DFT-based comparative study of mechanical, electro-optic, and transport response of halide double perovskites Na2MAlZ6 (M = Ag, Cu; Z = Br, I) for green energy applications

Abstract

A comparative exploration of mechanical, electronic, optical, and transport characteristics of the double perovskites Na₂MAlZ₆ (M = Ag, Cu; Z = Br, I) has been carried out. The optimized structure, tolerance factor, and formation energy analysis confirmed the stability. The ab initio molecular dynamics (AIMD) also verified the dynamic stability of Na₂MAlZ₆. The study of elastic aspects, Pugh’s ratio, and Poisson’s ratio is conducted to verify the structural stability under pressure and the characteristics of materials. The observed mechanical characteristics validate the presence of flexibility, durability, asymmetry, and an escalated melting temperature. The studied materials are mechanically stable and ductile. The analysis of electronic aspects revealed a direct band gap of 2.62 eV for Na₂AgAlBr₆, 1.30 eV for Na₂AgAlI₆, 1.15 eV for Na₂CuAlBr₆, and 0.56 eV for Na₂CuAlI₆. The Kramer-Kronig relationship is employed to assess the optical attributes of materials that demonstrate significant absorption over the investigated spectrum. The absorption, reflection, and loss of incident photons within materials enable their application in photovoltaic systems and optoelectronic technologies. The Boltzmann semi-classical concept is used to compute thermoelectric characteristics. These materials have significant promise for thermal energy conservation implications because of their elevated ZT values. Therefore, the outcomes of current work theoretically justify that these compounds are very suitable for efficiently harvesting renewable energy.