Reoxidation Effects of Ba-Excessive Barium Titanate Ceramics for Laminated Positive Temperature Coefficient Thermistors

摘要

Using tape casting technique Ba-excessive BaTiO_3 ceramics were prepared, and their reoxidation effects for laminated positive temperature coefficient thermistors are investigated. These ceramics exhibit fine grains of size -1.15 μm. A resistivity of 727 Ω·cm and a PTCR jump about 3.3 orders of magnitude can be observed when the sample was sintered in reducing atmosphere at 1150℃ and successively reoxidized at 850℃ for 15 min. The influences of reoxidation on ceramic characteristics are discussed. The correlation of room temperature resistivity against reoxidation temperature showed an anomalous trend. This anomaly can be explained by the enhancement of ferroelectricity led by annihilation of oxygen vacancies. The influences of reoxidation time on ceramic characteristics were found to be limited. The impedance analysis revealed that the resistance of grain boundary is more likely to be influenced during reoxidation compared to that of grain bulk. The low acceptor-state densities of 2 × 10~(12)-6 × 10~(12) cm~2 at grain boundaries were also estimated.