AN OPPOSITE DEPENDENCE OF TC ON QUENCHING IN YBA2CU4O8

An opposite TQ-dependence of Tc occurred on the samples, which have been directly pressed in a mould without grinding under higher pressure and quenced in LN2 after being sintered at T(Q) (300-degrees-C-820-degrees-C) in air for 15 minutes. The Tc of the pressed samples, which show a weak diamagnetism like that of the loosely packed superconducting powder, increases up to 67K at T(Q)=820-degrees-C. This fact implies that the ''mechanical'' disruption of the weaklink junction network, presumably at the intergranular boundaries, could be restored to a certain extent by sintering for short time at a certain T(Q). The original transition temperature Tc could be restored and even more narrow transition width could be achieved by sintering at one atmosphere pressure in oxygen for 60 hours.