First-principles studies on the structural, elastic, electronic and optical properties of K ₂ TiBr ₆ under high pressure

Abstract Based on first-principles calculations, the structural, mechanical, electronic, and optical properties of K 2 TiBr 6 , an ordered double perovskite with numerous titanium base positions, are investigated under pressure conditions from 0 to 150 GPa. This research seeks to thoroughly study the changes in physical properties caused by pressure and evaluate the applicability of the compound in optoelectronic applications. The structural characteristic fits well with published earlier research. A higher interaction between atoms is also a result of the significant drop in lattice characteristics. From the analysis of elastic constants, the material has mechanical stability and good toughness when pressurized. The band structure demonstrates that K 2 TiBr 6 is a direct band gap semiconductor with 1.749 eV at 0 GPa. The band gap decreases with increasing pressure until 110 GPa. After 110 GPa, it remains at 0 eV, indicating that the material undergoes a phase transition and becomes the conductor. Meanwhile, we also investigate the optical properties of K 2 TiBr 6 by calculating the dielectric function ε( ω ), absorption coefficient α ( ω ), reflectance R( ω ), energy loss spectrum L( ω ), and complex refractive index N( ω ), respectively. Those spectra are sensitive to pressure. Generally, the low-energy peaks are red-shifted, and the high-energy peaks are blue-shifted. In particular, the pressure increases the absorption of the material at UV and reduces the energy loss in the visible light range. In summary, this work highlights that K 2 TiBr 6 may have potential applications in ultraviolet devices and energy-conversion optoelectronic devices.