Growth, Microstructure and Electrochemical Oxidation of MBE-Grown C-Axis La(sub2)CuO(sub4) Thin Films

The growth, microstructure and electrochemical oxygen intercalation of {\em c}-axis La$_2$CuO$_{4+\delta}$ thin films on substrates with different lattice mismatch [SrTiO$_3$ (001) and SrLaAlO$_4$ (001) substrates] are compared. Except for the absence of planar defects in the latter case, the microstructural properties of both film types are very similar. For films on SrTiO$_3$, oxygen can be intercalated electrochemically into the grown {\em c}-axis thin film with a high diffusion coefficient ($D_{\rm ox} = 10^{-13} - 10^{-14}$~cm$^2$/s), and subsequently additional (00{\em l}) reflections, ${\em l} = 2n+1$, are observed by x-ray diffraction measurements. A double transition with a resistivity drop at $\simeq 55 - 58$~K --- suggesting a more strongly oxidized phase --- and a zero-resistance state at $\simeq 42$~K are found. For films on SrLaAlO$_4$, the value of $T_{\rm c}$ could not be raised further, as the films decompose during the anodic polarization. This comparison reveals the role of planar defects, and we propose an electrochemical oxidation mechanism that occurs in two steps: first oxygen is transported into the film by intercalation into the planar defects, then a slower oxygen diffusion into the interstitial sites occurs along the {\em ab}-planes. (Dept480)

By: Frederic Arrouy (Univ. of Zurich, Switz.), Jean Pierre Locquet, Erica J. Williams, Erich Maechler, Ruediger Berger, Christoph Gerber, Christophe Monroux (Inst. de Chimie de la Matiere, France), Jean Claude Grenier (Inst. de Chimie de la Matiere, France) and Alain Wattiaux (Inst. de Chimie de la Matiere, France)

Published in: Physical Review B, volume 54, (no 10), pages 7512-20 in 1996

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