Comprehensive analysis of structural, mechanical, optoelectronic, and thermodynamic properties of Ba₂XBiO₆ (X = Y, La) double perovskites using density functional theory

Abstract The structural, mechanical, optoelectronic, and thermodynamic properties of Ba 2 XBiO 6 (X = Y, La) double perovskites are critically analyzed using density functional theory. The Birch-Murnaghan equation of state confirms their structural stability, supported by tolerance factor analysis. For Ba 2 YBiO 6 and Ba 2 LaBiO 6 , negative formation energies are −0.935 eV for Ba 2 YBiO 6 and −0.836 eV for Ba 2 LaBiO 6 , confirming thermodynamic stability. Phonon dispersion curves indicate stable lattice vibrations, reducing the likelihood of spontaneous structural changes or phase transitions. Ba 2 YBiO 6 possesses higher elastic constants C 11 = 222 GPa shows stiffness and exhibits brittle mechanical behavior, whereas the Pugh ratio and C 11 = 217 GPa for Ba 2 LaBiO 6 shows ductility. The Poisson ratio classifies Ba 2 YBiO 6 as a non-central force crystal and Ba 2 LaBiO 6 as a central force crystal. Both materials are indirect band gap semiconductors, with band gap values of 0.75 eV for Ba 2 YBiO 6 and 2.05 eV for Ba 2 LaBiO 6 . Optical properties suggest applications in UV and visible light-based optoelectronic devices. Thermodynamic properties, such as Debye temperature and heat capacity, support the idea that these materials are suitable for high mechanical applications. These findings provide insights for designing high-performance optoelectronic and mechanical devices.