Fernández-García M, Martínez-Arias A, Fuerte A, Conesa J C
Instituto de Catalisis y Petroleoquímica, CSIC, C/ Marie Curie s/n, 28049-Madrid, Spain.
J Phys Chem B. 2005 Apr 7;109(13):6075-83. doi: 10.1021/jp0465884.
In this article, the structural and electronic properties of Ti-W binary mixed oxide nanoparticles are investigated by using X-ray diffraction, Raman, X-ray absorption spectroscopies (XAS; near edge XANES and extended EXAFS), UV-vis spectroscopy, and density functional calculations. A series of Ti-W binary oxide samples having W content below 20 atom % and with particle size between 8 and 13 nm were prepared by a microemulsion method. The atoms in these nanoparticles adopted the anatase-type structure with a/b lattice constants rather similar to those of the single TiO(2) reference and with a c cell parameter showing a noticeable expansion upon doping. Within the anatase structure, W occupies substitutional positions, while Ti atoms only suffer minor structural perturbations. A change in the W local order at first neighboring distance is observed when comparing samples having a W content below and above 15 atom %. Charge neutrality is mostly achieved by formation of cation vacancies located at the first cation distance of W centers. Upon addition of W to the TiO(2) structure, the Ti charge is not strongly modified, while changes in the W-O interaction appear to drive a modest modification of the W d-electron density throughout the Ti-W series. A combination of these geometrical and electronic effects produced Ti K- and W L(I)/L(III)-edge XANES/EXAFS spectra with distinctive features. UV-vis spectra show a nonlinear decrease of the band gap in the Ti-W solid solutions with a characteristic turning point at a W content of ca. 15 atom %. The relationship between local/long-range order and electronic parameters is discussed on the basis of these experimental results.
在本文中，通过使用X射线衍射、拉曼光谱、X射线吸收光谱（XAS；近边XANES和扩展EXAFS）、紫外可见光谱以及密度泛函计算，对Ti-W二元混合氧化物纳米颗粒的结构和电子性质进行了研究。采用微乳液法制备了一系列W含量低于20原子%且粒径在8至13纳米之间的Ti-W二元氧化物样品。这些纳米颗粒中的原子采用锐钛矿型结构，其a/b晶格常数与单一TiO₂参比物的非常相似，而c晶胞参数在掺杂时呈现出明显的膨胀。在锐钛矿结构中，W占据替代位置，而Ti原子仅受到轻微的结构扰动。当比较W含量低于和高于15原子%的样品时，观察到W在第一近邻距离处的局部有序性发生了变化。电荷中性主要通过在W中心的第一阳离子距离处形成阳离子空位来实现。在向TiO₂结构中添加W后，Ti的电荷没有被强烈改变，而W-O相互作用的变化似乎在整个Ti-W系列中驱动了W d电子密度的适度改变。这些几何和电子效应的组合产生了具有独特特征的Ti K边和W L(I)/L(III)边XANES/EXAFS光谱。紫外可见光谱表明，Ti-W固溶体中的带隙呈非线性下降，在W含量约为15原子%处有一个特征转折点。基于这些实验结果，讨论了局部/长程有序与电子参数之间的关系。
