Abstract: Glass ceramics with α-cordierite(2MgO·2Al₂O₃·5SiO₂) as main crystal phase, having low dissipation factor in high frequency range, are excellent materials
for microwave substrates. However, the dielectric constant of the material is not high enough for some applications. Recently, a novel glass ceramic with
dielectric constant higher than 7.0 and dissipation factor lower than 1.5×10^-4 (in the frequency range >1GHz) was developed. The density changes and the expansion
-shrinkage behaviour during crystallization process of the material were measured. The relationship between electric properties and composition and micro-structure
of the glass-ceramics was studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and electric property testing. The results show that:
(1) The changes of the density and volume of the materials during heat-treatment are caused by crystal phase transition. It’s possible to avoid the sample from
cracking during heat-treatment by selecting suitable heat-treated cycle. (2) The volume ratio of α-cordierite to MAT, the two main crystal phases in
the glass-ceramic, influence the dielectric constant of the material. Furthermore, the more developed crystal grain is of benefit to increasing of
dielectric constant.

Key words: glass-ceramics, crystallization process, dielectric property