GLASS MICROSTRUCTURE AND INITIAL CRYSTALLIZATION OF PB0.32BI1.68SR1.75CA2CU3OX

Microstructure and phase development of as-quenched and annealed sampl es of the glass of composition Pb0.32Bi1.68Sr1.75Ca2Cu3Ox have been st udied. Evidence for liquid-liquid phase separation during quenching wa s found. The microstructure of this glass during the early stage of cr ystallization is similar to that found for Bi2Sr2CaCu2Ox (2212) glass. The first phase that crystallizes on annealing at low temperatures ap pears to be Cu2O. In further heat treatments the sequential crystalliz ation of the R-phase of (PbyBi2-y)Sr2CuOx ('2201') composition and the PbyBi2-ySr2CaCu2Ox ('2212') phase was found, in agreement with other studies. Phase separation determines the initial crystal phase and the development of the superconducting phases. Phase separation observed in this glass points to the possibility that immiscibility may be a co mmon feature of a wide range of Bi(or Pb-Bi)-Sr-Ca-Cu-0 compositions.