Crystallization behavior, densification and microwave dielectric properties in MgO–Al₂O₃–SiO₂–TiO₂-based glass–ceramics with B₂O₃ addition

Glass–ceramics with a mass composition (wt%) of 19MgO–23Al₂O₃–53SiO₂–4TiO₂ with x wt% B₂O₃ addition (x = 2.5, 3, 3.5 and 4, abbreviated as samples B2.5, B3, B3.5 and B4) were prepared by two-step heat treatment of the parent glass at selected nucleation temperatures for 2 h and crystallization temperatures for 2h/20h, respectively. X-ray diffraction analysis revealed that the main crystalline phases of MgSiO₃ and SiO₂ could be successfully fabricated at relative low temperature (<1000 °C). With increasing B₂O₃ addition from 2.5 to 4 wt%, the nucleation temperature of the glass–ceramics was lowered from 820 to 740 °C. The content of main crystal phases for the B3 sample heat-treated at 850 °C/2 h + 950 °C/20 h was higher than that of other samples. Additionally, the dielectric properties of the B3 sample were closely dependent on not only its nucleation temperatures, crystalline temperatures and sintering time, but also its crystalline phases. Wherein, after two-stage heat treatment (850 °C/2 h + 950 °C/20 h), the good microwave dielectric properties of a lower \({{\varepsilon }_{r}}\) ~ 4.08, a higher Q × f ~ 14580 GHz (13.801 GHz) and a near-zero \({{t}_{f}}\tilde{\ }\)3.9 ppm/°C were obtained in the B3 sample.