First-Principles Investigation of Er-Based Perovskite Oxides ErXO ₃ (X = Os, Fe, Ru) for Optoelectronic and Energy Conversion Applications

Er-based perovskite oxides have emerged as promising multifunctional materials for photocatalytic, optoelectronic, and energy-conversion applications owing to their tunable electronic and optical properties. In this work, first-principles density functional theory (DFT) calculations were performed to systematically investigate the structural, electronic, elastic, thermodynamic, and optical properties of cubic ErXO 3 (X = Os, Fe, Ru) perovskite oxides. Structural optimization and negative formation energies (–2078.12, –3496.39, and –4250.99 eV for ErFeO 3 , ErRuO 3 , and ErOsO 3 , respectively) confirm the thermodynamic stability of all compounds. Electronic band structure calculations reveal semiconducting behavior with band gaps of 1.99 eV (ErOsO 3 ), 2.89 eV (ErFeO 3 ), and 3.51 eV (ErRuO 3 ), corresponding to visible, near-ultraviolet, and ultraviolet spectral regions, respectively. The calculated absorption edges at 623, 429, and 353 nm demonstrate broad spectral coverage, with ErOsO 3 exhibiting superior visible-light absorption, making it a promising candidate for visible-light-driven photocatalytic water splitting and pollutant degradation. In contrast, ErFeO 3 and ErRuO 3 are more suitable for ultraviolet-assisted photocatalytic processes. Mechanical analysis confirms that all compounds satisfy the stability criteria and exhibit ductile behavior with elastic anisotropy factors of 0.79 (ErOsO 3 ), 0.31 (ErFeO 3 ), and 0.539 (ErRuO 3 ), indicating favorable mechanical robustness. The enhanced optical response, together with their stable crystal structure and tunable electronic properties, highlights the potential of ErXO 3 perovskite oxides as multifunctional materials for next-generation photocatalytic, optoelectronic, photovoltaic, and sustainable energy-conversion technologies.