Eliseev E. The pecularities of dielectric properties and phase diagrams of ferroelectric films and relaxors

The complex theoretical investigation of the nanoscale effects of the basic dielectric and polar characteristics of ferroelectric films and relaxor ferroelectrics has been performed. The distribution function of correlation radius in relaxor ferroelectrics has been consequently obtained within the framework of the statistical random field theory in strongly polarizable materials. Its temperature dependence for different ferroelectric states (ordered state, mixed ferro-glass state and dipole glass phase) has been investigated. The method of calculations of phase diagrams for solid solutions has been introduced. At first it has been proved, than films free energy can be rewritten in the form of the bulk one but with renormalized coefficients depending on temperature, film thickness and extrapolation lengths. If extrapolation lengths are much higher than the correlation one, the depolarization field does not influence significantly on the problem. It has been shown that ferroelectric films low-frequency susceptibility can be described as the analogous value for bulk system, but static susceptibility and eigen frequency significantly depend on film thickness. The soft mode frequency thickness dependence has been studied analytically in ferroelectric phase of the system.