However electronic conductivity in fact is as small as 10 51C S. cm 51 .Therefore it can be assumed that the increase in total conductivity is generally attributed to the increase in ionic conductivity due to decrease in interior grain conductivity. Figure shows the dependent of the activation energy and the conductivity pre-exponential factor to the microstructure. In this study, activation energy and pre-exponential factor showed a reciprocal relation with the grain size where finer grains exhibited higher activation energy than coarse grains. analysis. The sample sintered at 1650 °C, while achieved the densification plateau, has the largest grain size, however, it is probable that at 𝑇 > 1600 °𝐶, grain coarsening followed by grain boundary broadening as well as pore size growth. Thus, migrating ions at the grain boundary pathways had been scattered and causing reduction in the measured total conductivity.