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

Abstract

Using tape casting technique Ba‐excessive BaTiO3 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°C and successively reoxidized at 850°C 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 × 1012–6 × 1012 cm−2 at grain boundaries were also estimated.

Recent Progress in Applications of the Cold Sintering Process for Ceramic–Polymer Composites

“…Developing resistive barriers by the control of grain boundaries is of interest in a number of applications, such as varistors, thermistors, and barrier layer capacitors . In the case of conventional varistors, ZnO is usually doped with Bi 2 O 3 , Sb 2 O 3 , CoO, MnO, or Cr 2 O 3 and sintered at high temperatures (≈1000 °C) to obtain an inorganic resistive intergranular boundary in the range of 1–10 nm .…”

Improved Energy Storage Properties Accompanied by Enhanced Interface Polarization in Annealed Microwave‐Sintered BST

“…13,14 Therefore, as-sintered ceramics were thermally annealed in air at 1100°C for 10 h with the aim to reduce the dielectric loss and recover the insulating characteristics. Although effects of thermal annealing on the dielectric properties and relaxation behavior of Ba(Sr)TiO 3 -based ceramics associated with oxygen vacancies were confirmed by many observations, [15][16][17][18][19][20] limited reports have been focused on the effective energy storage properties, or the important role on microwave-sintered ceramics. 16 The development of reoxidation was believed to occur primarily at grain boundaries, other than grains, controlled by the oxygen diffusion during the annealing process (generally, the grain-boundary diffusivity of oxygen is larger than the bulk diffusivity), 21 leading to the enhanced insulation of grain boundary.…”

Abnormal reoxidation effects in Ba‐excess La‐doped BaTiO3 ceramics prepared by the reduction‐reoxidation method

“…However, there was no such reduction in the PTCR jump. It was enhanced all the time with increased reoxidation temperature as shown in Figure B, which was attributed to an increased density of surface acceptor state at a higher reoxidation temperature . The PTCR jump was remarkably weakened in the ceramics with higher firing temperature.…”

“…Moreover, Liu et al. found an abnormal reduction in RT resistivity in the Ba‐excessive ceramics at reoxidation temperature ~800°C and a phenomenological explanation was given . However, this abnormal reoxidation behavior was not observed in some other works and thus a number of unknown mechanisms still existed for the reoxidation effects of PTCR ceramics …”