DISCUSSION ABOUT ELECTRICAL-RESISTIVITY IN NB-DOPED BATIO3 SINGLE-CRYSTAL AND CERAMIC

The temperature dependence of the DC electrical resistivity in a 0.2 at% Nb-doped BaTiO3 ceramic and of the corresponding single crystal has been measured from 60K to 420K. In both materials, resistivity discontinuities are observed at each phase transition. In the cubic phase, the PTC effect is only present in the ceramic, but in the rhomboedral phase, as the temperature decreases, a sharp increase of the resistivity, with the same activation energy, is clearly observed in the ceramic as well as in the single crystal. This suggests a common conductivity mechanism governed by bulk properties. Moreover, it appears that a polaronic type of conduction is relevant in the whole range of temperature, for the single crystal, even in the cubic phase. This conclusion is at variance with the usual assumption that the bulk conductivity behaves as that of an usual n-type semiconductor.