CHARACTERIZATION OF THE PHASE-RELATIONS AND SOLID-SOLUTION RANGE OF THE BI2SR2CA1CU2OY SUPERCONDUCTOR

The phase relationships and solid-solution region of the Bi2Sr2Ca1Cu2Oy (2212) superconductor were investigated for compositions around the ideal 2212 stoichiometry at 865-degrees-C in one bar of oxygen. Changes in the starting composition were accommodated by changes in the types and composition of the secondary phases present, the number of intergrowths within the 2212 phase, and the solid solution composition of the 2212 phase. Compositional analysis of the superconducting phase was carried out in the transmission electron microscope (TEM) in order to separate the effects of solid-solution changes and the presence of intergrowths upon measured compositions. The actual solid-solution region determined from TEM measurements showed most of the solid solution substitution to occur between Sr and Ca. The highest superconducting transition temperatures (T(c)) were found in annealed samples for which the measured Sr+Ca content of the 2212 phase was closest to the ideal stoichiometric ratio of 3 (42.86 at.%). No correlation was found between the transition temperature and lattice parameters of the superconducting phase.