Abstract
A study investigating first-principles properties of the double perovskite series \(\text {Cs}_{2} \text {AlAuM}_{6}\) ([M] = F, Cl and Br) and using Density Functional Theory (DFT) within the WIEN2K framework to calculate structural, mechanical, electronic, and optical properties, assessing their potential for optoelectronic and thermoelectric solicitations is proposed. Through structural optimization, the mechanical stability of every compound is confirmed, and the cubic Fm-3m phase is retained with tolerance factors ranging from 0.93 to 0.99. The electronic band structure evaluation reveals a direct band gap of 0.98 eV for \(\text {Cs}_{2} \text {AlAuBr}_{6}\) and an indirect band gap of 3.59 eV and 1.99 eV for \(\text {Cs}_{2}\text {AlAuF}_{6}\) and \(\text {Cs}_{2}\text {AlAuCl}_{6}\) , respectively. This suggests a significant capacity for electronic tunability that is contingent upon the halide. The optical computations indicate significant absorption of ultraviolet light. The refractive indices vary from 1.17 for fluorine (F) to 1.81 for bromine (Br), with reflectivity increasing in the sequence of F < Cl < Br. The thermoelectric evaluation, based on Boltzmann transport theory, identifies cesium aluminum gold chloride ( \(\text {Cs}_{2}\text {AlAuCl}_{6}\) ) as the most efficient material. It achieves a power factor of approximately \(4.22\times 10^{11}W/K^{2}ms\) and a maximum ZT of around 0.9 at a temperature of 450 K. \(\text {Cs}_{2}\text {AlAuF}_{6}\) demonstrates low thermal conductivity, suggesting its potential application as a thermal insulator. On the other hand, the evaluation of the electronic and optical characteristics of this series of halides reliably indicates that \(\text {Cs}_{2} \text {AlAuBr}_{6}\) exhibits a direct band gap and a strong optical response, suggesting its suitability for optoelectronic devices. The mechanical analysis reveals ductile behavior and elastic anisotropy across all compounds. Altogether, the various assessments conducted in this study demonstrate that \(\text {Cs}_{2}\text {AlAuF}_{6}\) and \(\text {Cs}_{2} \text {AlAuBr}_{6}\) emerges as the leading thermoelectric candidate, while \(\text {Cs}_{2}\text {AlAuF}_{6}\) and \(\text {Cs}_{2} \text {AlAuBr}_{6}\) offer significant advantages for thermal and optical applications.
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