Electronic And Optical Properties Of SrTiO₃ With Dopants

SrTiO₃ is a kind of typical perovskite metallic oxide, and its photocatalytic and conductivty have drawn widely attention. It not only can be used in the production of hydrogen energy, but also can be used for degradation of oxidative pollutants. For a long time, it is a good semiconductor material, and it is applied to the capacitors and sensors and other equipment. At present, although a lot of theoretical and experimental studies have been performed to describe the electronic structure of SrTiO₃ with element doping and to predict photocatalytic ability, the effect of doping elements and method of doping on influence mechanism about the electronic structure and optical properties of SrTiO₃ system still exist differences. In this paper, based on the first principle of density functional theory and plane wave super soft constraint potential method, the electronic structure, electrical conductivity and optical properties of SrTiO₃ with single element and co-doped element system have been studied. It provides the theory basis for the preparation of high quality transparent conductive film and efficient photocatalyst. We use the software called Materials of Studio 6.1 CASTEP software package. The main research contents and results are as follows:1. The metal elements Nb was doped into strontium titanate?SrTiO₃? crystal, by controlling different doping concentration. Based on first principles calculation, in order to study the effect of Nb doping concentration on the stability of SrTi O₃ and photoelectric properties, we mainly described the effect of Nb doping on the formation enthalpy of SrTiO₃ system, electronic structure, the conductivity and optical absorption. By analyzing the changes of electronic structure, from microscopic to we reveal the conductive mechanism and the effect on the optical absorption caused by doping elements. The results show that Nb doping system with different concentrations of has a different application. For the doping concentration of 1.11 at.%, it has a strong absorption in the visible light region, so it can be photocatalyst under visible light region. Nb- doped model of 1.67 at.% and 2.5 at.% will be the potential of transparent conductive material.2. We calculated electronic structure and optical absorption of SrTiO₃ system doped with S, C anion at different relative position, predicting the photocatalytic abilities of the four possible structures. It was found that there some impurity gap states in the original band gap. Although the impurity bands in the four different configurations show similar performance, they have different effect on optical absorption. In terms of the S-CI and S-CIII, they show weak lattice distrotion, narrower band gap and occupied states are stronger enough, also the hole number fall slightly. In the models of S-CII and S-CIV, the heavily lattice distortion happens and impurity band gap becomes isolated, not like interstitial impurity bands of the S-CI and S-CIII system, so it can't effectively narrow band gap. Moreover, there is a unoccupied impurity band far away from the valence band in S-CIV. The special and strong impurity band played as a combination center of electrons and holes. In the end, the configuration of S-CI was identified as the best photocatalyst materials.3. The electronic and optical properties of pure SrTiO₃, C-doped SrTiO₃, 2C-doped SrTiO₃, C-Nb doped SrTiO₃ and C-2Nb doped SrTiO₃. There are three gap states in the band gap of C doping SrTiO₃, and they are generated by C 2p states, which can effectively inhibit the band gap for electron transfer. However, C 2p states are partially occupied, these unoccupied states may play as recombination center of electrons and holes. Therefore, we introduce Nb to make charge compensation. Then we build two possible structures?C-Nb doped SrTiO₃ and C-2Nb SrTiO₃? to perform a comprehensive study and comparison. When two Nb atoms are introduced, original unoccupied C 2p states are fully occupied, because two Nb atoms contribute enough electrons. In addition, we calculate and study optical properties of pure SrTiO₃ and C-Nb codoped SrTiO₃. Eventually, we found that absorption of C-Nb codoped SrTiO₃ can cover the whole visible light area.