Cation Doping of Oxide Ceramics Using Solid Oxide Electrochemical Doping: Evaluation of the SOED 2 Method

Electrochemical cation doping into oxide ceramics has been carried out using the solid oxide electrochemical doping (SOED 2, electro-bi-injection) method. The SOED 2 method consists of the anode(Ag)/M–betaʹʹ-Al2O3/ceramics/YSZ/cathode(Pt) electrolysis system, where the metal cation M and oxygen anion are simultaneously injected into the oxide ceramics so that electrical neutrality is maintained in the ceramics. Ceramics of three kinds of oxides with different conductive properties (YB2Cu3Oy, Fe2O3, and BaTiO3) were studied in doping experiments. In general, graded doping occurred independent of the conductivity type of the oxide ceramics at relatively high temperature because the migration rate of the oxygen anions is close to that of the metal cation in the grain boundaries of the ceramics at high temperature. As a result, the metal cation was graded on the anode side of the oxide ceramics. However, doping is too difficult at low temperature because the migration of oxygen anions is much faster than that of the cations at low temperature. As expected, doping results depended on the valence of the doped cation. The doping mechanism is discussed in detail.