FACTORS THAT CONTROL JC IN HIGH-TC SUPERCONDUCTORS

A study of critical currents, flux creep and vortex line energy was undertaken for a variety of materials to determine some of the factors that control the intragranular critical current. Creep measurements for Nd1.85Ce0.15CuO4 and TI2Ba2Ca2Cu3O10, plotted as a function of reduced temperature, t = T/Tc, show essentially the same behaviour. This implies that the Nd compound, which has a much longer coherence distance and may have many electron carriers, has the same effective pinning potential to kT ratio at the same reduced temperature. Hence these two factors do not seem to be dominant in controlling Jc. A change in the vortex line energy, however, seems to be very important. With the addition of small amounts of Fe, the line energy and Jc both fall exponentially with Fe content in Y1Ba2(Cu1-x, Fex)3O7-σ. Hence the free energy per unit length of vortex is a very important factor controlling the intragranular critical currents. © 1990.