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Raman scattering studies on nanocrystalline BaTiO 3 Part I—isolated particles and aggregates
Author(s) -
Shiratori Y.,
Pithan C.,
Dornseiffer J.,
Waser R.
Publication year - 2007
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1764
Subject(s) - tetragonal crystal system , crystallite , raman spectroscopy , nanocrystalline material , materials science , orthorhombic crystal system , phase transition , phonon , crystallography , raman scattering , analytical chemistry (journal) , mineralogy , condensed matter physics , chemistry , crystal structure , nanotechnology , optics , physics , metallurgy , chromatography
Abstract BaTiO 3 powders with various crystallite sizes, which were prepared through microemulsion‐mediated synthesis, were thoroughly studied by Raman spectroscopy. Clear evidence for the presence of the tetragonal phase was found for ultrafine powders with an average crystallite size above 30 nm. The lifetime of phonons that are specifically assigned to the tetragonal phase decreased with decreasing crystallite size below a critical size of 100 nm. In particles as fine as 100 nm, the short mean free path of phonons, mainly due to internal pressure, causes decoupling of the coupled A 1 (TO) phonons and a diffuse phase transition behaviour ( T C = 115 °C). Coupled A 1 (TO) phonons, which give a spectral dip at around 180 cm −1 and a lesser extent of diffuseness, were revealed for powders consisting of particles as large as 0.17 µm ( T C = 123 °C). Further coarsening upon annealing induced the formation of aggregates, resulting in the shift of phase transition points to higher temperatures for the rhombohedral to orthorhombic and the orthorhombic to tetragonal transitions and to lower temperatures for the tetragonal to cubic transition, respectively. Phase stability in powders is discussed by considering possible factors such as internal pressure in isolated particles and internal stress in aggregates. Copyright © 2007 John Wiley & Sons, Ltd.