Quantitative phase analysis of PBSCCO 2223 precursor powders - an XRD/Rietveld refinement study
Superconductor Science & Technology 15(4): 543-554
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 800degreesC (13 h). At 820degreesC 2212 is in equilibrium with 14-24 and CP after 48 h calcination. In 8% O-2 at 800degreesC 2212 exists together with 14-24, 21, CP and CuO, in 99.999% N-2 at 760degreesC the stable phase assemblage consists of 2212, 21 and CuO. The highest amount of 2212 can be found in the powder calcined at 8% O-2 (72.4 wt%) compared with 68.9 wt% for the powder calcined in 21% O-2 and 69.3 wt% for the powder calcined in flowing N-2. A first trace of 2223 can be observed in powders calcined in air at temperatures of 838degreesC and 842degreesC. 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 7 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) approximate to0.12 for the 11 phase and Ca:(Ca + Sr + Bi) approximate to 0.57 for 14-24 in precursors from lattice parameter data.