Orbital-Driven Stability and Multifunctional Response in XYO3 (X = Nb, Ta; Y = Ag, Au) Cubic Perovskites: A First-Principles Study

Designing stable and multifunctional perovskite materials with tunable electronic and optical properties is crucial for advancing next-generation optoelectronic and high-temperature applications. In this study, the structural, electronic, optical, mechanical, and thermal properties of XYO3 (X = Nb, Ta; Y = Ag, Au) cubic perovskites were systematically investigated using density functional theory (DFT). Each compound crystallized into a cubic perovskite structure and was found to be both thermodynamically and dynamically stable. Hybrid functional (HSE06) calculations indicate semiconducting behavior with band gaps of 1.885 eV (NbAgO3), 1.298 eV (NbAuO3), 3.074 eV (TaAgO3), and 1.801 eV (TaAuO3). The density-of-state analysis reveals strong hybridization between the O-2p and Nb/Ta-d orbitals, which hints at mixed ionic/covalent bonding. Optical properties exhibit large absorption coefficients (about 106 cm−1) in the ultraviolet range and at lower reflectivity, especially of NbAgO3 and TaAgO3, indicating efficient light absorption. NbAgO3 and NbAuO3 possess moderate direct band gaps, making them suitable for optoelectronic and photovoltaic applications, whereas the wide bandgap of TaAgO3 is beneficial in ultraviolet optoelectronic devices. Mechanical analysis confirms the ductile nature of all compounds, with TaAuO3 exhibiting the highest ductility. Thermal analysis indicates that NbAgO3 and TaAgO3 exhibit higher lattice rigidity and thermal conductivity, but NbAuO3 and TaAuO3 are more anharmonic and have higher thermal expansion. Overall, these results demonstrate the multifunctional potential of XYO3 perovskites for applications in optoelectronics, photovoltaics, ultraviolet devices, flexible electronics, and high-temperature environments.