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Cooperative mechanisms of fast-ion conduction in gallium-based oxides with tetrahedral moieties.

By E. Kendrick, John Kendrick, K.S Knight, M.S. Islam and P.R. Slater

Abstract

NoThe need for greater energy efficiency has garnered increasing support for the use of fuel-cell technology, a prime example being the solid-oxide fuel cell1, 2. A crucial requirement for such devices is a good ionic (O2- or H+) conductor as the electrolyte3, 4. Traditionally, fluorite- and perovskite-type oxides have been targeted3, 4, 5, 6, although there is growing interest in alternative structure types for intermediate-temperature (400¿700 °C) solid-oxide fuel cells. In particular, structures containing tetrahedral moieties, such as La1-xCaxMO4-x/2(M=Ta,Nb,P) (refs 7,8), La1-xBa1+xGaO4-x/2 (refs 9,10) and La9.33+xSi6O26+3x/2 (ref. 11), have been attracting considerable attention recently. However, an atomic-scale understanding of the conduction mechanisms in these systems is still lacking; such mechanistic detail is important for developing strategies for optimizing the conductivity, as well as identifying next-generation materials. In this context, we report a combined experimental and computational modelling study of the La1-xBa1+xGaO4-x/2 system, which exhibits both proton and oxide-ion conduction9, 10. Here we show that oxide-ion conduction proceeds via a cooperative 'cog-wheel'-type process involving the breaking and re-forming of Ga2O7 units, whereas the rate-limiting step for proton conduction is intra-tetrahedron proton transfer. Both mechanisms are unusual for ceramic oxide materials, and similar cooperative processes may be important in related systems containing tetrahedral moieties

Topics: Fuel-cell technology, Tetrahedral moieties, La1-xBa1+xGaO4-x/2 system,, Cooperative mechanisms, Fast-ion conduction
Year: 2007
DOI identifier: 10.1038/nmat2039
OAI identifier: oai:bradscholars.brad.ac.uk:10454/3920
Provided by: Bradford Scholars
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