Comparative study for effect of Ti, Nb and W incorporation on the electronic and optical properties of pristine hafnia (m-HfO2): DFT theoretical prospective

First-principles calculations using the Hubbard approach (DFT + U) with PBEsol correlation were performed to compare the effects of incorporating 3d, 4d, and 5d metal atoms on the electronic and optical properties of m-HfO₂. Incorporating metal atoms in the HfO₂ crystal structure shifted the band gap edges and lowered the conduction band minimum, reducing the band gap as follows: 5.24 eV for HfO₂, 3.26 eV for HfO₂:Ti, 1.12 eV for HfO₂:W, and 0.92 eV for HfO₂:Nb. Total and partial density of states calculations showed that the valence band maximum of pristine HfO₂ is mainly constructed from O 2p states, while the conduction band minimum is mainly from Hf 4d states. For doped crystals, the conduction band minimum is mainly from 3d states of Ti, 4d states of Nb, and 5d states of W. For pristine HfO₂, the calculated dielectric constant, reflectivity and refractive index match available experimental and theoretical data. For doped systems, incorporating Nb (4d metal) and W (5d metal) had similar effects on the electronic and optical properties of HfO₂, differing more from incorporating Ti (3d metal). HfO₂ absorption roughly doubled upon Ti atom insertion (HfO2:Ti). Based on the results of this study, we would like to emphasize that these results provide a solid theoretical starting point that motivates further experimental studies into the application potential of these doped metal oxide systems.