Phase formation and growth mechanisms in Bi 2Sr 2CaCu 2O 8 glass ceramics

Abstract

Devitrification of Bi 2Sr 2CaCu 2O 8 (Bi-2212) glasses, including phase formation sequences and mechanisms, has been investigated using both thermal analysis and high-temperature X-ray diffraction (HTXRD). Differential scanning calorimetry (DSC) was used to determine the activation energy for crystallization to be 395 kJ/mol, and in addition showed that the crystallization of these glasses occurs via a bulk mechanism. Differential thermal analysis (DTA) and simultaneous differential thermal and thermogravimetric analysis (STA), in conjunction with HTXRD, were used to establish the phase evolution of both bulk and powdered glass samples heated under O 2 and N 2 atmospheres. The results clearly indicate that Bi 2Sr 2Cu 1O 6 (Bi-2201) crystallizes directly from the glass first, and that Bi-2212 forms at temperatures above ~800°C by the diffusion of Ca, Cu and O into the Bi-2201 lattices.