Effects of nitrogen annealing on structural, microstructural and superconducting properties of 2223 BPSCCO ceramics

The effects of nitrogen annealing of 2223 BPSCCO ceramics on the structural, microstructural and superconducting properties have been studied by means of X-ray and electron diffraction, TEM, EDAX and electrical and magnetic characterization. No appreciable variation of the intrinsic properties was found by annealing in nitrogen at relatively low temperatures (400-500°C), confirming for this phase the stabilizing effect of lead addition previously reported for 2212. By increasing the annealing temperature above 600°C, a decomposition process of the 2223 phase takes place. The mechanism of the process has been studied in detail at 630°C, where it occurs with slow kinetics at or near the grain boundaries involving a progressive decrease of the lead content of the 2223 grains. The worsening of the superconducting properties, observed in this work by increasing the annealing time at this temperature and previously reported by other authors for similar treatments in reducing atmosphere, was found to be due to the worsening of the intergrain coupling, which results from the modification induced on the weak-link structure of the ceramics by the decomposition process.