过渡金属掺杂钛酸纳米管的电子结构和光学性质研究

Electronic structure and optical properties of transition metal doped titanate nanotubes

采用平面波超软赝势方法计算了过渡金属(TM)(Fe,Co或者Ru)掺杂钛酸纳米管的电子结构及光学性质.对TM取代钛酸纳米管层间间隙位H+的几何结构进行优化,发现掺杂对几何结构的影响较大,其中Co或者Ru掺杂的形成能均较低.此外,掺杂的TM与周围的O原子成键,有形成固熔体的趋势.掺杂后的能带结构分析表明:Fe,Co或者Ru掺杂导致钛酸纳米管禁带宽度减小并且于禁带中引入了新的能级,这主要归因于b1g(dx2-y2)及a1g(dz2)态的出现;部分杂质能级处于半填充状态,成为空穴的俘获中心,减少电子和空穴的复合;掺杂后,价带顶向低能方向移动,使价带中形成的空穴氧化性更强.最后,掺杂的钛酸盐纳米管的吸收光谱显示,Ru掺杂的钛酸纳米管导致其在可见光范围内有更强的吸收.

The electronic structure and optical properties of transition metals （TM）-doped （Fe, Co or Ru） titanate nanotubes （TNTs） have been investigated by using the plane-wave ultrasoft pseudopotential method. TM atom intercalation into the interlayer region of the layered TNTs structure has great influence on the geometry of the original structure and the formation energy of Co-doping or Ru-doping is lower after geometry optimizations. Doped atoms bond with the surrounding O atoms to form a kind of solid solution. The results show that, Fe,Co or Ru intercalation reduces the band gap of TNTs and introduces new energy levels in the band gap, extending the absorption edge of the doped TNTs well into the visible region, which is due to the appearance of the b1g（dx2-y2） and a1g（dz2） states; partial impurity bands are in semi-filled states, which act as the capture centers of holes to reduce the recombination of electrons and holes; the valence bands of the doped TNTs move towards low energy, making the holes more oxidative. Finally, the absorption spectrum of the doped TNTs shows that Ru-doped TNTs has a stronger absorptive capacity in the visible region.