Crystallization kinetics of superconducting precursor glasses in the Bi-Pb-Sr-Ca-Cu-O system

The crystallization kinetics of Bi,Pb-based superconducting precursor glass es such as Bi1.6Pb0.4Sr2Ca2Cu3Oy (Sample A) with different copper valence s tates and Bi1.6Pb0.4Sr2CaxCu3Oz (Sample B) with different Ca contents have been examined by differential thermal analysis. The modified Kissinger equa tion for the nonisothermal crystallization process is used to evaluate the activation energy, E-a, for the crystallization,. The number of crystal nuc lei is almost independent of the heating rate in all samples, and the Bi2Sr 2CuOx phase appearing first grows three-dimensionally. The values of E-a of Sample A is around 320 kJ mol(-1). The values of E-a in Sample B with smal l Ca contents of y=0.5 and 1.0 are 299 and 287 kJ mol(-1), respectively. Co mpared with Bi-based glasses containing no Pb, Bi,Pb-based glasses tend to have small values of E-a. It is found that the values of E-a of Bi,Pb-based glasses are similar to those in TeO2-based and fluoride glasses which are known as fragile glass-forming systems. (C) 1999 Elsevier Science B.V. All rights reserved.