Physical properties of BaRu2X2 (X = P, As) superconducting compound sunder pressure effects: Ab initio study

Abstract

We report the results of a detailed ab initio investigation of the pressure effects up to 18 GPa on the structural, elastic and thermodynamic properties of the superconducting compounds BaRu2P2 and BaRu2As2. The exchange-correlation effects were modeled through the PBEsol version of the generalized gradient approximation. The calculated equilibrium lattice parameters are in good agreement with the available experimental counterparts. The lattice parameter c decreases with increasing pressure faster than the lattice parameter a. The computed single-crystal elastic constants (Cij) show that both BaRu2P2 and BaRu2As2 are mechanically stable under pressure effect up to 18 GPa. Pressure dependence of the single-crystal and polycrystalline elastic moduli, and related physical parameters, namely Cij, Young's modulus, shear modulus, bulk modulus, Poisson's ratio, average sound velocity, Debye temperature (θD), minimum thermal conductivity (Kmin), melting temperature (Tm) and Vickers hardness (HV), were successfully calculated for the pressure range 0-18 GPa. The quasi-harmonic Debye model was successfully used to explore the temperature and pressure dependencies of the unit cell volume, bulk modulus, isochoric and isobar heat capacities, volume thermal expansion coefficient and Debye temperature. The good agreement between the results obtained using the quasi-harmonic Debye model and those corresponding deduced from the elastic constants constitutes proof of the reliability of the results obtained.