BaCe0.5Zr0.4La0.1O3－α ceramic was prepared by high temperature solid state reaction. X-ray powder diffraction pattern shows that the ceramic is of a single orthorhombic phase of perovskite-type BaCeO3 and good stability in CO2 or water steam atmosphere at high temperature. Using the ceramic as solid electrolyte and porous platinum as electrodes, the conductivities of the material in different gases were measured by using ac impendence spectroscopy, and the ionic transport numbers in dry air, wet air and wet hydrogen were examined by using a gas concentration cell method in the temperature range of 500～900 ℃. The results indicate that the conductivities of the material increase with increasing the temperature and the oxygen partial pressure in the dry or wet gases. The material is a mixed conductor of oxide-ions and electronic holes with the oxide-ionic transport numbers of 0.685～0.147 in dry air. In wet air, the protonic transport number is 0.001～0.006, the oxide-ionic transport number is 0.618～0.164, and the material is a mixed conductor of protons, oxide-ions and electronic holes. In wet hydrogen atmosphere, the protonic transport number is unity and the material is a pure protonic conductor from 500 to 700 ℃. But in the temperature range of 800～900 ℃, the material exhibits a mixed conduction of protons and electrons with the protonic transport numbers of 0.957～0.954.

Key words: BaCe0.5Zr0.4La0.1O3－α, impedance spectroscopy, gas concentration cell, ionic conduction