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The ac response of ZnO varistors has been investigated over thetemperature range 100 to 380°C using impedance and modulusspectroscopy. Impedance spectra show only a single peak, which representsthe most resistive component in the sample and is responsible for the dcproperties, whereas an additional peak appears in the modulus spectrum. Thetwo components have temperature-dependent activation energies in the ranges,0.52–1.00 and 0.54–0.64 eV, respectively but their resistancesdiffer by 1 to 2 orders of magnitude. From their capacitance values, eachrepresents a region ∼100 to 500 A thick; they aretentatively assigned to an electrically-active interface and anintergranular layer.