Effect of Ca₂CuO₃ on the formation of (2223) phase in the BiPbSrCaCuO system

The effect of excess Ca₂CuO₃ on the superconducting properties of Bi_1.7Pb_0.3Sr₂Ca₂Cu₃ O_y was investigated through X-ray diffraction (XRD), resistivity and a.c. magnetic susceptibility measurements. The XRD patterns revealed that 2223 is the major phase. The intensities of the peaks corresponding to Ca₂CuO₃ at 2θ=35.1 and 36.3, and those corresponding to the high T_c (2223) phase increased with increasing Ca₂CuO₃ concentration. The T_c(0) values, however, decreased with increasing Ca₂CuO₃ concentration. The real part of the a.c. susceptibility showed a two-step transition and two sets of peaks were observed in χ″ vs. T plots. The first set of peaks were approximately 10 K less than the T_c(0) values, whereas the second set of peaks occured in the temperature range 40-60 K. Both sets of peaks shifted towards lower temperatures with increasing Ca₂CuO₃ concentration. The role of Ca₂CuO₃ in the growth of 2223 phase and the mechanism of energy loss are discussed.