Tailoring the microwave dielectric properties of MgNb2O6 and Mg4Nb2O9 ceramics

The columbites MgNb2O6, MgTa2O6, and corundum-type Mg4Nb2O9 ceramics were prepared by the conventional solid-state ceramic route. The structure and microstructure of the sintered samples were investigated by X-ray diffraction and scanning electron microscopic techniques. The microwave dielectric properties of the samples were measured by the resonance method in the frequency range 4-6 GHz. The dielectric properties have been tailored by forming a solid solution between MgNb2O6 and MgTa2O6 and by the substitution of TiO2 for Nb2O5 in both MgNb2O6 and Mg4Nb2O9 ceramics. The Mg(Nb0.7Ta1.3)O-6 has epsilon(r) = 29, Q(u) x f = 67 800 GHz, and tau(f) = 0.8 ppm/degrees C and the MgO-(0.4)Nb2O5-(1.5)TiO2 composition has epsilon(r) = 34.5, Q(u) x f = 81 300 GHz, and tau(f) = -2 ppm/degrees C.