trends combined with reported total spin state measurements using X-ray emission spectroscopy on samples of similar composition support the conclusion that Fe²⁺ undergoes a high-spin to intermediate-spin transition near the top of the lower mantle and an intermediate-spin to low-spin transition near the bottom of the lower mantle. No spin transition is observed to occur in Fe³⁺ for samples with compositions relevant for the lower mantle.

Keywords:

• Mössbauer spectroscopy
• spin transition
• lower mantle
• diamond anvil cell

Acknowledgements

We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities (ID18) and we thank J.-P. Celse for additional technical assistance at ESRF and S. Übelhack and S. Linhardt for technical assistance at Bayerisches Geoinstitut. The project was partly supported by funds from the German Science Foundation (DFG) in their normal funding programme and Priority Programme SPP1236, the Eurocores EuroMinSci Programme, the PROCOPE exchange programme and the German Federal Ministry for Education and Research (BMBF).

Notes

^†This contribution is part of the final report summarizing the results of the DFG-priority project SPP1236, which was funded by the Deutsche Forschungsgemeinschaft from 2006–2013.