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 °C. The main crystalline phases of Mg2B2O5 and MgSiO3 appeared at 800 and 950 °C, respectively. The Mg3TiB2O8 and TiB0.024O2 phases additionally crystallized in TiO2-added MBS glass–ceramics at 1000 °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 °C. Dense MBS glass–ceramics sintered at 850 ≤ T ≤ 950 °C exhibited Qxf-values of 5000–8000 GHz (at ∼12 GHz), which are comparable with the values of CaO–B2O3–SiO2-based glass–ceramics.