Elucidation of electronic structure and thermoelectric properties of I–III–IV class half Heusler compounds with eight valence electron count

Abstract

This paper presents the stability, electronic structure, electron and phonon transport properties of I–III–IV class half Heusler compounds RbXZ (X = Sc, Y; Z = Si, Ge, Pb) with an octet valence electron count using first-principles calculations and semiclassical Boltzmann transport theory. We predicted the lowest-energy structure and then checked phonon stability. Only RbYPb shows dynamical stability, while the rest five compounds are dynamically unstable. AIMD simulations indicate that RbYPb exhibits thermal stability at 800 K. The predicted stable compound has a direct narrow band gap of 0.11 eV at point X of Brillouin zone, using GGA with spin orbit coupling. The elastic constants and mechanical parameters confirm that RbYPb is mechanically stable, ductile, anisotropic, and has low rigidity. The compound shows a very low value of lattice thermal conductivity (${\kappa }_l$) even at 300 K. The thermoelectric parameters of RbYPb, including the Seebeck coefficient ($S$), electrical conductivity ($\sigma$), electronic thermal conductivity (${\kappa }_{el}$), and power factor ($PF$) under CRTA, are calculated, and discussed in detail. The maximum $PF$ of 110.47 $\mu$Wcm${}^{-1}$K${}^{-2}$ is achieved at 800 K with the doping concentration of 2.93 × 10${}^{21}$cm${}^{-3}$ for n-type carriers. The n-type RbYPb shows a higher zT $>$ 1 compared to the p-type carriers across all considered temperatures.