SOLID-SOLUTION REGION OF THE BI2SR2CACU2OY SUPERCONDUCTOR

Measurements were made of the compositional range of the Bi2Sr2CaCu2Ox superconductor in which the effects of intergrowths and grain-boundary phases were eliminated. At 800-degrees-C, the solid solution extends from Bi2.06Sr2.09Ca0.83Cu2.01Oy to Bi2.09Sr1.13Ca1.79Cu1.99Oy. Most of the cation interchange occurs between Sr and Ca while only a small variation in the Cu content was observed. In addition, substitution of Bi for Sr and/or Ca extends the range of compositions, although the reverse substitution of Sr or Ca for Bi does not seem to occur. The degree of interchange between Sr and Ca was found to decrease slowly with increasing temperatures in pure oxygen. In low oxygen partial pressures (0.1% O2), a significant portion of the Ca-rich solid solution region was found to be unstable.