X-RAY PHOTOELECTRON SPECTROSCOPY OF HIGH T_c SUPERCONDUCTOR YBa_2 Cu_3 O_(7-x)

The XPS spectra of superconducting(123-orthorhombic structure)and non-superconducting(123-tetragonal structure)YBa_2Cu_3O_(7-x)ceramics were obtained at room temperature and130 K with RIBER LAS 3000 surface analysis system,in which a sample cooling stage and asurface cleaning scraper,both made by the authors,were installed.No evidence of Cu~(3+)wasfound.The O 1s shows double lines.They are attributed to O1 and O4 with higher binding en-ergy and to O2 and O3 with lower binding energy respectively,and it was confirmed by cal-culation of SW-X_α method.The differences and changes in valence states of Y,Ba,Cu andO in both samples were discussed.