Grain growth behaviour of ZnO-based multilayer varistors

In the present study, a model multilayer structure composing of seven Bi2O3-doped ZnO layers and AgPd inner electrodes is prepared. The Bi2O3-doped ZnO bulk specimens are also prepared for comparison purpose. The size of ZnO grains in the multilayer specimens is smaller than that in the bulk specimen. Furthermore, the size of ZnO grains in the multilayer specimens decreases with the decrease of layer thickness. Microstructure analysis demonstrates that the Bi2O3-rich liquid phase wets not only the ZnO grains but also the AgPd electrodes.