The electrical conductivity and the mean transport number of pyrochlore-typc (La2-aCaa)Zr2O7 δ (x = 0.15, 0.03, 0.05) and La2(Zr2-a Caa)O7-δ (x = 0.015) were systematically studied as a function of temperature under wet hydrogen and oxygen atmospheres (PH2O = 1.7-2.5 ×103 Pa). Under wet hydrogen atmosphere, pure proton conduction was observed below 873 K for both (La2 aCax)Zr2O7-δ and La2(Zr2 aCaa)O7-δ systems. The proton conductivities at 873 K were 6.8 X 10-2 and 1.0 × 10-2 S m-1 for (La1.95Ca0.05)Zr2O7-δ and La2(Zr1.985Ca0.015)O7-δ. respectively. The proton conductivity of (La1.97Ca00.3)Zr2O7-δ was approximately three times higher than that of La2(Zr1.985Ca0.015)O7 δ, although the number of positive charges introduced by Ca2+ doping was equal for the two samples. The three times higher proton conductivity of (La1.97Ca0.03)Zr2O7 δ than La2(Zr1.985Ca0.015)O7 δ could be attributed to the higher proton concentration dissolved in (La1.97Ca0.03)Zr2O7-δ than in La2(Zr1.985Ca0.015)O7 δ This may have been because the oxygen and/or its vacant sites responsible for the proton dissolution were different between (La2 ,Caa)Zr2O7 δ and La2(Zr2-aCax)O7-δ systems, i.e., the 8b and the 48f oxygen sites for (La2 a,Ca2)Zr2O7 δ and the 48f oxygen site for La2(Zr2-a.Caa)O7. δ may have contributed to the proton dissolution. As a result, the proton conductivity of Ca2+-doped La2Zr2O7 depended on both the Ca2+ doping level and the Ca2+ 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.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry