Effect of Ca-doping on grain boundaries and superconducting properties of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

It is well known that the properties of grain boundaries in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films differ drastically from bulk material. It has been shown both experimentally and theoretically that the grain boundaries in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductors are depleted of carriers as compared to the bulk. This depletion leads to weak intergrain links and limits critical currents in the superconductor. Recently, the promise for improved grain boundaries has been shown in Ca-doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films and in Ca doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// biaxial grain boundaries. In this study, the effect of Ca-doping of grain boundaries in YBa/sub 2/Cn/sub 3/O/sub 7-/spl delta// films and bulk have been investigated in an attempt to increase the hole concentration at the grain boundaries and to improve J/sub c/. Ca-gels were applied to sintered YBa/sub 2/Cu/sub 3/O/sub 7-/spl 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 T/sub C/ and J/sub C/ was studied by VSM. In epitaxial thin films increased J/sub C/ were found at 40 K, but not at 77 K.