Crystal Structure and Microwave Dielectric Properties of Aeschynite-Type $R$(W0.5Ti1.5)O6 ($R = \text{Nd}$, Sm, Eu, Gd and Dy) Ceramics

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The microwave dielectric properties and crystal structure of aeschynite-type structured $R$(W0.5Ti1.5)O6 ($R=\text{Nd}$, Sm, Eu, Gd and Dy) ceramics were characterized to investigate a microwave dielectric ceramic that is suitable for use in the base station. A single phase of $R$(W0.5Ti1.5)O6 ceramics was obtained; it was recognized that the lattice parameters of the ceramics vary linearly, depending on the ionic radii of the $R$ ions. The dielectric constants of $R$(W0.5Ti1.5)O6 ceramics were also related to the ionic radii of the $R$ ions and changed linearly with the ionic radii. From the result of crystal structure analysis, a decrease in the covalency of the (W,Ti)-O bond was observed with increasing the ionic radii of the $R$ ions; these variations in covalency corresponded to the linear increases in the dielectric constants of the $R$(W0.5Ti1.5)O6 ceramics. The $Q\cdot f$ and $\tau _{ f}$ values significantly depended on the $R$ ions; the highest $Q\cdot f$ value with a near zero $\tau _{ f}$ value was obtained for the Sm(W0.5Ti1.5)O6 ceramic ($Q\cdot f =35000$ GHz and $\tau _{ f} =-0.7$ ppm/°C).
2005-09-15