Development of ferroelectric mixed states in a random field of static defects

A para→ferroelectric stress-free transition in a random field of static defects is studied by the computer simulation method. It is shown that the electrostatic dipole–dipole interaction may produce in the ferroelectric transition the same “martensitelike” effects as the strain-induced interaction in the martensitic transition. These effects are the formation of the mixed two-phase equilibrium between the ferroelectric and paraelectric phases, the thermal hysteresis, and the loss of ergodicity. The origin of the mixed state is discussed. It is shown that the free energy hypersurface forms a multiplicity of local minima corresponding to the metastable and stable states similar to those in a spin-glass system. The hysteresis loop obtained in computer simulations is a locus of projections of the local free energy minima points on the hysteresis loop plane. The pre-transitional mixed states predicted in this simulation can be attributed to the relaxor state observed in many ferroelectric materials.