PVT equation of state and PVT phase diagram of monosulfide solid solution (mss) (Fe,Ni,Cu)S

Monosulfide solid solution (mss), nominally (Fe,Ni,Cu)S is considered the main sulfide phase in the upper mantle.
Pure FeS is known to have at least four HP/HT polymorphs in the P-T range 0-10 GPa and 300-1000 K. It undergoes also an electronic spin transition at 6 GPa. Many efforts have been dedicated to investigate pure FeS system also at much more extreme conditions for the relevance that troilite have in mineralogy of planetary cores. Despite the petrological and geochemical interest of mss for upper mantle mineralogy, no experimental PVT data are available and its phase diagram is unknown. We propose to investigate mss in 0-10 GPa and 300-1100 K P-T range by single crystal diffraction to determine its compressibility; verify by anomaly in compressibility possible electronic transition; determine possible HP/HT polymorphs. The results will be used to model thermodynamic properties, to understand phase relationship of sulphides in the Earth’s upper mantle.

单硫化物固溶体（Monosulfide solid solution，mss）的标称成分为(Fe,Ni,Cu)S，被认为是上地幔中的主要硫化物相。纯硫化亚铁（FeS）在0~10 GPa、300~1000 K的温压范围内，已知至少存在四种高压高温（High Pressure/High Temperature，HP/HT）同质多象变体，且在6 GPa时会发生电子自旋跃迁。鉴于陨硫铁（troilite）在行星核矿物学中的重要意义，学界已开展诸多研究以探索极端条件下的纯FeS体系。尽管单硫化物固溶体（mss）对于上地幔岩石学与地球化学研究具有重要价值，但目前尚无可用的PVT（压强-体积-温度）数据，其相图也尚未明确。本研究拟通过单晶衍射法，在0~10 GPa、300~1100 K的温压范围内对mss开展研究，以测定其压缩性；通过压缩性异常验证可能存在的电子跃迁，并确定其可能存在的高压高温同质多象变体。研究结果将用于构建热力学性质模型，以阐明地球上地幔中硫化物的相平衡关系。