Abstract
The thermal and chemical expansivity of La1-xSrxFeO3-δ (x = 0.4) was measured using in situ powder neutron and synchrotron X-ray diffraction at temperatures between 932 K and 1170 K and oxygen partial pressures, PO2, between 10−19 bar and 0.1 bar, giving a wide range of oxygen non-stoichiometry from δ= 0.05 to 0.22. Changes in δ were measured independently using gas analysis. This PO2 and temperature range covers the material’s use as a chemical looping oxygen carrier, a sensor material and in solid oxide fuel cells. Thermal and chemical expansivities were found to be dependent on the oxygen non-stoichiometry, δ. For δ < 0.2 and T = 932–1050 K, the linear thermal expansivity was 5.72(4) × 10−5 Å/K and the linear chemical expansivity was 0.144(9) Å per unit change in δ. For δ > 0.2 and T = 973–1173 K, the linear thermal expansivity increases to 6.18(8) × 10−5 Å/K. For δ > 0.2, the linear chemical expansivity varies with both δ and temperature.
Highlights
Perovskite oxides such as strontium-doped lanthanum ferrite, La1xSrxFeO3-δ, have been investigated for use in various functional devices such as solid oxide fuel cell (SOFC) cathodes [1,2,3,4], oxygen permeation membranes [5], and chemical sensors [6,7,8] due to their high conductivity of both electrons and oxyide ions
Repeated oxidation and reduction of a crystalline oxygen carrier material (OCM) can cause relatively large changes in its unit cell parameters and can lead to decreased operational lifetime owing to decreased mechanical integrity
High temperature synchrotron X-ray diffraction (XRD) was used to determine expansivities to compare with those reported in previous work and our neutron diffraction experiments
Summary
Perovskite oxides such as strontium-doped lanthanum ferrite, La1xSrxFeO3-δ, have been investigated for use in various functional devices such as solid oxide fuel cell (SOFC) cathodes [1,2,3,4], oxygen permeation membranes [5], and chemical sensors [6,7,8] due to their high conductivity of both electrons and oxyide ions. In situ neutron and synchrotron X-ray powder diffraction studies were performed at temperatures between 932 K and 1170 K and PO2 between 10À19 bar and 0.1 bar under continuous gas flow, to determine the thermal and chemical expansivity of La0.6Sr0.4FeO3-δ over a wide range of oxygen non-stoichiometry from δ 1⁄4 0.05–0.22. The PO2 range extends to much lower oxygen partial pressures than previously studied This was coupled with analysis of the gas composition at the outlet of the system to determine the changes in δ caused by the different PO2 and temperature conditions. The use of gas analysis ensured that steady state was reached and that δ was well defined and corroborated by independent methods
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