Reactions between oxides and Ag-sheathed Bi₂Sr₂CaCu₂Oxconductors

We studied reactions between Ag-sheathed Bi 2 Sr 2 CaCu 2 O x (2212) conductors and a variety of oxides. We identified two intrinsic reactions: solid-state diffusion of a metallic species from the 2212 melt through the Ag sheath to react with an oxide, and direct reaction between Ag and an oxide. The dominant species that diffused through the Ag sheath was Cu because its solubility in Ag and diffusivity through Ag under 2212 melt processing conditions are the highest of the BSCCO metallic species. Al 2 O 3 , CeO 2 , pure SiO 2 , Y 2 O 3 , ZrO 2 , CaZrO 3 , and SrZrO 3 were identified as non-reactive when heat treated in contact with Ag-sheathed 2212 tape. Fe 2 O 3 , MgO, and NiO reacted with Cu that diffused through Ag during the heat treatment. Cr 2 O 3 and SiO 2 -based Pyrex glass reacted directly with Ag in the sheath during the heat treatment, which can create cracks and pinholes in the Ag sheath through which liquid can flow. Based on thermodynamic estimates, we calculated the Cu concentration in Ag at the 2212/Ag interface at 900 °C and 1 bar O 2 to be between 0.15 and 0.22 at.%, which is consistent with 0.19 ± 0.02 at.% deduced from the experimentally measured diffusion flux.