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Current–voltage and resistivity–voltage measurements have been made on donor-doped BaTiO3 ceramics in order to investigate the nature of the current transport processes. It is found that the characteristics of the current–voltage do not follow the Heywang model [Solid-State Electron. 3, 51 (1961)]. Hence, the classical Heywang model is modified and the thermionic emission model with smoothly changed barrier resulted from image force is suggested. The modified theory coincides better with the experimental observation. The dependence between current density and voltage is J=J0 exp[−(φ0−βV1/2)/kT]. The relationship between resistivity and voltage (voltage effect) is ρ=(2kT/dJ0β)V1/2 exp[(φ0−βV1/2)/kT . From the modified model, the maximum barrier height of BaTiO3 ceramics can be deduced experimentally as well.

In the article, the electrical properties of single grains and single grain boundaries in donor doped BaTiO3 ceramics have been investigated. The results show that the grains have no positive temperature coefficient of resistance effect (PTCR effect) if the influence of electrode was neglected. The results also show that different grain boundaries have various PTCR effect. The characteristics of current-voltage do not follow the Heywang model and accord with our modified model. The maximum barrier heights of single grain boundaries are also deduced experimentally.