Phase relations and microwave dielectric properties of ZnNb₂O₆-TiO₂

The phase relations and microwave dielectric properties of (1-x)ZnNb₂O₆-xTiO₂ were investigated using x-ray powder diffraction and a network analyzer. Four phase regions were studied with increasing TiO₂ mol% (x): columbite solid solution, ixiolite (ZnTiNb₂O₈) solid solution, mixture of ixiolite and rutile solid solutions, and rutile solid solution. It was suggested that the microwave properties depend on crystal structure rather than chemical composition. In the columbite solid solution region, an order-disorder transition was found with an increasing amount of TiO₂, and the quality factor decreased sharply. ZnTiNb₂O₈ (x = 0.5), has a fully disordered structure and possesses a quality factor of 42,500, relative dielectric constant (ε_r) of 34.3, and temperature coefficient of resonant frequency (τ_f) of -52 ppm/°C. In the mixture region of ixiolite and rutile structure, τ_f was modified to around 0 ppm/°C.