Correlation Radius in Thin Ferroelectric Films

In the paper we present analytical calculations of the profiles and average values of the correlation radius of polarization fluctuations and generalized susceptibility in thin ferroelectric films with in-plane and out-of-plane polarization orientation. The contribution of polarization gradient, surface energy and depolarization field were taken into account. For the second order ferroelectrics the correlation radius and generalized susceptibility diverge at the film critical thickness as anticipated. The surface energy, inhomogeneous distribution of polarization and depolarization field related with incomplete screening govern the size effects such as thickness-induced phase transition, corresponding correlation radius and a generalized susceptibility divergence in the phase transition point.