Measurement of the piezotronic effect on single grain boundaries in zinc oxide Varistors

In this work we propose a new way of applying biaxial strain on an electrically conductive material to investigate stress-induced change of properties, namely the piezotronic effect, at a microscopic level. A piezoelectric stage is actuated to certain biaxial compressive strain levels. The microsection of the sample attached to it experiences the same amount of strain. The external strain translates to inner stresses in the material which can be controlled with high accuracy.This method was applied on zinc oxide-based varistor ceramics which is known as a functional material with a pronounced piezotronic effect on its highly non-linear current-voltage characteristics. By setting up a micro four point probe measurement it was possible to record the current-voltage characteristics at single grain boundaries at certain stress levels. The results lead to an understanding how mechanical stresses modify the overall electrical behavior of zinc oxide varistors.