Abstract
The possibility to control oxygen transport in one of the most promising solid oxide fuel cell cathode materials, La0.6Sr0.4CoO3−δ, by controlling lattice strain raises questions regarding the contribution of atomic scale effects. Here, high-resolution transmission electron microscopy revealed the different atomic structures in La0.6Sr0.4CoO3−δ thin films grown under tensile and compressive strain conditions. The atomic structure of the tensile-strained film indicated significant local concentration of the oxygen vacancies, with the average value of the oxygen non-stoichiometry being much larger than for the compressive-strained film. In addition to the vacancy concentration differences that are measured by isotope exchange depth profiling, significant vacancy ordering was found in tensile-strained films. This understanding might be useful for tuning the atomic structure of La0.6Sr0.4CoO3−δ thin films to optimize cathode performance.
Highlights
The possibility to control oxygen transport in one of the most promising solid oxide fuel cell cathode materials, La0.6Sr0.4CoO3−δ, by controlling lattice strain raises questions regarding the contribution of atomic scale effects
In-plane tensile-strained epitaxial La0.8Sr0.2CoO3−δ showed a strong enhancement of the oxygen diffusion coefficient compared to a compressively strained La0.8Sr0.2CoO3−δ epitaxial layer[9]
An activation effect on the surface exchange coefficient is observed[9]. These differences are determined by at least two possible strain effects convoluted in the isotope exchange data: (i) a change in the migration barrier for the mobile oxygen species in certain directions and (ii) a strain-induced change of the oxygen vacancy formation enthalpy resulting in a higher concentration of vacancies
Summary
The possibility to control oxygen transport in one of the most promising solid oxide fuel cell cathode materials, La0.6Sr0.4CoO3−δ, by controlling lattice strain raises questions regarding the contribution of atomic scale effects. An activation effect on the surface exchange coefficient is observed[9] These differences are determined by at least two possible strain effects convoluted in the isotope exchange data: (i) a change in the migration barrier for the mobile oxygen species in certain directions and (ii) a strain-induced change of the oxygen vacancy formation enthalpy resulting in a higher concentration of vacancies. The latter effect may explain the measured higher surface exchange coefficient in tracer experiments on in-plane tensile-strained LSCO. Local crystal lattice changes observed by TEM in combination with analysis of the oxygen vacancy concentration and the diffusion coefficient measurements shed new light on the relationship of local crystal structure and composition with macroscopic electrochemical properties
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