Relationship of Crystal Structure and Microwave Dielectric Properties in Ni 0.5 Ti 0.5 NbO 4 Ceramics with Ta Substitution

We have prepared Ni 0.5 Ti 0.5 Nb 1– x Ta x O 4 microwave dielectric ceramics using a traditional solid‐state reaction method. The influence of Ta 5+ substituted at the Nb 5+ site on the crystal structures and dielectric properties of Ni 0.5 Ti 0.5 Nb 1– x Ta x O 4 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 NbO 6 octahedron. The Q × f value is improved as the Ta content increases, because of the increasing packing fractions. The τ f value is mostly dominated by distortions of the Nb–O bonds ( δ Nb–O ); and δ Nb–O reduces with increasing Ta ion doping in the Nb site, which makes the τ f value decrease with increasing Ta content. Optimal microwave dielectric properties ( ε r = 48.5, Q × f = 17500 GHz, and τ f = 88.6 ppm °C –1 at the resonant frequency of 6.05 GHz) are obtained for Ni 0.5 Ti 0.5 Nb 1– x Ta x O 4 ceramics at x = 0.2.