Defect Chemistry and Electrochemical Properties of BaZrO₃ Heavily Doped with Fe

To explore a novel concept of bi-percolating mixed conductor of proton and hole for a cathode material of solid oxide fuel cell (SOFC), we have studied a BaZrO3 heavily doped with Fe. The oxygen non-stoichiometry and electrical conductivity of BaZr1- xFexO3-δ with various x values have been prepared and examined by a thermogravimetry and ac two-probe impedance method as a function of temperature and Po2. At high oxygen partial pressures,the dominant charge carrier is estimated as holes, and the hole conductivity that exhibits a nonlinearity against the Fe concentration and marked increase at the percolation threshold is governed by a bond-percolation of Fe-O network. The effect of hydration on the electrical conductivity suggests that BaZr1-xFexO3-δ exhibits a mixed protonic-electronic conducting behavior in humidified conditions at lower temperature range.