OSCILLATOR STUDIES OF INTRAGRAIN AND INTERGRAIN DISSIPATION IN Y-BA-CU-O AND BI-PB-SR-CA-CU-O CERAMIC SUPERCONDUCTORS

An oscillator technique known as the swinging beam experiment has been used to study dissipation mechanisms in granular superconductors. Flux motion is detected from measurements of the resonance frequency and damping constant of a swinging beam of the superconductor. In the standard Y-Ba-Cu-O ceramic, damping measurements reveal two maxima: one immediately below Tc, and the other at a lower temperature. These dissipation maxima are interpreted as resulting, respectively, from intragrain and intergrain flux motion. The dependence of the intergrain dissipation on the oscillator amplitude is consistent with a simple flux creep model, and can be used to estimate the intergrain pinning energy. Swinging beam studies have been performed on the mixed phase superconductor Bi0.8Pb0.2Sr0.8Ca1Cu1.4Ox. The observed amplitude independence of the intragrain dissipation in Bi-Pb-Sr-Ca-Cu-O is suggestive of a phase transition of the assembly of flux lines. © 1990.