J. Khaled et al., IMPLICATIONS OF CU VALENCE ON THE STRUCTURE OF BI-BASED SUPERCONDUCTING PRECURSOR GLASSES, Journal of non-crystalline solids, 222, 1997, pp. 175-181
The implication of copper valence state on the structure of glasses in
the Bi-Sr-Ca-Cu-O system (Bi-based system) has been investigated. It
was found that the density of Bi2Sr2CaCu2Ox glass decreases with incre
asing the ratio of Cu+ to total copper, R(Cu+) = Cu+/Sigma(Cu+ + Cu2+)
, and goes from 6.25 +/- 1% for the glass with R(Cu+) = 0.82 to 6.10 /- 1% g cm(-3) for that with R(Cu+) = 0.98. The activation energy for
viscous flow also decreased with increasing R(Cu+) and went from 987 /- 5 kJ mol(-1) for the glass with R(Cu+) = 0.82 to 637 +/- 5 kJ mol(-
1) for that with R(Cu+) = 0.98. The decrease in both the density and t
he viscosity revealed that the structure of the glass becomes more loo
se with increasing Cu+ content. The study of the kinetics of the cryst
allization of Bi2Sr2CaCu2Ox glass showed a decrease in the activation
energy for crystal growth with the increase in Cu+ content. Based on t
he analyses of the change in the properties of the glass, the model st
ructure of [BiO6]-Cu-[BiO6] for the glass, which is composed of BiO6 o
ctahedra connected to each other through two coordinated Cu+, is propo
sed. (C) 1997 Elsevier Science B.V.