SURFACE AND BULK COMPOSITION OF YBA2CU3O6+X COMPOUNDS STUDIED BY XPS

YBa2Cu3O6+x compounds prepared by a formic acid route where characterized by XPS. The samples were investigated both after scraping in air and in vacuum to reveal the surface composition after partial degradation during short time air exposure and to gather data on the pure bulk state. The surface layer is characterized by the XPS data of O 1s = 530.8-531.5 eV, Y3d5/2 = 157.5 eV, Ba3d 5 2 = 779.9 eV, Ba4d 5 2 = 89.4 eV and Cu2p 3 2 = 934.4 eV with a strong satellite structure at 942.5 eV. The data indicate the presence of barium hydroxide and carbonate, copper(II) oxide, the green phase and some yttrium compound. The bulk state is characterized by XPS data of O 1s = 528.8 eV, Y3d 5 2 = 156.2 eV, Ba3d 5 2 = 778.6 eV, Ba4d 5 2 = 88.3 eV and Cu2p 3 2 = 932.6 eV without a satellite and a similar copper state as for the surface layer. There exist single states of yttrium and barium in the bulk, both copper(I) and copper(II) valence states and for oxygen possibly several components closely spaced accounting for the structurally different oxide ions. © 1990.