Role of oxygen vacancies on the structural, electronic, optical, and photocatalytic properties of Ba

Oxygen vacancies are known to critically influence the crystal structure, electronic properties, as well as photocatalytic performance of double perovskites. In this study, we employ first-principles density functional theory (DFT) with generalized gradient approximation (GGA) and Hubbard U corrections to systematically investigate the effects of oxygen vacancies on Ba2CeMO6 (M = Bi, Sb) double perovskites. The introduction of vacancies significantly modifies the band structure, generating intermediate electronic states that reduce the band gap energy and enhance photocatalytic performance, as evidenced by band edge potential analysis. Effective mass calculation supported the results and displayed lighter mass of charge carriers in the reduction potential. Structural relaxations reveal local distortions around the vacancy sites and exhibit vacancy-mediated phase transition phenomenon. The experimental zero band gap of Ba2CeBiO6 is rationalized by the oxygen vacancy-induced semiconducting to metallic electronic configuration. Thermodynamic calculations indicated high Debye temperature and melting point with minimum thermal conductivity. Furthermore, optical property analysis suggests improved light absorption in the visible range, highlighting the potential of defect-engineered Ba2CeMO6 (M = Bi, Sb) for efficient photocatalytic applications. These results provide fundamental insights into defect-mediated property tuning in perovskite semiconductors, offering to design for next-generation functional materials.