INFLUENCE OF THE SURFACE MELTING OF Y(1)BA(2)CU(3)O7-DELTA POLYCRYSTALLINE SAMPLES ON THEIR RESISTIVITY AND CRITICAL CURRENTS

Measurements of the electrical resistivity, rho, and of the critical c urrent, I-c, of polycrystalline Y1Ba2Cu3O7-delta samples before and af ter being melted superficially are presented. The melting was done by heating the samples at 1050 degrees C during a few minutes, and then a nnealing at 900 degrees C in flowing oxygen during several hours. This melting process may increase I-c by up to two orders of magnitude, wh ile rho changes by a factor of three or less. Scanning electron micros copy (SEM) and optical microscopy with polarization of the cross-secti on of the sample suggests that in the melted surface a grain alignment (typically 50 mu m to 100 mu m deep), similar to that observed in the whole volume in textured samples, appears. We relate such an importan t increase of I-c and the slight variations in rho with differences of the spatial current density redistributions associated with these two quantities (in surface for I-c and in volume for rho). (C) 1997 Publi shed by Elsevier Science Ltd.