High pressure structural stability of ThN: ab-initio study

Abstract

The high pressure structural stability of thorium nitride (ThN) has been examined through first principle total energy calculations. The structural sequence predicted through present theoretical simulation is NaCl type structure (B1) to tetragonal phase (B10) to CsCl type (B2) phase with corresponding transition pressures ∼75 GPa and 120 GPa, respectively. The B1 → B10 transition with volume discontinuity of ∼10% is found to be of first order type, whereas, the B10 → B2 displays second order nature. The predicted high pressure structural sequence in ThN is different from those reported in earlier works [Gupta and Singh, Sol. State Sci., 2010 and Modak and Verma, Phys. Rev. B 2011]. The pressure induced phase transition sequence so obtained is further supported by examining the mechanical and phonon stability of the predicted structures in their structural stability regime. Also, the activation barrier for B1 to B10 transition determined from the calculated Bain path at the transition pressure turns out to be ∼0.75eV/f.u.(72.36 kJ/mol).