ESCA studies of yttrium aluminum garnets

X-ray photoelectron spectroscopy (XPS/ESCA) has been employed to investigat e pure single crystals and powdered samples of yttrium aluminum garnet, Y3A l5O12 (YAG), and YAG crystals doped with several rare earth elements (Ln = Pr, Er, Ho, Tm) and a transition metal (Cr). Core level XPS peak shapes of the main elements forming the garnet structure can be rationalized due to d ifferent structural environments of particular ions modified by doping. The change of dopant oxidation state also results in variation of XPS peaks an d helps to identify the sites in which it takes place. Single-crystal and p owder samples give different XPS spectra. Possible sources of these differe nces are discussed. Similarities and differences between simple and mixed o xides are shown. The structure of YAG suggests the presence of only one ind ependent oxygen ion; however the O(ls) spectra of all YAG systems exhibit t wo readily discerned peaks, An explanation for this dichotomy is discussed, involving the possible polarization of the oxygen valence electron density between the aluminum and yttrium, Alternative explanations are also consid ered.