Knauth Philippe, Chadwick Alan V, Lippens Pierre E, Auer Gerhard
Université de Provence-CNRS, UMR 6264: Laboratoire Chimie Provence, Centre St Jérôme, 13397 Marseille Cedex 20, France.
Chemphyschem. 2009 Jun 2;10(8):1238-46. doi: 10.1002/cphc.200800806.
Nanocrystalline TiO(2) (anatase) is an essential oxide for environment and energy applications. A combination of EXAFS spectroscopy and DFT calculations on a series of dopants with quite similar ion radius, but increasing ion charge, show boundary space charge segregation of acceptor cations. The picture illustrates the Fourier-transformed EXAFS spectrum for Sn(4+)-doped TiO(2).A series of dopants, including acceptor ions (Zn(2+), Y(3+)), isovalent ions (Zr(4+), Sn(4+)) as well as a donor ion (Nb(5+)), were studied by EXAFS spectroscopy in nanocrystalline TiO(2) anatase powders and nanoceramics. Similar results were found for nanocrystalline powders and nanocrystalline ceramics, made by hot-pressing the powders. Boundary segregation was observed for the acceptor ions yttrium and zinc, whereas tin, zirconium and niobium ions were placed on substitutional bulk sites and did not segregate, whatever their concentration. These results can be interpreted based on defect thermodynamics, in the framework of a space charge segregation model with positive boundary core, due to excess oxide ion vacancies, and negative space charge regions, where ionized acceptors are segregated.
纳米晶TiO₂（锐钛矿型）是环境和能源应用中的一种重要氧化物。对一系列离子半径相近但离子电荷增加的掺杂剂进行扩展X射线吸收精细结构（EXAFS）光谱和密度泛函理论（DFT）计算相结合的研究，结果表明受主阳离子存在边界空间电荷分离现象。图中展示了Sn(4+)掺杂TiO₂的傅里叶变换EXAFS光谱。通过EXAFS光谱对纳米晶TiO₂锐钛矿粉末和纳米陶瓷中的一系列掺杂剂进行了研究，这些掺杂剂包括受主离子（Zn(2+)、Y(3+)）、等价离子（Zr(4+)、Sn(4+)）以及施主离子（Nb(5+)）。对纳米晶粉末以及通过热压粉末制成的纳米晶陶瓷也得到了类似结果。观察到受主离子钇和锌发生了边界偏析，而锡、锆和铌离子则占据了替代体位置，无论其浓度如何都不会发生偏析。这些结果可以在具有正边界核心的空间电荷分离模型框架内，基于缺陷热力学进行解释，该模型中存在由于过量氧离子空位导致的正边界核心以及电离受主发生偏析的负空间电荷区域。
