Electrical properties and proton conduction of gadolinium doped ceria

The electrical properties and proton conduction of Gd_0.1Ce_0.9O_1.95 (10GCO) were investigated via impedance spectroscopy in different atmospheres and various gas concentration cells. In oxygen atmosphere, GCO is nearly a pure oxygen ionic conductor, while in hydrogen GCO behaves as a mixed conductor of oxygen ions, electrons and protons. Depending on the temperature, the total conductivity is usually enhanced by one to two orders of magnitude in hydrogen than in air/oxygen due to mixed conduction. By examining ionic transport properties of oxygen ions and protons using gas concentration cells we have discovered that the ionic transport properties depend largely on the gas atmospheres and change from one type to the other. Proton conduction generally exists in GCOs, and becomes significant in hydrogen atmospheres, which normally results in a contribution between 5 to 10 % of the total conductivity for 10 GCO. A maximum value of 17 % of the contribution by protons has been observed. The reduction of Ce⁴⁺ to Ce³⁺ of the sample in reduced atmospheres causes the formation of additional oxygen vacancies and electrons, associated also with the creation of protons. All these charge carriers are responsible for the electrical and transport properties of the investigated GCO materials. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.