Internal size effect in condensed BaTiO3 ferroelectric films

Polycrystalline BaTiO3 films of equal thickness and with various size of the coherent scattering regions prepared by rf sputtering are studied. A distinct correlation between the dielectric permittivity and the size of coherent scattering region is established. It is shown that at a critical size of the coherent scattering region, D*≈ 300 Å, the dielectric permittivity considerably decreases and the ferroelectric state becomes unstable. The data obtained are interpreted in terms of the lattice dynamical theory of size effects in ferroelectrics.