Effects of TiO2 on sinterability and dielectric properties of high-Q forsterite ceramics

High-Q plain forsterite ceramics with Q·f =240,000 GHz were developed by the usual solid sintering process using raw materials of highly purified MgO and SiO2. The τf (temperature coefficient of the resonant frequency) was negative in range −60 to −70ppm/°C. To adjust this to zero we added rutile with high τf (450ppm/°C). The addition of TiO2 increased dielectric constant (εr), did not affect the Q value, but decreased the sintering temperature by about 100 °C for addition of 0.5 to 10 wt.% TiO2. These results were attributed to increasing the sinterability at low temperature by the TiO2 and the almost pore-free and glassy-phase free grain boundary microstructures. It was not possible to develop a compostion which had τf=0 ppm/°C, as a result of the chemical reaction between MgO–TiO2 and TiO2 during sintering.