First-principles study of phase stability of Ti₂N under pressure

Анотація

 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 TiN_x, 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