The size effect of ferroelectric materials is one of the most important issues to develop next-generation dielectric devices. In this paper, we reviewed our studies on the size effects of barium titante (BaTiO3) fine particles and ceramics. In the size effect of BaTiO3 fine particles, the maximum of dielectric permittivity was observed at a particle size of around 140 nm, and was explained by the composite structure model including a gradient lattice strain layer (GLSL) having a very high permittivity. In contrast, the grain size effect of BaTiO3 ceramics, where the permittivity showed a maximum at a grain size of about 1.1 μm, was interpreted as the superposition effect of domain-wall contributions and grain boundary effect.
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