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 fi nd a clean solid-state path to a pure Bi-Sr-Ca-Cu-O superconductor wit h two-layer structure, i.e., a suitable sequence of solid-state reacti ons such that each step gives a single-phase product. When starting fr om carbonate precursors of CaO and SrO plus Bi2O3 and CuO, the critica l point of a reaction path of this kind is an appropriate choice of th e external conditions of temperature, oxygen partial pressure, and cat ion molecularities, which must be different from the ideal ''2212'' va lues. The results show that a clean solid-state synthesis of a single- phase two-layer material is achieved by reacting at 750 degrees C unde r P(O-2) = 10(-3) atm the Sr14Cu24O41 phase and the ternary solid solu tion with monoclinic symmetry and cation molecularity near 0.376:0.082 :0.543 (Ca:Sr:Bi). (C) 1995 Academic Press, Inc.