First-principles study of high temperature and high-pressure behavior of carbides and nitrides of group IVB elements

Abstract

Full potential linearized augmented plane wave method combined with quasi-harmonic approximation, has been used to perform the calculations of thermophysical properties of carbides and nitrides of the group IVB elements at high temperature and pressure. Relative accuracy of linear density approximation (LDA) and generalized gradient approximation (GGA) exchange correlation potentials have been tested. Specific heat () obtained through LDA and GGA agrees with experimental data up to 1500 K. Above 1500 K, GGA gives better agreement whereas LDA under-estimates the specific heat. LDA overestimates the bulk modulus, GGA gives better agreement with the experimental data. High-temperature bulk modulus follows the Wachtman formula. Calculated isotherms agree with published experimental results. The transformation pressures () from NaCl-type structure (B phase) to CsCl-type structure (B phase), and collapsed volumes () at () have been predicted. The stability and hardness of these compounds are related with the calculated density of states.