Degradation of positive temperature coefficient of resistivity (PTCR) properties of semiconducting BaTiO3 ceramics that were annealed in reducing gases was studied from a mechanistic viewpoint mainly by measuring the electrical and dielectric properties, using reflectance and ESR spectroscopies, as well as by gas analysis using a quadrupole mass spectrometer. The results showed that after annealing, the density of the surface acceptor states decreased whereas the concentration of conduction electrons increased. The degradation in PTCR, properties was assumed to be caused by the diffusion of hydrogen atoms that were formed from reducing gases along the grain boundaries. These atoms reacted with chemisorbed oxygen ions, releasing trapped electrons and lowering the barrier potential.
