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

Glass-ceramics with a mass fraction composition (wt%) of 19MgO-23Al(2)O(3)-53SiO(2)-4TiO(2)-3Sb(2)O(3) (M-A-S-T-S) were prepared by two-step (nucleation and crystallization) heat treatment of the parent glass at selected temperatures for 2 h and/or 20 h, 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 (epsilon(r) < 4) dielectric substrate. X-ray diffraction analysis revealed that the addition of TiO2 and Sb2O3 into MgO-Al2O3-SiO2 glass could induce the coexistence mu-cordietire and alpha-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 similar to 20 h 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 similar to 880 degrees C of a short-time sintering (similar to 2 h) could reduce the dielectric loss. Wherein, after the two-step heat treatment (880 degrees C/2 h + 930 degrees C/2 h), a better microwave dielectric properties of epsilon(r) similar to 3.65, Q x f similar to 7900 GHz (at 13.293 GHz) and tau(f) similar to -7.92 ppm/degrees C can be obtained in this M-A-S-T-S glass-ceramic sample.