纤铁矿型TiO2纳米片层结构的稳定性与电子结构研究
Structure stability and electronic structures of lepidocrocite TiO2 nanosheet

采用平面波超软赝势方法研究了纤铁矿型TiO2纳米片层结构的稳定性和电子结构.结果显示该结构具有较高的稳定性,其带隙比锐钛矿型TiO2要大0.59 eV,带隙内没有出现表面态.通过对空位缺陷形成能的比较,结果显示这在还原性气氛下纤铁矿型TiO2纳米片层表面Ti空位的形成能明显低于O空位的形成能,确定出最容易出现的缺陷是-4价的Ti空位,该空位缺陷的出现会使带隙中产生表面缺陷态.与体相内缺陷不同,表面缺陷态可以促进电子和空穴的分离,这些发现可以合理的解释最近的实验结果.
The structure stability and electronic structures of lepidocrocite TiO2 nanosheet have been investigated using the method of plane-wave ultrasoft pseudopotentials. The results show that they are much stable and the calculated band gap is 0.59 eV broader than anatase TiO2. However, surface state doesn’t appear in band gap. By comparing the formation energies of Ti and O vacancies with different charges, it is found that under Ti-rich condition, the Ti vacancy has lower formation energy than the O vacancy. Furthermore, it is identified that the Ti vacancy in charge state -4 is easy to produce in lepidocrocite TiO2 nanosheet. But differing from the situation of defects in bulk structure, the charged defects of lepidocrocite TiO2 nanosheet with several surface levels in band gap will contribute to the separation of electron-hole pairs. These findings give a reasonable explanation of recent experimental results.