Photoacoustic and Ac Impedance Measurements for ZnO Varistors with ZnO Nanoparticles Addition

Abstract: Photoacoustic and AC impedance measurements of ZnOvaristors with ZnOnanoparticles addition (≤ 150nm) are performed by using gas-microphone detection method and precision impedance analyzer, respectively. It is found that the energy gap Egis slightly decreased from 3.07 eV, for pure sample, to 2.96 eV with increasing ZnO nanoparticles additions up to 50%, followed by an increase of Egup to 3.07 eV with further increase of ZnO

nanoparticles up to 100%. However, these samples have different shapes of spectrum depending on ZnO nanoparticles addition, such as one semicircle, two semicircle, one arc as one quarter of a circle and two arcs. Wehave found that the conductivity of grains is nearly about 103 times more than the conductivity of the grain boundaries. The conduction in the grains and grain boundaries occurs in the same process for the additions with 5%, 10%, 50%, and could not be separated by the impedance spectroscopy. Although the dielectric constant is not systematic with ZnOnanoparticles addition, it is generally improved by the additions. Our results are discussed in terms of the nano size of the grains which are localized at the grain boundaries of ZnO.