Phase transformation B1 to B2 in TiC, TiN, ZrC and ZrN under pressure

Abstract

Phase stability of various phases of MX (M= Ti, Zr; X = C, N) at equilibrium and under pressure is examined based on first-principles calculations of the electronic and phonon structures. The results reveal that all B1 (NaCltype) MX structures undergo a phase transition to the B2-structures under high pressure in agreement with the previous total-energy calculations. The B1-MX structures are dynamically stable under very high pressure (210÷ 570 GPa). The pressure-induced B2 (CsCl-type)MC phases are dynamically unstable even at high pressures, and TiN and ZrN are found to crystallize with the B2-structure only at pressures above 55 GPa. The first-order B1-to-B2 phase transition in these nitrides is not related to the softening of phonon modes, and the dynamical instability of B2-MX is associated with a high density of states at the Fermi level. © V.I. Ivashchenko, P.E.A. Turchi, V.I. Shevchenko, 2013.