A DFT+U study of site dependent Fe-doped TiO2diluted magnetic semiconductor material: Room-temperature ferromagnetism and improved semiconducting properties

Abstract

This article reports the crystal structure, impurity formation energy, electronic property, magnetic property, and dopant configuration site dependence of ferromagnetic temperature Tc of anatase (Ti15FeO32, Ti14Fe2O32, and Ti13Fe3O32) by first-principles calculations based on density functional theory (DFT) with Hubbard onsite correction (DFT+U). The estimated formation energy validated the structural stability of the Fe-doped TiO2 with 2.08% (Ti15FeO32), 4.17% (Ti14Fe2O32), and 6.25% (Ti13Fe3O32) concentrations at the Ti sites. The electronic structure analysis reveals that the bandgap in the doped system changed from a wide bandgap of 3.23 eV (pristine TiO2) to slightly lower bandgaps of 3.13, 3.08, and 3.04 eV with Fe concentrations of 2.08%, 4.17%, and 6.25%, respectively. The calculated partial density of states also show the hybridization of O with 2p- and Fe 3d-orbitals near the conduction band minimum and generate the impurity energy level reducing the bandgap. Furthermore, the estimated Curie temperature (Tc) varied depending on the Fe-Fe interactions, the concentration of the Fe dopants, and doping sites. For instance, Tc is calculated to be 343.57 K for 2.08% Fe at the symmetric point of the crystal while estimated to be 323.84 and 393.297 K for 4.17% at the nearest neighbor and the next-nearest neighbor configurations. Due to the increase of the Fe concentration to 6.25%, the calculated Tc monotonically improved to 342.5 and 513.174 K at the nearest neighbor and the next-nearest neighbor of the Fe-site, respectively. These indicate that all the calculated findings estimate the ferromagnetic transition temperature Tc to above room temperature. Moreover, the system's total magnetization reveals the augmentation of a number of unpaired electrons as a result of rise in oxygen vacancies and, hence, there could be more holes when the Fe content gets higher, perhaps generating more bound magnetic polarons that favor the critical temperature, Tc.