Transparent glass-ceramics achieved by inward orientational growth of single crystals

Abstract

It is known that surface crystallization usually lowers the transparency of oxide glasses. Here, we report a different scenario, where high transparency can be realized in surface-crystallized oxide glasses by proper composition design and optimized control over thermal treatment. Specifically, the composition of the glass system is designed as ZnO⋅Al₂O₃⋅2.5SiO₂ (molar ratio). The derived glass is subjected to an optimized heat-treatment protocol, which is determined through calorimetric measurements. The mechanism of the underlying surface crystallization is unraveled through morphological and kinetic analyses. The crystals in the surface layer are characterized as micrometer-sized single crystalline rods, identified as Zn-β quartz solid solution, which grow inward. The high transparency of the derived glass ceramics is attributed to the orientation of crystalline rods. This work offers a new way for the design and fabrication of transparent glass-ceramics with excellent optical performances.