La0.2Sr0.8Cu0.1Fe0.9O3-δ and La0.2Sr0.8Cu0.2Fe0.8O3-δ both exhibit cubic perovskite structures with lattice parameters a = 0.38711 and 0.38694 nm, respectively. The initial oxygen non-stoichiometry, δ, of the as-synthesized materials was 0.24 for the sample with 10% Cu and 0.34 for 20% Cu. La0.2Sr0.8Cu0.1Fe0.9O3-δ has a lower p O (2) stability limit at 1x10-4 atm, whereas La0.2Sr0.8Cu0.2Fe0.8O3-δ starts to decompose at 1x10-3 atm. The conductivity is approximately 10 S cm-1 and it decreases with decreasing p O (2) from 1 atm to the lower p O (2) stability limit, following a 1/4 power p O (2) dependence for temperatures above 800 K. The activation energy in O2 is 1-2 kJ mol-1 and this increases to about 10 kJ mol-1 for the lower p O (2) limit. The Seebeck coefficient is very small, usually within ±15 μV K-1 of zero. Below 650 K, the weight is constant with temperature, whereas above 750 K δ increases with increasing temperature, causing an increase in thermal expansion. The thermal expansion coefficient below 650 K is approximately 15x10-6 K-1, and approximately 30x10-6 K-1 above 750 K.


Materials Science and Engineering

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Publication Date

01 Jan 2000