X-RAY PHOTOELECTRON STUDY OF SURFACE OF SUPERCONDUCTIVE Y-BA-CU-O AS DEPENDENT ON CLEANING, TEMPERATURE, COMPOSITION AND DOPING

The core level X-ray photoelectron spectra of the high-temperature sup erconductor system YBa2Cu3Ox are studied in dependence on the oxygen c omposition x, temperature of the sample, doping by Ag and quality of c leaning the sample surface. Nowadays there are many X-ray photoelectro n investigations, but comparative investigations of electron structure in superconductive and unsuperconductive states are absent in the maj ority of them. The X-ray electron magnetic spectrometer used in our wo rk allows one to obtain spectra in the temperature range from room tem perature to the temperature of liquid nitrogen with simultaneous mecha nical cleaning of the sample surface from the contaminations and degra ded layers. Thus the obtained results are unique and allow one to obta in for the first time the following conclusions. Three charge states o f copper atoms are shown to exist in this system -Cu1+, Cu2+ and Cu3- but only the Cu2+ state plays the main role in the transition of the system to the superconductive state. New peaks arise in O1s, Ba3d and Ba4d spectra after the transition of the system to the superconductiv e state, which implies the changes in the surroundings of O and Ba ato ms in this state. In Ag-doped samples similar changes in X-ray photoel ectron spectra are observed and they are even more pronounced than in the undoped ones.