ENHANCED J(C)S OF YBA2CU3O7-X AG EX-SITU ANNEALED COEVAPORATED FILMS ON LAALO3(100) SUBSTRATES

A 5x increase of the critical current density (J(c)) at 77 K was obtai ned 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 uncoat ed samples to 1 MA/cm(2) for the Ag-coated sample without severely aff ecting the zero resistance transition temperature (T-c0). Scanning ele ctron microscopy showed that the surface morphology was improved and t hat the normally observed trellislike structure was greatly reduced. B y combining electron microscopy and sputter assisted Auger analysis it was found that the Ag nucleated in droplets on the surface of the sup erconductor with only small amounts of Ag in the superconductor matrix . X-ray diffraction confirmed that the Ag-coated film was highly c-axi s oriented. The increase in J(c) is believed to be due to the improved surface properties of the superconductor, indicating that a larger am ount of the film is c-axis oriented or that the single-crystalline gra ins are larger. (C) 1994 American Institute of Physics.