Bandgap engineering of Gd_0.8Ca_0.2BaCo₂O_5+δ double perovskite for photocatalysis applications

To design the material rationally, we predict the effect of oxygen vacancy on the material bandgap and electron state density based on the first principle density functional theory. Crystal structure, electronic properties, as well as the oxidation and reduction states of Gd_0.8Ca_0.2BaCo₂O_5+δ oxides were studied by GGA-PBE+U calculation. By changing one oxygen atom in the Gd-O_0.5 plane of supercell, Gd_0.8Ca_0.2BaCo₂O_5.25 and Gd_0.8Ca_0.2BaCo₂O_5.75 were created. And they show half-metallic and metallic properties respectively, which is related to the strong electronic correlations for 3d orbitals of Co. Calculation results of partial density of states suggest that O-2p and Co-3d orbits have a great effect on the band gap of Gd_0.8Ca_0.2BaCo₂O_5.5, and the location of cobalt may be an active site. Besides, Gd_0.8Ca_0.2BaCo₂O_5+δ were prepared and annealed in atmosphere to regulate the oxygen vacancy content. Hence, a deep and systematic study on Gd_0.8Ca_0.2BaCo₂O_5+δ was conducted based on theoretical calculations and experiments, including crystal structure, electron distribution and oxygen vacancy. Differing from the conventional doping modification to adjust the electronic energy band structure, this work is dedicated to synthesizing the stable and efficient materials from the theoretical design, which providing a new feasible thought for the efficient and stable material design.