Electric Field-Induced Unmixing in Mixed Ferrite Spinel (Co,Fe)₃O₄

Unmixing of a semiconducting ferrite spinel, (Co0.203Fe0.797)3O4 in an electric field was examined at 1200oC in its disorder regimes of prevailing (cation) vacancies and interstitials, respectively. It has been found that Co becomes enriched at the cathode in the interstitial-prevailing regime and at the anode in the vacancy-prevailing regime, but to much smaller a degree than expected. This confirms that the direction and degree of unmixing is governed by the difference in electrochemical mobility of the competing cations, and the effective charges of the mobile cations are appreciably reduced from their formal ones by the cross effect between the mobile ions and electrons.