摘要:
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。
Abstract:
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 rutile. 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.
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