A gas-tight electrochemical cell with flowing air was used to achieve O partial pressures that were as low as 10-16atm. It was found that, at high O partial pressures, interstitial O ions and electron holes were the predominant charge carriers. In the low O partial pressure range, O vacancies and electrons predominated. The ionic conductivity at 800C in air was 7S/cm, and the ionic transference number was 0.4. The defect dynamics were described in terms of a trivalence-to-divalence transition of Fe ions when the O partial pressure was reduced.

B.Ma, U.Balachandran, J.H.Park, C.U.Segre: Journal of the Electrochemical Society, 1996, 143[5], 1736-41