Crystallization Phase Regulation of BaO-CaO-SiO₂ Glass-Ceramics with High Thermal Expansion Coefficient

In this work, the influence of Ba/Ca ratios on the BaO-CaO-SiO₂ (BCS) glass network structure, crystallization phases, and coefficient of thermal expansion (CTE) was investigated. As the Ba/Ca ratio increases, the Qⁿ units in the glass network structure have undergone significant changes. The Q⁴ units in the BCS glass network transform into Q³ units, indicating the reduction of the glass network connectivity. The variation in the Ba/Ca ratio leads to a change in the crystallization phases of BCS glass-ceramics sintered at a temperature higher than Tc (crystallization temperature). The addition of α-SiO₂ (quartz) could regulate the crystallization phases and their ratio of the barium silicates (BaSi₂O₅, Ba₂Si₃O₈, and Ba₅Si₈O₂₁) in the BCS glass-ceramics. An abundant orthorhombic BaSi₂O₅ phase can be obtained in the BCS glass-ceramics with 15 wt% α-SiO₂ calcinated over 875 °C. The α-SiO₂ modified BCS glass-ceramics exhibited excellent properties (CTE = 12.10 ppm/°C, ε_r = 7.49 @ 13.4 GHz, tanδ = 4.96 × 10⁻⁴, Q × f = 27,034 GHz) sintered at optimized conditions, making it a promising candidate material for RF module and electronic packaging substrate.