Characterization of Co_0.5(Ti_1−xZr_x)_0.5NbO₄ microwave dielectric ceramics based on structural refinement

Zr-substituted Co_0.5Ti_0.5NbO₄ microwave dielectric ceramics with low losses were prepared by the conventional solid-state method. To obtain dense ceramics, sintering temperatures from 1000 °C to 1280 °C were systematically investigated. The microstructure and the microwave dielectric properties of the Zr-substituted Co_0.5Ti_0.5NbO₄ ceramics were analyzed using different characterization techniques, including field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, Rietveld refinement and microwave dielectric measurements. Analyses showed that the dielectric properties are strongly dependent on the crystal structure, which causes densification of the microstructure of the ceramics. The structure of Zr-substituted Co_0.5Ti_0.5NbO₄ ceramics transformed from tetragonal to monoclinic as substitution increased. Additionally, the permittivity(ɛ_r) declined from 64.3 to 24.4 due to a change in the polarizability. However, the quality factor(Q×f) increased considerably. The temperature coefficient of the resonant frequency(τ_f) was near zero due tothe compounding of tetragonal structure with a positive τ_f and monoclinic structure with a negative τ_f. Optimal microwave dielectric properties in Zr-substituted Co_0.5Ti_0.5NbO₄ included a ɛ_r of 27.6, a Q×f of 40,132.8 GHz and a τ_f of 5.8 ppm/℃.