Conditions and reaction sequence for the formation of Bi2223 from Bi2212

Abstract

Superconducting Bi₂Sr₂CaCu₂O_x (2212 phase) powders were synthesized by the conventional solid state reaction method from appropriate amounts of Bi₂O₃, SrCO₂, CaCO₃, and CuO. To determine the conditions for the transformation of the 2212 phase (Tc ≈ 80 K) into the 2223 phase (Tc ≈ 110 K), the synthesized 2212 powder was mixed thoroughly with the appropriate amounts of CaCO₃ and CuO by a three-hour grinding process. The mixed powder was then pelletized at 8.0 tons for 1 min. and then sintered at different conditions of temperature and time. Four sintering temperatures (790°, 810°, 830°, and 850°C) and three sintering times (12 hrs, 24 hrs, and 48 hrs) were used for a total of twelve samples. All twelve samples were characterized by x-ray diffraction (XRD) to determine the phase composition of each sample. Preliminary x-ray diffraction data indicate that the CaCO₃ first decomposes to CaO which then reacts to form an intermediate compound Ca₂CuO₃. This intermediate then reacts at T>810°C with the 2212 phase to form the 2223 phase. It is also observed that the transformation for 2212 to 2223 is not efficient for the sintering conditions and prepraration method selected as only about 15% by volume of 2223 is present. Ongoing activities are the use of pre-reacted Ca₂CuO₃ instead of CaCO₃ and CuO as the reactant to determine if degree of transformation improves and the characterization by scanning electron microscopy (SEM) of selected samples in order to observe the grain microstructures of the various phases.