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Average and Local Structure of (1− x )BaTiO 3 − x LaYO 3 (0≤ x ≤0.50) Ceramics
Author(s) -
Feteira Antonio,
Sinclair Derek C.,
Kreisel Jens
Publication year - 2010
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04006.x
Subject(s) - materials science , tetragonal crystal system , crystallography , raman spectroscopy , ferroelectricity , nanoclusters , crystal structure , transmission electron microscopy , solid solution , dielectric , nanotechnology , optics , chemistry , physics , optoelectronics , metallurgy
Dense ceramics of (1− x )BaTiO 3 − x LaYO 3 (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) BaTiO 3 (space group P 4 mm ) decreases with increasing x , reaching an average cubic symmetry (space group) 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 LaYO 3 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 LaYO 3 ‐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.