Effect of Ca-doping on grain boundaries and superconducting properties of YBa2Cu3O7-δ

It is well known that the properties of grain boundaries in YBa2Cu3O7-delta films differ drastically from bulk material. It has been shown both experimentally and theoretically that the grain boundaries in YBa2Cu3O7-delta superconductors are depleted of carriers as compared to the bulk. This depletion leads to weak intergrain links and limits critical currents in superconductor, Recently, the promise for improved grain boundaries has been shown in Ca-doped YBa2Cu3O7-delta thin films and in Ca doped YBa2Cu3O7-delta biaxial grain boundaries. In this study, the effect of Ca-doping of grain boundaries in YBa2Cu3O7-delta films and bulk have been investigated in an attempt to increase hole concentration at the grain boundaries and to improve Jc. Ca-gels were applied to sintered YBa2Cu3O7-delta pellets and thin films. High temperature post-anneals were used to diffuse Ca preferentially into the grain boundaries. The distribution of Ca in the samples was studied by secondary ion mass spectrometry (SIMS), The effect of Ca-doping on Te and Je was studied by VSM. In epitaxial thin film increased Je were found at 40K, but not at 77K.