The effect of Sm2O3 on the microstructure and electrical properties of SiO2-doped SnO2-Zn2SnO4 ceramic varistors

In this work, Sm2O3- and SiO2-codoped SnO2-Zn2SnO4 ceramic varistors were prepared through traditional ceramic processing, and the effect of Sm2O3 on the resulting microstructure and electrical properties was investigated. The results demonstrated that the ceramics were composed mainly of SnO2 and Zn2SnO4, and Sm was distributed homogeneously in the grains and along the grain boundaries. With 0.2 mol% Sm2O3 doping, the grain growth was obviously promoted. Further increases in Sm2O3 to 0.4 mol% resulted in trace amount of SiO2 and segregations containing elemental Sm via X-ray diffraction patterns and microstructure photos, respectively. In the sample doped with 0.3 mol% Sm2O3, optimal electrical characteristics of α=9.4, EB=10 V/mm, JL=46 μA/cm2 and ε′=1.2×104 were obtained. Simultaneously, the sample doped with 0.3 mol% Sm2O3 had the lowest conductance activation energy of 0.16 eV at temperatures lower than 110 °C. This good performance indicates that Sm2O3- and SiO2-codoped SnO2-Zn2SnO4 composite ceramics are viable candidate for the manufacture of capacitor-varistor functional devices.