Apparent Oxygen Uphill Diffusion in La0.8Sr0.2MnO3 Thin Films upon Cathodic Polarization

• Published in: ChemElectroChem Vol. 2; no. 10; pp. 1487 - 1494
• Main Authors: Huber, Tobias M., Navickas, Edvinas, Friedbacher, Gernot, Hutter, Herbert, Fleig, Jürgen
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01-10-2015; John Wiley and Sons Inc
• Subjects: cathodic bias; Diffusion; grain boundaries; Ions; Mass spectrometry; Thin films; tracer diffusion
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.201500167

The impact of cathodic bias on oxygen transport in La0.8Sr0.2MnO3 (LSM) thin films was investigated. Columnar‐grown LSM thin films with different microstructures were deposited by pulsed laser deposition. 18O tracer experiments were performed on thin film microelectrodes with an applied cathodic bias of −300 or −450 mV, and the microelectrodes were subsequently analyzed by time‐of‐flight secondary ion mass spectrometry. The 18O concentration in the cathodically polarized LSM microelectrodes was strongly increased relative to that in the thermally annealed film (without bias). Most remarkable, however, was the appearance of a pronounced 18O fraction maximum in the center of the films. This strongly depended on the applied bias and on the microstructure of the LSM thin layers. The unusual shape of the 18O depth profiles was caused by a combination of Wagner–Hebb‐type stoichiometry polarization of the LSM bulk, fast grain boundary transport and voltage‐induced modification of the oxygen incorporation kinetics,
Against the grain: Oxygen isotope depth profiles of voltage‐driven 18O incorporation exhibit very uncommon shapes resembling uphill diffusion; this is caused by the interplay of fast oxide‐ion diffusion along grain boundaries and stoichiometry polarization of La0.8Sr0.2MnO3 once the voltage is applied, which leads to a vacancy concentration gradient in the La0.8Sr0.2MnO3 grains.