非掺杂锐钛矿相TiO_2电子结构和光学性质的第一性原理研究

THE ELECTRONIC STRUCTURES AND OPTICAL PROPERTIES OF UN-DOPED ANATSE TIO_2:FIRST-PRINCIPLES CALCULATIONS

运用第一性原理的LDA+U(U_(Ti)=5.8 eV)方法研究了Ti空位(V_(Ti))和O空位(VO)对非掺杂锐钛矿相TiO_2的电子结构和光学吸收性质的影响.研究表明V_(Ti)可以有效提升TiO_2体系对可见光的响应,而VO则不能.在双V_(Ti)体系,由于杂质能级数目的增多可降低TiO_2体系的有效禁带宽度,进一步提升了TiO_2在可见光区的吸收强度.在V_(Ti)和VO共存的TiO_2体系,由VO引入的两个电子占据了费米能级处的杂质能级会使体系的价带顶上移,同时由VO引入的杂质能级位于禁带之间可以作为价电子由价带向导带之间跃迁的桥梁,因此此种结构对可见光的响应是最好的,有效的提高了TiO_2半导体的光电转换效率和光催化能力.

The effects of Ti vacancy （VTi） and O vacancy （VO） on electronic structures and optical absorp- tion properties in un-doped anatase TiO2 have been investigated by the first-principles calculations of LDA ＋ U method with U = 5.8eV for Ti-3d. The calculation results indicated that the VTi can enhance the response of TiO2 system to visible light effectively, while VO has not this effect. In the TiO2 system with two VTi, the increase of im- purity levels can reduce the effective band-gap, and therefore raise the absorption intensity in the visible light area. In the TiO2 system with VTi and VO, the two electrons introduced by VO occupy the impurity level near the Fermi level and therefore move up the valence band maximum. At the same time, the impurity level introduced by VO is located between the band-gap, which can benefit the valence electron transition from the valence band to the con- duction band. Therefore, the system has the best response to visible light, which can raise photoelectric transforma- tion efficiency and facilitate photocatalysis ability.