High Q microwave dielectric ceramics in (Ni1-x Zn-x)Nb2O6 system

Abstract

(Ni1-xZnx)Nb2O6, 0 <= x <= 1.0, ceramics with >97% density were prepared by a conventional solid-state reaction, followed by sintering at 1200 degrees-1300 degrees C ( depending on the value of x). The XRD patterns of the sintered samples (0 <= x <= 1.0) revealed single-phase formation with a columbite (Pbcn) structure. The unit cell volume slightly increased with increasing Zn content (x). All the compositions showed high electrical resistivity (rho(dc) = 1.6 +/- 0.3 x 10(11) Omega.cm). The microwave (4-5 GHz) dielectric properties of (Ni1-xZnx)Nb2O6 ceramics exhibited a significant dependence on the Zn content and to some extent on the morphology of the grains. As x was increased from 0 to 1, the average grain size monotonically increased from 7.6 to 21.2 mu m and the microwave dielectric constant (epsilon(r)') increased from 23.6 to 26.1, while the quality factors (Q(u) X f) increased from 18 900 to 103 730 GHz and the temperature coefficient of resonant frequency (tau(f)) increased from -62 to -73 ppm/degrees C. In the present work, we report the highest observed values of Q(u) X f = 103 730 GHz, and epsilon(r)' = 26.1 for the ZnNb2O6-sintered ceramics