First Principles Study of the Effect of Oxygen Vacancy and Mechanical Strain on the Photocatalytic Activity of Anatase TiO2

• Main Authors: Chien-Ming Huang, 黃千鳴
• Other Authors: chin-lung Kuo
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/95510636079016948999

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 98 === This study tried to use First Principles to study the effects of induced oxygen vacancies and mechanical strain on formation energy of oxygen vacancies, electronic density of states, band structure and optic absorption coefficient. Our results showed that in oxygen defective TiO2, the relative sites of vacancies have strong influence on the interaction between vacancies, which leads to totally different electronic and optical properties. For different oxygen vacancy concentration, the tendency of oxygen vacancy configuration differs, and this also makes difference on the properties. For TiO2-x system, when x, the concentration of oxygen vacancy, increases, the optical absorption coefficient also increases. However, when x is larger than 0.125, the configuration tendency of oxygen vacancies switches from B-type to A-type, and this leads to higher probability of defect level. Defect level may become the recombination center of electron-hole pairs and the life time of carriers is largely shortened. This has negative effects on photovoltaic conversion. On the other hand, we also used First-Principles Calculations to study the effects of mechanical strain on thin film anatase TiO2. We discussed the stress parallel to (001), (010) and (101) planes. The mechanical strain we induced on the system is no larger than 8%. We use this system to discuss how the deformation that induced by lattice mismatch affects the electronic and optical properties. Our result shows that when the stress is parallel to (001) plane, the biaxial tensile stress on [010] and [100] direction and uniaxial tensile stress on [100] direction decreases the band gap, and the absorption spectrum shift toward longer wavelength side. We also found out that if we induce uniaxial compressive stress on [001] direction parallel to (010) plane or uniaxial tensile stress on [010] direction and uniaxial compressive stress on [1 ̅01] direction parallel to (101) plane, there will be similar results. Otherwise, there is no significant improvement on photocatalysis ability. Our results may give an aid to the process of TiO2 photocatalyst.