For low magnetic-field amplitudes the imaginary part of the ac susceptibility, g (T), in ceramic high-temperature superconductors represents the intergranular bulk pinning loss. The loss peak at T~s hifts to lower temperature with increasing ac field and to higher temperature with increasing frequency. We have measured the shift of the y" peak in ceramic Bi-(Pb)-Sr-Ca-Cu-0 samples. TheAnderson Aux-creep model in conjunction with the critical-state model for Josephson vortices is employed to explain quantitatively the dependence of T~o n frequency and ac field. The model allows the determination of the intergranular pinning potential, where pinning occurs at grainboundary intersection points.
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