A 5x increase of the critical current density (J(c)) at 77 K was obtained by coating a coevaporated 500 nm thick Y, BaF2, Cu film with 50 nm Ag prior to the ex situ annealing. J(c) increased from 0.2 for uncoated samples to 1 MA/cm(2) for the Ag-coated sample without severely affecting the zero resistance transition temperature (T-c0). Scanning electron microscopy showed that the surface morphology was improved and that the normally observed trellislike structure was greatly reduced. By combining electron microscopy and sputter assisted Auger analysis it was found that the Ag nucleated in droplets on the surface of the superconductor with only small amounts of Ag in the superconductor matrix. X-ray diffraction confirmed that the Ag-coated film was highly c-axis oriented. The increase in J(c) is believed to be due to the improved surface properties of the superconductor, indicating that a larger amount of the film is c-axis oriented or that the single-crystalline grains are larger. (C) 1994 American Institute of Physics.
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