A cotunnite-type new high-pressure phase of Fe2S

We examined pressure-induced phase transitions in Fe2S based on high-pressure and high-temperature X-ray diffraction measurements in a laser-heated diamond-anvil cell. Fe2S is not stable at ambient pressure but is known to form above 21 GPa with the Fe2P-type (C22) structure. Our experiments demonstrate a novel phase transition in Fe2S from the C22 to C23 phase with the Co2P-type cotunnite structure above -30 GPa. The experiments also reveal a transformation from the C23 to C37 (Co2Si-type) phase above similar to 130 GPa. While the C23 and C37 structures exhibit the same crystallographic symmetry (orthorhombic Pnma), the coordination number of sulfur increases from nine in C23 to ten in C37. Such a sequence of pressure-induced phase transitions in Fe2S, C22 -> C23 -> C37, are similar to those of Fe2P, while they are not known in oxides and halogens that often adopt the C23 cotunnite-type structure. The newly found cotunnite-type Fe2S phase could be present in solid iron cores of planets, including Mars.

Automated summary

In this study, pressure-induced phase transitions in Fe2S were examined using high-pressure and high-temperature X-ray diffraction measurements. A novel cotunnite-type Fe2S phase was discovered, which has important implications for understanding the composition of iron cores in planets.