Räth, S.; Woodall, L.; Deroche, C.; Seipel, B.; Schwaigerer, F.; Schmahl, Wolfgang W.
Quantitative phase analysis of PBSCCO 2223 precursor powders - An XRD/Rietveld refinement study.
In: Superconductor Science and Technology, Vol. 15, No. 4: pp. 543-554
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We analysed x-ray powder diffraction data of spray pyrolytic precursor powders for the oxide-powder-in-tube (OPIT) technology by means of the Rietveld method. For calcinations in air we find a typical phase composition of 2212, 14-24, 11, CP and 3321 at 800°C (13h). At 820°C 2212 is in equilibrium with 14-24 and CP after 48 h calcination. In 8\% O2 at 800°C 2212 exists together with 14-24, 21, CP and CuO, in 99.999\% N2 at 760°C the stable phase assemblage consists of 2212, 21 and CuO. The highest amount of 2212 can be found in the powder calcined at 8\% O2 (72.4 wt\%) compared with 68.9 wt\% for the powder calcined in 21\% O2 and 69.3 wt\% for the powder calcined in flowing N2. A first trace of 2223 can be observed in powders calcined in air at temperatures of 838°C and 842°C. The crystallographic features of the 2212 phase correlate with the calcination atmosphere: under reducing atmospheres the satellite reflections of the x-ray powder diffractogram disappear and the orthorhombic lattice distortion z increases due to Pb2+-incorporation into 2212. With increasing O-content the c lattice parameter becomes significantly shorter in samples calcined in oxidizing atmospheres. It is possible to infer a cationic ratio of Sr:(Sr + Ca) ≈ 0.12 for the 11 phase and Ca:(Ca + Sr + Bi) ≈ 0.57 for 14-24 in precursors from lattice parameter data.