X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY OF SR AND BA COMPOUNDS

X-ray photoelectron spectroscopy (XPS) measurements of core level binding energies and kinetic energies of X-ray-induced Auger transitions for a comprehensive set of 25 Sr and Ba compounds are reported, including many for which there have been no previous XPS measurements. The majority of the Sr and Ba compounds measured here have cation core level binding energies which are lower than that of the metal, with the negative shifts largest for high temperature superconductors. These data are interpreted within a point charge model, which has previously been used to interpret XPS data from alkali halides and other ionic compounds. Data reported in the literature reveal that, rather than being anomalous, small or negative binding energy shifts are common to many ionic compounds. It is suggested that the large negative shifts observed for the high temperature superconductors are a consequence of large Madelung energies at the cation sites, and may be a measure of the hole distribution on the Cu-O planes. Measurements of the energy loss regions from the core levels of the Sr compounds are also reported. A peak which has previously been assigned as a configuration interaction satellite of the Sr4s peak is shown to be a plasmon loss from the Sr4p peak.