Effects of MgO on crystallization and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-CeO2 glass-ceramics

Glass-ceramics with dielectric constant epsilon(r) similar to 8.8-11.1 and maximum quality factor Q x f similar to 32,900 GHz were prepared from xMgO center dot 1.2Al(2)O(3)center dot 2.8SiO(2)center dot 1.4TiO(2)center dot 0.6CeO(2) (x = 1.2, 1.5, 1.8, 2.1) system. The effects of MgO on crystallization, microstructure, and dielectric properties were investigated by differential scanning calorimeter, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and network analyzer. The results show that the glass-ceramic consists of multicrystalline phases, including perrierite, cordierite, magnesium aluminotitanate (MAT), rutile, ceria and spinel (MgAl2O4). Higher content of MgO promotes the formation of MAT with compositions richer in magnesia, stabilizes spinel at high temperature and at the same time suppresses the precipitation of rutile in the material. The existence of more MAT and stable spinel contributes to the remarkable increase of the quality factor Q x f with rising MgO content in the material, while the drop of dielectric constant er and the negative shift of the temperature coefficient tau(f) are mainly related to the reduction of rutile.