EXPERIMENTAL LIMITATIONS IN IMPEDANCE SPECTROSCOPY .4. ELECTRODE CONTACT EFFECTS

A 'spreading resistance' contact between electrode and specimen can in crease or even dominate the apparent bulk resistance of an electrocera mic specimen. For true point contacts, a single are will appear in imp edance spectra, whose diameter is essentially the spreading resistance due to the contact and whose time constant is identical to that of th e bulk, but with a correspondingly smaller capacitance. When a planar electrode with multiple point contacts is involved, a separate electro de are occurs whose diameter is due to spreading resistance, but whose capacitance tends to be dominated by the 'air gap' capacitance betwee n the electrode and the rough surface of the ceramic. In this study im pedance spectroscopy was employed to study the effects of temperature, oxygen partial pressure, and mechanical loading on the contact impeda nce of gold electrodes on nanophase cerium dioxide. Results were confi rmed by pixel-based computer simulations.