Electronic Structure Of Anatase TiO2 Research Articles

High-throughput HSE study on the doping effect in anatase TiO2.

Titania is a widely used semiconductor due to its excellent optoelectronics and catalytic properties. Doping with other cations or anions by substitution of Ti or O is a common way to adjust the electronic structure of pristine TiO2. Here, using ab initio calculations at the Heyd-Scuseria-Ernzerhof (HSE06) level, the substitution energy, formation energy and electronic structures of anatase TiO2 doped with 40 kinds of elements including transition metals, alkali metals, alkaline earth metals, p-block metals, and nonmetals have been studied systematically. It is found that doping with most of these elements can narrow down the band gap of TiO2, while in some doped systems, a recombination center induced by intermediate bands is also observed. Besides, for transition metal-doped TiO2 systems, the electron spin state analysis of dopants and the doping level investigation reveal that a relatively high spin structure tends to be formed in Cr, Mn, Fe, Zn, Mo, Tc, Ru and Cd-doped TiO2, and the doping levels of 4d-orbital transition metals are generally higher than those of 3d-orbital transition metals.

The Electronic Structure and Optical Properties of Anatase TiO₂ with Rare Earth Metal Dopants from First-Principles Calculations.

The electronic and optical properties of the rare earth metal atom-doped anatase TiO2 have been investigated systematically via density functional theory calculations. The results show that TiO2 doped by Ce or Pr is the optimal choice because of its small band gap and strong optical absorption. Rare earth metal atom doping induces several impurity states that tune the location of valence and conduction bands and an obvious lattice distortion that should reduce the probability of electron–hole recombination. This effect of band change originates from the 4f electrons of the rare earth metal atoms, which leads to an improved visible light absorption. This finding indicates that the electronic structure of anatase TiO2 is tuned by the introduction of impurity atoms.

The conventional cell and the primitive cell electronic structure of anatase titanium dioxide crystal

The present discrepancy among the theoretical electronic structures of anatase TiO2 has been investigated by using first-principles calculations. This glaring disagreement among the theoretical electronic structures of anatase has been resolved by choosing proper unit cells and corresponding high-symmetry k-points. It is confirmed that anatase is an indirect band-gap material and any deviations, such as a change from indirect to direct which was reported earlier in the conventional cell, results when the equilibrium lattice parameters are modified and the structure is distorted. In the primitive cell scenario, the valence-band maximum gets modified when the equilibrium lattice parameters are changed, but the band gap stays indirect.

Tailoring the electronic structure of anatase TiO2(001) surface through W and N codoping: a DFT calculation

Using density functional theory, we calculated the geometries, band structures and densities of states of W-doped, N-doped, and W/N-codoped anatase TiO4 (001) and (101) surfaces, as well as while the formation energies, based on the overall reaction energy diagram. The calculated results reveal that, on the two surfaces, the absorption of W atoms are more stable than that of N atoms while a larger energy barrier blocks the transfer of W atoms from the surfaces to the body. For TiO2(001), the W-doping and the N/W-codoping lead to a visible lattice distortion while the recombination of photo-generated electron-holes pairs is reduced. A comprehensive analysis of the electronic structures show that the band-gap narrows and a new W-N bond appears, which obviously enhance the photocatalytic activity.

Effects of acceptor–donor complexes on electronic structure properties in co-doped TiO2: A first-principles study

We theoretically investigate the doping effects induced by impurity complexes on the electronic structures of anatase TiO2 based on the density functional theory. Mono-doping and co-doping effects are discussed separately. The results show that the impurity doping can make the band-edges shift. The induced defect levels in the band gaps by impurity doping reduce the band gap predominantly. The compensated acceptor–donor pairs in the co-doped TiO2 will improve the photoelectrochemical activity. From the calculations, it is also found that (S+Zr)-co-doped TiO2 has the ideal band gap and band edge, at the same time, the binding energy is higher than other systems, so (S+Zr)-co-doping in TiO2 is more promise in photoelectrochemical experiments.

First-principles study of atomic structure and electronic properties of Si and F doped anatase TiO2

Abstract Chemical doping represents one of the most effective ways in engineering electronic structures of anatase TiO2 for practical applications. Here, we investigate formation energies, geometrical structures, and electronic properties of Si-, F-doped and Si/F co-doped anatase TiO2 by using spin-polarized density functional theory calculation. We find that the co-doped TiO2 is thermodynamically more favorable than the Si- and F-doped TiO2- Structural analysis shows that atomic impurity varies crystal constants slightly. Moreover, all the three doped systems show a pronounced narrowing of band gap by 0.33 eV for the F-doped TiO2, 0.17 eV for the Si-doped TiO2, and 0.28 eV for the Si/F-co-doped TiO2, which could account for the experimentally observed redshift of optical absorption edge. Our calculations suggest that the Si/F-co-doping represents an effective way in tailoring electronic structure and optical properties of anatase TiO2.

