Study for d-electronic states in titanium dioxide by doping of transition metal and control of oxygen defects

点击翻译按钮获取中文摘要

Single-crystals of anatase form were grown by means of chemical transport reaction method. For the control of oxygen vacancies, the measurements of spectra and X-ray diffraction were performed to establish the experimental condition for heat-treatments under the oxygen or hydrogen atmosphere.Optical absorption and ESR spectra were measured for anatase single crystals as-grown, implanted by H ions, annealed under oxygen or hydrogen atmosphere at desired temperature. The color of the crystal changed from pale-blue (as-grown) through yellow to colorless ones on oxygen annealing. The colorless crystal was reduced to dark-blue one by hydrogen annealing. On repetitive heat treatment under oxygen atmosphere, it becomes dark-green, yellow and colorless, again. Since the difference in color of the crystal corresponds to that in the state of defects, it was established to control the defect states. Optical absorption and ESR spectra were same for the as-grown, hydrogen-heat-treated and H ion implanted samples. The obtained anisotropic g tensor to [001] direction is well interpreted by the presence of the delectrons centered at Ti.V-or Nb-doped anatase single crystals were successfully synthesized by the use of rutile form solid solution as raw material. They were 2×2×2mm^3 in size and transparent with purple or dark-blue color, respectively. The fundamental absorption edges of them were located at lower energy side than undoped crystal. The Nb-doped single crystal has strong absorption in lower energy region from 2.5 eV.The absorption spectrum of the Nb-doped single crystal resembles to that of undoped crystal with hydrogen annealing. This indicates the similarity in electronic structure each other.