Determination of Non-Stoichiometry in Mixed Conducting Oxide Thin Films of Arbitrary Chemistry

The dependence of oxygen non-stoichiometry on oxygen partial pressure and temperature is critical to many of the applications of non-stoichiometric oxides in  electrochemical energy conversion processes. It has been increasingly recognized that electrochemical methods, in particular, AC impedance spectroscopy, can be used to evaluate this non-stoichiometry. The method is particularly useful for determining the properties of thin films, for which conventional thermogravimetric methods are inapplicable. To date, analysis of the ACIS data to extract non-stoichiometry values has relied on application of various simplifying assumptions for the thermodynamic behavior, limiting the approach to oxides with ideal solution behavior.  In this work, we determine the oxygen non-stoichiometry of cerium oxide, which displays non-ideal behavior under certain thermodynamic conditions. The chemical capacitance of single crystal, epitaxial thin films of cerium oxide deposited on yttria stabilized zirconia substrates is measured and related to the oxygen non-stoichiometry using thermodynamic principles. This work will demonstrate the validity of the chemical capacitance measurements to reliably extract non-stoichiometry of a generalized oxide system.