The effective field approach applied to ferroelectric phase transitions

A physical system experiences a phase transition when it goes from an ordered configuration (low temperature) to a disordered state (higher temperature). An order parameter is related to the corresponding conjugated field, that drives the system behavior. Some properties that are temperature dependent change dramatically at a so called critical temperature, indicating the point at wich the phase transition takes place. All the entities of the system contribute to the process, that is the reason why these type of processes are named cooperative phenomena.Therefore, it seems convenient to consider a mean or effective field approach as each entity is influenced, not only by an eventual external field, but for all the others.In this work we have assumed an effective field approach in order to explain some of the well-known characteristics of the pure and mixed ferroelectic crystals.