Growth of a high Tc phase in the Bi 1.7Pb 0.3Ca 2Sr 2Cu 3O y system

Abstract

The effect of sintering time on the Bi 1.7Pb 0.3Ca 2Sr 2Cu 3O 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 2 θ = 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.