Low-breakdown, high-α SrTiO3 varistors via grain-boundary engineering with ZnBi2O4

SrTiO3 varistors are promising alternatives to ZnO for low-voltage applications when their grain-boundary barrier response is properly controlled. Here, ZnBi2O4 (ZB) addition and post-sintering reoxidation were employed to modify the electrical behavior of La-doped SrTiO3 ceramics. The optimized composition exhibited a low breakdown voltage, high nonlinearity coefficient, and reduced leakage current. Linearized C–V analysis indicated an increase in the effective grain-boundary barrier height after ZB addition and reoxidation, while impedance and AC conductivity results showed reduced grain-boundary carrier transport. Fracture-surface XPS revealed a reduced Ti3+ fraction and a modest increase in adsorbate-related oxygen species after reoxidation. Although direct grain-boundary-resolved chemical evidence was not obtained, the combined results consistently indicate that ZB addition and reoxidation strengthen the functional grain-boundary barrier network. This study demonstrates a practical grain-boundary engineering strategy for low-voltage SrTiO3-based varistors.