Comprehensive theoretical investigation of NaAlX (X=C, Si and Ge) half-Heusler compounds: Unveiling the multifaceted properties for advanced applications

Abstract

In this work, we have extensively investigated the characteristics of ternary half-Heusler (HH) materials, specifically NaAlX (X[Formula: see text][Formula: see text][Formula: see text]C, Si and Ge), employing ab-initio computations in density functional theory (DFT) framework. Various aspects, including stability parameters, electronic, optical and thermoelectric (TE) parameters have been examined. The computed lattice constants of NaAlX (X[Formula: see text][Formula: see text][Formula: see text]C, Si and Ge) were found to be, respectively, 5.398, 6.301 and 6.389[Formula: see text]Å which are in excellent agreement with the previously available data. The electronic band structures showed that the studied materials exhibit semiconducting behavior with a corresponding band gap of 1.961, 0.999 and 0.846[Formula: see text]eV, respectively. Specifically, NaAlC and NaAlGe compounds were found to have a direct energy band gap at the [Formula: see text]-point, while NaAlSi displayed an indirect band gap at the [Formula: see text]–X point. Elastic and thermodynamic parameters were examined, confirming that the titled compounds possess mechanical, dynamic and thermal stability. Additionally, the optical response of the materials has been analyzed within an energy range of 0–13[Formula: see text]eV. The TE parameters exhibited maximum ZT values of 0.998, 0.992 and 0.990 for NaAlX (X[Formula: see text][Formula: see text][Formula: see text]C, Si and Ge) materials, respectively, at 300[Formula: see text]K, suggesting promising TE performance at room temperature.