Electronic, mechanical, vibrational and thermodynamic properties of FeXSb (X = Hf and Nb) Half-Heusler alloys from first-principles approach

Abstract A comprehensive computational study of FeXSb (X = Hf and Nb) half-Heusler alloys have been performed by adopting ab initio density functional theory approach. Recent studies has shown that FeNbSb half-Heusler alloy is a potentially good and promising candidate for thermoelectric device when it is substitutionally doped with Hf. Therefore, the present study have investigated the electronic, elastic, mechanical, vibrational and thermodynamic properties of FeXSb (X = Hf and Nb) half-Heusler alloys for efficient and effective thermoelectric performance. The computed electronic properties affirmed the semiconductive nature of the FeNbSb alloy while FeHfSb alloy is predicted to be half metallic ferromagnetic compound with small magnetic moment of 0.9 μB. The contributions of the d-electrons of Fe Hf and Nb in the band structure is notable and significant as revealed in the projected density of states (PDOS). The mechanical stability of the two alloys was established when the computed elastic constants accurately satisfy the generalized mechanical stability conditions. Moreover, the mechanical properties revealed that our investigated materials are ductile and incompressible. Also, the alloys were predicted to be anisotropic in nature. The presence of positive frequencies obtained from the calculation of phonon dispersion throughout the Brillouin zone indicates that FeXSb alloys are dynamically stable. Moreso, LO-TO spliting is observed and reported in FeNbSb alloy. Various temperature dependent thermodynamic parameters such as debye temperature, sound velocity, internal energy, vibrational energy, entropy and constant volume heat capacity were computed within harmonic approximation. The obtained results pointed to the fact that the two alloys have impressive thermal response.