Microstructure and microwave dielectric properties of CaO-B2O3-SiO2 glass ceramics with various B2O3 contents

The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 (CBS) glass ceramics were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results show that the increasing amount of B2O3 causes the increase of the contents of [BO3], [BO4] and [SiO4], which deduces the increase of CaB2O4 and α-SiO2 and the decrease of CaSiO3 correspondingly. No new phase is observed throughout the entire experiments. A bulk density of 2.54 g/cm3, a thermal expansion coefficient value of 11.95×10−6°C−1 (20–500°C), a dielectric constant ɛr value of 6.42 and a dielectric loss tanδ value of 0.000 9 (measured at 9.7 GHz) are obtained for CBS glass ceramics containing 35% B2O3 (mass fraction) sintered at 850 °C for 15 min.