Grain size dependence of the Rayleigh coefficients in barium titanate ceramics

Grain size dependence of the initial dielectric constant and Rayleigh coefficients of BaTiO3 ceramics with grain sizes from 0.5 mu m to 20 mu m have been studied. A region of Rayleigh law validity was observed for each grain size. The initial dielectric constant show a maximum for the ceramic with 2.5 mu m grain size and the Rayleigh coefficient increases with increasing the grain size. Using a statistical theory of the low field P(E) loop and the hypothesis of a maximum domain wall density at a critical grain size in ceramics, theoretical grain size dependencies with maxims for both the initial dielectric constant epsilon(in)(g) and Rayleigh coefficient a(g) have been derived.