Effect of lead substitution in bismuth-based cuprate systems containing both low-Tc and high-Tc phases

Abstract

We report the results of resistivity, ac-susceptibility, and specific-heat measurements carried out on samples of Bi2−xPbxSr2Ca2Cu3O10+x (0≤x≤0.7) that were characterized by x-ray diffraction and high-resolution scanning tunneling microscopy. The zero resistance temperature, Tc (R=0), shows a peak at x=0.3 and the susceptibility data indicate that although a high-Tc 2:2:2:3 phase is present at 110 K, there is a second transition at 90 K that seems to indicate the existence of an additional low-Tc 2:1:2:2 phase. The specific-heat data unambiguously indicate a clear and distinct anomaly around Tc for samples with x=0.3–0.4 and smearing of the anomaly for x>0.5. Based on the results obtained from these combinations of experiments, the role of lead substitution in Bi samples, particularly in the stabilization of the 2:2:2:3 phase has been discussed.

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