Raman spectroscopic study on the structure in the surface and the bulk shell of Ce(x)Pr(1-x)O(2-delta) mixed oxides

The difference between the surface and the bulk shell of Ce(x)Pr(1-x)O(2-delta) mixed oxides was studied by Raman spectroscopy with four different excitation lasers. Two Raman peaks appear at 465 and 570 cm(-1) under all of the four lasers. The former is attributed to the Raman active F(2g) mode of CeO2, while the latter is attributed to oxygen vacancy. On the basis of the fact that the laser with shorter wavelength is closer to the electronic adsorption of samples, it is found that the Raman information detected by excitation laser with shorter wavelength is more sensitive to the surface region of samples. An inflection is observed in the relationship of the value I570/I465 to the Ce content in Ce(x)Pr(1-x)O(2-delta). With the increase in the wavelength of excitation laser, the Ce content corresponding to the inflection decreases. Combined with the surface concentration obtained by XPS, it can be deduced that the composition of Ce(x)Pr(1-x)O(2-delta) mixed oxide particles in the surface region and the bulk shell are different, the former is enrichment of Pr component and the latter is enrichment of Ce component. The thickness of the surface layer with rich Pr component decreases with the increase in the Ce content.