00/02878 Crystallization kinetics of superconducting precursor glasses in the Bi-Pb-Sr-Ca-Cu-O system

Abstract

The crystallization kinetics of Bi,Pb-based superconducting precursor glasses such as Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O y (Sample A) with different copper valence states and Bi 1.6 Pb 0.4 Sr 2 Ca x Cu 3 O z (Sample B) with different Ca contents have been examined by differential thermal analysis. The modified Kissinger equation for the nonisothermal crystallization process is used to evaluate the activation energy. E a , for the crystallization,. The number of crystal nuclei is almost independent of the heating rate in all samples. and the Bi 2 Sr 2 CuO x 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 small Ca contents of y=0.5 and 1.0 are 299 and 287 kJ mol -1 , respectively. Compared 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 TeO 2 -based and fluoride glasses which are known as fragile glass-forming systems.