P掺杂锐钛矿相TiO_2的第一性原理计算

First-principles calculations of P-doped anatase TiO_2

利用基于密度泛函理论的第一性原理对不同P掺杂形式(P替位Ti,P替位O,间隙P)的锐钛矿相TiO2的晶格常数、电荷布居、能带结构、分态密度和吸收光谱进行了计算.结果表明,P替位Ti时,TiO2体积减小,P替位O和间隙P的存在使TiO2的体积膨胀;替位Ti的P和间隙P均有不同程度的氧化,而替位O的P带有负电荷.三种P掺杂形式均导致锐钛矿相TiO2禁带宽度的增大,并在TiO2禁带之内引入了掺杂局域能级.P掺杂导致TiO2禁带宽度增大的程度依次为:间隙P>P替位Ti>P替位O.吸收光谱的计算结果表明,P替位Ti并不能增强TiO2的可见光吸收能力,但间隙P的存在大幅提高了TiO2的可见光光吸收能力,间隙P有可能是造成实验上P掺杂增强锐钛矿相TiO2光催化活性的重要原因.

The lattice parameters, charge populations, band structures, density of states and absorption spectra of P-doped anatase TiO2 are calculated using the first-principles based on the density functional theory. The results indicate that when the Ti atom is substituted for P atom, the volume of TiO2 decreases. When P atom substitutes for O atom or exists as interstitial atom, the volume of TiO2 increases. The substitutional P at Ti site and interstitial P are oxidized to different degrees, and the substitutional P at O site is reduced a little. The different three sites of P doping result in the increase of anatase TiO2 forbidden gap width and the introduction of local doping energy levels. The band gap increasing of P-doped anatase TiO2 is in the following sequence： interstitial P〉substitutional P at Ti site〉substitutional P at O site. The absorption spectra indicate that the substitutional P at Ti site cannot enhance the visible light absorption ability of the anatase TiO2, whereas the interstitial P strongly enhances the visible light absorption ability of the anatase TiO2. The interstitial P is probably an important reason for the experimental enhancement of the photocatalytic activity of P-doped anatase TiO2.