Abstract
Cs4W11O35 (CW) and Rb4W11O35 (RW) belong to the class of hexagonal
bronzes whose structure originates from the KxWO3 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 Cs4W11O35 system, in
which we have observed two structural phase transitions at similar to 4
and 7.5 GPa. We discuss these transformations and polarized Raman
spectra on the basis of lattice dynamics calculation in the related
system KNbW2O9. 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 (C)
2010 John Wiley & Sons, Ltd.
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