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Theoretical Studies On Matals Doped TiO2 And ZnO With First-Principles Methods

Posted on:2011-05-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H YuFull Text:PDF
GTID:1101330332472093Subject:Materials science
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Doping is the effective way to improve the physical properties of semiconductors. The bandgap structure and optical properties of doped TiO2 (or ZnO) will be modulated substantially, and the intrinsic property of TiO2 (or ZnO) will also be different when the metals or transition-metals ion doping. Currently, first principles calculation based on density functional theory is a more effective method to study the microstructure and properties of dopant. Using this theoretical approach to doping can understand the geometric and electronic structure properties of material in-depth. Some experimental results have been theoretically verified, and the unknown properties of dopant to be predicted. This method can save research costs, which has played an invaluable role in scientific research and development of new materials.Using this first principles calculation method based on density functional theory, the rutile-TiO2 and ZnO (or doped rutile-TiO2 and doped ZnO) have been studied by simulation in this thesis, and mainly three specific works are as follows:First, the electronic structure and optical properties of rutile-TiO2 and ZnO have been studied, e.g. band structure, density of states (DOS), partial density of states (PDOS), dielectric function and absorption et al. The results show rutile-TiO2 or doped ZnO is a direct wide band gap semiconductor and its optical absorption mainly in the UV region. Using the electronic structure information and interband transition theory, peaks of dielectric function and absorption spectrum were carried out to identify and analyze, and this study provides a theoretical basis for doping.Second, the electronic structure and optical properties of Sn-doped rutile-TiO2 have been calculated, and rutile-TiO2 has been doped with three different ways:â‘ rutile-TiO2 with a Ti atom substituted by Sn atom;â‘¡rutile-TiO2 with an interstitial Sn atom, which sits at the center of an octahedron made of Ti atoms;â‘¢With O vacancy in the rutile-TiO2 supercell, a Ti atom is substituted by Sn atom. On the basis of the most common doping methodâ‘ , this paper has innovatively discussed the doping method with interstitial atom and O vacancy. The results show that:when the Ti atom substituted by Sn atom, the outermost electron of Sn has a great influence on the doping system, and the dopant's band gap increases as the Sn concentration increasing, but still smaller than the band gap of rutile-TiO2. When rutile-TiO2 with an interstitial Sn atom, dopant's band gap increases compared with the rutile-TiO2. When the Sn was doped into rutile-TiO2 with O vacancy, dopant's band gap increases compared with the rutile-TiO2. However, a new defect band appears in the band gap which below the conduction band, and may be beneficial to the transition between the valence band and conduction band. Meanwhile, when Ti atom is substituted by Sn atom, optical properties of rutile-TiO2, e.g. dielectric function, absorption and energy-loss function et al, have been changed. From the absorption spectrum, the red shift of optical absorption of Sn-doped rutile-TiO2 appeares, which is consistent with the specific experiments.The electronic structure and optical properties of Mo-doped rutile-TiO2 have been innovatively calculated. The results show that:when Ti atom is substituted by transition-metals Mo atom, second outer layer (d layer) electronic plays a major role, and the dopant's band gap reduces as the Mo concentration increasing. Meanwhile, the research found that optical properties of rutile-TiO2, e.g. dielectric function, absorption and energy-loss function et al, have been changed when Mo doping. From the absorption spectrum, the red shift of optical absorption of Mo-doped rutile-TiO2 appeares, which provides a theoretical basis for Mo-doped rutile-TiO2.Finally, the geometric and electronic structure and optical properties of Mn-doped ZnO have been calculated. From the results, a, b and c value increased after Mn doping, and cell volume also increased slightly. By the calculation results of band structure and partial density of states, the band structure of ZnO shifted to lower energy region as the Mn concentration increasing, and Fermi level into the conduction band. Meanwhile, this thesis focuses on the optical properties of Mn-doped ZnO. Compared with pure ZnO, the results analysis shows that absorption peaks moved to the higher energy region after Mn doping, and the blue shift of optical absorption of Mn-doped ZnO appeares, which is consistent with the specific experiments.
Keywords/Search Tags:metals or transition-metals doped TiO2 and ZnO, first principle, lattice structure, electronic structures, optical properties
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