XPS studies of YBa2Cu3O7-delta/Ag high-T-c superconductor

The chemical nature of grain boundaries in YBa2Cu3O7-delta (YBC) ceramic an d YBC/Ag random composites was investigated using x-ray photoemission spect roscopy carried out on in situ fractured specimens. A change in the Ba core emission level indicated a cleaning of grain boundaries when silver was pr esent, For low silver content (5 wt.%), an increase of the formal Cu3+/Cu2 ratio was observed and interpreted as silver incorporation in the YBC latt ice. For higher silver content (20 wt.%), Ag-Cu intermetallic species were observed, resulting from reaction of the excess silver present at grain bou ndaries with the YBC. These chemical modifications were consistent with res istivity measurements. Copyright (C) 2000 John Wiley & Sons, Ltd.