Electrical transport properties of barium titanate-based capacitor ceramics

Electrical conduction mechanisms in BaTiO₃-based ferroelectric capacitor ceramics with an emphasis on the X7R type were studied. Dominant charge carriers in this material were identified as conduction band electrons below a temperature of 850°C. This was substantiated by the following results: negative Seebeck coefficients, zero galvanic cell voltage, and evidence of space charge-limited currents in MLC capacitors and related ceramic.

Effects of chip thickness on the electrical parameters, as well as the I-V characteristics, were studied. Chip electrical parameters such as resistivity, dielectric constant, and activation energy were found to be independent of chip thickness. Effects of ambient were also studied and differences in current-voltage behavior were attributed to surface effects.

Complex impedance spectroscopy proved to be a useful technique in separating grain, grain boundary, and contact contributions to the total impedance. Impedance plots for X7R ceramic revealed negligible contact impedance.

The most probable electrical transport mechanism in X7R ceramic is small polaron hopping, although the possibility of combining small polaron hopping and grain boundary transmission cannot be excluded.