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|Type:||Artigo de periódico|
|Title:||Raman And X-ray Studies Of A High-pressure Phase Transition In -liio3 And The Study Of Anharmonic Effects|
|Abstract:||Temperature- and pressure-dependent Raman scattering experiments have been performed to study the phonon behavior in -LiIO3. The temperature dependence of Raman-active phonons does not show anomalous frequency behavior in the temperature range 10-650 K; however, at least two Bg phonons, with frequencies 344 and 460 cm-1, and one Ag phonon, with frequency 249 cm-1, show anomalous increases in linewidth with temperature. The high-pressure Raman scattering experiments of -LiIO3 were performed at room temperature with a sapphire-anvil cell for hydrostatic pressures up to 95 kbar. The spectra show a discontinuous reversible change for all orientations at about 50 kbar. This change is interpreted as a phase transition in LiIO3 at 50 kbar. The Raman spectra of this new phase are quite different from those of the three other known phases of LiIO3 and reveal a lowering of symmetry upon passing from the to the phase. High-pressure x-ray measurements were performed to characterize the structural phase transition in -LiIO3, which transforms from tetragonal symmetry P4n (C4h3) to monoclinic symmetry P2n (C2h4) above 50 kbar. The complex behavior at high pressure appears to be analogous to that of some perovskite compounds, in which there exists an antipathetic lattice coupling between a and c of a tetragonal phase. The pressure and temperature dependence of Raman spectra of -LiIO3 were combined to analyze the explicit and implicit contributions to the isobaric temperature variation of phonons. The results show that at least two modes, the Bg phonon at 460 cm-1 and the Ag phonon at 249 cm-1, are highly anharmonic with increasing temperature. It is concluded from pressure Raman work that there exists strong mixing of internal and external modes in -LiIO3. Such a mixing of internal- and external-mode characters is also apparent from the study of fractional implicit and explicit contributions to the frequency variations of phonons with temperature. © 1984 The American Physical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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