Domain walls and phase transitions in finite size systems

Within the phenomenological description we study the surface effect around the phase transition temperature. In the case of compensated induced charges the phase transition shifts to lower or higher temperatures depending on the properties of the surface. The properties of domain walls depend on the grain size and it is shown that the domain walls do not exist in small enough particles. The depolarization fields can also cause the decrease of the phase transition temperature. In the low-temperature phase the multi-domain state is favored and the depolarization fields decrease the dielectric response.