Abstract
To investigate the formation of grain boundary barriers, composite SnO2–Zn2SnO4 varistor ceramics were prepared by traditional ceramic processing and, the electrical properties of grains and grain boundaries were evaluated by the measurement of complex impedances spectra. Calculated using the low frequency impedance data for each sample, a lower value about 0.09–0.32 eV and a higher value about 0.50–0.83 eV of activation energy Ea was obtained in the temperature range of 50–110 and 140–200 °C, respectively. The simulated results of complex impedances spectra by “Zsimpwin” software indicate that the equivalent circuit for SnO2–Zn2SnO4 composite ceramics is connected in series by one RC and two QR parallels. The relaxations in the dielectric dispersion spectra at low frequency of ∼1000 Hz suggest that one of the QR parallels is corresponding to oxygen vacancy. With increasing sintering temperature, the Ea values related to oxygen vacancy decreased whereas, the values related to grain boundary barriers increase obviously. The results suggest that the oxygen vacancy is the key factor to the semi-conductance of SnO2 grains and formation of grain boundary barriers.
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