Experimental limitations in impedance spectroscopy: Part IV. Electrode contact effects

A 'spreading resistance' contact between electrode and specimen can increase or even dominate the apparent bulk resistance of an electroceramic specimen. For true point contacts, a single arc will appear in impedance spectra, whose diameter is essentially the spreading resistance due to the contact and whose time constant is identical to that of the bulk, but with a correspondingly smaller capacitance. When a planar electrode with multiple point contacts is involved, a separate electrode arc occurs whose diameter is due to spreading resistance, but whose capacitance tends to be dominated by the 'air gap' capacitance between the electrode and the rough surface of the ceramic. In this study impedance spectroscopy was employed to study the effects of temperature, oxygen partial pressure, and mechanical loading on the contact impedance of gold electrodes on nanophase cerium dioxide. Results were confirmed by pixel-based computer simulations.