Cr、Mn掺杂锐钛矿相TiO2的第一性原理研究

First-principles Study of Electronic and Optical Property of Cr-doped and Mn-doped Anatase TiO_2

采用基于密度泛函理论的平面波超软赝势的方法,研究了纯锐钛矿相TiO2、Cr、Mn单掺杂TiO2的能带结构、电荷布居、态密度和光学性质。对电子性质分析发现:Mn掺杂引起杂质能带位于禁带中央,杂质能带最高点与导带相距大约0.6 eV,而最低点与价带相距大约0.65 eV,其中杂质能带主要由O原子的2p轨道和Mn原子的3d轨道杂化形成;Cr掺杂引起杂质能带位于导带底附近,杂质能带最高点与导带相距大约0.1 eV,而最低点与价带相距大约1.3 eV,其中杂质能带主要由O原子的2p轨道和Cr原子的3d轨道杂化形成,由于杂质能级的出现,使锐钛矿TiO2的禁带宽度变小。对光学性质分析发现:Cr、Mn单掺杂会使锐钛矿TiO2光学吸收带边红移,可见光区的光吸收系数明显增大,在低能区出现了新的吸收峰,Cr掺杂吸收峰对应能量为1.92 eV,Mn掺杂吸收峰对应能量为1.82 eV,与实验结果相符。

In this paper,the band structures,density of states,charge population and optical properties of pure,Cr-doped and Mn-doped anatase-phase TiO2 were studied by using the plane-wave ultrasoft pseudopotentials method based on the density functional theory.The analysis from the band structures,density of states and optical properties showed that there are three new impurity bands located in the middle of band gap in Mn-doped TiO2.The top of impurity band was apart from the conduction band by 0.6 eV and the bottom of the impurity band was at a distance of 0.65 eV from valence band.The impurity bands are formed mainly by the O-atom 2p orbital and the Mn-atom 3d orbital hybridized together.The Cr-doped TiO2 produced a new band near the bottom of conduct band.The top of impurity band was apart from the conduct band by 0.1eV and the bottom of the impurity band was at a distance of 1.3 eV from valence band.The impurity band was composed of the O-atom 2p orbital and the Cr-atom 3d orbital hybridized together.Because of the emergence of impurity level,the band gap became smaller.It is theoretically predicted that Cr-doped and Mn-doped anatase-phase TiO2 would lead to the red shift of absorption wavelength and the increase in coefficience of light absorption.A new absorption peak in the low-energy region,corresponding to energy 0.9 eV has been found experimentally in Cr-doped anatase-phase TiO2.A peak corresponding to energy 0.8 eV has been found experimentally in Mn-doped.The present theoretical conclusion is in agreement with the experimental result.