First principles prediction of structural, mechanical and thermodynamic stability in new 18-valence electron XVZ (X = Fe, Ni, Z = Ga, As) half-Heusler semiconductors

Abstract

A suitable semiconductor adds a significant advantage to the technology industry, and the need for better, available, and tunable materials is insatiable. Of the various materials in use as semiconductor devices, the half-Heusler alloys have proved to be promising premised on the possibilities of tuning the various properties to meet the desired demand. In this work, we have investigated the structural, electronic, elastic, mechanical, thermodynamic, and phonon properties of FeVAs and NiVGa half-Heusler alloys. The alloys have 18-valence electrons, and they obey the Slater–Pauling rule. They both belong to the C1b face-centered cubic crystal structure and exhibit indirect bandgap. The negative formation energy shows that experimental fabrication can be attempted; it also confirms the stability of the structures. The elastic properties obey the stability criteria set by Born and Huang and are, therefore, stable. We analyzed the mechanical strength of the alloys, and FeVAs proves to be a superhard material with a Vickers hardness of 78.8 while NiVGa alloy is not. The Debye temperature promotes FeVAs alloy over NiVGa alloy in terms of thermal conductivity. From investigations on the phonon properties using a supercell to facilitate convergence, there are no negative frequencies; hence, we submit that both alloys are dynamically stable.