Dynamics of KH2PO4 type ferroelectric phase transitions

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Abstract
We include the configuration energy in Kobayashi's theory for KDP-type ferroelectric crystals. The theory is then shown to be coherent from the thermodynamical point of view, as the order parameter and the frequency of the associated soft mode vanish at the same temperature. The results show that it is possible to have another kind of mixed ferroelectric, where the displacive phenomenon triggers the transition and induces an order-disorder phenomenon for the light ions (protons, deuterons). Great sensitivity to pressure of various static and dynamic relevant physical quantities suggests interesting experimental work on mixed ferroelectrics