Effects of the addition of alumina on the crystallization, densification and dielectric properties of CaO-MgO-Al2O3-SiO2 glass in the presence of ZrO2

The alumina addition effects on the crystallization, sintering behaviors and dielectric properties of CaO-MgO-Al2O3-SiO2 glass (CMAS) and CaO-MgO-Al2O3-SiO2-ZrO2 (CMASZ) were investigated using the differential thermal analyzer (DTA), dilatometer, scanning electron microscopy (SEM) and X-ray diffractometer (XRD). For CMAS glass, the phyllosiloxide crystallized first and then anorthite crystallites were observed during sintering at 800-950 °C. The crystallization temperature of phyllosiloxide shifted from 800 °C to 850 °C after adding ZrO2 to the glass. For CMAS glass added with 10 vol% alumina, the acicular phyllosiloxide phase, intergrowth anorthite and subrounded alumina particles were observed. For CMASZ glass added with 10 vol% alumina sintered at 900 °C for 1 h, homogeneously distributed zirconia precipitates, subrounded alumina particles and a small amount of acicular phyllosiloxide were found in the dense glass matrix. The CMASZ glass added with 10 vol% alumina sintered at 900 °C exhibited a dense microstructure, a low dielectric constant of 7.5 and a dielectric loss tangent of below 5×10−3, which provides a promising candidate for LTCC applications.