Electrotransport-induced demixing in semiconducting (MnxFe1-x)(3)O-4

Electrotransport-induced demixing has been studied experimentally and theor etically on the system of semiconducting spinel ferrite, (Mn0.334Fe0.666)(3 )O-4 in a constant current condition at P-O2 = 10(-6) atm and 1200 degrees C where interstitial defects are prevailing. The degree of unmixing is dete rmined not only by the difference in diffusivity of the cations but also by their effective charge. The latter is, in turn, determined by the cross ef fect between electronic and ionic flows. It has been found that the charge of transport as a measure of this cross effect is at least alpha*=1.2 simil ar to 1.5 fox the cations. Their mean effective charge is thus reduced from 8/3 to 8/3-alpha*, consequently reducing the degree of unmixing by ca. 40% compared to what would otherwise be. (C) 1998 Published by Elsevier Scienc e B.V. All rights reserved.