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High-frequency losses in Bi-Pb-Sr-Ca-Cu-O superconductors

A cavity resonance technique has been used to study losses at microwave frequencies in lead-substituted bismuth strontium calcium copper oxide superconductors, Bi2-xPbxSr2Ca2Cu3Odelta for x=0.1-0.3. The data show a decrease in the surface resistance with lead substitution for x<0.2. For x above 0.2, an increase in the surface resistance is observed. A linear variation of the surface resistance with temperature is observed in the normal and superconducting states. The superconducting energy gap has been estimated from the surface resistance data.