锐钛矿相和金红石相Nb:TiO_2电学性质的GGA(+U)法研究

Investigation on the electrical properties of anatase and rutile Nb-doped TiO_2 by GGA(+U)

采用基于密度泛函理论第一性原理GGA和GGA+U相结合的方法研究了不同掺杂浓度下锐钛矿相和金红石相Nb:TiO2的晶体结构、电子结构以及稳定性.结果表明:锐钛矿相Nb:TiO2能带结构与简并半导体类似,呈类金属导电机理.金红石相Nb:TiO2呈半导体导电机理.Nb原子比Ti原子电离产生出更多的电子.锐钛矿相Nb:TiO2中Nb原子的电离率比金红石相Nb:TiO2的大.以上结果说明锐钛矿相Nb:TiO2比金红石相Nb:TiO2更适宜用作TCO材料;掺杂浓度对其杂质能级,费米能级和有效质量都有影响.Nb原子掺杂浓度越高,材料电离率呈降低趋势;形成能计算结果显示:在富钛条件下不利于Nb原子的掺杂,而在富氧条件下有利于Nb原子的掺杂.对于金红石相和锐钛矿相Nb:TiO2,不论是在贫氧或富氧条件下,随着Nb原子掺杂浓度的提高,形成能均增大.

Crystal structure, electronic properties, and stability of anatase and rutile Nb-doped TiO2 （Nb：TiO2） compounds with different doping concentrations are studied by the combination of GGA and GGA＋U methods within the density functional theory based first-principle calculation. And the main research work and contents are listed as follows： The anatase Nb：TiO2 appears as a degenerated semiconductor which behaves as an intrinsic metal. Its metallic property arises from Nb substitution into the Ti site, providing electrons to the conduction band. In contrast, the rutile Nb：TiO2 shows insulating behaviors. Ionization efficiency of Nb in anatase Nb：TiO2 is higher than that in futile. We expect that anatase Nb：TiO2 is a potential material for transparent conducting oxide （TCO） while rutile Nb：TiO2 is not. The doped systems show different electronic characteristics, such as band structure, Fermi energy, and effective mass of carriers at different doping levels. In higher dopant concentration nNb, the ionization efficiency decreases slightly. Calculated defect-formation energy shows that Ti-rich material growth conditions are not in favor of the introduction of Nb while Nb can be easily doped in Nb：TiO2 under O-rich growth conditions. Nb dopant is difficult to be doped at higher doping level for both anatase and rutile Nb：TiO2.