Improved strong magnetic field performance of low angle grain boundaries of calcium and oxygen overdoped YBa2Cu3Ox

Critical currents and extended voltage-current characteristics of [001] tilt, low angle boundaries in thin film bicrystals of pure YBa2Cu3Ox and Y0.7Ca0.3Ba2Cu3Ox in strong magnetic fields (H < 10 T) have been measured. For 5 degrees [001] tilt boundaries, there are clear benefits to Ca additions, particularly when the sample is oxygen treated to further overdope the sample after growth. Ca-doping decreases excess grain boundary resistance and diminishes the gap between inter- and intragrain current density over a wide field and temperature range. In spite of the lower T-c of the 0.3 Ca-doped samples, Ca doping increases the intergrain critical current density at 44 K as high as 30% over 0-3 T and threefold at 5 T. (C) 2000 American Institute of Physics. [S0003-6951(00)03644-5].