Photovoltaic infrared-photodetector based on perovskite Fe-BaTiO3 with further investigations for X-BTO (X = V, Cr, Mn, and Fe): A DFT study

[Display omitted] •The substituting of Ti in BTO by V, Cr, and Fe transition metals led to a reduction in cell volume with increasing atomic number.•Fe-BTO showed the lowest band gap which is around 0.579 eV at zero kelvin.•Fe-BTO had a band gap value of around 0.15 eV at 1300 K according to Bose-Einstein model.•The dielectric constant and refractive index reached 6.04 and 2.45 for Fe-BTO, while in pure BTO are 3.96 and 1.99. Density functional theory (DFT) is exploited to comprehensively investigate the effects of transition metal doping on the electronic and optical properties of Barium Titanate (BTO). By incorporating vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) as dopants or substitutions within the BTO superlattice (Ba4Ti4-xO12), where x always represents a single atom, significant changes in the properties are observed. The structural investigation indicates a change in the cubic symmetry of BTO to tetragonal for V, Cr, and Fe doping, while Mn-BTO adopts an orthorhombic structure. The volume of the lattice structure decreases upon increasing the atomic number of the dopant elements, with the exception of orthorhombic Mn-BTO. In addition, the reduction in volume varies from 1.1 % to 2.1 % (excluding Mn), reaching 56.606 Å for Mn-BTO and 61.325 Å for Fe-BTO. While V-BTO and Mn-BTO exhibit weak metallic behavior, Cr and Fe-BTO display narrow band gaps of 0.974 and 0.579 eV, leading to a notable reduction in the band gap. Particularly Further, Fe-BTO demonstrates the highest absorption in the IR region due to its low band gap in addition to increasing the energy loss. Furthermore, the optical properties of these doped materials are characterized by low reflectivity (below 0.17) and a relatively high refractive index (in the range of 2–2.5) in the IR region, positioning them as promising candidates for efficient IR detectors and particularly Fe-BTO.