Ferroelectric phase transitions in the small particles in constrained conditions

The contribution of depolarizing electric fields and internal stress fields to the thermodynamics of phase transitions in a ferroelectric–dielectric composite material has been found. This contribution leads to renormalization [Formula: see text] and [Formula: see text] coefficients in the decomposition into a series of the order parameters for thermodynamic potential. It has been established that electric fields always decrease the phase transition temperature. The internal stresses can both increase or decrease the temperature of a first-order phase transition and the width of temperature hysteresis. In the case of the first-order transitions, internal stresses can cause a change in the order of phase transition with appropriate material parameters.