The Fe–Fe₂P phase diagram at 6 GPa

ABSTRACT

Here, we report experimental results on melting and subsolidus phase relations in the Fe–Fe₂P system at 6 GPa and 900–1600°C. The system has two P-bearing compounds: Fe₃P and Fe₂P. X-ray diffraction patterns of these compounds correspond to schreibersite and barringerite, respectively. The Fe–Fe₃P eutectic appears at 1075°C and 16 mol% P. Schreibersite (Fe₃P) melts incongruently at 1250°C to produce barringerite (Fe₂P) and liquid containing 23 mol% P. Barringerite (Fe₂P) melts congruently at 1575°C. Maximum solid solution of P in metallic iron at 6 GPa is 5 mol%. As temperature increases to 1600°C, the P solubility in the metallic iron decreases to 0.5 mol%, whereas the P content in coexisting liquid decreases to 3 mol%. The composition of quenched phases from Fe–P melt coincides with the compositions of equilibrium phases at corresponding temperature. Consequently, the composition of quenched products of Fe-P melts in meteorites can be used for reconstruction of P–T conditions of their crystallization under ambient or low pressures or during shock melting by impact collisions.

KEYWORDS:

• Iron
• phosphorus
• phosphide
• schreibersite
• barringerite
• high-pressure
• core formation
• meteorites

Acknowledgements

The SEM and EDS studies of experimental samples were performed in the Analytical Center for multi-elemental and isotope research SB RAS. We are grateful to the anonymous referee for useful suggestions, to Professor Hiroyuki Kagi for editorial handling, and to Nikolay S. Karmanov and Anatoliy T. Titov for their help in analytical work. KL and HO also thank for the support of X-ray diffraction measurements from PRIUS program (No. 2017-A42) from Ehime University, Matsuyama, Japan.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by Russian Science Foundation No. 17-17-01177.