DEVELOPMENT OF FERROELECTRIC MIXED STATES IN A RANDOM-FIELD OF STATICDEFECTS

A para-->ferroelectric stress-free transition in a random field of sta tic defects is studied by the computer simulation method. It is shown that the electrostatic dipole-dipole interaction may produce in the fe rroelectric transition the same ''martensitelike'' effects as the stra in-induced interaction in the martensitic transition. These effects ar e the formation of the mixed two-phase equilibrium between the ferroel ectric and paraelectric phases, the thermal hysteresis, and the loss o f 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 simulat ions is a locus of projections of the local free energy minima points on the hysteresis loop plane. The pre-transitional mixed states predic ted in this simulation can be attributed to the relaxer state observed in many ferroelectric materials. (C) 1998 American institute of Physi cs.