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Vibrational properties of Cs 4 W 11 O 35 and Rb 4 W 11 O 35 systems: high pressure and polarized Raman spectra
Author(s) -
da Silva K. Pereira,
Paraguassu W.,
Maczka M.,
Filho A. G. Souza,
Freire P. T. C.,
Filho J. Mendes,
Hanuza J.
Publication year - 2011
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.2737
Subject(s) - raman spectroscopy , octahedron , raman scattering , tungsten , soft modes , spectral line , lattice (music) , crystallography , chemistry , condensed matter physics , materials science , ferroelectricity , crystal structure , dielectric , physics , optics , optoelectronics , astronomy , acoustics , organic chemistry
Cs 4 W 11 O 35 (CW) and Rb 4 W 11 O 35 (RW) belong to the class of hexagonal bronzes whose structure originates from the K x WO 3 superconductor hexatungstate. Charge‐imbalanced tungsten bronzes are dielectric materials with rich polymorphism, ferroelectric properties and second‐harmonic generation. In this work, we report the polarized Raman spectra results for both CW and RW, as well as results of high‐pressure Raman scattering experiments (0.0–11.0 GPa) for the Cs 4 W 11 O 35 system, in which we have observed two structural phase transitions at ∼4 and 7.5 GPa. We discuss these transformations and polarized Raman spectra on the basis of lattice dynamics calculation in the related system KNbW 2 O 9 . Polarized Raman spectra provide strong indication that the highest wavenumber modes observed in these systems originate from tungsten or oxygen vacancies. The observation of a soft‐like mode indicates that the observed phase transitions exhibit a displacive‐type behavior, thus further indicating that these transformations are likely related to reorientations of the octahedral units. The soft mode nature is discussed as well. PACS: 77.80.Bh; 78.30.Hv; 78.30.‐j. Copyright © 2010 John Wiley & Sons, Ltd.