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Vibrational studies of hexagonal bronze systems: phonon calculation and high pressure induced phase transformation
Author(s) -
Coelho J. Santos,
Paraguassu W.,
Maczka M.,
Souza Filho A. G.,
Freire P.T.C.,
Mendes Filho J.,
Hanuza J.
Publication year - 2009
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.2248
Subject(s) - raman spectroscopy , phonon , valence (chemistry) , octahedron , raman scattering , condensed matter physics , hexagonal crystal system , superconductivity , phase transition , crystallography , materials science , ambient pressure , molecular vibration , lattice (music) , crystal structure , chemistry , thermodynamics , physics , optics , organic chemistry , acoustics
Hexagonal bronzes and valence‐balanced hexatungstates (VBHT) have attracted great attention for presenting rich polymorphism and displaying superconductor or ferroelectric properties. In the present work, structural and vibrational properties of RbBi 1/3 W 8/3 O 9 (RBW) crystal (VBHT type) were investigated by high‐pressure Raman scattering experiments. The results suggest the existence of a reversible pressure‐induced structural phase transition at about 4 GPa. This transformation is most likely related to rotations of octahedral units along the c ‐axis with no abrupt changes of apical OWO bonds length. In order to get further understanding of RBW vibrational properties, we performed phonon calculations, by using classical lattice dynamics, in the related hexagonal structure of the K 0.26 WO 6 system. These calculations revealed that most of vibrational properties of K 0.26 WO 6 are governed by tubular ‘like’ vibrations of the hexagonal cavity, which resemble similar vibrations of tubular nanostructures. The pressure dependence of Raman modes is understood in terms of calculated phonon eigenvectors at ambient pressure. Copyright © 2009 John Wiley & Sons, Ltd.