Morphology, structure, and nucleation of out-of-phase boundaries (OPBs) in epitaxial films of layered oxides
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Morphology, structure, and nucleation of out-of-phase boundaries (OPBs) in epitaxial films of layered oxides M.A. Zurbuchena) Ceramics Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899; and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802-5005
W. Tian and X.Q. Pan Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136
D. Fong and S.K. Streiffer Materials Science Division, Argonne National Laboratory (ANL), Argonne, Illinois 60439
M.E. Hawley Materials Science and Technology, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
J. Lettieri,b) Y. Jia, G. Asayama, S.J. Fulk, D.J. Comstock, S. Knapp, A.H. Carim,c) and D.G. Schlom Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16803-6602 (Received 23 July 2006; accepted 26 February 2007)
Out-of-phase boundaries (OPBs) are translation boundary defects characterized by a misregistry of a fraction of a unit cell dimension in neighboring regions of a crystal. Although rarely observed in the bulk, they are common in epitaxial films of complex crystals due to the physical constraint of the underlying substrate and a low degree of structural rearrangement during growth. OPBs can strongly affect properties, but no extensive studies of them are available. The morphology, structure, and nucleation mechanisms of OPBs in epitaxial films of layered complex oxides are presented with a review of published studies and new work. Morphological trends in two families of layered oxide phases are described. The atomic structure at OPBs is presented. OPBs may be introduced into a film during growth via the primary mechanisms that occur at film nucleation (steric, nucleation layer, a-b misfit, and inclined-c misfit) or after growth via the secondary nucleation mechanism (crystallographic shear in response to loss of a volatile component). Mechanism descriptions are accompanied by experimental examples. Alternative methods to the direct imaging of OPBs are also presented.
I. INTRODUCTION
Many layered complex oxides, including Aurivillius,1–5 Ruddlesden–Popper,6,7 and layered cuprate8 phases, have been intensively studied over the past
a)
Address all correspondence to this author. e-mail: [email protected] Present address: Electronics and Photonics Laboratory, The Aerospace Corporation, El Segundo, CA 90245. b) Deceased c) Present address: United States Department of Energy, Germantown, Maryland DOI: 10.1557/JMR.2007.0198 J. Mater. Res., Vol. 22, No. 6, Jun 2007
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fifteen years for the interesting and potentially useful behaviors they exhibit, such as superconductivity,9 colossal magnetoresistance,10 or ferroelectricity.11 These phases are of further interest as quasi-two-dimensional systems for study of reduced dimensionality material systems.12–14 Altho
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