Exploring the physical properties of quaternary fluoro-elpasolites A₂ NaInF₆ (A = Cs,Rb)compounds for prospective technological applications

The double perovskite materials possess exceptional traits that make them highly suitable for energy-related applications, owing to their eco-friendliness, efficiency, and lack of toxicity. Using the density functional theory implemented in WIEN2K, we conducted a thorough examination of the electronic, structural, optical, and elastic characteristics of A₂NaInF₆ (A = Cs, Rb) double perovskite materials. The energy formation and the Birch-Murnaghan equation of state fitting curve guarantee both thermodynamic and structural stability. The optimized lattice parameters obtained from our computations are in agreement with the experimental values for the relevant compounds. For calculating the electronic and optical properties of both materials, the widely used TB-mBJ (Trans Blaha modified Becke-Johnson) approximation is utilized. The replacement of ‘Cs’ with ‘Rb’ results in the tuning of the band gap from 7.70 eV to 5.01 eV. After analyzing the mechanical properties, it is anticipated that both materials exhibit elastic stability, brittleness, and relatively lower hardness. The optical properties are computed, analyzed, and presented across a broad energy range of 0-30 eV of incident photon energy. The absorption coefficient, which is a part of the optical properties, highlights the potential of these materials as fundamental components for optoelectronic devices operating in the extreme ultraviolet (XUV) region. The outcomes of our study could provide valuable insights for the development of high-performance optoelectronic devices.