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

The microwave dielectric properties and the microstructures of the (1-x)MgTiO3-x(Ca0.8Sr0.2)TiO3 ceramic system prepared by the conventional solid-state route were investigated. (Ca0.8Sr0.2)TiO3 was employed as a tau(f) compensator and was added to MgTiO3 to achieve a temperature-stable material. Ilmenite-structured MgTiO3 and perovskite-structured (Ca0.8Sr0.2)TiO3 were coexisted and the two-phase system was confirmed by the X-ray diffraction patterns and the energy-dispersive X-ray analysis. Although the epsilon(r) of the specimen could be boosted by increasing amount of (Ca0.8Sr0.2)TiO3, it would instead render a decrease in the Qxf. The tau(f) value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, tau(f) could be adjusted to a near-zero value by mixing 94 mole% MgTiO3 and 6 mole% (Ca0.8Sr0.2)TiO3. A dielectric constant (epsilon(r)) of 21.42, a high Qxf value of 83,700 GHz (at 9 GHz) and a temperature coefficient of resonant frequency (tau(f)) of - 1.8 ppm/degrees C were obtained for 0.94MgTiO(3)-0.06(Ca0.8Sr0.2)TiO3 sintered at 1300 degrees C for 4 h. It is proposed as a low-loss and low-cost dielectric material for microwave and millimeter wave applications. (C) 2010 Elsevier B.V. All rights reserved.