Electrical Properties of Proton-Conducting Ca2 + -Doped La2Zr2 O 7 with a Pyrochlore-Type Structure

Abstract

The electrical conductivity and the mean transport number of pyrochlore-type 0.03, 0.05) and were systematically studied as a function of temperature under wet hydrogen and oxygen atmospheres Under wet hydrogen atmosphere, pure proton conduction was observed below 873 K for both and systems. The proton conductivities at 873 K were and for and respectively. The proton conductivity of was approximately three times higher than that of although the number of positive charges introduced by doping was equal for the two samples. The three times higher proton conductivity of than could be attributed to the higher proton concentration dissolved in than in This may have been because the oxygen and/or its vacant sites responsible for the proton dissolution were different between and systems, i.e., the 8b and the 48f oxygen sites for and the 48f oxygen site for may have contributed to the proton dissolution. As a result, the proton conductivity of -doped depended on both the doping level and the doping site. Above 873 K under a wet hydrogen atmosphere, the mean transport number of oxygen ions increased with increasing temperature. Under a wet oxygen atmosphere, the positive hole was a dominant carrier for both systems, in contrast to under the wet hydrogen atmosphere. © 2001 The Electrochemical Society. All rights reserved.