A new low-loss microwave dielectric using (Ca0.8Sr0.2)TiO3-doped MgTiO3 ceramics

Abstract The microwave dielectric properties and the microstructures of the (1– x )MgTiO 3 – x (Ca 0.8 Sr 0.2 )TiO 3 ceramic system prepared by the conventional solid-state route were investigated. (Ca 0.8 Sr 0.2 )TiO 3 was employed as a τ f compensator and was added to MgTiO 3 to achieve a temperature-stable material. Ilmenite-structured MgTiO 3 and perovskite-structured (Ca 0.8 Sr 0.2 )TiO 3 were coexisted and the two-phase system was confirmed by the X-ray diffraction patterns and the energy-dispersive X-ray analysis. Although the e r of the specimen could be boosted by increasing amount of (Ca 0.8 Sr 0.2 )TiO 3 , it would instead render a decrease in the Q × f . The τ f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, τ f could be adjusted to a near-zero value by mixing 94 mole% MgTiO 3 and 6 mole% (Ca 0.8 Sr 0.2 )TiO 3 . A dielectric constant ( e r ) of 21.42, a high Q × f value of 83,700 GHz (at 9 GHz) and a temperature coefficient of resonant frequency ( τ f ) of − 1.8 ppm/°C were obtained for 0.94MgTiO 3 –0.06(Ca 0.8 Sr 0.2 )TiO 3 sintered at 1300 °C for 4 h. It is proposed as a low-loss and low-cost dielectric material for microwave and millimeter wave applications.