ELECTRICAL-CONDUCTIVITY AND OXYGEN SEMIPERMEABILITY OF TERBIA AND YTTRIA-STABILIZED ZIRCONIA

This paper reports an electrochemical study on terbia and yttria stabi lized zirconia. (Tb, Y)-ZrO2 solid solutions with a fluorite type stru cture were prepared by using citrate synthesis and sintered at 1500-de grees-C. They are mixed electronic and oxygen ionic conductive, as wel l as oxygen semipermeable materials at elevated temperatures. The tota l electrical conductivity reaches 3.8 S m-1 at 900-degrees-C and the o xygen permeation is about 6.5 x 10(-6) mol m-2 s-1 at 1100-degrees-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 ris es above 10(-2) atm. This is ascribed to the defect association and th e predomination of oxygen ionic conductivity. The oxygen semipermeatio n is proportional to the square root of the oxygen partial pressure, a nd is not influenced by the variation of oxygen ionic or electronic co nduction. The results indicate that the surface exchange reaction is m ost probably the rate limiting step for the oxygen semipermeation.