科研之友
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摘要
Mixed ionic-electronic conducting perovskite materials are of interest as solid oxide fuel cell electrodes, though improved surface exchange and diffusion coefficients are desired. As a first step towards compositional optimization of thin film (La1-xSrx)CoO3-delta, we present here fabrication and characterization of films with nominal composition of the end members: LaCoO3 and SrCoOx. Isotope exchange depth profiling allowed straightforward measurement of the surface exchange coefficient of the roughly 100 nm thick films. The surface exchange coefficient for LaCoO3 was measured to be 2.3 center dot 10(-8) cm center dot s(-1) at 400 A degrees C and 1.1 center dot 10(-7) cm center dot s(-1) at 500 A degrees C. The values for SrCoOx were significantly lower at 7.0 center dot 10(-10) cm center dot s(-1) at 400 A degrees C and 2.1 center dot 10(-9) cm center dot s(-1) at 500 A degrees C. The diffusion coefficient was predictably more difficult to measure using such thin samples. It could not be reliably determined for LaCoO3 at 400 A degrees C, but was about 2.4 center dot 10(-12) cm(2)center dot s(-1) at 500 A degrees C. The values measured for SrCoOx were again lower, at 2.9 center dot 10(-14) cm(2)center dot s(-1) at 400 A degrees C and 6.1 center dot 10(-14) cm(2)center dot s(-1) at 500 A degrees C. The diffusion and-especially-surface exchange coefficients are all somewhat higher than expected based on data from literature reports, but may be increased due to various thin film-related effects. It is shown that future isotope exchange measurements of thin films would benefit greatly from examining both the time dependence and depth dependence of isotope concentration.
- 出版日期2012-12
