Pham Hieu H, Wang Lin-Wang
Joint Center for Artificial Photosynthesis and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Phys Chem Chem Phys. 2015 Jan 7;17(1):541-50. doi: 10.1039/c4cp04209c.
The amorphous titanium dioxide (a-TiO2) has drawn attention recently due to the finding that it holds promise for coating conventional photoelectrodes for corrosion protection while still allowing the holes to transport to the surface. The mechanism of hole conductivity at a level much higher than the edge of the valence band is still a mystery. In this work, an amorphous TiO2 model is obtained from molecular dynamics employing the "melt-and-quench" technique. The electronic properties, polaronic states and the hole conduction mechanism in amorphous structure were investigated by means of density functional theory with Hubbard's energy correction (DFT + U) and compared to those in crystalline (rutile) TiO2. The formation energy of the oxygen vacancy was found to reduce significantly (by a few eV) upon amorphization. Our theoretical study suggested that the oxygen vacancies and their defect states provide hopping channels, which are comparable to experimental observations and could be responsible for hole conduction in the "leaky" TiO2 recently discovered for the photochemical water-splitting applications.
非晶态二氧化钛（a-TiO₂）近来受到关注，因为有研究发现它有望用于涂覆传统光电极以实现防腐蚀，同时仍能让空穴传输至表面。空穴电导率在远高于价带边缘的水平上的机制仍是个谜。在这项工作中，通过采用“熔融淬火”技术的分子动力学获得了一个非晶态TiO₂模型。利用含哈伯德能量校正的密度泛函理论（DFT + U）研究了非晶态结构中的电子性质、极化子态和空穴传导机制，并与晶体（金红石）TiO₂中的情况进行了比较。发现非晶化后氧空位的形成能显著降低（降低了几个电子伏特）。我们的理论研究表明，氧空位及其缺陷态提供了跳跃通道，这与实验观察结果相符，并且可能是最近发现的用于光化学水分解应用的“漏电”TiO₂中空穴传导的原因。
