Abstract
Polarized Raman spectra and polycrystalline spectra of isomorphous
Sc-2(MoO4)(3) and Al-2(WO4)(3) crystals have been measured at room
temperature and ambient pressure. Some Raman spectra Of Sc-2(MoO4)(3)
were taken at different values of pressures in the range of 0.0-3.0 GPa.
Lattice dynamics calculations have been performed on the orthorhombic
phase (ambient phase) of these materials using a rigid ion model in
order to calculate the phonon frequencies at the Brillouin zone Center (k = 0). The calculated results fit qualitatively well the Raman spectra
observed in these materials at room temperature and ambient pressure,
and allowed us to establish their Raman signature. A higher coupling
among the modes of the Al-2(WO4)(3) material compared with Sc-2(MoO4)(3)
material was observed. The pressure dependent studies revealed that the
362 and 433 cm(-1) modes of Sc-2(MoO4)(3) and Al-2(WO4)(3),
respectively, exhibit unusually high awlaP values. The presence of these
unstable modes in both materials is probably related to the mechanism of
the phase transition from the monoclinic high-pressure phase to the
unknown phase of lower symmetry. (c) 2006 Elsevier B.V. All rights
reserved.
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