Computing the Tungsten–Nitrogen Phase Diagram at High Pressure and High Temperature and Further Ternary W–N Compounds*

We compute the tungsten–nitrogen (W–N) pressure–temperature phase diagram through a combination of density functional theory and thermodynamic calculations. Augmenting standard enthalpy-pressure calculations by the chemical potential change of nitrogen at high pressure and high temperature conditions, we estimate Gibbs energies under nitrogen-rich conditions. The approach allows to predict temperature and pressure conditions necessary to synthesize W–N polymorphs and to locate optimum pressure/temperature conditions with maximum driving force for successful syntheses. Our investigations includeW₂N₃, W₃N₅, W₂N₂(N₂), WN₆, and recently synthesized WN₈-N₂. Further studies address ternary Li–W–N compounds with W in high oxidation state, namely Li₆WN₄, Li₆WN₆, and Li₆WN₈.