Calculation of phase diagrams for solid solutions of ferroelectrics

The integral equations for calculating ferroelectric and antiferroelectric phase transition temperatures, order parameters, and critical concentration s of solid solution components are derived. The electric dipoles randomly d istributed in the system are treated as sources of random fields. The rando m field distribution function is constructed taking into account the contri bution of nonlinear effects and the differences in the dipole orientations for different solid solution components. The dependence of the phase transi tion temperature on the composition of a binary solid solution in the ferro electric-antiferroelectric and ferroelectric-paraelectric systems is calcul ated. Numerical calculations are carried out for the PbTixZr1-xO3 and BaZrx Ti1-xO3 solid solutions. The results obtained are in good agreement with th e experimental phase diagrams of these systems. Analysis of the results ind icates that any solid solution containing ferroelectric (antiferroelectric) and paraelectric components transforms into a relaxor state at sufficientl y high concentrations of the paraelectric component. (C) 2001 MAIK "Nauka/ Interperiodica".