Abstract: Fine-grained pure BaTiO₃ ceramics with homogeneous microstructures were obtained at 900℃
by means of a new sintering method---Spark Plasma Sintering (SPS). The result of HRTEM analysis shows that there are only 180℃ domains exiting in
the grains and the thickness of grain boundary is approximately two times of the crystal lattice constant. Meanwhile some twin grains can be found
in the micrographs, and an obvious dependence of dielectric constant on grain sizes obtained on the basis of measuring the dielectric properties of the
fine-grained ceramics. The existence of twins is one of the reasons that result in the dielectric constant of the fine-grained ceramics
decreasing not sharply. This effect cannot be accurately fitted by the common series-parallel model.

Key words: HRTEM, dielectric properties, grain-size effect