Spin states and hyperfine interactions of iron incorporated in MgSiO₃ post-perovskite

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• 作者：Yonggang G. Yu ; ^{yuxxx135@umn.edu} ; Han Hsu ; Matteo Cococcioni ; Renata M. Wentzcovitch
• 关键词：Fe-bearing post-perovskite (MgSiO3) ; ferrous and ferric iron (Fe2  ; + and Fe3  ; +) ; spin state crossover ; quadrupole splittings ; equation of state ; lower mantle ; D&Prime ; layer ; LDA  ; +  ; U
• 刊名：Earth and Planetary Science Letters
• 出版年：2012
• 期刊代码：18_0012821x
• 类别：ph
• 出版时间：15 May, 2012
• 卷：331-332
• 期：Complete
• 页码：1-7
• 文件大小：922 K

摘要

Using density functional theory + Hubbard U (DFT + U) calculations, we investigate the spin states and nuclear hyperfine interactions of iron incorporated in magnesium silicate (MgSiO₃) post-perovskite (Ppv), a major mineral phase in the Earth's D鈥?layer, where the pressure ranges from ~ 120 to 135 GPa. In this pressure range, ferrous iron (Fe^2 +) substituting for magnesium at the dodecahedral (A) site remains in the high-spin (HS) state; intermediate-spin (IS) and low-spin (LS) states are highly unfavorable. As to ferric iron (Fe^3 +), which substitutes magnesium at the A site and silicon at the octahedral (B) site to form (Mg,Fe)(Si,Fe)O₃ Ppv, we find the combination of HS Fe^3 + at the A site and LS Fe^3 + at the B site the most favorable. Neither A-site nor B-site Fe^3 + undergoes a spin-state crossover in the D鈥?pressure range. The computed iron quadrupole splittings are consistent with those observed in M枚ssbauer spectra. The effects of Fe^2 + and Fe^3 + on the equation of state of Ppv are found nearly identical, expanding the unit cell volume while barely affecting the bulk modulus.