A novel method for preparing Ta-doped TiO2 via using Ta2O5 as tie doping source is proposed.The preparation process combines the hydrothermal fluorination of Ta2 O5 and the subsequent formation of Ta-doped TiO2 sol.The results show that the doped sample annealed at 393 K generates an unstable intermediate NH4TiOF3,which converts into anatase TiO2 with the increase of temperature.After annealing at >673K,the Ta-doped TiO2nanocrystals with the grain size <20nm are obtained.Both the XRD and TG-DSC results confirm that Ta doping prevents the anatase-rutile crystal transition of TiO2.The band gap values of the doped samples,as obtained by UV-vis diffuse reflectance spectra,are smaller than that of pure anatase TiO2.The first-principle pseudopotential method calculations indicate that Ta5+ iies in the TiO2 lattice at the interstitial position.