A Chemla-type electrotransport experiment in magnetite, Fe3-delta O4

Abstract

We have performed a Chemla-type electrotransport experiment on magnetite, Fe3O4, from which the tracer diffusion coefficient of iron and its effective charge can be determined simultaneously. The experiment was conducted with radiotracer Fe-59 by measuring the spread and drift of the tracer source in a constant electric field at a temperature of 1200 degrees C and an oxygen activity of log(a(O2)) = - 4. The tracer diffusion coefficient and the effective charge of Fe in magnetite were determined from the tracer profiles using both the residual activity and the tracer sectioning method. While the tracer diffusion coefficient agrees well with the values reported in literature, the effective charge number of Fe was found to be + 2, in contrast to the average, formal charge number 8/3 of Fe in magnetite. This result can be explained either due to the interaction between ionic and electronic charge carriers which has been observed in other semiconducting oxides or due to a much higher mobility of Fe2+ compared to Fe3+.