Three-dimensional subnanoscale imaging of unit cell doubling due to octahedral tilting and cation modulation in strained perovskite thin films

Nord, M., Ross, A., McGrouther, D. , Barthel, J., Moreau, M., Hallsteinsen, I., Tybell, T. and MacLaren, I. (2019) Three-dimensional subnanoscale imaging of unit cell doubling due to octahedral tilting and cation modulation in strained perovskite thin films. Physical Review Materials, 3(6), 063605. (doi: 10.1103/PhysRevMaterials.3.063605)

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Determining the three-dimensional (3D) crystallography of a material with subnanometer resolution is essential to understanding strain effects in epitaxial thin films. A scanning transmission electron microscopy imaging technique is demonstrated that visualizes the presence and strength of atomic movements leading to a period doubling of the unit cell along the beam direction, using the intensity in an extra Laue zone ring in the back focal plane recorded using a pixelated detector method. This method is used together with conventional atomic resolution imaging in the plane perpendicular to the beam direction to gain information about the 3D crystal structure in an epitaxial thin film of LaFeO3 sandwiched between a substrate of (111) SrTiO3 and a top layer of La0.7Sr0.3MnO3. It is found that a hitherto unreported structure of LaFeO3 is formed under the unusual combination of compressive strain and (111) growth, which is triclinic with a periodicity doubling from primitive perovskite along one of the three ⟨110⟩ directions lying in the growth plane. This results from a combination of La-site modulation along the beam direction, and modulation of oxygen positions resulting from octahedral tilting. This transition to the period-doubled cell is suppressed near both the substrate and near the La0.7Sr0.3MnO3 top layer due to the clamping of the octahedral tilting by the absence of tilting in the substrate and due to an incompatible tilt pattern being present in the La0.7Sr0.3MnO3 layer. This work shows a rapid and easy way of scanning for such transitions in thin films or other systems where disorder-order transitions or domain structures may be present and does not require the use of atomic resolution imaging, and could be done on any scanning transmission electron microscopy instrument equipped with a suitable camera.

Item Type:Articles
Glasgow Author(s) Enlighten ID:McGrouther, Dr Damien and MacLaren, Dr Ian and Nord, Dr Magnus
Authors: Nord, M., Ross, A., McGrouther, D., Barthel, J., Moreau, M., Hallsteinsen, I., Tybell, T., and MacLaren, I.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Physical Review Materials
Publisher:American Physical Society
ISSN (Online):2475-9953
Published Online:14 June 2019
Copyright Holders:Copyright © 2019 The Authors
First Published:First published in Physical Review Materials 3(6):063605
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
655181Fast Pixel Detectors: a paradigm shift in STEM imagingIan MaclarenEngineering and Physical Sciences Research Council (EPSRC)EP/M009963/1S&E P&A - PHYSICS & ASTRONOMY