Narrow Results

Titanium dioxide nanoparticles were prepared by precipitation of aqueous TiCl₄ solution with ammonium hydroxide as precipitation agent. Freshly prepared Titania gel is allowed to crystallize under refluxing and stirring condition for 6 h over 90°C and oven dried over night in temperature above 100 C. X-ray diffraction studies on oven dried powder indicate formation of anatase phase TiO₂ with average crystalline size of 4.5 nm. Powders with variable amount of anatase and rutile phase were prepared by calcination of pure anatase in the temperature range 400-1000 c for 4 h. the XRD patterns show that phase transition from anatase to rutile occur in calcination above 600°C. The morphology and microstructure characteristics were obtained by XRD, TEM. and TGA.

Ab initio study has been carried out to investigate the band structure, density of state and optical dielectric function of pure and Nitrogen (N)-doped rutile phase of TiO₂. The band structure obtained with the inclusion of U parameter of 8.5 eV compared favorably with experimental result. Bandgap of N-doped rutile decreases with respect to pure rutile which is traceable to 2p state of the Nitrogen dopant as revealed in partial density of state (PDOS). The optical properties calculated revealed that N-doped rutile has at least one optical peak in the visible light region of the electromagnetic spectrum which suggests it to be a potential material for photovoltaic application than pure rutile. Our results suggest that optical properties of rutile can be adapted by doping with Nitrogen at different concentration which enhances its potential as photocatalyst.

The spin Hamiltonian parameters (the anisotropic g factors and the hyperfine structure constants) and the local structure for the rhombic Cu²⁺ center in rutile (TiO₂) are theoretically investigated using the formulas of these parameters for a 3d⁹ ion in rhombically elongated octahedra. From the studies, the planar impurity-ligand bond angle is found to be about 5.8° larger than that for the host Ti⁴⁺ site due to the Jahn–Teller effect via bending the planar Cu²⁺–O^2- bonds, which yields much smaller rhombic distortion in the impurity center. The theoretical spin Hamiltonian parameters based on the above local angular distortion show good agreement with the experimental data, and the improvement of the calculation results are also achieved as compared with those of the previous works.

The rutile titanium dioxide (TiO₂) has attracted enormous interest in sensor field owing to its stability at high temperature. But less is known about electron transfer efficiency of rutile TiO₂, which is mainly influenced by the electron mobility. The aim of this study is to investigate the relationship between carrier mobility and bicrystalline grains boundary of rutile TiO₂ film. In this study, TiO₂ film was deposited by the direct current pulsed magnetron sputtering technology with sputtering power from 150 to 900 W. Then the TiO₂ films were annealed at $1000^{\circ }\mathrm{\text{C}}$ in air atmosphere. By this way, the rutile TiO₂ films were obtained. Special attention was paid to the carrier mobility of rutile TiO₂ films. The Hall measurement results showed that with the increase of sputtering power from 150 to 900 W, the carrier mobility of rutile TiO₂ films increased from 0.75 to $38.88{\mathrm{\text{cm}}}^2/\mathrm{\text{V}}\cdot \mathrm{\text{s}}$, gradually. Taking the TEM and SAED results together, our data indicated that the carrier mobility of rutile TiO₂ film was influenced by the bicrystalline grains boundary. The large angle bicrystalline grain boundary seriously deteriorates the carrier mobility of rutile TiO₂ film. On the contrary, the low angle bicrystalline grain boundary has little influence on the carrier mobility of rutile TiO₂ film.

Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band gap of TiO₂ plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO₂ thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO₃ substrates was correlated to the lattice constants. The optical band gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO₃. In order to interpret this expansion, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. The conclusion from these calculations is, in order to achieve a smaller band gap for both, rutile or anatase, the lattice constant c has to be compressed, and a has to be expanded.

Chestnut-bur-like assemblies composed of rutile TiO₂ acicular nanocrystals with radial coagulation in all directions are synthesized by a sonochemical method. High resolution electron microscopy investigations indicate that the growth direction of the acicular nanocrystals is along rutile TiO₂ [001], bending features almost all of these nanocrystals, and misoriented attachment of them results in chestnut-bur-like secondary particles.

Rutile TiO₂ nanorods have been successfully prepared by a sonochemical method. The microstructures of TiO₂ nanorods were investigated in detail by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HREM). Probable mechanisms for the sonochemical formation of TiO₂ nanorods are proposed.

C-doped Ti–O films with different titanium suboxide contents are prepared by DC magnetron sputtering deposition at different sputtering powers. The films with different phases are formed after annealing at 873K in air. The structure of the films is characterized by X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The optical properties and surface roughness of the films are investigated by UV–vis spectroscopy and atomic force microscopy, respectively. Photocatalytic activity of the thin films is studied by degrading the methyl orange solution under xenon lamp (300W) irradiation. The results show that the C-doped Ti–O thin films with higher titanium suboxide contents (${\text{Ti}}^{4+}<45.4$%) tend to form the rutile phase after annealing, whereas the films with a lower titanate content (${\text{Ti}}^{4+}>54.8$%) are easy to form anatase phase by annealing.

Thin TiO₂-films were synthesized for the first time by solid-phase low-temperature pyrolysis technique onto quartz glasses or silicon substrates. The obtained films are nanoscale; crystallize in a mixed anatase-rutile modification, which was confirmed by X-ray diffraction, scanning electron and atomic force microscopy (AFM) methods. The three-layer films’ thickness was 140 nm. The TiO₂-films consist of crystallites 12–27 nm, depending on the temperature treatment and phase composition. In addition, all of the obtained TiO₂-films are optically transparent regardless of synthesis conditions; the calculated band gap was 3.55 eV, which makes it possible to recommend TiO₂-films for use in optical filters and gas sensors.