Abstract
High‐temperature dc electrical conductivity and emf of oxygen concentration cells with A12O3 as the electrolyte were studied. The defect structure of α‐Al2O3 doped with Fe and Y was investigated to test an explanation proposed for the favorable effect of Y addition to super alloys (Fe, Cr, Ni, Al) which leads to well‐adherent and nonconvoluted A12O3 oxide scales. Results indicate that Y is a singly ionizable donor in Al2O3 and Y additions are effective in compensating Fe acceptors in A12O3 at iron concentrations up to the solubility limit of Y. At higher acceptor concentrations leading to a decrease in [V“‘Al] and an increase in [Al…i], incorporation of Y leads to a small increase in the concentration of V’”Al. This suggests that the mechanism proposed for the prevention of oxide scale spallation based on the Y donor action to suppress the bulk diffusion of aluminum interstitials created by the Fe acceptors cannot explain the effect. Energy level positions of Fe and Y in A12O3 are estimated, and values for electron and hole mobility at 1500°C are derived.
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