Crystallization of indialite/cordierite glass ceramics for millimeter-wave dielectrics

Abstract Indialite/cordierite (Mg 2 Al 4 Si 5 O 18 ) glass ceramics have been reported to show excellent millimeter-wave dielectric properties of low dielectric constant of 4.7 and high quality factor Qf of >200,000 GHz when crystallized at the temperature range of 1200–1300 °C. The glass ceramics were crystallized to the intermediate indialite phase at 1200 °C, which phase was then transformed to the stable cordierite phase as crystallization temperature increased. In this paper, the crystallization procedure of the glass with pure cordierite composition was clarified by macro difference thermal analysis (DTA) and X-ray powder diffraction (XRPD) patterns. The crystallization of the glass occurred in two steps above the T g of 778 °C: the 1st step is the formation of β -quartz solid solutions (s. s.) at 919 °C, and the 2nd step is the transformation from β -quartz s. s. to indialite at 946 °C. As increasing the crystallized temperature, indialite phase converted to cordierite. This phenomenon indicates that indialite is an intermediate phase during the crystallization process from glass to cordierite.