First Principles Study of the Structural, Mechanical, Electronic, and Lattice Dynamical Properties of the Half-Heusler Alloys ZrCoY (Y=Sb, Bi )

Abstract: First-principles calculation has led to significant discoveries in materials science. Half heusler (HH) alloys, which are potential thermoelectric materials have demonstrated significant improvements in thermoelectric performance owing to their thermal stability, mechanical strength, and moderate ZT. Using Density Functional Theory (DFT), the structural, mechanical, electronic, and lattice dynamical properties of cubic Half Heusler alloys ZrCoY (Y=Sb, Bi) have been investigated. The unknown exchange-correlation functional is approximated using the generalized gradient approximation (GGA) pseudopotential plane-wave approach. The structural parameters, that is, equilibrium lattice constant, elastic constants, and their derivatives are consistent with reported experimental and theoretical studies where available. Mechanical properties such as anisotropy factor A, shear modulus G, bulk modulus B, Youngs modulus E, and Poisons ratio n, are calculated using the Voigt-Reuss-Hill average approach based on elastic constants. The Debyes temperature, as well as longitudinal and transverse sound velocities, are predicted from elastic constants at GGA-PBE and GW approximations. The study of elastic constants showed that the compounds are mechanically stable, and the phonon dispersion study showed that they are dynamically stable as well. The ductility and anisotropic nature of the compounds are confirmed by the elastic constants and mechanical properties.