Statics and dynamics of incommensurate-commensurate phase transitions in A2BX4 type crystals

A unified treatment has been constructed which gives a perspective view of incommensurate(IC)-commensurate (C) phase transition schemes in A2BX4 type crystals. We have shown that a microscopic treatment based on 'Extended Antiferroelectric Interaction Ising' model can explain most of the observed features of IC-C phase transitions. Within this model, each substance is characterized by a point in a two-dimensional interaction parameter space. The unified view has been visualized by constructing a distribution map of the representative points of the hitherto observed materials in this interaction parameter space. The kinetic process of IC-C phase transition in real crystals is discussed in terms of the dislocation loop in soliton lattices.