Abstract
The temperature, frequency, and ac field dependence of the ac susceptibility components χ′ and χ″ have been studied in polycrystalline samples of Bi2−xPbxSr2Ca2Cu3Oδ with x values ranging from 0.2 to 0.3. The data do not show any evidence for the presence of low-Tc phases in the samples and perfect diamagnetism is observed at about 80 K. Data on χ″ vs T show the expected intrinsic peak near Tc and a coupling peak at a lower temperature Tp. For a specific field and frequency, Tp is found to increase with increasing lead substitution. The activation energy for flux creep, determined from the frequency dependence of Tp, is much smaller than the values reported for Y-Ba-Cu-O superconductors. The ac field H dependence of Tp is found to follow the relation 1 − Tp/Tc∝Hq with q =1/2. The estimated q value does not compare favorably with the values reported for Y-Ba-Cu-O compounds.
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