Abstract
An efficient synthesis technique has been developed to obtain theCu2Ba2(Y, Ca)Cu2O8±δ (Cu-2212 or `124') phase in areasonably short firing period under ambient or `semiambient' pressure. TheCu-2212 phase forms in a single-phase, highly crystalline form from astoichiometric mixture of CuBa2(Y, Ca)Cu2O7-δ (Cu-2212 or`123') and CuO at 850-880 °C in 24 h by encapsulating the precursormixture together with Ag2O2 in a fused-quartz ampoule. Under theseconditions, Ag2O2 decomposes into Ag2O/Ag acting as an efficientexcess-oxygen source in the synthesis. By changing the amount of Ag2O2added it is possible to control the partial pressure of oxygen inside thesynthesis ampoule up to ~40 atm. The Ca-free Cu-2212 phase forms evenwithout Ag2O2, but obtaining the 10% Ca-substituted phase in asingle-phase form requires 20 mol% Ag2O2. The synthesizedsuperconductive phases are found to be free from Ag contamination within thedetection limit of EDX analysis. The obtainedCu2Ba2YCu2O8±δ andCu2Ba2(Y0.9Ca0.1)Cu2O8±δ samples showed asingle-step superconductivity transition at 81 and 90 K, respectively.
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