Study Of The Point Defect In The SrTiO₃Crystal

In recent years, the problem of environment and energy becomes more and moreserious. Hydrogen Energy has been attracted widely attention by its nonpolluting formsof green-power. SrTiO₃is a kind of perovskite type photocatalyst, which can createelectron-hole pairs by absorbing the photon of exceeding the threshold, and the electroncan be used to decompose H2O by combining with H+to produce H2. Because the bandgap of SrTiO₃is3.2eV which is located at the ultraviolet light. However,43%of thewhole solar energy lies in visible light while only4%lies in ultraviolet light. In order toimprove the efficiency of photocatalysis, usually use the ways of impurity doping etc. tointroduce the visible light.In this paper, we mainly calculate the formation energy and electronic structure ofperfect crystal and SrTiO₃with oxygen vacancy, Mn and Rh dopant. The thesis mainlyconsists of seven sections: the chapter1is introduction of SrTiO₃; the charter2is theintroduction of the related computer programs and theoretical method; the charter3isthe electronic structure of perfect SrTiO₃; the charter4is formation energy andelectronic structure of different position Mn dopant in SrTiO₃; The charter5isformation energy and electronic structure of different position Rh dopant in SrTiO₃.1) Introduce the study background, the recent achievement and the study in this paperof SrTiO₃crystal.2) Brief introduce the CRYSTAL code and the thermodynamic formalism of defectformation energy.3) The electronic structure of the perfect SrTiO₃crystal has been calculated usingCRYSTAL-09code. We obtain the types of chemical bond for the perfect SrTiO₃crystal by analyzing its electronic structures.4) The electronic structure of the SrTiO₃crystal with oxygen vacancy has beencalculated using CRYSTAL-09code. A new defect band occurs in the forbiddenband, which belongs to the orbital. The2.4eV luminescence band might be caused bythe electron transition from orbital to*orbital.5) The defect formation energies and electronic structures of Mn and Rh doped SrTiO₃have been studied using CRYSTAL-09code. It is shown that only in the O richcondition Mn would more likely substitute on Ti site and Mn prefer substituting onSr site in other condition. Only MnTican effectively narrow the band gap, MnSrcanhardly change the band gap. When doping Rh in SrTiO₃crystal, it is shown that Rh prefers substituting on Sr site and creates a defect energy level which consists of4dof Rh in the band gap. Because the bottom of the conduction band is belonged to the3d of Ti, the transition between4d-3d is forbidden. Thus, the electron excited canhardly transits from the bottom of the conduction band to the defect band. It willcause more steady electronic in the bottom of the conduction band to combine withH⁺to produce H₂.6) Conclusion of the thesis.