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

• Published in: Condensed Matter Physics
• Main Authors: V.I. Ivashchenko, P.E.A. Turchi, V.I. Shevchenko
• Format: Article
• Language: English
• Published: Yukhnovskii Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine 2013-01-01
• Subjects: titanium and zirconium carbides and nitrides; first-principles calculations; phase transformation; electronic and phonon structures
• Online Access: http://dx.doi.org/10.5488/CMP.16.33602

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 (NaCl-type) 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.