A.c. and d.c. susceptibility studies on silver-doped BPSCCO (2223) superconductors

A.c. and d.c. susceptibility studies were undertaken on Ag-doped Bi_1.7Pb_0.3Ca₂Sr₂Cu₃ O_y samples to investigate the quality of the materials and the critical current density. X-ray diffraction (XRD) and resistance measurements were also performed to determine the phase of the samples and the influence of Ag addition on T_c(0). XRD results show that the (2223) high-T_c phase is retained and T_c(0) varies between 103 and 107 K. These results suggest that the superconducting properties are not destroyed by Ag addition. The a.c. susceptibility results show two troughs in the χ′ vs. T curves and two peaks in the χ″ vs. T plots. The first peak is smaller, is close to the transition temperature and corresponds to the midpoint of the first trough in the χ-T curve. The second peak appears below 98 K and corresponds to the midpoint of the second trough. The positions of both sets of peaks remain almost the same. The low-temperature peaks are sharper in samples containing silver compared with the pure sample, and the sharpness increases with an increase in silver concentration. J_c was calculated from d.c. susceptibility data using Bean's critical state and plate-like models. J_c was calculated from d.c. susceptibility data using Bean's critical state and plate-like models. J_c increases with silver doping. The increase in sharpness of the low-temperature loss peak with an increase in Ag concentration and critical current density suggests that Ag probably precipitates along the grain boundaries and improves the interconnectivity between the grains.