Abstract
The dielectric response of the relaxor ferroelectrics PbMg1/3Nb2/3O3 and Sr0.998Ca0.002TiO3 is measured via the complex permittivity, ε(ω), and the relaxation of the field-cooled polarization in zero-field, P(t), respectively. Its polydispersivity is attributed to dynamically correlated domains with percolation size distribution. They are induced by spatial fluctuations of intrinsic quenched random-fields. Whereas activated dynamics prevails above T c, non-activated domain wall dynamics occurs below T c. This contrasts with the activated random-bond controlled ordering kinetics of field-induced domains in the diluted two-dimensional Ising antiferromagnet Rb2Co0.85Mg0.15F4.