Fig. 5 shows the SEM micrographs and EDS elemental mappings of glass-ceramics held at 700 ◦C for 100 h. It is clear that the amount of residual glass (dark zone) in glass#2Bi2O3 (Fig. 5a) is much greater than that in glass#9Bi2O3 (Fig. 5b).
This is in good agreement with the increasing crystalline content with Bi2O3 content in XRD patterns (Fig. 4). In addition,EDS elemental mappings reveal the presence of Bi-rich zone in glass#2Bi2O3 (Fig. 5c), which does not contain Sr, Ca, Al and Si. This confirms the formation of boron-containing phase, i.e., BiBO3. In addition to the Bi-rich zones, some bright areas enrichment in Bi and Si can be observed in glass#9Bi2O3 (Fig. 5d), which verifies the presence of Bi12SiO20 in glass-ceramics.