Systematic enhancement of in-field critical current density with rare-earth ion size variance in superconducting rare-earth barium cuprate films

Enhanced in-field critical current densities (J(c)'s) have been obtained in epitaxial superconducting (RE1,RE2) Ba2Cu3O7-x ( RE1=rare-earth ion 1, and RE2=rare earth ion 2) films grown on both single crystal and buffered metallic substrates. For a constant average RE ionic radius (equal to that of yttrium), there is a systematic dependence of the in-field J(c) on the RE ion size variance, with a small, but nonzero, variance being optimum. Compared to the standard YBa2Cu3O7-x composition, a factor of two improvement in J(c) (75.5 K) is reproducibly observed at 0.2 T (parallel toc) for the composition Dy1/3Ho2/3Ba2Cu3O7-x on both single crystal and buffered-metallic substrates. Angular dependent magnetic field studies and transmission electron microscopy indicate the presence of additional pointlike random defects. (C) 2004 American Institute of Physics.