Correlation between surface-crystallized ZnO and the amount of Al ₂O₃ in borate-based glass-ceramics

The correlation between the Al₂O₃ content and the crystallization behavior of the oxide semiconductor ZnO in 5CaO-25B ₂O₃-45ZnO-xAl₂O₃-10K ₂O-15SiO₂ (CaBZAKSx) glass-ceramics was investigated, with a particular focus on the c-oriented crystallization behavior of ZnO. C-oriented precipitation of ZnO crystallites in glass-ceramics is brought about by the in-plane crystal growth of ZnO along the a-axis. Addition of Al ₂O₃ promotes the formation of ZnO₄ rather than ZnO₆ in the mother glass, and the ZnO₄ unit affects the nucleation and selective crystallization of ZnO that also takes the four-coordination state of Zn. The present results suggest that crystallization of ZnO from multi-component glass is also dominated by the local coordination state of the mother glass.