Structural change in Bi4(SixGe1−x)3O12 glasses during crystallization

Structural changes in Bi4(SixGe1−x)3O12 glasses during crystallization, where x=0, 0.33, 0.5, 0.66 and 1, were investigated systematically by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman spectroscopy and scanning electron microscopy (SEM). The results showed that the glass transition temperature Tg, crystallization temperature Tc and maximum crystallization temperature Tp, observed on DSC, increased as the Si content increases. The presence of two crystalline phases, metastable Bi2(Si, Ge)O5 and stable Bi4(Si, Ge)3O12, were detected by XRD. For x=0.5, it was possible to detect only the metastable crystalline phase at the early stage of crystallization. For the rest of the compositions, the metastable and stable crystals were almost formed simultaneously at this early stage. SEM morphology showed that the crystallization was dominated by crystal growth without prominent nucleation. It was concluded that the structural change occurs as follows: amorphous→amorphousʹ+Bi2(Ge, Si)O5 crystal→Bi4(Ge, Si)O12 crystal.