Computing the iron–nitrogen phase diagram at high pressure and high temperature

Abstract

Locating pressure and temperature conditions relevant to concurrent diamond-anvil-cell (DAC) experiments is imperative for the discovery of new high–pressure nitrogen-rich compounds. In this work we provide a pressure-temperature phase diagram of the iron–nitrogen system for pressures up to 200 GPa and temperatures up to 4000 K through a combination of Density Functional Theory computations and thermodynamic calculations. The work includes an assessment of the chemical potential of nitrogen and its change at high pressure and high temperature. We deliver stability fields of various Fe–N compounds in the presence of excess nitrogen. Our results are in agreement with recent synthesis of FeN2 and FeN4, and predict a hitherto unknown FeN8 attainable at 100 GPa and 1500 K.