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, εr = 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.