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A study of how the partial substitution of Bi with Pb impacts the mechanism of excess conductivity in a Bi-Sr-Ca-Cu-O system. It is found that such a substitution leads to an increase in the critical temperature of the Bi1.7Pb0.3Sr2Ca2Cu3Oy(B2) sample, in comparison to Bi2Sr2CaCu2Ox (B1) [Tc (B2) = 100.09 K and Tc (B1) = 90.5 K, respectively]. At the same time, the resistivity ρ of the sample B2 in the normal phase decreases by almost 1.5 times in comparison to B1. The mechanism responsible for the generation of excess conductivity in cuprate HTSCs Bi2Sr2CaCu2Ox and Bi1.7Pb0.3Sr2Ca2Cu3Oy is examined using the local pair model with consideration of the Aslamazov-Larkin theory, near Tc. The temperature T0 of the transition from the 2D fluctuation region to the 3D (i.e., the temperature of the 2D-3D crossover), is also determined. The coherence length ξc(0) along the c axis of fluctuation Cooper pairs is calculated. It is shown that the partial substitution of Bi with Pb in the Bi-Sr-Ca-Cu-O system leads to a decrease in ξc(0) by a factor of 1.3 (4.205 and 3.254 Å, respectively), and that there is a narrowing of both the region of pseudogap existence and the region of superconducting fluctuations near Tc. The temperature dependence of the pseudogap Δ*(T) and the value Δ*(Tc) are determined, and the temperatures Tm, which correspond to the maximum of the pseudogap as a function of temperature in these materials, are estimated. The pseudogap maxima in samples B1 and B2 are found to be 61.06 and 38.18 meV, respectively.

Long-lived minima are detected at Tmin1 = 275 K and Tmin2 = 252 K in the ρ(T) curve of polycrystalline CdBa2Cu3O7−δ, which has a superconducting transition at 86.8 K. It is shown that the excess conductivity Δσ(T) near Tmin obeys the classical Aslamazov-Larkin fluctuation theory. This suggests that fluctuation Cooper pairs may develop in CdBa2Cu3O7−δ at T ≫ Tc. The experimental data are used to calculate the coherence length ξc(0), the 2D-3D crossover temperature T0, and the interplanar pairing constants. The magnitude and temperature dependence of the pseudogap for a sample without the minima are found to be typical of cuprate HTSC materials.