Conduction Properties of Valve Metal-Oxide Systems

Abstract

A theory of cooperative ion transport in anodic oxide films on valve metals has been developed on the basis of a dielectric mosaic model. The oxide, which is "amorphous," is considered to be composed of very small crystallites or polymeric units. Ion transfer from one such unit to another is strongly influenced by the distribution of ions within these units since the field assisting the transfer will be a function of the polarization of the dielectric oxide medium. Tran- sient ionic conduction phenomena and anomalous charging currents arise as a result of the slow adjustment of the polarization of the medium to new con- ditions. Two mechanisms for the rate of change of the polarization are em- ployed, one involving thermally activated ion migration, the other being as- sociated with the large energies dissipated during an 1on transfer event. The equations arising from this model have been solved for a number of particular experimental conditions.