Microwave Dielectric Properties of Perovskite-Like Structured Ba8Ta6(Ni1-xMx)O24 ($\textit{M}=\text{Co}$, Cu, and Zn) Solid Solutions

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Perovskite-like structured Ba8Ta6(Ni1-xMx)O24 ($\textit{M}=\text{Co}$, Cu, and Zn) solid solutions were prepared by solid-state reaction method and the crystal structure and microwave dielectric properties of the solid solutions were characterized in this study. The structural refinements of all the solid solutions in the composition range of 0–1 fit well with the hexagonal structure with the space group $P6_{3}cm$ (No. 185). All the lattice parameters of the solid solutions linearly increased, depending on the composition $x$ and, such variations in lattice parameters were attributed to an increase in the (Ni/M)–O bond. No remarkable differences between the dielectric constants were observed with M substitution for Ni and these dielectric constants ranged from 27 to 29. On the other hand, the $Q\cdot f$ value of the solid solutions was significantly influenced by M substitution for Ni. In the case of Ni substitution for Cu, the $Q\cdot f$ value decreased from 81000 to 8500 GHz. The temperature coefficient of resonant frequency ($\tau_{\text{f}}$) varies from 33 to 77 pm/°C with Cu substitution for Ni and such a variation in $\tau_{\text{f}}$ may be related to the increase in the covalency of M–O bonds in an MO6 octahedron caused by an increase in temperature.
2006-09-30