Pressure-induced phase transition of tantalum mononitride

Three synthesized stable phases for TaN are studied by the first-principles calculations. We confirm that TaN undergoes a phase transition from the hexagonal є phase to the hexagonal θ one with a volume collapse of 5.25% when the applied pressure is 3.2 GPa. The obtained phase transition pressure is in good agreement with the experimental results. An analysis of the calculated results shows that this phase transition is mainly caused by the higher bulk modulus and lower electron states on the Fermi level of the hexagonal θ phase for TaN. The superior elastic properties indicate that TaN in the hexagonal θ phase is an ultra-incompressible and hard material.