The origin of varistor property of SrTiO₃-based ceramics

The role of oxygen in the heat-treatment process of SrTiO₃ varistor ceramics has been investigated in this paper. The varistor voltage of SrTiO₃ ceramics has been found to be independent of the sample thickness and it increases with the heat-treatment temperature. It has been further revealed that the dielectric property is mainly governed by a highly resistive surface layer. The XPS results of Mn 2p and O 1s suggest that the surface layer is formed by oxygen diffusion and surface chemisorption at grain boundaries during the heat treatment in air. The chemisorption of oxygen in grain boundaries, which leads to the highly resistive surface layer, is the origin of the varistor property of SrTiO₃ ceramics.