IMF2017

The percolation theory is often used to interpret the sequence of phases which is observed in relaxors with the change of temperature. In relaxors the polar nanoregions growing upon cooling from paraelectric to relaxor phases are considered as finite percolation clusters which transform to infinite cluster at the percolation threshold temperature associated with the glassy freezing temperature or the ferroelectric Curie temperature. In the present work we show that in relaxor ferroelectric solid solutions the percolation behavior can be observed not only for the size of polar clusters as a function of temperature, but also for the size of compositional clusters as a function of concentration of ferroactive ions. Using the experimental techniques of x-ray diffraction, dielectric spectroscopy and the measurements of polarization-field hysteresis loops, we studied the solid solutions of classical perovskite ferroelectric (1-x)BaTiO₃ -xABO₃ wwhere ABO₃ =BaZrO₃, BaSnO₃, BaHfO₃, and DyFeO₃. The analysis of experimental data based on the percolation theory revealed the existence of a critical concentration, x_c, which is larger than the relaxor-to-normal ferroelectric crossover concentration and above which the infinite percolation cluster and the related relaxor phase cannot be developed. The temperature of the transition into the relaxor ferroelectric cluster state was found to follow the critical behavior T*~(x_c - x)^ζ with the critical exponent ζ = 0.5. The characteristics of polar clusters are estimated from the electric field and frequency dependences of polarization.