Structure and Microwave Dielectric Property Relations in Barium Cobalt Magnesium Niobate Ceramics

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The effects of cobalt substitution for magnesium on the microstructure and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 are investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Raman spectra, and microwave dielectric properties measurement. The structure of NbO6 octahedra displays a significant effect on the relative dielectric constant ($\varepsilon_{\text{r}}$) and the quality factor ($Q \times f$). The cobalt substitution shows a great quantity of nucleation of ordered domains, and result in a higher ordering degree. However, an annealing treatment also results in a higher ordering degree because of the growth of ordered domains. A compounds with near-zero $\tau_{\text{f}}$ can be obtained by the cobalt substitution. The Ba(Mg1-xCox)1/3Nb2/3O3 ceramic with cobalt substitution at $x = 0.5$ has the 32.2 of $\varepsilon_{\text{r}}$, 40,275 GHz of $Q \times f$, and 5.4 ppm/°C of $\tau_{\text{f}}$, and it is suitable for microwave resonator application. This study indicates that the cobalt substitution cause a variant of the ordering degree, and consequently has a significant effect on the microwave dielectric properties.
2011-09-25