Effects of two-step heat treatment on crystallization behavior, densification and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-Sb2O3 glass-ceramics

Abstract

Glass-ceramics with a mass fraction composition (wt%) of 19MgO-23Al2O3-53SiO2-4TiO2-3Sb2O3 (M-A-S-T-S) were prepared by two-step (nucleation and crystallization) heat treatment of the parent glass at selected temperatures for 2h and/or 20h, respectively. A microwave dielectric characterization was performed in order to evaluate the suitability of M-A-S-T-S glass-ceramics as a lower permittivity (εr<4) dielectric substrate. X-ray diffraction analysis revealed that the addition of TiO2 and Sb2O3 into MgO-Al2O3-SiO2 glass could induce the coexistence of μ-cordietire and α-cordietire as the main phases, a small fraction of SiO2, MgSiO3 and Sb6O11 additionally crystallized as the second phases in this glass-ceramic system. Meanwhile, the prolonged heat treatment time~20h at selected nucleation and crystallization temperatures would cause the appearance of a small amount of MgTiO3 phase. The longer annealing time could not promote the densification and final dielectric properties, while a slightly increase in nucleation temperature~880°C of a short-time sintering (~2h) could reduce the dielectric loss. Wherein, after the two-step heat treatment (880°C/2h+930°C/2h), a better microwave dielectric properties of εr~3.65, Q×f~7900GHz (at 13.293GHz) and τf~−7.92ppm/°C can be obtained in this M-A-S-T-S glass-ceramic sample.