CHARACTERIZATION OF THE BI1.6PB0.4SR2CA2CU3OY SUPERCONDUCTOR BY X-RAY-DIFFRACTION, LOW-FIELD MICROWAVE-ABSORPTION, AND ELECTRON-SPIN-RESONANCE

X-ray diffraction (XRD) and low-field microwave absorption (LFMA) have been measured for a series of Bi1.6Ph0.4Sr2Ca2Cu3Oy superconducting samples prepared at different sintering temperatures that display zero resistance between 50 and 98 K. Multiphase formation is observed in all samples. XRD results suggest that the fraction of the high-transition temperature (T(c)) phase denoted as 2223 grows with increasing sintering time and temperature compared to the low-T(c) phase denoted as 2212, although the 2212 phase always predominates. Simultaneously, several impurity phases also increase. The 2223 phase and 2210 phase seem to be formed by the disproportionation of the 2212 phase. The incorporation of Pb in the lattice accelerates this disproportionation process. LFMA signals reveal the presence of two superconducting phases with T(c) close to 75 and 115 K. The intensity of the microwave absorption due to the low T(c) phase is 3-6 times higher than that of the high T(c) phase. This suggests that between the two transition temperatures, the magnetic shielding of the high T(c) phase is weakened by penetration of the magnetic flux in the bulk material through the low T(c) phase, when the latter becomes nonsuperconducting above its transition temperature. No electron spin resonance signal has been detected for this superconducting system above or below T(c), which indicates the lack of paramagnetic impurity phases.