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

Structural changes in Bi-4(SixGe1-x)(3)O-12 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 T-g, crystallization temperature T-c and maximum crystallization temperature T-p, observed on DSC, increased as the Si content increases. The presence of two crystalline phases, metastable Bi-2(Si, Ge)O-5 and stable Bi-4(Si, Ge)(3)O-12, 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 --> amorphous' + Bi-2(Ge, Si)O-5 crystal --> Bi-4(Ge, Si)O-12 crystal. (C) 2001 Elsevier Science Ltd. All rights reserved.