Sodium tantalate, NaTaO₃, is one of the best semiconductors for photocatalytic water splitting and CO₂ reduction. Doping with metal cations is crucial for enhancing the quantum efficiency of the desired reactions. Nevertheless, details related to the doping of the host metal oxide and activation by guest metal cations are not sufficiently known. The most fundamental question concerns the increase in the quantum efficiency via doping with guest cations that are impurities in the host lattice. In this study, the local environment of Sr cations, which are the typically used guest cations in NaTaO₃, was characterized by extended X-ray absorption fine structure spectroscopy. The results reveal the presence of two Sr–O shells in the Sr-doped NaTaO₃ photocatalysts. The small shell with an unexpectedly short Sr–O bond length of 1.96 Å corresponds to SrO₆ octahedra embedded in the corner-shared network of TaO₆ octahedra. The other shell with a Sr–O bond length of 2.60 Å corresponds to SrO₁₂ cuboctahedra with Sr cations at positions previously occupied by Na cations. Rietveld analysis of the X-ray diffraction data confirmed the formation of a NaTaO₃–Sr(Sr_1/3Ta_2/3)O₃ solid solution to accommodate the two Sr–O shells in NaTaO₃ with no requirement for creating oxygen anion vacancies. Mechanisms for increasing the quantum efficiency via doping with Sr cations are discussed in the context of the revealed environment.

中文翻译：

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锶阳离子活化NaTaO ₃光催化剂的局部环境

钽酸钠NaTaO ₃是用于光催化水分解和CO ₂还原的最佳半导体之一。掺杂金属阳离子对于提高所需反应的量子效率至关重要。然而，与主体金属氧化物的掺杂和客体金属阳离子的活化有关的细节还不够充分。最基本的问题涉及通过掺杂作为主晶格中杂质的客体阳离子来提高量子效率。在这项研究中，通过扩展的X射线吸收精细结构光谱对Sr阳离子的局部环境（即NaTaO _3中常用的客体阳离子）进行了表征。结果表明，在掺Sr的NaTaO _3中存在两个Sr-O壳光催化剂。具有意想不到的短Sr-O键长1.96Å的小壳对应于嵌入TaO ₆八面体角共享网络中的SrO ₆八面体。Sr–O键长为2.60Å的另一个壳层对应于SrO ₁₂立方八面体，其中Sr阳离子在先前被Na阳离子占据的位置。Rietveld对X射线衍射数据的分析证实，形成了NaTaO ₃ -Sr（Sr _1/3 Ta _2/3）O ₃固溶体，以容纳NaTaO _3中的两个Sr-O壳。无需创建氧阴离子空位。在揭示的环境中讨论了通过掺杂Sr阳离子来提高量子效率的机制。