High-resolution transmission electron microscopy observations of La 2 Zr 2 O 7 thin layers on LaAlO 3 obtained by chemic
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roff and C. Millon Laboratoire des Mate´riaux et du Ge´nie Physique (LMGP)—UMR 5628 CNRS—Grenoble INP, Grenoble 38016, France; and Consortium de Recherche pour l’Emergence de Technologies Avance´es (CRETA)—Centre National de la Recherche Scientifique (CNRS) UPS2070, Grenoble 38042, France
S. Morlens Consortium de Recherche pour l’Emergence de Technologies Avance´es (CRETA)—Centre National de la Recherche Scientifique (CNRS) UPS2070, Grenoble 38042, France
P. Bayle-Guillemaud CEA-Grenoble, INAC/SP2M/LEMMA, Grenoble 38054 Cedex 9, France
F. Weiss Laboratoire des Mate´riaux et du Ge´nie Physique (LMGP)—UMR 5628 Centre National de la Recherche Scientifique (CNRS)—Grenoble INP, Grenoble 38016, France (Received 30 June 2008; accepted 11 December 2008)
La2Zr2O7 (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. LZO can crystallize into two similar structures: fluorite or pyrochlore. Coated conductor application focuses on pyrochlore structure because it is a good barrier against oxygen diffusion. Classical x-ray diffraction is not able to separate the contribution of these two structures. Transmission electron microscopy and high-resolution transmission electron microscopy were used to determine the local distribution of these two phases in epitaxial LZO layers grown on LaAlO3. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single-crystal structure of LZO pyrochlore phase. For comparison, LZO layers deposited by metalorganic chemical vapor deposition were also studied. In this last case, the film is compact without voids and the structure corresponds to pyrochlore phase. Thus, the formation of nanovoids is a characteristic feature of MOD grown films. I. INTRODUCTION
Coated conductors developed from rolling-assisted biaxially textured substrates (RABiTs) are considered a low-cost architecture: nickel-based textured substrate is used as a template to biaxially grow the superconducting YBa2Cu3O7 (YBCO) layer.1 Nevertheless, the YBCO layer cannot be deposited directly on nickel because of the chemical interaction of nickel with YBCO at the usual deposition temperature. Buffer layers filling several characteristics (for instance, structural and chemical compatibility between substrate and active layer) have to be used between the substrate and the superconducting layer. Good results are obtained when using lanthanum zirconate, La2Zr2O7 (LZO), as the first buffer layer. Metal organic decomposition (MOD) allows the growth of LZO on Ni-based substrates in reducing atmosphere, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0162
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J. Mater. Res., Vol. 24, No. 4, Apr 2009 Downloaded: 05 Feb 2015
which avoids the undesirable oxidation of the substrate. This material has already been probed on a simple low-cost architecture obtained by all-chemical routes YBCOMOCVD/LZOMOD/NiWRABiTS in a previous work.2 Pyrochlore LZO behaves
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