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

Indialite/cordierite (Mg2Al4Si5O18) 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 degrees C. The glass ceramics were crystallized to the intermediate indialite phase at 1200 degrees 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 degrees C: the 1st step is the formation of beta-quartz solid solutions (s. s.) at 919 degrees C, and the 2nd step is the transformation from beta-quartz s. s. to indialite at 946 degrees 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. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.