Excess Conductivity, Diamagnetic Transition and FTIR Spectra of Ca Substituted by La in (Bi,Pb):2212 Superconducting System

Abstract

We report here measurements of the excess conductivity, the diamagnetic transition and the FTIR spectra of Bi1.7Pb0.30 Sr2Ca1−xLaxCu2Oy superconductor with various x values (0.00 ≤ x ≤ 0.30). It is found that the magnetic moment is negative below the diamagnetic transition in both field cooling (FC) and zero-field cooling (ZFC) for all samples. Furthermore, the magnetic moment is gradually shifted to lower values close to zero as the La concentration increases up to 0.30, but their values for FC are higher than that of ZFC. Moreover, the onset of diamagnetism (TcM) for the La = 0.30 sample is 80 K, which is about 29 K higher than that obtained from resistivity (TcR= 51 K). On the other hand, the logarithmic plots of excess conductivity ∆σ and reduced temperature Є reveal three different exponents corresponding to two crossover temperatures in the slope of each plot for all samples. The first exponent occurs in the normal field region (NFR) and its values are 0.90 (2D), 0.67 (2D), 0.23 (3D) and 0.77 (2D). The second exponent occurs in the mean field region (MFR) and its values are 0.51(3D), 0.23 (3D), 1.05 (2D) and 0.17 (3D). The third exponent occurs in the critical field region (CFR) and its values are 0.90 (2D), 0.78 (2D), 0.70 (2D) and 0.35 (3D). Interestingly, The Ginzburg-Landau parameter, critical magnetic fields and critical current density are gradually increased with La concentration up to 0.30, while the interlayer coupling, coherence lengths, anisotropy and Ginzburg number are decreased. Finally, the FTIR absorption spectra of the samples show nine successive peaks due to O–H, Bi(Pb):2223, residual carbon, SrCO, CaCO3 and CuO, and M–O, respectively. These results are discussed in terms of the correlation between hole carriers/Cu ions and excess oxygen which are introduced by La through CuO2 planes of BSCCO superconductors.