Local structure and vortex phase diagram in ceramic Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ superconductors with Fe-Pd nanoparticle addition

This study investigates the effect of adding Fe-Pd nanoparticles on the local structure and vortex phase diagram of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ ceramics with weight ratios of x = 0.1 % and 0.2 %, both with and without cetyltrimethylammonium bromide (CTAB) used as a surfactant at a concentration of 50 mmol/L. The samples were fabricated using the conventional solid state reaction technique and their structure was analyzed using Cu-K edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The offset temperature (T_c, _offset) decreased with increasing applied magnetic field where the resistivity dropped to zero and T_c, _offset decreased from 95.76 K at 0 T to 47.62 K at 7 T. The maximum upper critical field (B_c2) was 100.24 K at 0.5 T for the sample doped with x = 0.1 % weight ratio with CTAB, while the minimum value was 95.75 K for the sample doped with x = 0.2 % weight ratio without CTAB. The XANES spectra showed a decrease in the valence state value of Cu. The Fourier transformation of the EXAFS structure demonstrated a monotonous increase in the values of Cu-O bond length and Debye Waller factor, possibly explaining the decrease in the critical temperature (T_c) of the samples. However, improvements in the upper critical field (B_c2) of Bi-2223 ceramics were achieved by adding FePd nanoparticles with the use of proper additional contents. By combining the characteristic parameters of small bundle pinning (B_sb), large bundle pinning (B_lb), irreversibility (B_irr), and B_c2 fields, the field temperature (B-T) vortex phase diagrams of Bi-2223 phase were well established. An obvious expansion of the B-T vortex phase diagram of FePd-added Bi-2223 samples compared with that of the pure one was observed. Such expansion could be attributed to the addition of FePd nanoparticles, which effectively worked as volume (three-dimensional) pinning centers. PACS: 74.25.Qt, 74.62.Dh, 74.72.Hs.