ELECTRICAL-CONDUCTIVITY OF SIMILARLY DOPED BATIO3 SINGLE-CRYSTALS ANDCERAMICS IN THE RHOMBOHEDRAL PHASE

The temperature dependence of the DC electrical resistivity in a 0.2 a t% Nb-doped BaTiO3 single crystal has been studied, by comparison with the corresponding ceramic, from 40K to 420K for the single crystal an d from 130K to 420K for the ceramic, with the special attention to the rhomboedral phase. While the resistivity is always greater in the cer amic than in the single crystal, the temperature dependence is similar in both materials. In this phase, the observed sharp increase of the resistivity, as the temperature decreases, results mainly from the dis appearance of polarons, in both materials. Below 70K, the temperature dependence of the conductivity of the single crystal suggests a long r ange hopping process in an impurity band. Low temperature results down to 40K, from other authors, also imply the long range hopping process in doped ceramics.