Revealing vibrational, elastic, electro-optic, and thermoelectric aspects of double perovskites Na₂ScCuX₆ (X=Cl, Br) for energy harvesting applications by implementing DFT approach

Currently, the novel combination of double perovskites Na₂ScCuX₆ (X = Cl, Br) is being investigated as a potential solution to fulfil the energy requirements. For this purpose, the stability, vibrational, mechanical, electro-optic, and transport properties are addressed systematically. The tolerance factor and Born mechanical criteria ensure structural and mechanical stabilities. The calculated formation and Gibbs free energies ensure the thermal stabilities. Thermodynamic properties against temperature and pressure are explored by discussing entropy, thermal expansion, and Debye temperature. The elastic characteristics have provided insight into anisotropy and mechanical strength. Meanwhile, ductile nature is characterized by the Poisson ratio and Pugh's ratio. The electronic aspects have estimated the band gaps of Na₂ScCuCl₆ and Na₂ScCuBr₆, which yielded values of 1.63 and 1.58 eV, respectively. The materials demonstrated substantial light absorption (order of 10⁵ cm⁻¹) and minimal reflectivity (below 25 %) in the visible range. The thermoelectric performance has been evaluated in the temperature range of 100–600K using the Seebeck effect, conductivities, and figure of merit. Lastly, the superior figure of merit (ZT) values ranging between 0.78 and 0.84 demonstrate the suitability of materials for thermal energy conversion. Therefore, Na₂ScCuCl₆ and Na₂ScCuBr₆ have the potential to be considered feasible candidates for energy harvesting applications.