Insight into the structural, mechanical, electronic and optical properties of X2CuAsF6 (X = Na, K) double perovskites for high energy applications employing DFT

Halide double perovskites offer a broad compositional space with versatile properties, applicable in various fields such as thermoelectric systems, memory devices, light-emitting diodes, sensors, X-ray detectors and beyond outdoor photovoltaics. In this work, we present novel Pb-free double halide perovskites, X2CuAsF6 (X = Na, K), for applications in renewable energy, as investigated through density functional theory calculations. Utilizing the Brich-Murnaghan equation of state alongside the tolerance factor provides conclusive evidence regarding the structural stability of both compounds in their cubic configurations. Both compounds demonstrate semiconducting behavior from the W to L symmetry points, featuring respective band gap values of 0.8 eV and 1.56 eV, indicating an indirect band gap nature. Both compounds display mechanical stability, ductility, resistance to crack deformation, and anisotropy, as determined by their elastic constants. In evaluating their viability for optoelectronic devices, we evaluate the optical characteristics. Our findings could provide comprehensive insights into predicting the fundamental properties of these compounds, potentially paving the way for experimentalists to explore new directions.