Journal of the Electrochemical Society, Vol.142, No.10, 3483-3485, 1995
Anodic Oxide-Growth on Tantalum with Ac+dc Fields .2. Modeling and Theory
The small signal ac response of the ionic conductivity process, investigated in Part I, with its inductive phase relation between ionic current and field, is a manifestation of the dependence of the ionic current density on the previous history of the film. This history dependence is probably caused by structural changes in the oxide. Equations previously formulated to predict the ionic current density for all situations were modified to account for the observed behavior by introducing a distribution of relaxation times. The type of distribution found is consistent with structural changes in a glassy oxide. The relaxation times involved in the adjustment of the structure to a new field are expected to be a function of the field, temperature, and the state of the oxide. For the present experiments, since the state of the oxide corresponded to steady state (growth at constant current and field for long enough), tau(m) could be fitted by a function of field and temperature alone. The implications of the fact that tau(m) was close to inversely proportional to the ionic current density independent of temperature are discussed.