Electrical conductivity and oxygen semipermeability of terbia and yttria stabilized zirconia

This paper reports an electrochemical study on terbia and yttria stabilized zirconia. (Tb, Y)-ZrO₂ solid solutions with a fluorite type structure were prepared by using citrate synthesis and sintered at 1500°C. They are mixed electronic and oxygen ionic conductive, as well as oxygen semipermeable materials at elevated temperatures. The total electrical conductivity reaches 3.8 S m^–1 at 900°C and the oxygen permeation is about 6.5 × 10^–6 mol m^–2 s^–1 at 1100°C. The electrical conductivity of zirconia doped with a total of 30 mol % of terbia and yttria increases with oxygen partial pressure when P _{O 2} is below 10^–2 atm, and decreases as the oxygen partial pressure rises above 10^–2 atm. This is ascribed to the defect association and the predomination of oxygen ionic conductivity. The oxygen semipermeation is proportional to the square root of the oxygen partial pressure, and is not influenced by the variation of oxygen ionic or electronic conduction. The results indicate that the surface exchange reaction is most probably the rate limiting step for the oxygen semipermeation.