Exploring the structural, electronic and optical properties of Rb₂InGaCl₆ and Rb₂InGaF₆ double perovskite compounds for high-energy applications: a DFT-based investigation

Double perovskites have harvested considerable attention in the realm of solar cells and renewable energy applications. Therefore, in this current study, we explored the structural, electronic, and optical properties of Rb₂InGaCl₆ and Rb₂InGaF₆ using DFT-based simulations with WIEN2K codes. It is unequivocally established that both compounds demonstrate structural and mechanical stability. Structural stability is further evaluated using Goldsmith’s tolerance factor (τ_G). The τ_G values of 4.29 and 3.77 are considered acceptable for ensuring the stability of cubic structures for Rb₂InGaCl₆ and Rb₂InGaF₆ respectively. It is determined that both compounds are stable elastically and possess ductile characteristics, allowing them to undergo plastic deformation without fracturing. Our investigation reveals indirect band gaps of 1.7 eV (semiconductor) for Rb₂InGaCl₆ and 4.8 eV (insulator) for Rb₂InGaF_6. These diverse band structures open up exciting possibilities for optoelectronic applications. Regarding optical properties, the spectral curves of various parameters are examined in the range of 0 eV to 15 eV incident photon energy. The findings reveal the exceptional optical performance of Rb₂InGaCl₆ and Rb₂InGaF₆, particularly by their notably high absorption coefficients α(ω). Specifically, Rb₂InGaCl₆ demonstrates a remarkable absorption of 6.635 at 2.05 eV, while Rb₂InGaF₆ exhibits a significant absorption of 3.91 at 4.78 eV. The optical conductivity σ(ω) attains peak values, reaching 4.60 for Rb₂InGaCl₆ and 2.85 for Rb₂InGaF₆. Furthermore, the optical reflectivity R(ω) peaks at 13.60 eV for Rb₂InGaCl₆ and 6.30 eV for Rb₂InGaF₆. Lastly, the energy loss functions L(ω) attain their highest values of 0.57 and 7.58 for Rb₂InGaCl₆ and Rb₂InGaF₆, respectively. These results collectively emphasize the impressive optical characteristics of these compounds across a range of energy levels. These findings suggest promising potential energy applications for these materials, particularly in influencing electromagnetic radiation within the ultraviolet (UV) spectrum ranges.