Retrograde Densification in Bi2Sr2CaCu2O8 Superconductors

Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} was prepared using the mixed oxide-carbonate method and sintered at temperatures ranging from 850{degrees} to 911{degrees} C. The samples were characterized for density, mechanical strength, phase composition, microstructure, and superconducting transition temperatures. A unique retrograde densification characteristic is demonstrated in the temperature range 850{degrees} to 890{degrees}C whereby the material first becomes less dense as the sintering temperature is raised, and only in a narrow temperature range from 900{degrees} to 905{degrees}C does the material densify then with the formation of a liquid phase. This retrograde densification, coupled with a narrow sintering range overlapping the melting temperature, makes this compound a difficult one to process.