First-principles Study Of Defects' Property In Anatase TiO₂

Titanium dioxide (TiO₂) is a well-known photocatalyst because of its cheap , nontoxic peculiarities and stable , effieient performances in the depuration of air and Water.However , it is activated only under UV light irradiation ( about 3% of the solar spectrum ) because of its large band gap ( 3.2eV for anatase ) . So , it is in urgent need to develop efficient visible-lighe-driven photocatalysts by modification of TiO₂ which allow the main part of the solar spectrum ( 45% or so ) to be used. So that , doped TiO₂ received a lot of attention as the doping could efficiently extend the photoresponse of TiO₂ to low energy ( visible ) region.In this paper,firsr-principles calculations within the Local Density Approximation (LDA) are carried out on the electronic structure of anatase TiO₂ and anatase TiO₂ with defect , moreover , the band structure , the Fermi level and the population of anatase TiO₂ and anatase TiO₂ with defect have been analyzed in this paper . So we come to the following conclusions:1. Anatase TiO₂ without defect is a large band gap semiconductor . The band diagram and the density of states diagram show that valence band of anatase TiO₂ is constituted by mixing the electrons of Ti atom on the 3d orbit and the electrons of O atom on the 2p orbit , it also show that the electrons of O atom on the p orbit and the electrons of Ti atom on the d orbit offer up the band beside the Fermi level .2. Anatase TiO₂ with oxygen vacancy is n-type conduction and with titanium vacancy is p-type conduction. The movement of structure and the analysis of population all indicate that when anatase TiO₂ with oxygen vacancy the negative electricity of the oxygen around the oxygen vacancy would be largened and when anatase TiO₂ with titanium vacancy the positive electricity of the titanium around the titanium vacancy would be largened .3. Studies of the electronic structure of N , S , C doping anatase TiO₂ show that doping them , in different extent , would made band gap of anatase TiO₂ narrow , so that improve the effect of avail oneself of sun'rays . Thereinto , in N-doping anatase TiO₂ , studies of band structures and densities of states and densities of electron distributing show that Ti atoms and N atoms at the valence band area , happens a kind of strong correlated interaction , which will produce an impurity state . The impurity state is half full , so that it not only promote electronic transition with the valence band but also cause the Fermi level move to the conduction band .So band gap will turn narrow . In S-doping anatase TiO₂ , a direct-band-gap is predicted in TiO₂-xS x . Electronic structure analysis shows that the doping S could substantially lower the band gap of TiO₂ by the presence of an impurity state of S3p and O2p on the upper edge of valence band . In C-doping anatase TiO₂ , electronic structure analysis indicated that , there are two impurity states composed of C2p orbital present in the band gap of TiO₂ , which are localized above the upper edge of valence band and between the band gap , respectively . Partial density of states analysis indicates that the impurity state of C2p not only lower the band gap of TiO₂ but also produce a non-full band which will greatly improve the absorptivity of sun'rays .Some of our results have been inosculated with the data of experiments so that our calculating method is feasible . Although some of our results still need to be modified by experiments , they have some certain directive purport and reference worth on further investigating TiO₂ as a photocatalyst and the electronic structure of TiO₂ .