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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 >Al2O3 incorporation in MgSiO3 perovskite and ilmenite
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Al2O3 incorporation in MgSiO3 perovskite and ilmenite

机译：Al2O3掺入MgSiO3钙钛矿和钛铁矿中

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摘要

First-principles calculations in the MgSiO3-Al2O3 system predict that MgSiO3-perovskite dissolves about 15 mol% Al2O3 at the top of the lower mantle, limited by coexistence with Al-rich ilmenite (corundum). The solubility increases with pressure so that the lower mantle is likely undersaturated in alumina in all but the coldest parts of the uppermost lower mantle. The akimotoite-corundum solid solution is highly non-ideal with a symmetric regular solution parameter W=66 kJ/mol per formula unit at the top of the lower mantle. The critical temperature for exsolution of ilmenite is predicted to be 2000 K. The MgSiO3 solution is also significantly non-ideal; assuming only Tschermak substitutions, the value of W=12 kJ/mol per formula unit. Total energy calculations over a range of compositions and several configurations for each composition are based on density functional theory in the local density approximation. We find that the entropy of solution of both structures is nearly ideal on the basis of random sampling of simulations using semi-empirical interatomic potentials. Results also confirm previous experimental and computational results showing that aluminum has little effect on the elasticity of MgSiO3 perovskite. (c) 2006 Elsevier B.V. All rights reserved.
机译：MgSiO3-Al2O3系统的第一性原理计算预测，MgSiO3-钙钛矿在下地幔顶部溶解约15 mol％Al2O3，受与富Al钛铁矿（刚玉）共存的限制。溶解度随着压力的增加而增加，因此除了最上面的下地幔的最冷部分之外，所有氧化铝中的下地幔都可能不饱和。 moto石刚玉固溶体是高度不理想的，在下地幔顶部，每个配方单元对称的正则固溶参数W = 66 kJ / mol。预计钛铁矿溶解的临界温度为2000K。MgSiO3溶液也明显不理想;假设仅用Tschermak取代，则W的值等于每个公式单位12 kJ / mol。整个组成范围内的总能量计算以及每种组成的几种配置均基于局部密度近似中的密度泛函理论。我们发现，在使用半经验原子间电势的模拟随机采样的基础上，两种结构的解的熵都几乎是理想的。结果还证实了先前的实验和计算结果，表明铝对MgSiO3钙钛矿的弹性影响很小。 （c）2006 Elsevier B.V.保留所有权利。

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