First-principles and machine-learning-guided study of 65 Sc-based quaternary Heusler alloys with high thermoelectric performance and promising optoelectronic properties

Abstract

In this work, 65 Sc-based quaternary Heusler alloys with 18 valence electrons are systematically investigated by density functional theory in search of new semiconducting materials with multifunctional properties. Structural optimization identifies Y-type (I) and Y-type (II) as the dominant ground-state configurations, and the negative formation energies indicate energetic favorability with respect to the elemental constituents. Electronic calculations reveal 28 semiconducting alloys. Because generalized gradient approximation in the Perdew–Burke–Ernzerhof underestimates the band gap, the electronic structures were further refined using the HSE06 hybrid functional, yielding band gaps in the range of about 0.32–1.57 eV. The calculated elastic constants confirm mechanical stability and indicate predominantly ductile behavior. Optical results show strong dielectric response, high refractive indices, and significant absorption, suggesting promising optoelectronic potential. Thermoelectric calculations further reveal favorable transport combined with low lattice thermal conductivity, with ScVTcGa, ScMoWGa, and ScZrReSn reaching ZT values above 1, and ScTaReIn reaching the practical threshold ZT ≈ 1. Descriptor-based machine-learning analysis further provides physically interpretable insight into the structural ordering, elastic response, and thermoelectric optimization of these alloys. Overall, these results establish Sc-based quaternary Heusler alloys as promising candidates for thermoelectric and optoelectronic applications.