Photovoltaic potential of doped MgTiO3 (F, Br, I): prediction of optoelectronic and catalytic within ab initio approach

Abstract

This study investigates the structural, electronic, optical, and photocatalytic properties of the perovskite MgTiO₃, for pure and doped with halogens F, Br, and I at x = 8.33 % and 16 % concentrations, using an ab initio FP-LAPW method within the DFT framework and employing the GGA-mBJ approximation. The results of structural optimization indicate that both compounds exhibit negative formation energies for pure and doped states, respectively, showing their thermodynamic stability, while doping MgTiO₃ at oxygen sites with Y (F, Br, and I) significantly decreases the band gap energy compared to pure MgTiO₃, which has a band gap of 2.926 eV. Specifically, the band gaps for doped ${Mg}_4{Ti}_4{O}_{\left(12-n_i\right)}{Y}_{ni}$ where YF, Br, and I decrease as follows: at x = 8.33 %, the gaps are 2.61, 1.91, and 1.28 eV; at x = 16 %, they are approximately 2.82, 1.85, and 1.53 eV, respectively. This reduction results from introducing additional energy levels just below the conduction band, narrowing the band gap, and raising the Fermi level. Consequently, the material transitions into an n-type semiconductor. Additionally, doping ${Mg}_4{Ti}_4{O}_{10}{Y}_2$ (YBr, I) at x = 16 % reduces the bandgap, which enhances absorption and optical conductivity in the visible range, thus increasing the photocatalytic activity of the materials for hydrogen production. Our results indicate that Br and I doping at this level improves MgTiO₃ performance in photocatalytic water splitting for hydrogen generation. Furthermore, regarding the impact on photocatalytic activity related to the redox zones (H⁺/H₂ and O₂/H₂O at pH = 7), ${Mg}_4{Ti}_4{O}_{10}{Br}_2$ and ${Mg}_4{Ti}_4{O}_{10}{I}_2$ are optimally positioned within the redox potential range. These materials exhibit differences in the intensities of the redox couples, with increased activity observed in the O₂/H₂O redox zone. This theoretical foundation underscores the potential of halogen-doped MgTiO₃ as an efficient photocatalyst for solar-driven hydrogen production.