Semiconducting Cubic Titanium Nitride in the Th3P4 Structure

We report the discovery of a long-sought-after phase of titanium nitride with stoichiometry Ti3N4 using diamond anvil cell experiments combined with in situ high-resolution x-ray diffraction and Raman spectroscopy techniques, supported by ab initio calculations. Ti3N4 crystallizes in the cubic Th3P4 structure [space group I43d (220)] from a mixture of TiN and N2 above ≈75 GPa and ≈2400 K. The density (≈5.22 g/cc) and bulk modulus (K0=290 GPa) of cubic-Ti3N4 (c-Ti3N4) at 1 atm, estimated from the pressure-volume equation of state, are comparable to rocksalt TiN. Ab initio calculations based on the GW approximation and using hybrid functionals indicate that c-Ti3N4 is a semiconductor with a direct band gap between 0.8 and 0.9 eV, which is larger than the previously predicted values. The c-Ti3N4 phase is not recoverable to ambient pressure due to dynamic instabilities, but recovery of Ti3N4 in the defect rocksalt (or related) structure may be feasible.