The ionic conduction in mixed ions (proton and oxide ion)-conducting solid electrolyte, BaCe0.9Y0.1O3-α, has been studied by complex impedance analysis method and H2 concentration cell technique over the temperature range from 600℃ to 1000℃. The ionic transport numbers (ti) of BaCe0.9Y0.1O3-α under different atmospheres were determined by studying the dependence of total conductivity on oxygen partial pressure, po2, and by measurement of the EMF of H2 concentration cell. At low oxygen partial pressure (<10 Pa), BaCe0. 9Y0.1O3-α was almost a pure ionic conductor (ti≈1),whereas at high oxygen partial pressure (10～10^5 Pa) it exhibits a mixed ionic and p- type electronic conduction (ti＜1). The ionic conductivity values determined under different atmospheres are higher than 10^-2 S·cm^-1. The high ionic conductivity under various atmospheres and high ionic transport number at low oxygen partial pressure suggest that BaCe0. 9Y0.1·O3-αmight be a satisfactory candidate for various electrochemical devices.

Key words: YTTRIUM OXIDE, BARIUM OXIDE, CERIUM OXIDE, ELECTROLYTE, ELECTRICAL CONDUCTIVITY, PEROVSKITE TYPE STRUCTURE, CONDUCTORS