First-principle study of electronic, optical and transport properties for A₂CdB₄ (A = Sc, Y; B = S, Se) spinel chalcogenides under strain condition

The electronic, optical, and thermoelectric properties of A₂CdB₄ (A = Sc, Y; B = S, Se) spinel chalcogenides were systematically studied using first-principles calculations within the FP-LAPW + lo framework. Structural optimization was performed using GGA, while the TB-mBJ potential was employed to accurately calculate the electronic band structure. All the studied compounds exhibit direct bandgaps, which show strong dependence on applied biaxial strain from − 8% to + 8%. Compressive strain deceases the bandgap, whereas tensile strain increases it, enabling band edge engineering through lattice deformation. Thermoelectric transport coefficients were evaluated in the temperature range 200–800 K. Electrical conductivity increases with temperature and is enhanced under tensile strain, while thermal conductivity shows slight reduction under tensile strain due to phonon scattering effects. The Seebeck coefficient exhibits strong strain sensitivity, and the thermoelectric figure of merit (ZT) reaches maximum values near + 8% strain, with ZT ≈ 0.78—0.79 at 800 K. These results demonstrate that strain engineering provides an effective rout to tune and optimize the optoelectronic and thermoelectric performance of A₂CdB₄ spinel chalcogenides for advanced device applications.