Microwave dielectric properties and microstructures of Nb2O5-Zn0.95Mg0.05TiO3+0.25TiO2 ceramics with Bi2O3 addition

The effects of Bi2O3 addition on the microwave dielectric properties and the microstructures of Nb2O5-Zn0.95Mg0.05TiO3 + 0.25TiO(2) (Nb-ZMT') ceramics prepared by conventional solid-state routes have been investigated. The results of X-ray diffraction (XRD) indicate the presence of four crystalline phases, ZnTiO3, TiO2, Bi2Ti2O7, and (Bi1.5Zn0.5)(Ti1.5Nb0.5)O-7 in the sintered ceramics, depending upon the amount of Bi2O3 addition. In addition, in order to confirm the existence of (Bi1.5Zn0.5)(Ti1.5Nb0.5)O-7 phase in the samples, the microstructure of Nb-ZMT' ceramic with 5 wt.% B2O3 addition was analyzed by using a transmission electron micrograph. The dielectric constant of Nb-ZMT' samples was higher than ZMT' ceramics. The Nb-ZMT' ceramic with 5 wt.% Bi2O3 addition exhibits the optimum dielectric properties: Q x f = 12,000 GHz, epsilon(r) = 30, and tau(f) = -12 ppm/degrees C. Unlike the ZMT' ceramic sintered at 900 degrees C, the Nb-ZMT' ceramics show higher Q value and dielectric constant. Moreover, there is no Zn2TiO4 existence at 960 degrees C sintering. To understand the co-sinterability between silver electrodes and the Nb-ZMT' dielectrics, the multilayer samples are prepared by multilayer thick film processing. The co-sinterability (900 degrees C) between silver electrode and Nb-ZMT' dielectric are well compatible, because there are no cracks, delaminations, and deformations in multilayer specimens. (C) 2009 Elsevier Ltd. All rights reserved.