Fluctuation, Diamagnetic Transition, and FTIR Spectra of La Substituting Ca in (Bi,Pb):2223 Superconductor

Abstract

We report here fluctuation, diamagnetic transition, and FTIR spectra in Bi1.7Pb0.30 Sr2Ca2-xLaxCu3Oy superconductor with various x values (0.00 < x < 0.30). It is found that the magnetic moment is negative for the samples below the onset of diamagnetism in both field cooling (FC) and zero-field cooling (ZFC). Although the magnetic moments are shifted to lower values close to zero as La increases up to 0.30, they are higher for Fc than for ZFC. Furthermore, the onset temperature of diamagnetic transition (TcM) for La = 0.30 sample is 83 K, which is about 30 K higher than that obtained from resistivity data (TcR = 53 K). On the other hand, the logarithmic plots of excess conductivity ∆σ and reduced temperature e for the samples reveal three different exponents corresponding to two crossover temperatures in the slope of each plot. The first exponent occurs in the normal field region (NFR) and its values are 0.30 (3D), 0.50 (3D), 0.20 (3D), and 2.04 (0D). The second exponent occurs in the mean field region (MFR) and its values are 0.75(2D), 0.44 (3D), 0.65 (2D), and 0.36 (3D). The third exponent occurs in the critical field region (CFR) and its values are 0.51 (3D), 0.99 (2D), 0.38 (3D), and 0.65 (2D). Interestingly, the Ginzburg-Landau parameter, critical magnetic fields, and critical current density are gradually increased as La increases 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. PACS: 74.25.Bt74.62.Dh74.62.En74.72.gh