Phase stabilities and spin transitions of Fe (sub 3) (S (sub 1-x) P (sub x) ) at high pressure and its implications in meteorites

Fe-S-P compounds have been observed in many meteorites and could be the important components in planetary cores. Here we investigated the phase stability of Fe (sub 3) (S,P) solid solutions and synthesized high-quality Fe (sub 3) (S (sub 1-x) P (sub x) ) high-pressure phases in the multi-anvil press. The physical properties of Fe (sub 3) (S (sub 0.5) P (sub 0.5) ) were further studied in the diamond-anvil cell by synchrotron X-ray diffraction and emission spectroscopy. The solubility of S in the Fe (sub 3) (S,P) solid solution increases with increasing pressure. The minimum pressure to synthesize the pure Fe (sub 3) S and Fe (sub 3) (S (sub 0.13) P (sub 0.87) ) is about 21 and 8 GPa, respectively. The observed discontinuity in unit-cell parameters at about 18 GPa is caused by the high-spin to low-spin transition of iron, supported by X-ray emission spectroscopy data. The sulfur solubility in Fe (sub 3) (S,P) solid solutions could be an excellent pressure indicator if such solid solutions are found in nature.