Varistor and dielectric properties of SiO2 doped SnO2-Zn2SnO4 ceramic composites

In this work, SiO2 doped SnO2-Zn2SnO4 ceramic composites with excellent varistor and dielectric properties were prepared through traditional ceramic processing. The obtained nonlinear coefficient α was as high as 9.6, and the breakdown electrical field EB and leakage current density JL was as low as 5.9 V/mm and 62 μA/cm2, respectively. At a low frequency of 40 Hz, the relative permittivity εr measured at room temperature was higher than 2.5×104. The nonlinear decrease of the semicircle diameter in the complex impedance spectra with increasing DC bias voltage indicates that the grain boundary effect is an important origin of the varistor and giant permittivity properties. With an increase of temperature, the relaxor peak of the imaginary part M″ of the complex electric modulus shifted to high frequency and the activation energy Ea obtained from the M″ spectrum was about 0.31 eV, much lower than the grain boundary barrier height ϕb. The results suggest that other mechanisms may also be responsible for the giant permittivity property besides grain boundary barriers.