THE REACTIONS OF BI(PB)-SR-CA-CU-O-AG SUPERCONDUCTING MICROCOMPOSITES PLACED IN CONTACT WITH SILVER, GOLD, PALLADIUM, NICKEL, COPPER AND PLATINUM SUBSTRATES

Bi(Pb)-Sr-Ca-Cu-O-Ag (BSCCO-Ag) superconducting microcomposites were produced by oxidation, annealing and deformation of metallic precursor alloys. Silver, gold, palladium, nickel, copper and platinum sheets have been used to produce two-dimensional superconducting composites via deformation-annealing processes. The reactions between BSCCO-Ag and these metallic elements and the effects of these reactions on the superconducting properties of the BSCCO-Ag microcomposites were studied by a combination of microstructural observation and microanalysis. Silver, gold and palladium do not oxidize at elevated temperatures, and they have very little or no reaction with BSCCO-Ag microcomposites. Microcomposite specimens in contact with silver, gold and palladium sheets possess a high T(c) (T(R = 0) = 102-108 K) and reasonably good J(c) (J(c)(77 K) = 400-1000 A cm-2). The microstructure of these samples showed a well-developed textured 2:2:2:3 phase embedded in the silver matrix. Nickel and copper partially or fully oxidized under the annealing conditions. These elements reacted with BSCCO, prevented the formation of the 2:2:2:3 phase and resulted in a 2:2:1:2 phase dominant microstructure with lower T(c) (T(R = 0) almost-equal-to 75 K). Platinum entered the silver phase in the BSCCO-Ag microcomposites, forming Ag-Pt solid solutions, and reacted with the BSSCO compounds to form several complicated oxide phases. Thin silver sheets have been successfully used to separate BSCCO-Ag and stainless steel and thereby to prevent reactions between stainless steel and the microcomposite.