Tailoring the Microwave Dielectric Properties of MgNb ₂ O ₆ and Mg ₄ Nb ₂ O ₉ Ceramics

The columbites MgNb ₂ O ₆ , MgTa ₂ O ₆ , and corundum‐type Mg ₄ Nb ₂ O ₉ 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 MgNb ₂ O ₆ and MgTa ₂ O ₆ and by the substitution of TiO ₂ for Nb ₂ O ₅ in both MgNb ₂ O ₆ and Mg ₄ Nb ₂ O ₉ ceramics. The Mg(Nb _0.7 Ta _1.3 )O ₆ has ɛ _r =29, Q _u × f =67 800 GHz, and τ _f =0.8 ppm/°C and the MgO–(0.4)Nb ₂ O ₅ –(1.5)TiO ₂ composition has ɛ _r =34.5, Q _u × f =81 300 GHz, and τ _f =−2 ppm/°C.