Influence of microstructural disorder on the current transport behavior of varistor ceramics

Modeling of electrical transport in Zinc Oxide varistors

“…The grain boundary resistances determine varistor currents for voltages in the nonlinear breakdown voltage region of the electrical characteristics as well as in the linear pre-breakdown region. The resistance of the varistor at higher voltages becomes again Ohmic as it is essentially determined by grain bulk resistivity (Vojta et al, 1996).…”

“…Almost all of the models so far presented in the literature operate in 2-D planar geometry. They are based either on a Cartesian mesh representation (Vojta et al, 1996;Wen and Clarke, 1993) or on a Voronoi-type tessellation of the varistor sample (Bartkowiak et al, 1996a;Zhao et al, 2007). Given a microstructure representation, electrical transport can be modeled by means of an equivalent electrical circuit with voltage nodes and current branches associated with the grain centers and grain boundaries, respectively.…”

“…Several numerical models have been proposed to describe electrical transport in varistors (Bartkowiak and Mahan, 1995;Vojta et al, 1996;Qingheng et al, 2002;Hofstaetter and Supancic, 2013). In these models, the varistor microstructure is first represented geometrically by a space filling mesh.…”

“…Since percolation thresholds for 2-D and 3-D systems are in general very different, the commonly used 2-D models fail to reproduce properly the current distribution in the material and thus compute the varistor characteristic accurately. We perform a comparison between 2-D and 3-D varistor models using the approach of (Vojta et al, 1996) based on a Cartesian mesh representation. The second aspect is related to the effect of grain bulk resistivity.…”

“…Given a microstructure representation, electrical transport can be modeled by means of an equivalent electrical circuit with voltage nodes and current branches associated with the grain centers and grain boundaries, respectively. The grain boundary resistances are taken into account by introducing diode-like elements with specified electrical characteristics (Vojta et al, 1996) in the current branches. The macroscopic electrical response is, then, obtained by the solution of the resulting circuit equations.…”