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 group P4mm) 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 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.

Effects of average and local structure on the dielectric behavior of (1−x)BaTiO3–xLaYO3 (≤x≤0.40) ceramics

“…24 Gold sputtered electrodes were applied to the major faces of the ceramics. 24 Gold sputtered electrodes were applied to the major faces of the ceramics.…”

“…[19][20][21] Invariably, these materials exhibit temperature stable permittivity behavior but the dielectric losses at MW frequencies are too high for technological applications. 24 Here, the dielectric properties of LBTY ceramics are presented and used to establish the structure-property relationships for this system. 23͒ is not fully understood and is therefore worthy of further investigation.…”

Chemical and structural effects on the high-temperature mechanical behavior of (1−x)(Na1/2Bi1/2)TiO3-xBaTiO3 ceramics

“…38 Two other features appear in pure BT, namely, a dip at $180 cm À1 and a sharp peak at $305 cm À1 . The former is an interference effect due to coupling between A 1 phonons, [39][40][41] whereas the latter is the so-called "silent" mode of B 1 symmetry, which involves only oxygen atoms and whose frequency remains constant regardless of the presence of strain of any nature within the lattice. These two features, together with the peak at $715 cm À1 , are generally regarded as the signature of the ferroelectric phase in BT.…”

Structure and properties of Fe-modified Na0.5Bi0.5TiO3at ambient

“…In relaxor or morphotropic ferroelectrics with short-range phase segregation, Raman signals from second phases of nanometer scale but with the same correlation length are superimposed on the overall signal belonging to a macroscopic matrix phase. [16][17][18][19] Raman spectroscopy has been used to study phase transitions and the nanoscale structural characteristics of NBT and its solid solutions. 15,[20][21][22][23][24] Due to challenges of intrinsic broadening and overlapping of phonon modes in the assignment of mode symmetries, structural analysis thus relies on analyzing soft-mode or hard-mode behavior as a function of composition, pressure or temperature.…”