Published online by Cambridge University Press: 15 February 2011
An electron microscopy investigation has been conducted in ZnO:Pr:Co varistor structures prepared by a new in-diffusion method. It has been shown that some boundaries host intergranular precipitates of a Prx Oy-based phase. All observations lead to the conclusion that grain boundaries exhibit Pr segregation, while Co is homogeneously distributed in the ZnO matrix. No continuous intermediate layer is present at the ZnO/ZnO boundary nor at the Pr2O3/ZnO interfaces. This is consistent with a barrier model based solely on a space charge depletion region(s).