Effect of grain size on the grain boundary resistance of undoped barium titanate ceramics

The effect of grain size on the grain boundary resistance of undoped BaTiO₃ ceramics fired at 1270~1410°C was investigated, assuming cubic grains sharing their faces with adjacent grains. A two-step firing technique was used to produce samples of different grain sizes ranging from about 1 to over 40 μm. Grain boundary resistance values were estimated from the complex impedance plots of samples measured at about 455°C. It was found that the grain boundary resistivity is approximately constant and is in the range of 2.7×10^-3~2.8×10^-2 if the average grain size is larger than 1 μm. It was also found that the grain resistivity is in the range of 37~180 Ω-m² at 455°C when the grain is partially depleted of mobile charge. When the grain was smaller than about 1 μm, it was totally depleted of mobile charge, and, as a result, the grain boundary controlled the overall resistance. In this case, the grain boundary layer extended to the center of the grain, and the situation might be viewed as the disappearance of the grain