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Average and Local Structure of (1−x)BaTiO3xLaYO3 (0≤x≤0.50) Ceramics

Authors

  • Antonio Feteira,

    Corresponding author
    1. Ceramics and Composites Laboratory, Department of Engineering Materials, University of Sheffield, S1 3JD, U.K.
      †Author to whom correspondence should be addressed. e-mail: a.feteira@bham.ac.uk
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      ‡Present address: School of Chemistry, University of Birmingham. Edgbaston, B15 2TT Birmingham, U.K.
  • Derek C. Sinclair,

    1. Ceramics and Composites Laboratory, Department of Engineering Materials, University of Sheffield, S1 3JD, U.K.
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  • Jens Kreisel

    1. Laboratoire des Matériaux et du Génie Physique, Minatec, CNRS, Grenoble Institute of Technology,38016 Grenoble, France
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  • EIC Johnson—contributing editor

  • This work was financially supported by the EPSRC and EU (FAME and NUOTO).

  • Present address: School of Chemistry, University of Birmingham. Edgbaston, B15 2TT Birmingham, U.K.

†Author to whom correspondence should be addressed. e-mail: a.feteira@bham.ac.uk

Abstract

Dense ceramics of (1−x)BaTiO3xLaYO3 (LBTY) (0≤x≤0.50) have been fabricated by the conventional solid-state route. Phase purity and crystal structure of LBTY ceramics were investigated using a combination of X-ray diffraction (XRD), electron diffraction (ED), and Raman spectroscopy. XRD analysis shows the tetragonal distortion of undoped (x=0) BaTiO3 (space group P4mm) decreases with increasing x, reaching an average cubic symmetry (space group

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) at x=0.05. For x>0.05, the lattice parameter a increases almost linearly up to x=0.40, above which a secondary phase isostructural with LaYO3 precipitates. ED patterns along [110]p for 0.30≤x≤0.40 exhibit superlattice reflections at 1/2 (hkl) positions, indicating a doubling of the unit cell, which may arise from either octahedral tilting and/or chemical 1:1 B-site ordering within nanoclusters. Existence of nanodomains was revealed by dark-field transmission electron microscopy (TEM). Raman spectroscopy reveals nanoclustering to occur readily at low substitution levels and to increase progressively toward a nanoscale phase separation-like phenomenon, which precedes the precipitation of individual crystals of an LaYO3-based solid solution. Three distinctive subgrain microstructures are revealed by conventional TEM imaging. x=0 exhibits ferroelectric microdomains which completely transverse the grains, whereas for x=0.025 and 0.05, ferroelectric microdomains coexist with nanodomains. Other structural features such as core-shell-type substructures, {111} twins and dislocations are also observed in some grains. For x>0.10, only nanodomains are observed.

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