THE EFFECTS OF DIFFERENT THERMAL PRETREATMENTS ON THE MAGNETIC-PROPERTIES OF YBCO MPMG SAMPLES

YBCO MPMG samples, with 40% Y2BaCuO5 (Y-211) phase excess, were prepared using different thermal pretreatments during the temperature increase up to the partially melted state. No temperature gradient was applied during the stow-cooling growth process. Presintered samples turned out to be almost single grain, while all the others were characterized by the presence of a higher number of randomly oriented domains. Presintering favours compositional homogeneity, but, most important, enhances YBa2CU3O7-x (Y-123) phase solidification kinetics. Though various samples show similar behaviours, concerning the values of magnetization critical-current densities (J(cm)) measured at 77 K (J(cm) similar or equal to 10(4) A cm(-2) with B parallel to c, B = 1 T), levitation forces are subject to noticeable variations related to granular macrostructures and reach a peak of over 2 kg, at 77 K, in the case of presintered material.