Impedance studies of layers with a vertical decay of conductivity or permittivity

Several types of dielectric layers on metals were investigated. It was obse rved that not only the CPE capacitance bur also the CPE exponent alpha chan ge if the thickness of the oxide layer, the thickness of the space charge l ayer or the penetration depth of water into an organic coating is changed. This behavior agrees with the predictions resulting from the theory of Youn g. The Young impedance can be considered as a more general model than the C PE for the description of the behavior of metals covered by dielectric laye rs. The measured frequency dependence of the phase angle phi can be explain ed with an exponential distribution of conductivity and/or permittivity acr oss the dielectric layer perpendicular to the surface. If cp is nearly inde pendent of frequency, the impedance response can be approximated by a simpl e CPE.