Ionic Conduction in Ba_0.95Ce_0.8Ho_0.2O_3−α

Ba_0.95Ce_0.8Ho_0.2O_3−α was prepared by high temperature solid-state reaction. X-ray diffraction (XRD) pattern showed that the material was of a single perovskite-type orthorhombic phase. Using the material as solid electrolyte and porous platinum as electrodes, the measurements of ionic transport number and conductivity of Ba_0.95Ce_0.8Ho_0.2O_3−α were performed by gas concentration cell and ac impedance spectroscopy methods in the temperature range of 600–1000 °C in wet hydrogen, dry and wet air respectively. Ionic conduction of the material was investigated and compared with that of BaCe_0.8Ho_0.2O_3−α. The results indicated that Ba_0.95Ce_0.8Ho_0.2O_3−α was a pure protonic conductor with the protonic transport number of 1 during 600–700 °C in wet hydrogen, a mixed conductor of protons and electrons with the protonic transport number of 0.97–0.93 in 800–1000 °C. But BaCe_0.8Ho_0.2O_3−α was almost a pure protonic conductor with the protonic transport number of 1 in 600–900 °C and 0.99 at 1000 °C in wet hydrogen. In dry air and in the temperature range of 600–1000 °C, they were both mixed conductors of oxide ions and electronic holes, and the oxide-ionic transport numbers were 0.24–0.33 and 0.17–0.30 respectively. In wet air and in the temperature range of 600–1000 °C, they were both mixed conductors of protons, oxide ions and electronic holes, the protonic transport numbers were 0.11–0.00 and 0.09–0.01 respectively, and the oxide-ionic transport numbers were 0.41–0.33 and 0.27–0.30 respectively. Protonic conductivity of Ba_0.95Ce_0.8Ho_0.2O_3−α in both wet hydrogen and wet air was higher than that of BaCe_0.8Ho_0.2O_3−α in 600–800 °C, but lower in 900–1000 °C. Oxide-ionic conductivity of the material was higher than that of BaCe_0.8Ho_0.2O_3−α in both dry air and wet air in 600–1000 °C.