铁菱镁矿（Mg，Fe）CO3的反常热性质和自旋交叉
Anomalous thermal properties and spin crossover of ferromagnesite (Mg,Fe)CO3
摘要：
铁菱镁矿（Mg，Fe）CO3，在高铁浓度下也称为镁菱铁矿，是菱镁矿（MgCO3）和菱铁矿（FeCO3）的固溶体。铁菱镁矿被认为是通过俯冲作用进入地球下地幔的，被认为是地球下地幔中主要的碳载体，在地球深部碳循环中起着关键作用。实验表明，在下地幔压力范围内，铁菱镁矿经历了压力诱导的自旋交叉，伴随着体积和弹性异常。本文采用第一性原理计算研究了（Mg，Fe）CO3的热性质。研究表明，铁磁菱镁矿的几乎所有热性质都被铁的自旋交叉所改变，包括体积的反常减小、体积模量的反常软化、热膨胀、热容和Guneisen参数的反常增加.值得注意的是，热容量的异常在高温下仍然很突出（高达40%），而没有涂抹出来，这表明铁自旋交叉可能会显着影响俯冲板的热性质和地球深部碳循环。
英文摘要：
Ferromagnesite (Mg,Fe)CO3, also referred to as magnesiosiderite at high iron concentration, is a solid solution of magnesite (MgCO3) and siderite (FeCO3). Ferromagnesite is believed to enter the Earth's lower mantle via subduction and is considered a major carbon carrier in the Earth's lower mantle, playing a key role in the Earth's deep carbon cycle. Experiments have shown that ferromagnesite undergoes a pressure-induced spin crossover, accompanied by volume and elastic anomalies, in the lower-mantle pressure range. In this work, we investigate thermal properties of (Mg,Fe)CO3 using first-principles calculations. We show that nearly all thermal properties of ferromagnesite are drastically altered by iron spin crossover, including anomalous reduction of volume, anomalous softening of bulk modulus, and anomalous increases of thermal expansion, heat capacity, and Guneisen parameter. Remarkably, the anomaly of heat capacity remains prominent (up to 40%) at high temperature without smearing out, which suggests that iron spin crossover may significantly affect the thermal properties of subducting slabs and the Earth's deep carbon cycle.
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