Pressure-Induced Evolution of Structural, Mechanical, and Optoelectronic Properties of Na ₂ LiYBr ₆ : A First-Principles Investigation

The present study examines the effect of pressure on a new cubic Na 2 LiYBr 6 on structural, electronic, elastic, and optical properties from 0 to 90 GPa. The purpose of this study is to employ pressure to reduce the electrical band gap of Na 2 LiYBr 6 in order to improve its optical characteristics and assess its potential for usage in optical electronic devices. Our results show that increasing pressure leads to a consistent reduction in both the lattice parameter and the overall cell volume. Based on the band-structure analysis, Na 2 LiYBr 6 exhibits a direct band gap at ambient pressure. The electronic band gap gradually narrows from 3.08 eV to 1.35 eV as the pressure increases to 90 GPa. The calculated elastic parameters confirm that the material remains mechanically stable up to 90 GPa, while also displaying noticeable anisotropy and a predominantly ductile nature. Importantly, the mechanical strength of the compound improves significantly under applied pressure. Furthermore, the dielectric function, refractive index, reflectivity, absorption, and other optical properties were evaluated within the 0-14 eV energy range under different pressure conditions. At 0 GPa, the static dielectric function ε 1 (0) for Na 2 LiYBr 6 is at its lowest (3.52). For 45 GPa, Na 2 LiYBr 6 is found to have the highest optical conductivity σ(ω) values at 9 eV (10.1 × 10 3 (Ω·cm) -1 ), indicating that they are appropriate for the UV region. These optica responses indicate that Na 2 LiYBr 6 perovskite can be employed in pressure-sensitive optoelectronic devices, including photodetectors, LEDs, and solar cells, due to its band gap tunability and improved mechanical stability