Effect of sintering temperature on the dielectric and varistor properties of SnO2-Zn2SnO4 composite ceramics

The effect of sintering temperature from 1350 to 1450 degrees C on the dielectric and varistor properties of SnO2-Zn2SnO4 composite ceramics has been systematically investigated. With the increasing of sintering temperature, the average grain size increased from about 1 to 5 mu m and the breakdown electric field decreased from 117 to 3 V/mm. The relative dielectric constant increased with sintering temperature and it achieved the maximum of 1.2 x 10(4) (40 Hz, 0 degrees C) at 1425 degrees C. With excessive increasing of sintering temperature, the relative dielectric constant decreased and the microstructure of the ceramic bulk became porous. In the spectra of imaginary part of the complex modulus, a peak was exhibited and the peak's position shifted to high frequency with increasing testing or sintering temperature. The activation energy related to the peak was about 0.4 eV and this value was thought to be associated with the oxygen vacancies. Based on the sintering effect, the mechanism of oxygen vacancies in SnO2-Zn2SnO4 composite ceramics was proposed and accordingly, the varistor and giant permittivity properties are well understood based on the grain boundary barrier model.