[S-IT14] Deep Earth Sciences

[SIT14-P04] Equation of state of high-spin FeS V and its stability field

*Satoru Urakawa¹, Natsumi Adachi¹, Moe Sakurai¹ (1.Department of Earth Sciences, Okayama University)

Keywords:Iron sulfide, spin state, planetary core

FeS has been considered to be one of the constituents of the planetary cores. Many polymorphs are known for FeS, which have superlattice structures related to NiAs-type structures. Under high pressure and high temperature conditions in planetary interiors, the FeS V phase with a simple NiAs-type structure has a wide stability region. At room temperature, FeS undergoes a transition from the high-spin FeS II to the low-spin FeS III around 6 GPa, while FeS V, which is stable at high temperatures, is also considered to be in a high-spin states below 5 GPa and a low-spin states above 10 GPa. In this study, we have investigated the stability region and the equation of state of the high-spin FeS V up to 5 GPa from the high-temperature and high-pressure experiments using synchrotron X-rays. The isothermal bulk modulus of high-spine FeS is about 20% smaller than the bulk modulus of low-spine FeS V determined by Urakawa et al. (2004). The present experiments show that the phase boundary between FeS IV and FeS V is consistent with the Néel temperature at 1 atm. These are important fundamental data for discussing the internal structure of relatively small bodies.