Comparison of Auger electron spectra obtained from intergranular and transgranular areas exposed on fracture surfaces of sintered YBa2Cu3O7−xspecimens indicates that most grain‐boundary surfaces are deficient in oxygen and rich in copper compared to the bulk. The thickness of this region of altered composition is estimated to be in the range of 15–50 A˚. No evidence of segregation of impurities to grain boundaries was seen. The results suggest that the grain‐boundary layer is nonsuperconducting and a likely contributor to the problem of low critical current densities in these materials. It is believed that carbon at grain boundaries which has been reported results from incomplete calcination in material which is slightly off stoichiometry.
展开▼
