MICROSTRUCTURE AND SUPERCONDUCTIVITY IN YBA2CU3O7-X CERAMICS DEFORMEDAT HIGH-TEMPERATURES .2. MAGNETIC AND TRANSPORT DATA

The effect of the microstructure formed in a sintered YBa2Cu3O7-x cera mics deformed at 875-degrees-C on its magnetic and transport propertie s has been studied. The refinement of the microstructure was found to eliminate weak links at grain boundaries and to weaken the dependence of the transport critical current on magnetic field, J(ct)(H). In the deformed ceramics the initial magnetization curve is non-linear for al l fields exceeding the first critical field for weak links at grain bo undaries, H-c1(gb). Owing to the density of intragrain dislocations be ing increased by two to three orders of magnitude, the intragrain crit ical current density J(cm)g is increased by a factor of ten. For insta nce, at a field of 1 T at 77 K the value of J(cm)g measured according to the Bean model is 5 x 10(3) and 6 x 10(4) A cm-2 for the initial an d deformed ceramics, respectively.