Microstructure and Dielectric Properties of Ca(Fe1/2Nb1/2)O3-Modified PbZrO3 Ceramics

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($1-x$)PbZrO3–$x$Ca(Fe1/2Nb1/2)O3 dielectrics were prepared by a solid-state reaction process and structure analysis was performed together with the dielectric characterization. The rhombohedral phase for $x$= 0.2–0.6 and orthorhombic phase for $x{=}0.8--1$ were observed by X-ray diffraction. The ordering is observed in all compositions due to the observation of the A1g mode in double perovskite. Raman spectra also showed that the Fe/Nb ordered region dispersed in the disordered matrix by comparing the spectra in the case of $x{=}0.2$ with the spectra of the (PbCa)ZrO3 rhombohedral phase. Low loss dielectrics (${\sim}10^{-4}$ measured at 1 MHz) with high dielectric constant (55–340) were obtained in ($1-x$)PbZrO3–$x$Ca(Fe1/2Nb1/2)O3 solid solutions. The temperature coefficient of dielectric constant changed from negative to positive and a zero temperature coefficient could be expected for a composition between $x{=}0.6$ and $x{=}0.8$ at which the dielectric constant was between 55 and 84. Modified microwave dielectric properties were obtained for $x{=}0.4$: $\varepsilon{=}140$, $Qf{=}1,776$ GHz, and $\tau_{\text{f}}{=}{+}120$ ppm/°C.
2004-01-15