Initial crystallization of Bi4Ca3Sr3Cu4Oy glasses.

Abstract

The initial crystallization of ${\mathrm{Bi}}_{4}$${\mathrm{Ca}}_{3}$${\mathrm{Sr}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{\mathit{y}}$ glasses has been studied. It is found that the first crystalline phase from the glasses is the ${\mathrm{Bi}}_{2}$(Sr,Ca${)}_{2}$${\mathrm{CuO}}_{\mathit{y}}$ crystalline phase, and that the bulk crystallization dominates for the glasses with a low [${\mathrm{Cu}}^{+}$]/[${\mathrm{Cu}}_{\mathrm{total}}$] ratio. The isothermal and nonisothermal differential-scanning-calorimetry (DSC) studies indicate that the crystallization of the glasses follows the Avrami equation, x=1-exp[-(kt${)}^{\mathit{n}}$], where x is the fraction crystallized after time t. The value of the Avrami exponent n is about 3, implying three-dimensional crystal growth at a constant number of nucleation sites. The activation energy of the crystallization ranges from 437 to 489 kJ/mol.