Abstract
The height of potential barriers formed at the grain boundaries in porous semiconducting barium titanate ceramics have been determined on the basis of the Heywang model using both the resistivity-temperature and the dielectric constant-temperature characteristics. All the porous barium titanate ceramics used here showed the PTCR effect of more than seven orders of magnitude, and the experimental results obtained showed a good fit with the Heywang model. The present study gives a strong support to the validity of the Heywang model in conjunction with a description of the nature of surface acceptor states, the existence of which was assumed in the Heywang model to be necessary for the formation of grain boundary potential barriers in barium titanate ceramics. An investigation made of the ambient gas dependence of the resistivity-temperature characteristic revealed that oxygen adsorbed on the grain surface formed a surface acceptor state necessary for the appearance of the PTCR effect.
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