铋掺杂的钽酸钠（Bi-doped NaTaO3）的能量稳定性、氧化态和电子结构：第一性原理杂化泛函研究

Joo Paul H, Behtash Maziar, Yang Kesong

Department of NanoEngineering, University of California San Diego, La Jolla, CA 92093-0448, USA.

Phys Chem Chem Phys. 2016 Jan 14;18(2):857-65. doi: 10.1039/c5cp05556c.

We studied the defect formation energies, oxidation states of the dopants, and electronic structures of Bi-doped NaTaO3 using first-principles hybrid density functional theory calculations. Three possible structural models, including Bi-doped NaTaO3 with Bi at the Na site (Bi@Na), with Bi at the Ta site (Bi@Ta), and with Bi at both Na and Ta sites [Bi@(Na,Ta)], are constructed. Our results show that the preferred doping sites of Bi are strongly related to the preparation conditions of NaTaO3. It is energetically more favorable to form a Bi@Na structure under Na-poor conditions, to form a Bi@Ta structure under Na-rich conditions, and to form a Bi@(Na,Ta) structure under mildly Na-rich conditions. The Bi@Na doped model shows an n-type conducting character along with an expected blueshift of the optical absorption edge, in which the Bi atoms exist as Bi(3+) (6s(2)6p(0)). The Bi@Ta doped model has empty gap states consisting of Bi 6s states in its band gap, which can lead to visible-light absorption via the electron transition among the valence band, the conduction band, and the gap states. The Bi dopant is present as a Bi(5+) ion in this model, consistent with the experimental results. In contrast, the Bi@(Na,Ta) doped model has occupied gap states consisting of Bi 6s states in its band gap, and thus visible-light absorption is also expected in this system due to electron excitation from these occupied states to the conduction band, in which the Bi dopants exist as Bi(3+) ions. Our first-principles electronic structure calculations revealed the relationship between the Bi doping sites and the material preparation conditions, and clarified the oxidation states of Bi dopants in NaTaO3 as well as the origin of different visible-light photocatalytic hydrogen evolution behaviors in Bi@Ta and Bi@(Na,Ta) doped NaTaO3. This work can provide a useful reference for preparing a Bi-doped NaTaO3 photocatalyst with desired doping sites.

我们使用第一性原理混合密度泛函理论计算研究了Bi掺杂的NaTaO₃的缺陷形成能、掺杂剂的氧化态和电子结构。构建了三种可能的结构模型，包括Bi位于Na位的Bi掺杂NaTaO₃（Bi@Na）、Bi位于Ta位的（Bi@Ta）以及Bi同时位于Na和Ta位的[Bi@(Na,Ta)]。我们的结果表明，Bi的优选掺杂位点与NaTaO₃的制备条件密切相关。在贫Na条件下形成Bi@Na结构在能量上更有利，在富Na条件下形成Bi@Ta结构，在适度富Na条件下形成Bi@(Na,Ta)结构。Bi@Na掺杂模型显示出n型导电特性以及预期的光吸收边缘蓝移，其中Bi原子以Bi(3+)（6s²6p⁰）形式存在。Bi@Ta掺杂模型在其带隙中有由Bi 6s态组成的空能隙态，这可以通过价带、导带和能隙态之间的电子跃迁导致可见光吸收。在该模型中，Bi掺杂剂以Bi(5+)离子形式存在，与实验结果一致。相比之下，Bi@(Na,Ta)掺杂模型在其带隙中有由Bi 6s态组成的占据能隙态，因此由于这些占据态的电子激发到导带，该体系中也预期有可见光吸收，其中Bi掺杂剂以Bi(3+)离子形式存在。我们的第一性原理电子结构计算揭示了Bi掺杂位点与材料制备条件之间的关系，并阐明了NaTaO₃中Bi掺杂剂的氧化态以及Bi@Ta和Bi@(Na,Ta)掺杂的NaTaO₃中不同可见光光催化析氢行为的起源。这项工作可为制备具有所需掺杂位点的Bi掺杂NaTaO₃光催化剂提供有用的参考。