Dual effect of ZrO2 on phase separation and crystallization in Li2O–Al2O3–SiO2–P2O5 glasses

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AbstractZrO2 is an effective nucleation agent for low‐expansion lithium–aluminum silicate (LAS) glass–ceramic (GC) with high Al2O3 content. However, the effect of ZrO2 is still not fully understood in LAS glasses with low contents of Al2O3 and P2O5. In this work, the effect of ZrO2 on the phase separation and crystallization of Li2O–Al2O3–SiO2–P2O5 glasses were investigated. The results revealed that ZrO2 significantly increased Tg and the crystallization temperature of Li2SiO3 and Li2Si2O5 crystals. Li3PO4 crystals precipitated preferentially in the glass containing 3.6‐mol% ZrO2, wherein Zr was stable in the network and no precipitation of ZrO2 nanocrystals was observed. Moreover, the separation of phosphate‐rich phases in the as‐quenched glasses increased with the addition of ZrO2. The findings of the study revealed a dual role of ZrO2. First, ZrO2 acted as a glass network former rather than a nucleation agent, increasing glass viscosity and the nucleation barrier of Li2SiO3 through its strong network connectivity. Second, as Zr preferentially combined with non‐bridging oxygen to form Si–O–Zr linkages, a sufficient amount of charge‐balancing Li+ ions existed in the network, which promoted the separation of phosphate‐rich phases. It indicated that the incorporation of ZrO2 contributes to the activation of the nucleation role of P2O5, thus contributing to the formation of nanocrystals and fine microstructure of GCs.