Pinpoint doping using a β″-Al2O3 microelectrode as one application of the solid oxide electrochemical doping (SOED) method

Pinpoint metal cation doping was carried out using the solid oxide electrochemical doping (SOED) method, where a microelectrode of M-β″-Al2O3 as the solid electrolyte was used as a cationic source. Two different electrolysis systems were employed. One is the Ag (anode)/M-β″-Al2O3 (microelectrode)/doping target/Na-β″-Al2O3/Ag (cathode) electrolysis system, where the electrosubstitution of Mn+ for the cation in the target occurs under an electric field. The other used an oxide ion conducting solid electrolyte at the cathode side instead of Na-β″-Al2O3, where Mn+ can be injected into the target together with the injection of an oxide ion (electro-bi-injection). The pinpoint doping strongly depends on the conductive properties of the doping target and the valence of the dopant cation. Therefore, the cation doping into the alkali borosilicate glass occurs using only the former system because the glass shows a pure cationic conduction. In contrast, a cation can be doped into the superconducting Bi2Sr2CaCu2Oy ceramics using only the latter system because the electrosubstituion of a cation was difficult in an electron-conducting ceramics. In this case, the migration of the metal cations and the oxide ions primarily proceeds through the defects of ceramics (pore surfaces, grain boundaries, etc.). The monovalent cation can be easily injected into the doping target, while the divalent cation cannot be doped. The fact that the pinpoint distribution of the dopant can be controlled by the contact area between the microelectrode and the doping target indicates the migration of dopant was dominated by the potential distribution in the target materials under an electric field. As a result, we have achieved pinpoint doping on a 102-μm scale using the SOED method.