Influences of metallic doping on anatase crystalline titanium dioxide: From electronic structure aspects to efficiency of TiO2-based dye sensitized solar cell (DSSC)

In this work, we examined the influences of metallic X dopants (X = Be, Mg, Ca, Zn, Al, W and Nb) on the electronic structure of anatase TiO2 in the framework of density functional theory (DFT). The dopant-induced electronic structure modifications are believed to directly change the photovoltaic (PV) behaviors of the X-doped TiO2 based DSSCs. The dopants are shown to either directly inhibit the intrinsic Ti3+ and oxygen vacancy surface defects of TiO2 or enhance these defects depending on their valence states. These dopant-induced defect modifications, in turn, strongly affect the PV behaviors of the DSSCs. The combined effect of electronic structure and surface-defect modifications determined the photoelectric efficiency of the device.

Electronic properties of anatase TiO2 doped by lanthanides: A DFT+U study

The effects of mono-doping of 4f lanthanides with and without oxygen vacancy defect on the electronic structures of anatase TiO2 have been studied by first-principles calculations with DFT+U (DFT with Hubbard U correction) to treat the strong correlation of Ti 3d electrons and lanthanides 4f electrons. Our results revealed that dopant Ce is easy to incorporate into the TiO2 host by substituting Ti due to its lower substitutional energy (∼−2.0eV), but the band gap of the system almost keeps intact after doping. The Ce 4f states are located at the bottom of conduction band, which mainly originates from Ti 3d states. The magnetic moment of doped Ce disappears due to electron transfer from Ce to the nearest O atoms. For Pr and Gd doping, their substitutional energies are similar and close to zero, indicating that both of them may also incorporate into the TiO2 host. For Pr doping, some 4f spin-down states are located next to the bottom of the conduction band and narrow the band gap of the doping system. However, for Gd doping, the 4f states are located in deep valence band and there is no intermediate band in the band gap. The magnetic moment of dopant Gd is close to the value of isolated Gd atom (∼7μB), indicating no overlapping between Gd 4f with other orbitals. For Eu, it is hard to incorporate into the TiO2 host due to its very higher substitutional energy. The results also indicated that oxygen vacancy defect may enhance the adsorption of the visible light in Ln-doped TiO2 system.

First-principles study of N-doped and N-V co-doped anatase TiO2

The ground state atomic configurations and electronic structures of anatase TiO2, N-doped TiO2 and N-V co-doped TiO2 are studied by the projector augmented wave method and the generalized gradient approximation plus U (Hubbard correction) (GGA+U) based on the density functional theory. The results indicate that the volume of cell is slightly larger and the ground state configuration has no change significantly for N-doped TiO2, but the symmetry of cell is broken and the position of V atom is more close to N atom after co-doping with N and V. The band gap of anatase TiO2 is calculated to be 3.256 eV, which is in agreement with experimental value (3.23 eV). When N is doped, the gap is reduced by more than 0.4 eV. but for N-V co-doped system, the gap reduces to 2.555 eV. Moreover, the acceptor level and donor level, which can be formed between the valence band maximum and the conduction band minimum because of co-doping with N and V, are more favorable to the separation of photoelectron-hole pairs and reduce the rate of recombination. Therefore, the co-doping of anatase TiO2 with N and V can effectively improve the photocatalytic performance of anatase.

Effect of carbon/hydrogen species incorporation on electronic structure of anatase-TiO2

The energy band structure and optical properties of C-doped and C/H-codoped anatase TiO2 are investigated using the first-principles based on density-functional theory. The obtained results indicate that the structure of C/H-codoping is more stable than that of C-doping. For C-doped anatase TiO2, the band gap narrowing is small, and the high visible-light catalytic ability originates from the isolated C 2p states above the valence-band maximum. With the same carbon doping level, the C/H-codoping produces significant bandgap narrowing, which leads to higher visible-light photocatalytic efficiency than the C-doping does.

First-principles study of the electronic structure of N-doping anatase TiO2

In order to investigate the effect of N-doping on the electronic structure of anatase TiO2,and discover the mechanism of band gap narrowing after N-doping, we have carried out first-principles calculations based on density-functional theory(DFT) for anatase TiO2 system. Studies of band structures and densities of states and densities of electron distributing show that Ti atoms and N atoms at the conduction band(CB) area, happens a kind of strong correlated interaction, which will lead electrons of Ti atom on the 3d orbit to move to 2p orbit of N atom, and the entire conduction band will move to the Fermi level. Band gap will narrow and the Red Shift electrophoresis will happen. Theoretical result has been compared with the experiment result.