Varistor properties of Sc2O3-doped Sn·Co·Nb ceramics

Abstract The varistor properties of Sc 2 O 3 -doped SnO 2 ·Co 2 O 3 ·Nb 2 O 5 ceramics were investigated. It was found that the non-linear coefficient presents a peak of 17.1 at the concentration of 0.06 mol% Sc 2 O 3 , the average grain size decreases from 10 to 5 μm, the breakdown electrical field increases from 199 to 1790 V/mm and relative electrical permittivity decreases from 2600 to 60 as Sc 2 O 3 concentration was increased up to 0.09 mol%. The increase of the breakdown electrical field with increasing Sc 2 O 3 concentration is mainly attributed to the decrease of the average grain size. The reason why the permittivity decreases with increasing Sc 2 O 3 concentration was originated from the ratio of the grain size to the barrier width. To illustrate the grain-boundary barrier formation of (Sc, Co, Nb)-doped SnO 2 varistors, a modified defect barrier model was introduced, in which the negatively charged acceptors substituting for Sn ions should be located at SnO 2 lattice sites in the depletion layers, instead at the grain interfaces.