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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Valence state and spin transitions of iron in Earth's mantle silicates
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Valence state and spin transitions of iron in Earth's mantle silicates

机译：地球地幔硅酸盐中铁的价态和自旋跃迁

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Using ab initio simulations, we investigated the valence and spin states of iron impurities in the perovskite (Pv) and post-perovskite (PPv) polymorphs of MgSiO3. In agreement with the previous experimental work, we find a valence disproportionation reaction: 3Fe(3+)-> 2Fe(3+) Fe-metal(0). This exothermic reaction results in the predominance of Fe3+ impurities in lower mantle silicates and produces free metallic iron. It occurs both in Pv and PPv, Al-free and Al-rich, at all lower mantle pressures. This reaction provides a possible mechanism for the growth of the Earth's core and core-mantle chemical equilibration. In the presence of Al3+, iron forms Fe3+-Al3+ coupled substitutions in Pv, but separate Fe3+-Fe3+ and Al3+-Al3+ substitutions in PPv. Only the high-spin state is found for Fe2+ impurities at all mantle pressures, while Fe3+ impurities on the Si-site are low-spin at all pressures in both phases. Fe3+ impurities on the Mg-site are in the high-spin state in PPv at all mantle pressures, but in Pv we predict a high-spin-low-spin transition. The pressure at which this transition occurs strongly depends on the Al3+ content and according to our calculations increases from 76 GPa for Al-free to 134 GPa for aluminous Pv; this reconciles many of the previous experimental results. Our findings have implications for the chemical evolution of the Earth and for the radiative conductivity and dynamics of the D" layer. (c) 2006 Elsevier B.V. All rights reserved.
机译：使用从头算模拟，我们研究了MgSiO3的钙钛矿（Pv）和钙钛矿后（PPv）多晶型物中铁杂质的价态和自旋态。与以前的实验工作一致，我们找到了价歧化反应：3Fe（3 +）-> 2Fe（3+）Fe-金属（0）。这种放热反应导致下地幔硅酸盐中Fe3 +杂质占优势，并生成游离金属铁。它在所有较低的地幔压力下都存在于Pv和PPv中，无铝和富铝。该反应为地球核心的生长和核心幔化学平衡提供了一种可能的机制。在存在Al3 +的情况下，铁在Pv中形成Fe3 + -Al3 +耦合取代，但在PPv中分离Fe3 + -Fe3 +和Al3 + -Al3 +取代。在所有地幔压力下，仅发现Fe2 +杂质处于高自旋状态，而在两个阶段中，Si部位的Fe3 +杂质在所有压力下均为低自旋。在所有地幔压力下，PPv中Mg位点上的Fe3 +杂质均处于高自旋状态，但在Pv中，我们预测高自旋至低自旋转变。发生这种转变的压力很大程度上取决于Al3 +的含量，根据我们的计算，从无铝的76 GPa增加到铝的Pv的134 GPa。这与许多先前的实验结果一致。我们的发现对地球的化学演化以及D''层的辐射电导率和动力学都有影响。（c）2006 Elsevier B.V.保留所有权利。

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