锐钛矿型La_(x)Ti_(1-x)O_(2)光电性质的第一性原理研究

A Study of First Principles on Photoelectric Properties of Anatase La_(x)Ti_(1-x)O_(2)

利用第一性原理计算,基于密度泛函理论(DFT)的平面波赝势法,首先构建了x=0、03215、0.0625和0.125的La_(x)Ti_(1-x)O_(2)掺杂体系超胞模型,并分别对这4种模型进行了几何结构优化,然后计算了优化晶胞的能带结构分布和态密度分布。同时还计算了掺杂体系的载流子浓度、电子有效质量。计算结果表明,随着x值的增大,掺杂体系的杂质能级变多,且带隙值呈现减小的趋势;而当x过大时,将会导致TiO_(2)晶胞的体积的膨胀变大并且晶格表面缺陷数目增多,这些不利于TiO_(2)的光子吸收和发射,从而导致载流子浓度却呈现先变大后减小的现象,且在x=0.0625时得到最大值。从计算出的吸收光谱以及复介电函数可以看出,La掺杂后的TiO_(2)光吸收出现红移的现象,具有一定可见光的吸收能力,提高了光催化能力。理论计算结果与文献中实验结果一致。

This research uses the first principle calculation and the plane wave pseudopotential method to construct the supercell models of La_(x)Ti_(1-x)O_(2)doped system with x=0,0.03215,0.0625 and 0.125 based on density functional theory(DFT).The geometric structures of these four models are optimized respectively,and then the energy band structure distribution and density of states distribution of the optimized cell are calculated.The carrier concentration and electron effective mass of the doped system are also calculated.The calculation results show that with the increase of x value,the impurity energy levels of the doped system increase and the band gap decreases.When x is too large,it will lead to the expansion of the volume of TiO_(2)cell and the increase of the number of lattice surface defects,which is not conducive to the photon absorption and emission of TiO_(2),resulting in the phenomenon that the carrier concentration first increases and then decreases,and the maximum value is obtained when x=0.0625.From the calculated absorption spectrum and complex dielectric function,it can be concluded that the light absorption of La doped TiO_(2)is red shifted,which has a certain absorption ability of visible light and improves the photocatalytic ability.The theoretical results are in accord with the experimental results in the literatures.