THERMAL-STABILITY AND HOPPING CONDUCTION IN BI4SR3CA3CUXOY GLASSES (X=4-9)

The thermal stability and transport properties of Bi(4)Sr(3)Ca3Cu(x)O( y) glasses with different Cu contents, 4 less than or equal to x less than or equal to 9, and Cu valence states, R(Cu+>=Cu+/(Cu++Cu2+) With 0.7 less than or equal to R less than or equal to 1, have been examine d. The Cu content dependence of thermal stability, electrical conducti vity and activation energy for conduction is not monotonic, but the ma gnitudes of these properties change at the composition x congruent to 6.5: The effect of R(Cu+) on the conduction of Bi-Sr-Ca-Cu-O glasses h as been measured and the conductivity is analyzed using the Mott equat ion for electron conduction of glasses containing transition metal ion s; the results suggest that the polaron hopping mechanism between Cuand Cu2+ is appropriate for the conduction of all Bi(4)Sr(3)Ca(3)Cu(x) Oy glasses irrespective of Cu content. A new structure model, particul arly on the role of Cu+, has been proposed for the present glasses, in which Cu+ ions act as both network formers and modifiers depending on the ratio of Cu+/Bi3+.