Microwave dielectric properties of low-fired ZnNb2O1 ceramics with BiVO4 addition

The BiVO4 additive was found effective for low-temperature firing of ZnNb2O6 polycrystalline ceramics below 950degreesC in air without a serious degradation in their microwave dielectric properties. Dense BiVO4-doped ZnNb2O6 samples of a relative sintered density over 95% could be prepared even at 925degreesC. An optimally processed specimen exhibited excellent microwave dielectric properties of Q(.)f = 55000 GHz, epsilon(r) = 26, and tau(f) = -57 ppm/degreesC. With increasing BiVO4 addition up to 20 mol% relative to ZnNb2O6, while the quality factor Q(.)f was gradually decreased, the relative dielectric constant, epsilon(r), was linearly increased and the temperature coefficient of resonant frequency, tau(f) was slightly increased. The variations in Q(.)f and epsilon(r) are surely attributable to the residual BiVO4 in the ZnNb2O6 matrix. An unexpected slight increase in tau(f) is probably due to the formation of the Bi(V,Nb)O-4-type solid solution.