Characterisation of PSZ/Al2O3 composite coatings using electrochemical impedance spectroscopy

Impedance measurements have been made with metallic substrate as one electrode and a silver paint at top surface of the coating as another electrode. By using a small paint electrode, five separate relaxation frequencies have been observed corresponding to grain and grain boundary of partially stabilized zirconia (PSZ), Al2O3 in the PSZ matrix, a thermally grown oxide (TGO) layer, and the electrode effect. It was found that both electrode size and coating thickness had effects on the measured electrical properties of elements. The dependence of resistance on electrode size and coating thickness of the blocking effect is interpreted according to deformation of electric field. The spectral resolution and features in relation to the changes of electrical properties have been discussed in detail based on derived analytical equations.