Characterization of individual interfacial barriers in a ZnO varistor material

Abstract

The role of different types of interfaces in a ZnOvaristormaterial has been investigated by directly measuring the current/voltage characteristics of individual interfacial junctions. The electrically characterized interfaces were subsequently studied by analytical transmission electron microscopy. It was shown that barriers to electrical conduction form during cooling from the sintering temperature. The ZnO/ZnO junctions exhibited breakdowns at either 3.2 or 3.6 V, where the higher breakdown was observed at boundaries which contained a thin (∼2 nm) intergranular amorphous Bi‐rich film, while the breakdown at 3.2 V was found at boundaries without secondary phases but which contained intergranularly segregated Bi atoms. Junctions between ZnO and intergranular Bi2O3 exhibited asymmetric current/voltage characteristics with breakdowns at 3.2 V for one polarity of the applied voltage and either 0.4 or 0.9 V for the other polarity. No varistor behavior was observed at interfaces between ZnO and pyrochlore, Zn2Sb3Bi3O1 4. This gives rise to a significant number of ‘‘inactive’’ grain boundaries in the material.