Melting Equilibria of the Bi‐Sr‐Ca‐Cu‐O (BSCCO) System in Air: The Primary Crystallization Phase Field of the 2212 Phase and the Effect of Silver Addition

The subsolidus and primary crystallization phase field of the “2212” (Bi:Sr:Ca:Cu) phase in the BSCCO system have been investigated. At 830°C, this phase was observed to be in equilibrium with ten phases. Sixteen four‐phase equilibrium regions that surround the 2212 phase have been identified at this temperature. The melting events as‐sociated with these four‐phase regions were studied with differential thermal analysis, quenching experiments, and wicking experiments, in which samples of the liquid for analysis were absorbed by capillary action. The melt com‐positions were obtained by using quantitative energy‐dis‐persive X‐ray spectrometry. The 2212 phase melts incon‐gruently, beginning at ∼825°C. Its primary crystallization field encompasses a compositional range of 24–42 mol% BiO 1.5 , 7–33 mol% SrO, 2–27 mol% CaO, and 19–43 mol% CuO. The compositions of melts in equilibrium with the 2212 phase were mostly on the calcium‐deficient side of the 2212 solid solution. An approximate polygonal model of the 2212 primary crystallization field has been presented. The addition of silver depresses the melting temperatures in the vicinity of the 2212 phase, from 4°C to 22°C. Silver entered the melt at a saturation level of 2–8 mol%. In the more copper‐rich liquids, silver replaced some of the copper, which resulted in a shift of the 2212 crystallization field away from the copper oxide corner.