Optical phonon modes and infrared dielectric properties of monoclinic CoWO 4 microcrystals.
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2016
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Resumo
The phonon characteristics of CoWO4 microcrystals with monoclinic Wolframite structure
were investigated by far-infrared (IR) and Raman spectroscopies. Near-normal spectra were
taken for IR light polarization along the principal b-axis (Au modes) and along several angles
within the ac-plane (Bu modes). The IR spectra were analyzed with a generalized Drude–
Lorentz model, and all predicted polar phonon modes were fully determined, including their
symmetries, the dielectric Lorentz parameters and the non-orthogonal phonon polarizations
for the Bu modes. Anomalous dispersion and negative values for the real and imaginary parts
of the off-diagonal components of the dielectric tensor functions were identified and discussed
under the light of the varying phonon polarization directions (spread out in the ac-plane).
The obtained static and background dielectric tensors gave an average permittivity of 16.1
(at microwave region), refractive indices along the principal dielectric axes of 2.22, 2.33 and
2.44 (at 1 μm), the optical axes, and an estimated value for the biaxial angle of the crystal.
Polarized Raman spectra on appropriate scattering configurations revealed the 18 non-polar
gerade phonons of CoWO4 crystals, with their correct symmetries attributed.
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Infrared spectroscopy, Monoclinic crystals, Multiferroics, Raman scattering
Citação
MOREIRA, R. L. et al. Optical phonon modes and infrared dielectric properties of monoclinic oWO 4 microcrystals. Journal of Physics. D, Applied Physics, v. 49, p. 045305, 2016. Disponível em: <http://iopscience.iop.org/article/10.1088/0022-3727/49/4/045305/pdf>. Acesso em: 05 ago. 2017.