Published online by Cambridge University Press: 10 February 2011
Nonlinear current flow in real 3-d composite materials is far more complex than suggested by usual brickstone models. We present experimental results on controlled seeding of structural inhomogeneities in varistor ceramics. In particular, we discuss the influence of mesoscopic imperfections on the characteristic electrical parameters. A main effect is a change in the statistical distribution of the grain size. As a consequence, the breakdown voltage drops very sensitively due to the disorder, while the shape of the I-V curve is hardly affected. We discuss also the extremely nonuniform filamentary current pattern, being illustrated by electroluminescence studies.