CHEMICAL DIFFUSION IN THE BI, SR, CA, CU/O SYSTEM - THE KINETICS AND MECHANISM OF THE SOLID-STATE SYNTHESIS OF A SINGLE-PHASE 2212 MATERIAL

Monodimensional (chemical) diffusion measurements have been used to find a clean solid-state path to a pure Bi-Sr-Ca-Cu-O superconductor with two-layer structure, i.e., a suitable sequence of solid-state reactions such that each step gives a single-phase product. When starting from carbonate precursors of CaO and SrO plus Bi2O3 and CuO, the critical point of a reaction path of this kind is an appropriate choice of the external conditions of temperature, oxygen partial pressure, and cation molecularities, which must be different from the ideal ''2212'' values. The results show that a clean solid-state synthesis of a single-phase two-layer material is achieved by reacting at 750 degrees C under P(O-2) = 10(-3) atm the Sr14Cu24O41 phase and the ternary solid solution with monoclinic symmetry and cation molecularity near 0.376:0.082:0.543 (Ca:Sr:Bi). (C) 1995 Academic Press, Inc.