Niobium Anodic Oxide Films: Effect of Incorporated Electrolyte Species on DC and AC Ionic Current

Abstract

Ellipsometric measurements on anodic oxide films grown on niobium in phosphoric acid were found to show behavior characteristic of films consisting of two layers, but films grown in chloride solution showed the behavior typical of uniform films. It was concluded that as with tantalum, phosphate but not chloride ions are taken up in the outer part of the film, which grows by metal ion motion. The logarithm of the steady‐state current density was linear in the field in the oxide for films grown in chloride solution and nonlinear for films formed in phosphate solution. It is concluded that, as with tantalum, the nonlinearity for some electrolyte solutions is caused by incorporation of electrolyte species in the outer part of the films rather than being a fundamental feature of the ionic transport process. The small signal ac response of the ionic current density was studied for both electrolyte solutions. These measurements gave information on steady‐state and stepped field kinetics and on the distribution of relaxation times involved in the transients observed when the current or field is suddenly changed. The steady‐state and stepped field admittivities from the ac + dc measurements were normalized by the dielectric permittivities of the films grown in the different solutions. © 2000 The Electrochemical Society. All rights reserved.

Preparation of Tantalum Anodic Oxide Film in Citric Acid Solution - Evidence and Effects of Citrate Anion Incorporation

“…Li et al reported that the dielectric constant of oxide is affected by the amount of anion incorporated into the anodic oxide film. 32) It is reasonable to consider that the amount of anion incorporated into the anodic oxide film is higher as the electrolyte concentration is increased. As a result, the ionic species in the oxide film would increase the DOS of the local states, which in turn influence the differential capacitance.…”

Growth of barrier-type anodic films on magnesium in ethylene glycol electrolytes containing fluoride and water

“…The similar values in both films are reasonable since MgF 2 is present predominantly in both films. It is interesting that the incorporation of phosphate increases the relative permittivity of the present fluoride-based anodic films on magnesium, although the incorporation of phosphate often reduces the relative permittivity of oxide-based anodic films [46]. This may be partly due to the increased oxygen content in the phosphate-containing anodic films; the oxide-based anodic films have higher relative permittivity compared with fluoride-based anodic films.…”

Physicochemical characterization of passive films on niobium by admittance and electrochemical impedance spectroscopy studies

“…From the slope of such a plot, it is possible to derive the anodizing ratio A, i.e. the inverse of anodizing electric field A = 1/F el , according to the relation: where ε is the dielectric constant of a-Nb 2 O 5 , assumed equal to 42 [3,20] and ε 0 is the vacuum permittivity. An anodizing ratio of 26.8Å V −1 was obtained in agreement with data reported in Refs.…”