Spin transition of ferric iron in Al-bearing Mg-perovskite up to 200 GPa and its implication for the lower mantle
Spin transition of ferric iron in Al-bearing Mg-perovskite up to 200 GPa and its implication for the lower mantle
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DOI：
10.1016/j.epsl.2011.12.006
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发表时间：
2012-02-01
影响因子：
5.3
通讯作者：
Tsuei, Ku-Ding
中科院分区：
文献类型：
--
作者：
Fujino, Kiyoshi;Nishio-Hamane, Daisuke;Tsuei, Ku-Ding
以往关于镁钙钛矿（Pv）中铁的自旋跃迁的报道仍存在很大差异。为了解决这个问题，我们研究了自旋态的Mg 0.85 Fe 0.153 + Al 0.15 Si 0.85 O3 Pv高达200 GPa的X射线发射光谱（XES）和X射线衍射（XRD）。在XES中，Fe ~（3+）的高自旋（HS）比在60 GPa以上低温退火时逐渐降低，在XRD中，在50-60 GPa退火时晶胞体积随压力的变化趋势表明，Fe ~（3+）占据A位，在50 GPa以下HS，在50-60 GPa以上逐渐取代B-位的Al。通过退火进行阳离子交换反应，使A位的Fe ~（3+）变成低自旋（LS），而保留在A位的Fe ~（3+）在高达200 GPa时变成HS。这意味着Fe ~（3+）的自旋状态取决于Fe ~（3+）在A位和B位之间的占位，而这些占位又通过阳离子交换反应受到合成条件和样品退火温度的强烈控制。结合前人的研究结果表明，在下地幔含铝Mg-Pv中，Fe ~（2+）占据A位，整个下地幔保持HS; Fe ~（3+）占据A位，在50 GPa以下HS，在50-60 GPa以上取代B位Al，变为LS，假设A位Fe ~（2+）的自旋跃迁压力高于Fe ~（3+）的自旋跃迁压力。(C)2011 Elsevier B. V.保留所有权利。
There are still large discrepancies among the previous reports on the spin transition of iron in Mg-perovskite (Pv). To alleviate this problem, we examined the spin state of Fe3+ in Mg0.85Fe0.153+Al0.15Si0.85O3 Pv up to 200 GPa by X-ray emission spectroscopy (XES) and X-ray diffraction (XRD). The gradual decrease of the high spin (HS) ratio of Fe3+ by low temperature annealing of the samples above similar to 60 GPa in XES and the change of the trend of unit cell volumes with pressure by annealing at 50-60 GPa in XRD indicate that Fe3+ occupies the A-site and is HS below similar to 50 GPa but above 50-60 GPa it gradually replaces Al at the B-site through cation exchange reaction by annealing and becomes low spin (LS), while Fe3+ remaining at the A-site is HS up to 200 GPa. This means that the spin state of Fe3+ depends on Fe3+ occupancies between the A- and B-sites and these Fe3+ occupancies are strongly controlled by the synthesis condition and annealing temperature of the samples through the cation exchange reaction. The present results combined with the previous reports indicate that in Al-bearing Mg-Pv in the lower mantle Fe2+ occupies the A-site and remains HS for the whole lower mantle, while Fe3+ occupies the A-site and is HS below similar to 50 GPa but above 50-60 GPa it replaces Al at the B-site and becomes LS, on the assumption that spin transition pressure of Fe2+ at the A-site is higher than that of Fe3+ at the same site. (C) 2011 Elsevier B.V. All rights reserved.