Investigation Of Electron And Energy Band Structure Of Metal And Nonmetal Doped NaTaO₃

As a novel photocatalyst, NaTaO3 have received much research attention due to its excellent chemical stability, light resistance and non-toxic properties. However, the photocatalytic activity of NaTaO3 is limited due to large band gap that incapable to absorb visible light. Basing on previous literatures, it has been found that doping of foreign ions into NaTaO3 host lattice may provide an effective way for enhancement of photocatalytic activity and visible light response. In this work, the doping effects of non-metallic elements (B, C, N, F and S) as well as metal elements (Ca, Sr, Ba, La, Nb, Cr and Ir) on NaTaO3 geometry structure, electronic structure, optical absorption spectra and catalytic activity were systematically investigated by utilizing first principles simulations.1. Firstly, this work provides an image of computer simulation technologies, their applications, and the development in materials science. We focus on the basic principles, the basic approach, the achievements and so on. Density functional theory (Density Functional Theory DFT), local density approximation (Local Density Approximation, LDA), generalized gradient approximation (Generalized Gradient Approximation, GGA), and several other important concepts are simply instructed.2. The software package-Castep was used in theoretical simulation. The modeling tools in the package were adopted to build NaTaO3 supercell model. Based on density functional theory, the structure of NaTaO3 was optimized in the supercell to obtain the most stable structure. Subsequently, we calculated and got geometry structure, electronic structure, and optical absorption spectra of NaTaO3 cell in the four different crystalline forms.3. On the basis of the optimized stable structure, certain non-metal or metal elements were introduced in the supercell. Generalized gradient approximation method was used to describe the exchange correlation effect of electron. We implemented structural optimization to the doped NaTaO3 and obtained geometry structure, electronic structure, and optical absorption spectra of doped NaTaO3 cell. It is found that non-metallic elements (B, C, N, F and S) and transition metals (Nb, Cr and Ir) showed significant impact on the geometry structure, electronic structure, and optical absorption spectra of NaTaO3.4. Combined with photocatalytic data on water, we obtained the impurity level position and shape on the optical absorption and photocatalytic activity of NaTaO3:(1) When the impurity energy level is located in the valence band top and O2p orbital hybridizes Ta5d orbital in the conduction band, it can effectively reduce the band gap of NaTaO3, and the absorption edge of NaTaO3 shifts to longer wavelength. Meanwhile If no impurity level was observed in the middle forbidden band, the photocatalytic performance would improve effectively.2. When the impurity energy level is similar with the O2s orbital energy, the orbital hybridization between impurity energy level and 02s would occur, which makes the covalent bond between the impurity atoms and O atoms more strengthen. This will enhance the stress in the cell and make the crystal grain size of NaTaO3 decrease and form step-like structure at the surface. These changes in the structure of the catalyst will allow the photocatalytic activity increase significantly.