Grain-boundary polarization screening effect in semiconducting barium titanate ceramic

The charge-screening mechanism of spontaneous polarizations at the grain boundary was studied. Semiconducting barium titanate ceramic has an interesting positive temperature coefficient of resistance effect at the grain boundaries. The grain-boundary resistance can change several orders of magnitude at the Curie point region. It was demonstrated that this effect can be described by a double-depletion-layer model; the high resistance at temperatures above the Curie point was attributed to a high potential barrier created by the charges trapped at the grain boundaries. At low temperature, the instantaneous polarizations compensate part of the trapped charges, and the potential was subsequently lowered and the resistance value was decreased. The polarization screening mechanism for T<T₀ was explored. The residual charges at the grain boundary were found to be proportional to the total charges trapped at the grain boundary and inversely proportional to the local spontaneous polarizations