Size effect on the dielectric susceptibility of ferroelectrics

Using Landau theory, the influence of size on the dielectric behaviour of ferroelectric films, cylinders and spheres has been investigated. For cylinders and spheres, a size-driven phase transition occurs and the dielectric susceptibility is always enhanced at small size. However for films, whether there is a size-phase transition depends on the surface ferroelectricity. Our calculations are in qualitative agreement with measurements on barium titanate and lead titanate.