Enhancement of the transport properties in α-axis oriented YBa/sub 2/Cu/sub 3/O//sub 7-γ/ thin films by calcium doping

High critical current densities (J/sub c/) are required for applications, but grain boundaries suppress the attainable J/sub c/ values. Because of the presence of 90/spl deg/ grain boundaries and because of poor structural and electrical properties, a-axis thin films are of great interest to investigate the role played by Y/sub 0.8/Ca/sub 0.2/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YCaBCO) cap layers in the transport properties. The transport critical current densities of the films under various magnetic fields and the angular dependence of J/sub c/ at fixed temperature were measured before and after irradiation. A thin YCaBCO cap layer deposited on top of a-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films, is found to improve the electrical transport properties. Ca-doping decreases the resistivity and strongly increases J/sub c/ of a-axis oriented YBCO films. Furthermore, strong pinning by 90/spl deg/ grain boundaries was observed.