Bulk Grain Resistivity of ZnO-Based Varistors

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Abstract

We study the temperature dependence of grain resistivity in ZnO ceramic varistors (300–430 K), finding a positive temperature coefficient (PTC). We devise a high-frequency procedure that allow us to obtain the concentration and energy position of the shallow donor. The observed behavior is consistent with a shallow donor approaching complete ionization, and with an electron mobility mainly controlled by lattice (both optical and acoustical) scattering. The impact of this behavior on varistor performance under high-current pulse loads is discussed.

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