Comment on an article by Gonzaga et al. J Am Ceram Soc. 2020;103:6280-6288

I argue that the authors' interpretation of X-ray photoelectron spectroscopy (XPS) Ce3d spectra of their materials is untenable because it largely neglects the electronic structure of cerium ions and spin-orbit interaction of the Ce3d subshell. I conclude that at %Ce3+ values the authors derived from their Ce3d spectra offer an inaccurate account of the cerium chemistry of their materials.