Superconducting and normal state transport properties of epitaxial 10 at.% Ca substituted YBCO thin films

Abstract

The improvement of the critical current density in YBCO coated conductor tapes necessarily concerns the study of grain boundary (GB) properties and the study of different pinning mechanisms involving both GB and the interior of the grain (IG). Recently, it has been proposed that the introduction of Ca substituting Y enhances Jc in YBCO grain boundaries (GB). On the other hand enhanced correlated pinning, as observed in YBCO thin films grown on CeO2 buffered substrates, has been ascribed to elongated defects along the c-axis of the film. In order to evaluate the role of calcium and CeO2 buffer layer on the superconducting transport properties of YBCO films, critical current density measurements as a function of temperature, magnetic field and angle between magnetic field direction and c-axis of the film have been performed on epitaxial thin films of unsubstituted and 10at.% Ca substituted YBCO grown on CeO2 buffered Al2O3 single crystal substrates. Results are compared with data obtained on 10at.% Ca substituted YBCO grown on SrTiO3 single crystal substrate.