High-temperature dielectric response of ferroelectric relaxors

It has long been considered that polar nanoregions in relaxors form at Burns temperature T_d - 600K. High-temperature dielectric investigations of Pb(Mg_1/3Nb_2/3) O₃ (PMN) single crystal, PMN-PbTiO₃ ceramics, and (Pb,La) (Zr,Ti)O₃ ceramics reveal, however, that dielectric dispersion, detected around 600K, is due to the Maxwell-Wagner-type contributions of surface layers. The intrinsic response was analyzed in terms of the universal scaling, taking into account the asymptotic and the correction-to-scaling behavior, and the results imply much higher T_d or formation of polar nanoregions in a broad temperature range. High values of the dielectric constant indicate, however, that polar order already exists at the highest measured temperatures of 800K. The obtained critical exponents indicate critical behavior associated with universality classes typically found in spin glasses.