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Abstract
The random field based model for calculation of mixed systems of ferroelectric relaxors is proposed. Different orientations of electric dipoles related to different solid solution components and contribution of random field nonlinear and correlation effects were taken into account. Calculations of transition temperature Tc and order parameters concentrational and temperature dependence were performed. The integral equations for these quantities calculation were derived. The theory was applied for description of mixed (PSN)1−x (PST)x with different degree of order and (PMN)1−x(PST)x systems. The higher Tc value for more disordered (PSN)1−X(PST)x system in the region 0 ≤ x < 0,5 was shown to be related to larger nonlinearity coefficient of PSN in comparison with PST. Temperature dependent concentration of morphotropic region existence was obtained in (PMN)1−x(PT)x. Numerical calculations with the fitting parameters derived mainly from Tc values of solid solution components describes pretty good observed phase diagram of both aforementioned mixed systems of ferroelectric relaxors.