Figure 3. Voltage profiles.

(a) Initial voltage profile across a bare YSZ substrate compared with the profile across a 51 nm thick In₂O₃-on-YSZ sample when a 1.6 volt battery is connected to electrodes 1 and 7 at 330 °C (electrode configuration shown in Fig. 1). Minimal contact resistances are present initially. (b) The voltage profiles after 5 min (at steady state) for the same two samples. For the bare YSZ substrate, a large contact resistance has developed at the negative electrode (where oxygen entry occurs). A smaller contact resistance appears at the positive electrode (oxygen exit). A Schottky-type resistance appears at the positive electrode of the In₂O₃-on-YSZ sample. As a result of these resistances, a voltage drop develops between YSZ and the In₂O₃ film, with the substrate at a higher potential than the film. (c) The voltage profile that develops across the In₂O₃ /YSZ interface causes oxygen ions to move across the interface from In₂O₃ to YSZ. A screening charge appears in the In₂O₃ film near the interface. This interfacial electron doping increases the conductivity of the In₂O₃. In the YSZ, charge neutrality is maintained by mobile excess oxygen ions moving away from the interface.