Effect of Impurities on the Defects in Oxides and Their Relationship to Oxidation of Metal

Abstract

Abstract The defect structure of the oxygen-deficient oxides of Nb2O5, Ta2O5, and ZrO2 are discussed. It is suggested that the oxygen vacancies are probably the important defects, except possibly at the most oxygen deficient part of the homogeneity ranges where interstitial cations may predominate. At high oxygen pressures, (small deviations from stoichiometry) effects of impurities become important and, in reported studies, probably determine the point defect concentration. Oxidation of Nb, Ta, Zr, resulting in growth of compact scales of Nb2O5 Ta2O5, and ZrO2, is discussed on the basis of these considerations. It is shown that effects of impurities may explain apparent deviations from the simple behavior predicted by the Wagner theory. It is emphasized that analysis and control of impurities is essential in interpretation of defect structures of oxides and defect-controlled properties and reactions.