Fig. 2 illustrates, for this sample

Fig. 2 illustrates, for this sample, the evolution of the bulk and grain boundary conductivity as function of temperature. Two distinct regimes of conductivities operating in two different temperature zones can be distinguished. In the low temperature range < 200 °C, the bulk conductivity is observed to be slightly higher. For this temperature range the total conductivity is therefore limited by the grain boundary. At 200°C, the curves intersected and the two contributions exhibit a same conductivity level. A noticeable change occurred for temperatures higher than 200 °C, for which the total conductivity is limited by the bulk since the grain boundary conductivity is actually higher.