Cross Effect Between Ion and Electron Flows in Fe_3–δO₄

The effective valence,of mobile cations (Fe²⁺, Fe³⁺) in semiconducting Fe₃O₄was determined at elevated temperatures via Tubandt-type electrotransport experiments in association with the literature data on the cation diffusivity and total electrical conductivity. It has been found that the value forvaries systematically from below 2 up to 3 with oxygen partial pressure at a fixed temperature. The effective valence is determined not only by the mobility difference of Fe²⁺and Fe³⁺ionsbut also by the cross effect between the cations and electrons upon their transfer. A value ofbetween 2 and 3 may be attributed to the mobility difference between Fe²⁺and Fe³⁺ions even in the absence of the cross effect, but the values of< 2 clearly indicate that the cross effect is in play in Fe₃O₄.