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Author Frey, M. H. ♦ Payne, D. A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ BARIUM COMPOUNDS ♦ PHASE TRANSFORMATIONS ♦ TITANATES ♦ ALKYLATING AGENTS ♦ GRAIN SIZE ♦ LATTICE PARAMETERS ♦ CERAMICS ♦ MICROSTRUCTURE ♦ RAMAN SPECTRA ♦ INFRARED SPECTRA ♦ X-RAY DIFFRACTION ♦ CALORIMETRY ♦ HARMONIC GENERATION ♦ CRYSTAL GROWTH ♦ SOL-GEL PROCESS ♦ BARIUM TITANATES ♦ SECOND HARMONIC GENERATION ♦ XRD ♦ DSC
Abstract We report the results of an investigation into the grain-size dependence of lattice structure for barium titanate (BaTiO{sub 3}) ceramics prepared by a sol-gel method. Raman and infrared spectroscopy, x-ray diffraction, and differential scanning calorimetry were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with heat treatment and grain growth from the nano scale to the micron scale for BaTiO{sub 3} polycrystals. Raman spectroscopy and optical second-harmonic-generation measurements indicated the onset of local room-temperature acentric crystal symmetry with heat treatment and crystallite growth, well before the observation of any tetragonal structure by x-ray diffraction. Analysis of the room-temperature Raman spectra for ultrafine grain (grain size {lt}0.1 {mu}m) polycrystals suggested that a locally orthorhombic structure preceded the globally tetragonal form with grain growth. In support of this observation, differential scanning calorimetry suggested the orthorhombic-tetragonal phase transformation shifts up through room temperature with decreasing grain size. Hot-stage transmission electron microscopy studies revealed that fine grain (grain size {approx_equal}0.1 {mu}m) ceramics, which showed a thermal anomaly associated with the cubic-tetragonal phase transformation, were untwinned at room temperature, as well as on cycling through the normal Curie temperature, suggesting a single-domain state for individual grains. The findings are discussed in light of a number of possible causes, including the presence of processing-related hydroxyl defects and the effect of elastic constraints on phase transformation behavior for BaTiO{sub 3} grains in a polycrystalline microstructure. {copyright} {ital 1996 The American Physical Society.}
ISSN 01631829
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-08-01
Publisher Department University of Illinois
Publisher Place United States
Journal Physical Review, B: Condensed Matter
Volume Number 54
Issue Number 5
Organization University of Illinois


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