Measurement of Bulk Oxygen Diffusivity in (La0.8Sr0.2)0.95MnO3±δ
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Strontium-doped lanthanum manganite is widely used as a cathode material for solid oxide fuel cells (SOFCs). In this study, the oxygen diffusivity in A-site-deficient (La0.8Sr0.2)0.95MnO3±δ (LSM-20) was measured as a function of temperature (600°C, 700°C, and 800°C) and oxygen partial pressure (0.03 atm, 0.16 atm, and 0.30 atm). Tracer (O-18) concentration profiles were measured in single-crystal epitaxial thin films of LSM-20 by time-of-flight secondary-ion mass spectroscopy (TOF-SIMS). The profile was fit to a diffusion equation to obtain the diffusivity of oxygen in bulk LSM-20 as a function of temperature and oxygen partial pressure. A defect model was used in conjunction with the experimental data to calculate the activation energies of oxygen migration, Schottky reaction, redox reaction, and charge disproportionation reaction in LSM-20. These calculated data were then used to calculate the Brouwer diagram of (La0.8Sr0.2)0.95MnO3±δ at 800°C, a typical operating temperature of SOFCs.
This work has been supported in part through the DOE SECA program under Contract No. DE-NT0004104. A portion of the research was performed at EMSL, a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory under Proposal 46707. The authors acknowledge the contributions of Dr. Tiffany Casper, Dr. Zihua Zhu, and Dr. Laxmikant Saraf at PNNL.