Ab initio study of Fermi surface and dynamical properties of Ni2XAl (XÂ =Â Ti, V, Zr, Nb, Hf and Ta)

A detailed study on the pressure and temperature effects on ternary Ni-based inter-metallic compounds Ni2XAl (X = Ti, V, Zr, Nb, Hf and Ta) have been carried out using density functional theory. The calculated ground state properties are in good agreement with experiments for all the investigated compounds. The band structures and Fermi surface topology is found to be quite similar for all the compounds except for Ni2NbAl, where we find an extra band to cross the Fermi level under compression resulting in a new electron pocket at X-point. Ni2NbAl is found to be a superconductor with superconducting transition temperature of 3.1 K which agrees quite well with the experimental value and the calculated Tc is found to vary non-monotonically under pressure. From the calculated phonon dispersion relation, we find all the investigated Ni-based Heusler compounds to be dynamically stable, until high pressure. The ductile nature of these compounds is confirmed from the calculated Cauchy's pressure, Pugh's ratio and Poisson's ratio. In addition, the thermodynamic properties show Ni2TiAl to have lower specific heat and entropy but higher internal energy and free energy among all the investigated compounds.