Thermodynamics and Dielectric Properties of Rb(H1−xDx)2PO4Mixed Ferroelectrics

We researched the Rb(H 1-x D x ) 2 PO 4 mixed crystals within the framework of the proton ordering model. For the proton ordering model with and without tunnelling in the four-particle cluster approximation for the short-range interaction and in the molecular field approximation for the long-range interaction the expressions for thermodynamic and static dielectric properties were presented. The procedure for determination of the theory model parameters was proposed and on the basis of the derived parameters the thermodynamic and static dielectric characteristics were calculated. The results were compared with the experimental ones. The problem of application of the mean crystal approximation to investigation of the disordered Rb(H 1-x D x ) 2 PO 4 crystals was examined.