Electronic spin state of Fe,Al-containing MgSiO₃ perovskite at lower mantle conditions

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• 作者：I. Kupenko ; C. McCammon ; R. Sinmyo ; C. Prescher ; A.I. Chumakov ; A. Kantor ; R. R眉ffer ; L. Dubrovinsky
• 关键词：Silicate perovskite ; Mö ; ssbauer spectroscopy ; Nuclear Forward Scattering ; Lower mantle
• 刊名：Lithos
• 出版年：15 February, 2014
• 年：2014
• 卷：189
• 期：Complete
• 页码：167-172
• 全文大小：1209 K

文摘

We have investigated silicate perovskite with composition Mg_0.83Fe_0.21Al_0.06Si_0.91O₃ relevant for the lower mantle at pressures up to 81 GPa and temperatures up to 2000 K using conventional M枚ssbauer spectroscopy and synchrotron Nuclear Forward Scattering (NFS) combined with double-sided laser heating in a diamond anvil cell. Room temperature M枚ssbauer and NFS spectra at low pressure are dominated by high-spin Fe^2 +, with minor amounts of Fe^3 + and a component assigned to a metastable position of high-spin Fe^2 + in the A-site predicted by computational studies. NFS data show a sharp transition (< 20 GPa) from high-spin Fe^2 + to a new component with extremely high quadrupole splitting, similar to previous studies. M枚ssbauer data show the same transition, but over a broader pressure range likely due to the higher pressure gradient. The new Fe^2 + component is assigned to intermediate-spin Fe^2 +, consistent with previous X-ray emission studies. NFS data at high temperatures and high pressures comparable to those in the lower mantle are consistent with the presence of Fe^2 + only in the intermediate-spin state and Fe^3 + only in the high-spin state. Our results are therefore consistent with the occurrence of spin crossover only in Fe^2 + in Fe-, Al-containing perovskite within the lower mantle.