On the curve-fitting of XPS Ce(3d) spectra of cerium oxides

A paper by Truffault et al. (Mater. Res. Bull. 45 (2010) 527) describing the structural and chemical properties of pure and calcium-doped ceria nanopowdered materials, is commented upon. The area of major disagreement is concerned with the peak fitting procedures which the authors adopted to extract Ce3+ and Ce4+ atomic percentages from their XPS Ce(3d) spectra. It is argued that these results are largely unwarranted because they do not take into account the physical contraints arising from electron correlation phenomena, which regulate the intensities of the Ce(3d) peaks relevant to Ce3+ and Ce4+ ions.