Pressure-induced C23–C37 transition and compression behavior of orthorhombic Fe2S to Earth’s core pressures and high temperatures

Autor: Claire C. Zurkowski, Barbara Lavina, Nigel M. Brauser, Anne H. Davis, Stella Chariton, Sergey Tkachev, Eran Greenberg, Vitali B. Prakapenka, Andrew J. Campbell
Rok vydání: 2022
Předmět:
Zdroj: American Mineralogist. 107:1878-1885
ISSN: 1945-3027
0003-004X
Popis: The phase stability of orthorhombic Fe2S was explored to 194 GPa and 2500 K using powder and multigrain synchrotron X-ray diffraction techniques. Between 30 and 120 GPa, a C23-like (Co2P, Pnma, Z = 4) Fe2S structure is observed and determined to exhibit a highly compressible a axis. A softening of the a axis occurs between 120 and 150 GPa and a relative stiffening of the b and c axes accompanies this compressibility change. Above 150 GPa, the a axis stiffens as the b and c axes soften, and a C37-like (Co2Si, Pnma, Z = 4) Fe2S unit cell is measured. On the basis of these changes in unit cell geometry, a pressure-induced C23–C37 Fe2S phase transition is inferred between 120–150 GPa. The C23 and C37 (Pnma, Z = 4) structures are closely related and share the same site symmetries. Forming the C37 structure from the C23 structure requires a shortening of the a axis and lengthening of the b and c axes accompanied by a four- to fivefold coordination change. The softening of the a axis above 120 GPa may therefore indicate the onset of a coordination change, and the final compressibility change above 150 GPa may mark the completion of this phase transition. The presented pressure-temperature (P-T) stabilities of C23 and C37 structures of Fe2S are in agreement with and resolve the differing observations of two previous studies (Tateno et al. 2019; Zurkowski et al. 2022). As C37 Fe2S is observed to core-mantle boundary pressures and high temperatures, the C37 Fe2S density profile through Earth’s outer core was determined by fitting the C23 Fe2S equation of state (
Databáze: OpenAIRE
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