Freezing of dipole dynamics in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 as evidenced by dielectric spectroscopy

Complex dielectric susceptibility (chi'+j chi ) has been studied at f = 10(-2)-10(-5) Hz in the relaxer ferroelectric 0.75Pb(Mg1/3Nb2/3)O-3-0.25PbTiO(3). In addition to the well known relaxer dispersion observed at temperatures around and below the temperature of permittivity maximum T-m, a new and comparatively weak dispersion has been disclosed at T > T-m. It is described by the 'universal relaxation law', chi = cot(n pi/2)chi' alpha f(n-1). The temperature dependence of the exponent n follows the Vogel-Fulcher relation, indicating a process of freezing into the nonergodic state.