Ni掺杂TiO_2电子和几何结构的第一性原理研究

First principle study on the electronic and geometical structures of Ni-doped anatase TiO_2

利用密度泛函理论框架下的第一性原理方法,对不同掺杂量、不同方式的Ni掺杂锐钛矿相TiO_2(anatase TiO_2:A-TiO_2)的晶胞结构、缺陷形成能和态密度图像等进行了研究,并着重讨论了掺杂Ni离子周围配位场改变对体系电子结构的影响.结果表明,掺杂方式的不同对Ni-TiO_2超晶胞的几何结构有较大影响.正是几何结构的变化导致掺杂Ni离子处于不同类型的晶体配位场之中,这是掺杂体系电子结构差异的本质原因.通过对掺杂体系形成能的比较,发现Ni掺杂TiO_2的具体方式取决于晶体生长过程中的氧环境.通过对体系电子结构的研究,发现各种掺杂体系的禁带中都出现由Ni 3d-O2p轨道杂化形成的杂质能级.Ni离子替代晶格Ti掺杂会使吸收光谱红移,而Ni的晶隙掺杂则使吸收光谱蓝移,且这种光谱吸收带边的差异会随掺杂浓度的增加而增大.

With the first principle method of spin density functional theory, the crystal structure, formation energy of defect, and the density of states of anatase TiO2（ A - TiO2） , doped with different nickel content and different ways, were studied. Here, effect of change of the ligand field around the doping nickle ions on the electronic structure of the system was discussed. The results showed that, the difference of the doping ways has a great influence on geometric structures of the doped supercell, which makes change of the crystal ligand field around doping Ni ions. That is the essential reason for the difference of the electronic structure of the doped system. Compared the formation energy of the system, it was found that the doping ways depends on the oxygen environment in the crystal growth process. Through research on the electronic structure of the system it was found that the impurity band level is formed by the hybridization of Ni3J and O2ρ orbitals. Replacement of the titanium crystal lattic by the nickel one causes red shift for the absorption spectrum. While the doped nickel results in blue shift for the spectrum. And furthermore, the difference of the absorption borderline will increase with the doped concentration.