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Electronic and optical properties of aluminium-doped anatase and rutile TiO_2 from ab initio calculations

机译:从头算计算铝掺杂锐钛矿和金红石型TiO_2的电子和光学性质

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The electronic-structure and optical properties of aluminium-doped rutile and anatase TiO_2 have been investigated using density-functional theory with plane-wave basis sets and pseudopotentials. This was done using the periodic supercell method as implemented within the CASTEP software package with Al concentrations approaching the very low levels present in industrial samples of rutile TiO_2. Defect states involving substitution of a titanium atom for an aluminium atom were studied along with the more stable configuration of two adjacent aluminium substitutions with an oxygen vacancy in between. In the latter case, aluminium does not introduce band-gap states but leads to an increase in the band gap in both anatase and rutile. This suggests that aluminium doping pushes the absorption edge further into the UV and therefore reduces the photocatalytic activity. Single oxygen vacancies in anatase were also studied. Reactions to form the most stable defects are exothermic for both phases. Finally, migration of aluminium in both phases is investigated. Migration transition states are found to have a significantly lower energy in rutile. At industrially relevant temperatures, overcoming the barrier to migration is probably only possible in rutile.
机译:利用密度泛函理论,平面波基组和伪势,研究了掺铝金红石和锐钛矿型TiO_2的电子结构和光学性质。这是使用CASTEP软件包中实现的周期性超级电池方法完成的,其中Al的浓度接近金红石TiO_2工业样品中的极低水平。研究了涉及钛原子取代铝原子的缺陷状态,以及两个相邻的铝取代之间的氧空位的更稳定构型。在后一种情况下,铝不会引入带隙态,但是会导致锐钛矿和金红石带隙的增加。这表明铝掺杂将吸收边缘进一步推向紫外线,因此降低了光催化活性。还研究了锐钛矿中的单氧空位。形成最稳定缺陷的反应对于两个阶段都是放热的。最后,研究了铝在两个相中的迁移。发现迁移过渡态的金红石能量明显较低。在与工业相关的温度下,可能仅在金红石中才可能克服迁移的障碍。

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