PROTONIC CONDUCTION IN ACCEPTOR-DOPED CUBIC RARE-EARTH SESQUIOXIDES

Using ac conductivity and the concentration cell emf method, conductivity contributions from protons, native ions, and electrons have been measured as a function of temperature (560-degrees to 1156-degrees-C) in wet oxygen/air for the cubic systems Y2O3 + 1 mol% MgO, Sm2O3 + 1 mo CaO, Gd2O3 + 1 mol% CaO, and YYbO3 + 5 mol% CaO. All exhibit significant proton conductivities as well as native-ion and electronic conductivities at all temperatures. In wet atmospheres and reduced temperatures, the oxides dissolve protons to compensate for the acceptor doping, at the expense of native positive defects. This dissolution of protons seems to be relatively more favorable in oxides of smaller rare-earth cations (e.g., Y3+ and Yb3+). On the other hand, larger cations (e.g., Sm3+ and Gd3+) give higher proton mobilities. As compared to oxides of the true lanthanides with similar cationic radii, yttrium-containing oxides have lower proton mobilities.