Phase stability and structural properties of Fe2S and its analog Co2P at high pressures and temperatures
Abstract
Earth's core is an Fe-rich alloy with a significant contribution from cosmochemically abundant light elements such as sulfur. Understanding the phase stability and structural properties of iron-rich sulfides to core conditions is critical for assessing the core's composition and dynamics. In the current study, we examined the high pressure polymorphism of Fe 2 S coexisting with Fe to outer core pressures and high temperatures by combining in - situ powder and multigrain diffraction with ex - situ chemical analysis. We further conducted multigrain diffraction experiments on Co 2 P as a moderate pressure analog to the high pressure behavior of Fe 2 S. Pnma Co 2 P is stable at moderate temperatures to at least 48 GPa. Upon heating at 30 GPa and 1870 K, Pnma Co 2 P transitions to P -62 m Co 2 P. Experiments to 175 GPa and 2600 K reveal analog structural behavior in Fe 2 S, and that these are stable sulfides coexisting with Fe. Both Pnma Co 2 P and Fe 2 S exhibit anisotropic compression where the a axis is ~3x more compressible than the b and c axes. Structural refinements of Co 2 P indicate that the anisotropy is attributable to the broadening of Co-P-Co bond angles along the a axis. Through this work we have determined that Fe 2 S, rather than Fe 3 S, is stable coexisting with Fe to outer core pressures and high temperatures and, using the Co 2 P analog, we conducted an in-depth structural examination of these M 2 X compounds relevant to Earth's core.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMMR024..05Z
- Keywords:
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- 3939 Physical thermodynamics;
- MINERAL PHYSICS;
- 3672 Planetary mineralogy and petrology;
- MINERALOGY AND PETROLOGY;
- 5134 Thermal properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 5460 Physical properties of materials;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS