Early‐Stage Microstructure Development in Bi‐Sr‐Ca‐Cu‐O Glasses

Amorphous samples of Bi₂Sr₂Ca₁Cu₂O_x were produced by quenching from the melt. The early‐stage microstructure development in these samples was monitored using XRD, DTA, and hot‐stage TEM. It was observed that the molten glass undergoes phase separation during initial quenching and that subsequent refinement of these features generates the initial DTA exotherm during heating. This exotherm has been found for many related compositions, and has been shown not to correspond to crystallization. This initial phase separation strongly impacts the final microstructure by providing copious nucleation sites for the R‐phase that ultimately crystallizes first.