In this paper, we present a microscopic model for heterogeneous ferroelectric and an order parameter for relaxor phase. We write a Landau theory based on this model and its application to ferroelectric PbFe1/2Ta1/2O3(PFT) and antiferroelectric NaNbO3:Gd. We later discuss the coupling between soft mode and domain walls, soft mode and quasi‐local vibration and resulting susceptibility function. © 2003 American Institute of Physics