Phase evolution and microwave dielectric properties of MgO-B2O3-SiO2-based glass-ceramics

The densification and crystallization behaviors of MgO-B2O3-SiO2 (MBS) glass with various amounts of TiO2 additions (0-10 wt.%) were investigated by means of thermal analysis, X-ray powder diffraction and scanning electron microscopy. A microwave dielectric characterization was performed in order to evaluate the suitability of MBS glass-ceramics as a low-permittivity dielectric substrate. The densification of the MBS glass started below 700 degrees C. The main crystalline phases of Mg2B2O5 and MgSiO3 appeared at 800 and 950 degrees C, respectively. The Mg3TiB2O8 and TiB0.024O2 phases additionally crystallized in TiO2-added MBS glass-ceramics at 1000 degrees C. The permittivity increased from 6.1 in pure MBS glass to 6.9 in MBS glass with 10 wt.% of TiO2. The addition of TiO2 enhanced the crystallization and consequently increased the Qxf-values of the MBS glass (11 300 GHz) up to 16 500 GHz. The improvement of the Qxf-values became the most evident at 1050 degrees C. Dense MBS glass-ceramics sintered at 850 <= T <= 950 degrees C exhibited Qxf-values of 5000-8000 GHz (at similar to 12 GHz), which are comparable with the values of CaO-B2O3-SiO2-based glass-ceramics. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.