Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 359, Issue -, Pages 34-39Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2012.09.029
Keywords
spin crossover; quadrupole splitting; perovskite; post-perovskite; lower mantle; first-principles
Categories
Funding
- MRSEC Program of NSF [DMR-0212302, DMR-0819885]
- [EAR-081272]
- [EAR-1047629]
- Division Of Earth Sciences
- Directorate For Geosciences [1019853] Funding Source: National Science Foundation
- Division Of Earth Sciences
- Directorate For Geosciences [0810272] Funding Source: National Science Foundation
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Using density functional theory + Hubbard U (DFT + U) calculations, we investigate how aluminum affects the spin crossover of iron in MgSiO3 perovskite (Pv) and post-perovskite (Ppv), the major mineral phases in the Earth's lower mantle. We find that the presence of aluminum does not change the response of iron spin state to pressure: only ferric iron (Fe3+) in the octahedral (B)-site undergoes a crossover from high-spin (HS) to low-spin (LS) state, while Fe3+ in the dodecahedral (A)-site remains in the HS state, same as in Al-free cases. However, aluminum does significantly affect the placement of Fe3+ in these mineral phases. The most stable atomic configuration has all Al3+ in the B-site and all Fe3+ in the A-site (thus in the HS state). Metastable configurations with LS Fe3+ in the B-site can happen only at high pressures and high temperatures. Therefore, experimental observations of LS Fe3+ at high pressures in Al-bearing Pv require diffusion of iron from the A-site to the B-site and should be sensitive to the annealing temperature and schedule. In the Earth's lower mantle, the elastic anomalies accompanying the B-site HS-LS crossover exhibited in Al-free Pv are likely to be considerably reduced, according to the B-site Fe3+ population. (C) 2012 Elsevier B.V. All rights reserved.
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