Frequency dependence of the intergranular AC loss peak in a high-T-c Bi-(Pb)-Sr-Ca-Cu-O bulk superconductor

We have performed AC susceptibility measurements as a function of temperatu re; frequency and AC field amplitude on a rectangular bar shaped high-tempe rature superconductor with nominal composition of Bi1.8.4Pb0.34Sr1.91Ca2.03 Cu3.06O10 prepared by the liquid ammonium nitrate method. We have observed that as the frequency (AC field amplitude) increases, the intra- and interg ranular AC loss peaks move higher (lower) temperature, which indicates that AC losses are due to both hysteretic bulk pinning losses and viscous (flux flow) losses. M-H curves exhibit a hysteresis which is similar to that of hysteretic superconductors. Activation energy at the grain boundary is extr acted from the loss peak at some selected AC fields. Experimental results a re qualitatively discussed in the framework of the critical state model (CS M). (C) 1998 Elsevier Science B.V. All rights reserved.