Trends in elasticity and electronic structure of transition-metal nitrides and carbides from first principles

摘要

The elastic properties of selected transition-metal (TM) nitrides and carbides in B_1 structure are studied using the ab initio density-functional perturbation theory. We find that (1) the inequality B > G′ > G > 0 holds for all these materials, where B = (C_(11)+2C_(12))/3, G′ = (C_(11)-C_(12))/2, and G = C_(44) with C_(ij) the elastic constants, and (2) G has large values when the number of electrons per unit cell Z_V = 8 or 9. The fitted curve of G vs. Z_V predicts that rocksalt MoN is unstable, and TM carbonitrides (e.g., ZrC_xN_(1-x)) and di-TM carbides (e.g., Hf_xTa_(1-x)C) have maximum G at Z_V ≈ 8.3.