Average and Local Structure of (1−x)BaTiO3−xLaYO3(0≤x≤0.50) Ceramics

Abstract

Dense ceramics of (1−x)BaTiO3−xLaYO3(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 groupP4mm) decreases with increasingx, reaching an average cubic symmetry (space groupimage) atx=0.05. Forx>0.05, the lattice parameteraincreases almost linearly up tox=0.40, above which a secondary phase isostructural with LaYO3precipitates. ED patterns along [110]pfor 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 forx=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. Forx>0.10, only nanodomains are observed.