A DFT+U study of site dependent Fe-doped TiO2 diluted 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.

Ortho-atomic projector assisted DFT+U study of room temperature Ferro- and antiferromagnetic Mn-doped TiO2 diluted magnetic semiconductor

“…A lot of work has been done, both experimental and theoretical, as discussed below. For example, experimentally as reported in [4], high T c = 400 K ferromagnetism in Co-doped TiO 2 synthesized via molecular beam epitaxy (MBE) using combinatorial pulsed-laser deposition (PLD) with a measured magnetic moment of 0.32μ B /Co for Co concentrations up to 8% was observed. In another report, Ogale et al [17] studied FM at room temperature in Co-doped rutile TiO 2 using pulsed laser deposition (PLD).…”

“…The Diluted magnetic semiconductors of transition metal (TM)-doped oxides have drawn a lot of attention recently because they are thought to be the best prospects for spintronic materials. As a semiconductor(SC) with a wide bandgap, TiO 2 is interesting for photonic, electronic, and magnetic applications [1][2][3][4].…”

Rational Design of Biaxial Tensile Strain for Boosting Electronic and Ionic Conductivities of Na2MnSiO4 for Rechargeable Sodium‐Ion Batteries

“…The delocalization problem in the 3d‐orbitals of the Mn atom in Na 2 MnSiO 4 was solved using the DFT+U approach following the previous studies. [ 29 , 30 ] Despite the fact that determining the correct U‐value is a difficult task, Table 1 displays the computed E g with several U‐values ranging from 1 to 6 eV with 0.5 intervals, with the U‐value of 1.5 eV (E g =2.35 eV) being fixed for further analysis. [29] …”

“…The Na 2 MSiO 4 family crystallizes in a monoclinic crystal system with Pn or Pc symmetry,[ 27 , 28 , 30 , 31 , 32 , 33 , 34 ] whereas Li 2 MSiO 4 crystallizes in an orthorhombic system with Pmn 2 1 symmetry. [ 34 , 35 , 36 ] The lattice parameters for monoclinic Na 2 MnSiO 4 with Pn symmetry computed by Nalbandyan and coworkers are a=7.02857, b=5.60957, c=5.33391,=90.0°,=89.7949°, and=90°.…”

“…Previous computational studies based on ab initio molecular dynamics (AIMD), density functional theory with (out) Hubbard‐correction (DFT, DFT+U), and classical molecular dynamics simulation (CMD) have demonstrated the structural stabilities, electronic structures, and electrochemical properties of materials. [ 27 , 28 , 29 , 30 , 31 , 32 ] For example, DFT and DFT+U study of di‐sodium orthosilicate compounds indicates that Na 2 MSiO 4 (M=Mn, Fe, Co, Ni) with Pc‐symmetry has better structural stability and faster ionic conductivity than lithium orthosilicate. This is due to the wider distance between atomic layers and non‐directional bonding between Na and neighboring atoms, indicating di‐sodium orthosilicate electrode materials′ potential suitability for SIBs.…”