Electronic spin states of ferric and ferrous iron in the lower-mantle silicate perovskite
Electronic spin states of ferric and ferrous iron in the lower-mantle silicate perovskite
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DOI：
10.2138/am.2012.4000
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发表时间：
2012-04
影响因子：
3.1
通讯作者：
Jung‐Fu Lin;E. Alp;Z. Mao;T. Inoue;C. McCammon;Yuming Xiao;P. Chow;Jiyong Zhao
中科院分区：
文献类型：
--
作者：
Jung‐Fu Lin;E. Alp;Z. Mao;T. Inoue;C. McCammon;Yuming Xiao;P. Chow;Jiyong Zhao
摘要在高压条件下，利用各种实验和理论方法研究了下地幔硅酸盐钙钛矿中铁的电子自旋和价态。然而，实验结果及其解释仍然存在很大争议。本文利用同步辐射穆斯堡尔谱研究了一种表征良好的硅酸盐钙钛矿起始样品[（Mg0.9，Fe0.1）SiO 3]在化学惰性Ne压力介质中的压力高达120 GPa。穆斯堡尔谱的分析明确地表明，八面体位Fe 3+在~13-24 GPa发生高自旋到低自旋的跃迁，这从超精细四极分裂的显著增加中得到了证明。两个四极偶极子的A位Fe 2+，具有极高的QS值为4.1和3.1 mm/s，同时发生的自旋跃迁的八面体位Fe 3+，并继续发展到120 GPa。可以想象，八面体位Fe 3+的自旋配对转变导致体积减小和局部原子位构型的改变，从而导致十二面体位Fe 2+在13-24 GPa下的四极分裂的显著增加。我们的研究结果为最近钙钛矿中铁的自旋和价态的实验和理论结果提供了一个连贯的解释，并有助于理解铁的自旋和价态对下地幔矿物性质的影响。
Abstract The electronic spin and valence states of iron in lower-mantle silicate perovskite have been previously investigated at high pressures using various experimental and theoretical techniques. However, experimental results and their interpretation remain highly debated. Here we have studied a wellcharacterized silicate perovskite starting sample [(Mg0.9,Fe0.1)SiO3] in a chemically inert Ne pressure medium at pressures up to 120 GPa using synchrotron Mössbauer spectra. Analyses of the Mössbauer spectra explicitly show a high-spin to low-spin transition of the octahedral-site Fe3+ occurring at ~13-24 GPa, as evidenced from a significant increase in the hyperfine quadrupole splitting. Two quadrupole doublets of the A-site Fe2+, with extremely high-QS values of 4.1 and 3.1 mm/s, occur simultaneously with the spin transition of the octahedral-site Fe3+ and continue to develop to 120 GPa. It is conceivable that the spin-pairing transition of the octahedral-site Fe3+ causes a volume reduction and a change in the local atomic-site configurations that result in a significant increase of the quadrupole splitting in the dodecahedral-site Fe2+ at 13-24 GPa. Our results here provide a coherent explanation for recent experimental and theoretical results on the spin and valence states of iron in perovskite, and assist in comprehending the effects of the spin and valence states of iron on the properties of the lower-mantle minerals.