Relationship of Crystal Structure and Microwave Dielectric Properties in Ni0.5Ti0.5NbO4 Ceramics with Ta Substitution

We have prepared Ni0.5Ti0.5Nb1-xTaxO4 microwave dielectric ceramics using a traditional solid-state reaction method. The influence of Ta5+ substituted at the Nb5+ site on the crystal structures and dielectric properties of Ni0.5Ti0.5Nb1-xTaxO4 ceramics is discussed. Structural refinement indicates that the distortion in the oxygen octahedron is affected by Ta substitution. The dielectric constant is dependent on the polarization of the NbO6 octahedron. The Q x f value is improved as the Ta content increases, because of the increasing packing fractions. The (f) value is mostly dominated by distortions of the Nb-O bonds ((Nb-O)); and (Nb-O) reduces with increasing Ta ion doping in the Nb site, which makes the (f) value decrease with increasing Ta content. Optimal microwave dielectric properties (epsilon(r) = 48.5, Q x f = 17500 GHz, and (f) = 88.6 ppm degrees C-1 at the resonant frequency of 6.05 GHz) are obtained for Ni0.5Ti0.5Nb1-xTaxO4 ceramics at x = 0.2.