Phase transformation, reaction kinetics and microwave characteristics of Bi2O3-ZnO-Nb2O5 ceramics

Abstract

Oxide powders of Bi2O3, ZnO and Nb2O5 were used to investigate the phase transformation, reaction kinetics and microwave properties of both Bi-2(Zn1/3Nb2/3)(2)O-7 and (Bi1.5Zn0.5)(Zn0.5Nb1.5)O-7 phases in the Bi2O3-ZnO-Nb2O5 system. Kinetic studies indicate that the formation mechanism of Bi-2(Zn1/3Nb2/3)(2)O-7 phase belongs to diffusion controlled reaction with a zero nucleation rate. In contrast, (Bi1.5Zn0.5)(Zn0.5Nb1.5)O-7 phase was interpreted as diffusion controlled reaction with a constant nucleation rate with either Bi5Nb3O15 or BiNbO4 phases as the nuclei. Furthermore, a lower activation energy and formation temperature were observed in the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O-7 than Bi-2(Zn1/3Nb2/3)(2)O-7 phase. Additionally, the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O-7 phase exhibits a higher dielectric constant but a lower Q value as compared with Bi-2(Zn1/3Nb2/3)(2)O-7 phase. (C) 2002 Elsevier Science Ltd. All rights reserved.