Growth of a high T_c phase in the Bi_1.7Pb_0.3Ca₂Sr₂Cu₃ O_y system

The effect of sintering time on the Bi_1.7Pb_0.3Ca₂Sr₂Cu₃ O_y sample was investigated through XRD, DC resistance, AC magnetic susceptibility, SEM and critical current density (J_c). The XRD patterns revealed that the intensity of the low angle line at 2θ = 4.7° which corresponds to the high T_c phase, increases gradually with sintering time and reaches a maximum for nearly 200-240 hours. It is also found that the percentage of the high T_c phase is around 94% and that of the low T_c is approximately 6%. DC resistance results also showed an increase in T_c with sintering time and reached a maximum of 110 K. The real part of the AC susceptibility showed a step which corresponds to the transition from a normal to a superconducting state which gradually shifts to higher temperatures with an increase in sintering time. The magnitude of the step, which is a measure of the Meissner signal, also increased gradually with sintering time. The χ″ vs. T plots showed that with increase in sintering time, the width at half maxima decreased and the height of the peak increased. For still longer sintering times (200-240 h) the loss peak became sharper. The J_c value increased linearly with increasing sintering time. SEM studies revealed that the grain size increases and an increase in J_c may therefore be due to a reduction in the number of grain boundaries and other defects such as voids.