Varistor and giant permittivity properties of SnO₂–Zn₂SnO₄ ceramic matrix composites

(1 − x)SnO₂–xZn₂SnO₄ ceramic matrix composites with x = 0.15, 0.20, 0.25 and 0.30 are prepared by traditional ceramic processing. The varistor and dielectric properties have been measured before, and after heat treatment in vacuum and atmosphere. Before heat treatment, the ceramic with x = 0.20 has good nonlinear electrical property (α = 5.5), low breakdown electric field (E _1.0 = 7.4 V/mm) and giant permittivity (40 Hz, 40 °C, ε _r = 2 × 10⁴). However, the good varistor and dielectric properties are greatly degraded after vacuum treatment. By a following heat treating in atmosphere, the degradations of the electrical properties are restored except the high permittivity. The results strongly suggest that varistor and dielectric properties are related to oxygen and/or oxygen vacancies. Reference to the sintering behavior, the original mechanism of oxygen vacancies in SnO₂–Zn₂SnO₄ ceramic composites is proposed and accordingly, the varistor and giant permittivity properties are well understood based on the grain boundary barrier model.