Electrode noise in beta aluminas

Experimental contact noise spectra of Na β″ alumina and Ag β″ alumina ceramics at room temperature exceed low-frequency thermal noise for both blocking and ohmic electrodes. Contact noise spectra above 102 Hz for ohmic electrodes of sodium amalgam and NaI in propylene carbonate agree with Nyquist noise levels determined from ac impedance measurements, and the low-frequency excess noise is shown to be associated with nonequilibrium electrochemical processes. Similar effects are found for ohmic silver amalgam and aqueous AgNO3 electrodes on Ag β″ alumina. Greatly increased voltage fluctuations are observed to accompany current in the sample, and both contact current noise and bulk granular current noise have similar characteristics. A total dc charge flow fo 25 C/cm2 at sodium amalgam electrodes to Na β″ alumina increases both contact and current noise many orders of magnitude and can be returned to initial levels by equivalent reverse charge flow. No corresponding changes in conventional experimental measurements, e.g., current-voltage characteristics, are detected.