Low-temperature sintering and microwave dielectric properties of 3Z2B glass–Al2O3 composites

A potential low temperature co-fired ceramics system based on zinc borate 3ZnO–2B2O3 (3Z2B) glass matrix and Al2O3 filler was investigated with regard to phase development and microwave dielectric properties as functions of the glass content and sintering temperature. The densification mechanism for 3Z2B–Al2O3 composites was reported. The linear shrinkage of 3Z2B glass–Al2O3 composites exhibited a typical one-stage densification behavior. XRD patterns showed that a new crystalline phase, ZnAl2O4 spinel, formed during densification, indicating that certain chemical reaction took place between the 3Z2B glass matrix and the alumina filler. Meanwhile, several zinc borate phases, including 4ZnO·3B2O3, crystallized from the glass matrix. Both of the reaction product phase and crystallization phases played an important role in improving the microwave dielectric properties of composites. The optimal composition sintered at 850–950 °C showed excellent microwave dielectric properties: ɛr = ∼5.0, Q·f0 = ∼8000 GHz, and τf = ∼−32 ppm/°C at ∼7.0 GHz.