Valence Electron Count-Based Density Functional Theory to Investigate Structural Stability, Optoelectronic and Thermoelectric Properties of New p-Type Half-Heusler Zryau (Y=B, Al) Alloys

The full-potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT) and semi-classical Boltzmann transport theory under the constant relaxation time approximation has been employed to investigate the structural, mechanical, optoelectronic and thermoelectric properties of novel half-Heusler (HH) ZrYAu alloys (where Y=B or Al) with a valence electron count (VEC) of 8. Our results indicate that both compounds are mechanically stable in structure Type 1 and possess negative formation energies. Additionally, ZrBAu and ZrAlAu display semiconducting behavior, with ZrBAu showing a direct band gap, 0.753 eV (0.774 eV) at point Γ→X and ZrAlAu exhibiting an indirect band gap, 0.431 eV (0.482 eV) at point Γ→Γ, using the generalized gradient approximation (GGA) and Modified Becke and Johnson-generalized gradient approximation (mBJ-GGA), respectively. Based on optical properties, both ZrBAu and ZrAlAu exhibit high optical conductivity within the visible spectrum. In terms of visible light absorption, ZrBAu primarily absorbs blue light, while ZrAlAu absorbs yellow, blue-green and violet light. However, both compounds are effective absorbers of UV light. Regarding thermoelectric performance, the thermoelectric parameters reveal that ZrBAu and ZrAlAu demonstrate significant p-type thermoelectric power. These half-Heusler alloys have a high-power factor, making them promising candidates for thermoelectric applications.