Grain boundary engineering for improved PTCR behavior in BaTiO ₃ semiconducting ceramics

The inherent trade-off between achieving high density and forming effective grain boundary barriers in BaTiO₃ thermistors limits the simultaneous attainment of low room-temperature resistivity (R₂₅) and a high Positive Temperature Coefficient of Resistance (PTCR) jump, hindering the development of miniaturized PTCR devices. To overcome this limitation, we optimized the grain boundary properties of BaTiO₃-based PTCR ceramics via nano-BTO incorporation (with and without acceptor doping), thereby promoting oxygen vacancy recombination and acceptor state formation at grain boundaries. This multifaceted strategy yielded ceramics exhibiting a synergistic combination of high density, fine grains (~2 μm), and exceptional PTCR performance, characterized by a low R₂₅ (≤ 50 Ω·cm) and a high PTCR jump (≥ 10⁵). These PTCR ceramics exhibit characteristic ferroelectric domain configurations, with both ordinary and coherent domains observed, and optimized grain boundary potential barriers. This enhanced performance is attributed to significantly improved oxygen diffusion at the grain boundaries. Specifically, this nanoparticle dopant strategy promotes oxygen vacancy recombination, the formation of adsorbed oxygen species, and the oxidation of Mn at the grain boundaries, collectively establishing multiple effective surface acceptor states. This work represents a significant advancement in PTCR ceramic fabrication.