Electronic, mechanical, vibrational and optical properties of TaIrX (X = Ge and sn): a DFT approach

Abstract

First-principles calculation investigated the structural, electronic, mechanical, thermodynamic, optical properties and the lattice dynamics of 18 valence electron half-Heusler alloys TaIrX (X = Ge and Sn). The results reveal that the two alloys have a semiconducting nature with flat bands at the valence band maximum, favouring p-type doping. Also, they are dynamically stable with phonon–phonon scattering. TaIrX (X = Ge and Sn) are mechanically stable and ductile. This is because their B/G ratios are higher than the critical ratio of 1.75. The optical properties, such as the real and dielectric function, absorption coefficient, refractive index, and electron energy loss, were investigated. The dielectric constants for TaIrGe and TaIrSn are 16.6 and 16.9, respectively . The refractive index of TaIrGe and TaIrSn are 4.08 and 4.11, respectively. The maximum reflectivity of the two alloys are 59.2%(57.6%) at 13.5 eV(10.6 eV) for TaIrGe (TaIrSn). The Debye temperatures and the average sound velocities of TaIrX (X = Ge and Sn) were also investigated.