Crystallization and Microwave Dielectric Properties of MgO-Al_2O_3-SiO_2-TiO_2-CeO_2 Glass-ceramics

The crystallization process and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-Ce02 system glass-ceramics were studied by means of DTA, XRD, SEM and TEM. The results show that the parent glass has already been two-phase separated before nucleation and crystallization. The droplet phase is rich in Ti4+ and Ce4+, and the matrix phase is rich in Si4+ and A13+. During heat-treatment of the glass, rutile nucleates in the droplet phase at about 800℃ and perrierite appears at 900℃. At 1100℃, α-cordierite precipitates from the matrix phase. With increasing the heat-treatment temperatures, the crystallized volume fraction of the glass increases, which leads to the increase of the microwave dielectric constant (er) and the decrease of the microwave loss (tgδr). However, at temperatures higher than 1100℃, δr decreases because of the precipitation of large amount of a-cordierite. At the same time, tgδ increases slightly because of the coarse structure of the crystals. The glass-ceramics obtained by crystallization of the glass have dielectric constant of 8-11, and microwave loss less than 6×10~(-4).