Effect of substituting Li2O with ZnO on the crystallization and properties of Li2O–Al2O3–SiO2 transparent glass ceramics

The transparent glass ceramic Li2O–Al2O3–SiO2 (LAS) was successfully prepared through a melting method. The impact of ZnO substitution for Li2O on the crystallization and properties of LAS glass ceramics was investigated. The results revealed that with the increase in ZnO substitution from 0% to 4%, the Q4 structural units in the base glass increased, reinforcing the integrity of the glass network structure. This led to an elevation in the glass transition temperature (from 533.5°C to 545.7°C), crystallization temperature (from 728.6°C to 832.3°C), and Vickers hardness (from 5.98 to 6.44 GPa). Additionally, the primary crystalline phases in the glass ceramics transformed from Li2Si2O5 and LiAlSi4O10 to cristobalite, and the multiphase crystalline structure transitioned to a single phase with a spherical morphology of the crystalline grains. The discussion delved into the size distribution of crystals in the glass ceramics, revealing that the increase in ZnO content refined the size and homogenized the distribution of the cristobalite crystals. Glass ceramics with 0% and 4% ZnO substitution, nucleated at 570°C for 4 h and crystallized at 700°C for 2 h, yielded lithium disilicate glass ceramic and cristobalite glass ceramic, respectively, with maximum transmittances (at 550 nm) of 86.92% and 88.79%. The study indicated that the type and size of precipitated crystalline phases significantly influenced the whiteness of the glass ceramics, with minimal impact on other color parameters. Moreover, the presence of fine grains in the glass ceramics, compared with the base glass, imparted a higher hardness. The addition of ZnO exhibited an increasing trend in the toughness of the glass ceramics. At a ZnO substitution of 4% and a crystallization temperature of 700°C, the glass ceramic with cristobalite as the crystalline phase demonstrated optimal comprehensive performance.