Computation of relaxational dielectric polarization of composites

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Effective relaxational polarizations of dielectric composite materials are computed with a microscopic model based on the electrostatic interactions between charges and dipoles as well as based on the Boltzmann statistics. Input parameters of the simulations are the material structure, the polarizabilities of the atoms and molecules with induced dipole moment and the activation energies for charges which fluctuate thermally activated in double well potentials. The fluctuating charges yield the relaxational part of the polarization. The high frequency behavior of the system is determined by the induced dipoles. With iterative algorithms, the fields at the locations of all dipoles and double well potentials are calculated with respect to the fields of all charges and dipoles in the material. The electrodes are taken into account via the method of images for dipoles and charges. With the local fields the induced dipole moments are computed. The charge displacements in double well potentials are calculated using a dynamic Monte-Carlo method regarding the local fields. In this way the method inherently includes all interactions and all depolarizing fields within the material. Particularly with regard to composite materials, the topology, interfaces and the interaction between different phases are considered. We investigate single phase dielectrics and dielectric composites with different interior geometries. The composites are composed of interacting phases which can differ in their relaxational polarization behavior and in their high frequency responses. As the result we calculate polarization responses in the time domain on steps of the applied field and on oscillating applied fields. Frequency dependent complex permittivities are computed from the time domain polarization via Fourier transformation. They are compared to the results obtained by the calculation using oscillating fields. Furthermore the impact of a temperature gradient in a dielectric on its polarization is simulated.