Vibrating-reed studies on non-single-phase Bi-Ca-Sr-Cu-O superconducting ceramics

The resonance frequency $\omega$ and damping $\Gamma$ of two selected reeds of Bi-Ca-Sr-Cu-O ceramics were measured between 4.2 and 100 K in different applied magnetic fields up to 0.3 T. The samples showed large anomalies in $\omega$ and $\Gamma$ at ≃60 and ≃45 K indicating the existence of different superconducting phases. These anomalies can be interpreted in terms of pinning and hysteretic motion of flux lines. Within experimental resolution x-ray-powder patterns resemble that of the 85-K superconductor ${\mathrm{Bi}}_2$Ca${\mathrm{Sr}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$.