FLUX PINNING AND IRREVERSIBILITY TEMPERATURE IN MELT-GROWN, QUENCH-MELT-GROWN, AND SINTERED YBA2CU3O6+Y SUPERCONDUCTORS

The intragranular critical current density J(c), the apparent pinning potential U0, and the irreversibility temperature T(irr) of melt-grown (MG), quench-melt-grown (QMG), and sintered YBa2Cu3O6+y (123) were studied. A systematic increase in U0 and a slower drop in J(c) with temperature and magnetic field have been observed as one progresses from sintered 123 to the QMG and MG 123. Contrary to expectation, the somewhat weaker pinning in the QMG 123 compared to the MG 123 indicates no significant role of the size or amount of Y2BaCuO5 (211) precipitates in flux pinning within the range of present study. The T(irr) line shifts to higher temperatures with increasing pinning and follows a power law 1-T(irr)/T(c)=AH(n), where A and n are sample-dependent values related to the flux pinning properties of the samples. The implication of this result for theoretical models is discussed.