The microstructure and electrical properties of the varistors, which are composed of

ceramics, were investigated for different

contents. The increase of

content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0 mol%. The highest nonlinearity was obtained from 0.5 mol%

, with the nonlinear coefficient of 81.6 and the leakage current of

. The increase of sintering time and temperature greatly decreased the nonlinear properties. As the

content increased, the donor density increased from

and the barrier height greatly decreased with increasing

content, reaching a maximum (1.47 eV) in 0.5 mol%

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