A feedback model for relaxors

We develop a model to simulate the behavior of relaxors, e.g. their high permittivity in a broad temperature range. Our model is based on charges fluctuating thermally activated in intrinsically asymmetric double well potentials. The asymmetry is caused by disorder and can be modulated by a local field. The transition probabilities depend on the barrier height, the asymmetries of the double well potentials and on the local electric field. We use a mean local field which is the superposition of the applied field and a field proportional to the polarization due to the electrostatic interaction between the charges. In that way we get a feedback loop for the polarization. The dynamic permittivity is computed for systems of interacting charges in double well potentials with intrinsic asymmetry. The intrinsic asymmetry causes relaxor behavior: the permittivity as function of the temperature has a broad and high peak. The maximum of the permittivity decreases and is shifted to higher temperatures with increasing frequency.