First-principles study of phase stability of Ti2N under pressure


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Phys. Rev. B, 2012, #86, P.064109 - 7 pp.


 In this work we present the results of investigations of various phases of TiN and Ti2N under pressure within a first-principles puseudopotential method. We used the “Quantum EXPRESSO” code. For the exchange-correlation potential, the generalized gradient approximation (GGA) was employed. For the stoichiometric TiN, the B1→B2 structural transformation at P=342 GPa was revealed. Below we will accent on the substoichiometric ordered phase of TiNx, x=0.5 (Ti2N). In Fig. 1 we show the total energy (ET) for various phases of Ti2N as functions of cell volume. The phonon spectrum (FS) of the δ'-phase (I41/amd) is presented in Fig. 2. It follows from Fig. 1 that the δ'-phase TiNx is stable for x>0.5 (larger cell volumes) and at high temperature, since the FS has the soft modes. At low temperature, the ε-phase (P4/mnm) is most stable in accordance with an experiment