Anomalous thermal properties and spin crossover of ferromagnesite (Mg,Fe) CO 3

摘要: Ferromagnesite $[({\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}){\mathrm{CO}}_{3}]$, also referred to as magnesiosiderite at high iron concentration ($xg0.5$), is a solid solution of magnesite $(\mathrm{Mg}{\mathrm{CO}}_{3}$) and siderite ($\mathrm{Fe}{\mathrm{CO}}_{3}$). believed enter the Earth's lower mantle via subduction considered major carbon carrier in mantle, playing key role deep cycle. Experiments have shown that ferromagnesite undergoes pressure-induced spin crossover, accompanied by volume elastic anomalies, lower-mantle pressure range. In this work, we investigate thermal properties $({\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}){\mathrm{CO}}_{3}$ ($0lx\ensuremath{\le}1$) using first-principles calculations. We show nearly all are drastically altered including anomalous reduction volume, softening bulk modulus, increases expansion, heat capacity, Gr\"uneisen parameter. Remarkably, anomaly capacity remains prominent (up $\ensuremath{\sim}40%$) temperature without smearing out, which suggests crossover may significantly affect subducting slabs