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Quantitative theory of the oxygen vacancy and carrier self-trapping in bulk TiO_2

机译：本体TiO_2中氧空位和载流子自捕的定量理论

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Standard approximations of density functional theory often fail for defects in transition metal oxides. Despite its significance in applications and decades of research, the oxygen vacancy in TiO_2 is also poorly understood from the theory point of view. The Heyd-Scuseria-Ernzerhof functional (HSE06) provides a total energy that is a linear function of the occupation number (as it should be for the exact functional) also in TiO_2 This allows reproduction of the measured infrared absorption, photoluminescence, and thermal ionization data within ~0.1 eV. From our calculations, a consistent and quantitative interpretation of the conflicting experiments emerges. Electron self-trapping in rutile makes the properties of the vacancy concentration dependent. In oxidized samples the vacancies are passivated by native Ti~(3+)/Ti~(4+) traps. This explains why electrons localized to the vacancy could only be observed after illumination at very low temperature in magnetic resonance experiments. In strongly reduced samples, electrons may stay localized in the vacancy and even the neutral state gives rise to two vertical electronic transitions (at 0.8 and 1.2 eV). The situation is much simpler in anatase, where only holes are self-trapped by O~(2-)~/O~(1-) transitions. The oxygen vacancy is a shallower donor in anatase than in rutile.
机译：密度泛函理论的标准近似法经常会因过渡金属氧化物中的缺陷而失效。尽管在应用中和数十年的研究中具有重要意义，但从理论的角度来看，TiO_2中的氧空位也知之甚少。 Heyd-Scuseria-Ernzerhof官能团（HSE06）所提供的总能量也是TiO_2中占位数（对于确切的官能团而言）的线性函数。这允许所测得的红外吸收，光致发光和热电离的再现数据在〜0.1 eV之内。通过我们的计算，出现了对冲突实验的一致和定量的解释。金红石中的电子自陷使空位浓度的性质取决于。在氧化的样品中，空位被天然的Ti〜（3 +）/ Ti〜（4+）陷阱钝化。这解释了为什么只能在磁共振实验中在非常低的温度下照射后才能观察到定位于空位的电子。在大量还原的样品中，电子可能会停留在空位中，甚至中性状态也会产生两个垂直电子跃迁（在0.8和1.2 eV时）。锐钛矿中的情况要简单得多，其中只有孔被O〜（2-）〜/ O〜（1-）跃迁自陷。锐钛矿中的氧空位比金红石中的氧空位更浅。

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