Elucidating the Doping Concentration-Dependent Burstein–Moss Shift and Optical Band Transitions of BaZr 1– x Ta x O ₃ Perovskite for Photocatalytic Applications

Foreign element doping in the BaZrO 3 perovskite oxide is a widely used technique for enhancing its physical properties. This has led to experimental reports showing that Ta-doped BaZrO 3 is suitable for photocatalytic applications and the absorption edge undergoes Burstein–Moss shift, Δ E BM, with increasing Ta concentration. In the present work, the impact of Ta-doping concentration on BaZrO 3 has been analyzed using accurate first-principles density functional theory (DFT) calculations. The exchange-correlation effects are treated with the meta-GGA functionals of DFT, and structural, thermodynamic, and optoelectronic properties of three Ta-doping concentrations ( x = 0.037, 0.0625, and 0.125) are examined. The calculated defect formation energies clearly indicate that doping with Ta at the Zr site of BaZrO 3 is thermodynamically feasible under oxygen-rich chemical conditions. Moreover, trends in the structural properties and simulated powder X-ray diffraction patterns with increasing Ta-doping concentration are found to be consistent with experimental observations. Our results reveal that, unlike the undoped BZ, which is a wide-band gap semiconductor, the substitutional doping of Ta at the Zr site of BZ injects electrons in hybridized Ta 5d and Zr 4d states of the conduction band, leading to a degenerate (electron-doped) semiconductor. Furthermore, increasing the Ta-doping concentration from x = 0.037 to 0.125 shifts the Fermi energy deeper inside the conduction band, and the apparent band gap undergoes a blue shift. Based on our calculated structural, electronic, and optical properties of Ta-doped BaZrO 3, we conclude that the doping concentration-dependent Burstein–Moss shift, together with the disordered electronic states originating from structural imperfections, can explain the good photocatalytic properties of BaZr 1– x Ta x O 3 observed in experiments. Our results may provide important insights for the experimental community for designing more complex and high-efficiency photocatalytic systems.