The intrinsic strain effect on critical current under a magnetic field parallel to the c axis for a MOCVD-YBCO-coated conductor

A new experimental set-up was developed to evaluate the strain dependence of critical current (Ic(epsilona)) for YBa2Cu3O7-delta (YBCO)-coated conductors under a magnetic field in a variable temperature environment. In this paper, we report the first results on the effect of a magnetic field parallel to the c axis () on Ic(epsilona) up to 10 T at temperatures of 60-77 K. We found that the magnetic field affects Ic(epsilona) in a different manner, depending on the field region. When the magnetic field increases from B = 0 T, normalized Ic(epsilona) is first improved and the optimal situation is realized under the characteristic magnetic field of Bp = 0.2 T at 77 K and Bp = 0.4 T at 70 K, respectively. For higher magnetic field, Ic(epsilona) degrades further with increasing strain. From the results of a fitting analysis, we confirmed that the strain at the peak of Ic(epsilona) shifts to higher strain and reaches the maximum value at Bp. The peak shift as a function of magnetic field found in the YBCO-coated conductors is in contrast with the Ic(epsilona) behavior for conventional low temperature superconducting composites, in which all of the critical parameters are optimized when the intrinsic strain of the superconductor is zero. From the present result, we can conclude that the peak strain of the Ic(epsilona) curve under a magnetic field is not determined only by the thermal residual strain of the YBCO film in the coated conductor. For the high field region, the curvature of the Ic(epsilona) curve increases with increasing magnetic field and temperature. It results in a steep decrease in Ic(epsilona) at high magnetic fields and temperatures.