Dielectric response of materials: extension to the Debye model

The Debye model is frequently used to explain the dielectric behaviour of m aterials. A good description of the experimental results is often obtained by using a distribution of relaxation times. In this work, it is proposed t o extend the Debye model to the depolarisation of two or more types of dipo les occurring simultaneously. With this procedure, it is observed that perm ittivity Cole-Cole plots appear with two or move semicircles overlapping ea ch other, and can give origin to one flattened semicircle. The same type of behaviour is observed for the impedance Cole-Cole plots, and both type of description of experimental data usually give very similar results. Assumin g that relaxation times ave thermally activated parameters, with positive o r negative activation energies depending on the type of the dipoles, it is possible to obtain dielectric responses similar to those of the paraelectri c regions of ferroelectric materials, and dielectric peaks on the permittiv ity-versus-temperature graphs similar to the relaxor behaviour found in som e ferroelectric materials. (C) 1999 Elsevier Science Limited All rights res erved.