Co-improvements of chemical stability and glass transition temperature via a mixed alkali effect in low-melting Li2O-Na2O-CaO-P2O5 sealing glasses

Enhanced chemical stability and reduced glass transition temperature are surely desirable for the low-melting sealing glasses. An elusive trade-off between the glass transition temperature and chemical durability in the phosphate glass systems, however, greatly limits the applications of low-melting sealing glasses. In this work, the co-improvements of chemical stability and glass transition temperature are achieved in the xLi₂O-(25-x)Na₂O-17CaO-58P₂O₅ glass system (0 ≤ x ≤ 20 mol%) via a mixed-alkali effect, and this effect on the glasses structures, thermal properties and chemical stability were systematically investigated. The FTIR, Raman and XPS spectra showed that the replacement of Na₂O with Li₂O will enhance and cross-link the glassy network. Particularly, the significantly reduced glass transition temperature (T_g∼331 °C) and softening temperature (T_s∼366 °C) were achieved in the glass with an optimized 10 mol% substitution of Li₂O, demonstrating a great potential of such the mixed-alkali-modulated glasses in the low-temperature sealing applications.