Sulfur and phosphorus in the Earth's core: The Fe‐P‐S system at 23 GPa

Abstract

Phosphorus is an important element believed to be present in the Earth's core. As a non‐metal, its solubility in iron is limited, leading to the precipitation of phosphides at high concentrations. Here we present experimental results for the iron‐rich portions of the Fe‐P and Fe‐P‐S systems at 23 GPa. We find a Fe‐P eutectic point occurring at 9 wt% P and 1275°C at 23 GPa. Up to 4 wt% P is soluble in the Fe‐rich solid coexisting with the eutectic liquid at these conditions. The ternary Fe‐P‐S system displays a simple cotectic between the Fe‐P and Fe‐S binary eutectics with minimum melting temperature on the S‐side at 1075°C. At subsolidus conditions there is complete solid solution between Fe 3 P and Fe 3 S. The high solubility of phosphorus in iron along with its miscibility in Fe 3 S and iron‐sulfur liquids at high pressures, combined with expectation of only minor concentrations in planetary cores, indicate phosphorus will not form a distinct phase within terrestrial planet cores.