Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Phys Rev Lett. 2013 May 31;110(22):228501. doi: 10.1103/PhysRevLett.110.228501. Epub 2013 May 30.
The discovery of a pressure induced iron-related spin crossover in Mg((1-x))Fe(x)O ferropericlase (Fp) and Mg-silicate perovskite, the major phases of Earth's lower mantle, has raised new questions about mantle properties which are of central importance to seismology. Despite extensive experimental work on the anomalous elasticity of Fp throughout the crossover, inconsistencies reported in the literature are still unexplained. Here we introduce a formulation for thermoelasticity of spin crossover systems, apply it to Fp by combining it with predictive first principles density-functional theory with on-site repulsion parameter U calculations, and contrast results with available data on samples with various iron concentrations. We explain why the shear modulus of Fp should not soften along the crossover, as observed in some experiments, predict its velocities at lower mantle conditions, and show the importance of constraining the elastic properties of minerals without extrapolations for analyses of the thermochemical state of this region.
在镁铁尖晶石 (Fp) 和镁硅酸盐钙钛矿中发现了压力诱导的与铁有关的自旋交叉，它们是地球下地幔的主要相，这引发了关于地幔性质的新问题，这些问题对地幔学具有核心重要性。尽管在整个交叉过程中对 Fp 的异常弹性进行了广泛的实验研究，但文献中报道的不一致性仍未得到解释。在这里，我们引入了一种用于自旋交叉系统热弹性的公式，通过将其与具有局域排斥参数 U 计算的预测第一性原理密度泛函理论相结合，将其应用于 Fp，并将结果与具有不同铁浓度的样品的现有数据进行对比。我们解释了为什么 Fp 的剪切模量不应该沿着交叉软化，正如一些实验所观察到的那样，预测了在下地幔条件下的速度，并表明了在没有外推的情况下限制矿物弹性性质对于分析该区域的热化学状态的重要性。
