Low-temperature sintering and microwave dielectric properties of CaF2-doped MgTiO3 ceramics

Low-fired microwave dielectric ceramics CaF2-doped MgTiO3 (MT) were synthesized by the solid-state reaction method. The effects of CaF2 additions on the phase composition, sintering behaviors and microwave dielectric properties of MgTiO3 ceramics were investigated systematically. It demonstrated that CaF2 could not only effectively lower the sintering temperature of MT ceramics from 1400 °C to about 1000 °C, but also could significantly tune the temperature coefficient of resonant frequency (τf) to ~5 ppm/°C. Interestingly, the resonant frequencies of the 10~20 wt% CaF2-doped specimens were found to shift to lower values and thereafter to higher ones during the characterizations, making it difficult to obtain the τf values. It was further ascribed to the phase transition-like behaviors around 50 °C by the dielectric-temperature spectra. Meanwhile, good microwave dielectric characteristics of er=17.51, Q×f=37,000 GHz and τf=4.8 ppm/°C were achieved from the 5 wt% CaF2-doped specimens sintered at 1050 °C, which would be highly beneficial for LTCC applications.