Sulfur in the Earth’s inner core

Experiments have been conducted to study the Fe–S binary phase diagram near the pure iron end member, at pressures between 7 and 25 GPa and temperatures between 1223 and 1473 K. We observed that more than 1 atomic percent (at.%) sulfur dissolved in solid iron at 25 GPa and near the eutectic temperature. Incorporation of sulfur has non-negligible effects on the lattice parameters of solid iron. At 24.2 GPa, the unit-cell volume of a quenched solid iron is 1.2% larger, and its c/a ratio 0.5% larger than pure iron. These results support the prediction that the Earth’s inner core contains a significant amount of sulfur.