Electronic structure reconstruction and low-energy optical response in La/Co-codoped BaTiO₃: a first-principles study

BaTiO₃ is a lead-free perovskite whose wide band gap limits its response to lower-energy photons. Spin-polarized GGA + U calculations were used here to examine the effect of simultaneous La substitution at Ba sites and Co substitution at Ti sites. For the La/Co-codoped model, the calculated gap decreases from 2.1728 eV for BTO to 0.9889 eV for BLTC. On the supercell path considered, the band-edge extrema of BLTC occur at different k-points, unlike the coincident Γ-point extrema calculated for BTO. Projected densities of states place Co 3d-derived states near the band edges, where they overlap with O 2p states; La mainly changes the local A-site charge environment. These electronic changes are accompanied by enhanced low-energy optical features and a stronger response below 5 eV. An alternative La-Co arrangement remains semiconducting, whereas a representative near-Co oxygen vacancy makes the model metallic, exposing strong defect sensitivity. Together, the calculations show that La/Co codoping can be used to reshape the band edges and extend the low-energy optical response of BaTiO₃-based materials.