溶胶凝胶法制备Ce_xPd_(1-x)O_(2-δ)纳米晶的结构表征及紫外拉曼光谱研究

Structure Characterization and UV Raman Study on Ce_xPd_(1-x)O_(2-δ) Nanocrystallines Prepared by a Sol-Gel Method

通过溶胶凝胶法合成了Ce_xPd_(1-x)O_(2-δ)(x=1,0.7,0.5,0.3)系列纳米晶,X射线衍射(XRD)结果显示所得晶体为立方相。X射线光电子能谱(XPS)测试结果显示Pd的价态有Pd^(4+),Pd^(2+)及Pd0,其中Pd4+的出现说明形成了固溶体结构。结合高分辨透射电镜(HRTEM)、XRD和Raman光谱数据,发现掺杂物的物相中含有PdO。HRTEM谱图显示CeO_2表面分布有Pd单质,说明形成固溶体后高温导致晶格中的Pd析出。对系列化合物分别进行可见光拉曼谱(λ_(ex)=532nm)和紫外光拉曼谱(λ_(ex)=325nm)测试,并采用归一化法对比PdO的峰面积及CeO_2的峰面积,发现紫外光谱下CeO_2的F2g峰得到增强,同时还在593cm-1,1170cm-1,1750cm-1处出现三个峰,分别归为CeO_2本征纵向光学吸收LO(longitudinal optic),2LO和3LO,该现象由于共振拉曼效应导致的。结合紫外拉曼光谱,对不同比例Pd掺杂的CeO_2纳米晶中的氧缺位进行了量化研究。结果表明,随着Pd掺杂量的提高,氧缺位浓度逐渐增加,这与XPS测试结果的趋势基本一致。

A series of nanocrystallines with general formula CexPd1-xO2-δ（x = 1,0.7,0.5,0.3）were prepared by a sol-gel method. The nanocrystallines were characterized by X-ray diffraction（XRD）, X-ray photoelectron spec- troscopy（XPS）, high resolution transmission electron microscopy（HRTEM） and Raman Spectroscopy. XRD results showed the crystallines phase was cubic phase. XPS results showed that the valence states of Pd contained Pd^4＋ ,Pd^2＋ and Pd^0 ,and the presence of Pd^4＋ showed that the structure of solid solution was formed. HRTEM images.XRD profiles and Raman spectra indicated that the doped-CeO2 complexes contained PdO. The HRTEM images showed that there were some Pd distributed on the surface of CeO2, which indicated the formation of solid solution and then high temperature resulted in the precipitation of Pd from the lattice . The normalization result of visible RamanO, λ ex= 532 nm） and UV Raman（λex = 325 nm）showed that F2g peak became more obviously in the UV Raman spectra. At the same time, other three peaks were observed at 593 cm^-1,1170 cm^-1 and 1750 cm^-1 in the spectrum, which belong to longitudinal optic（LO）, 2LO and 3LO respectively. The F2g peak along with LO band activation detected here was due to the resonance Raman effect. UV Raman spectra of CeO2 nanocrystals doped with different amout of Pd showed that the concentration of oxygen vacancies increased gradually with the increase of Pd content,and this was consistent with the trend of XPS test.