Equilibrium phases in the Bi 2O 3-rich region of the ZnO–Bi 2O 3 system

Abstract

Varistors manufacturing is one of the most important applications of ceramic materials based in ZnO–Bi 2O 3 system. This system ZnO–Bi 2O 3 is especially relevant for both the formation of the microstructure that originates the varistor behavior and the sintering behavior. However, despite of its technological relevance, many aspect related to these materials remain unclear. Phase equilibrium diagram, specially the Bi 2O 3-rich region of the ZnO–Bi 2O 3, is still controversial. The 24Bi 2O 3·ZnO phase with sillenite structure is reported to be at equilibrium, however recent works point to the existence of 19Bi 2O 3·ZnO as the equilibrium phase. In this work, a set of samples have been studied in order to elucidate this point. Equilibrium phases and thermal behaviour of the samples have been analysed by XRD, SEM and DTA. Presented results show that the stoichiometry at equilibrium is 19Bi 2O 3·ZnO which is agreement with the recent published results.