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Spectroscopy Coherent Neutron or x-ray Scattering Form Factors The phonon dispersion curves can be measured by neutron scattering and/or x-ray scattering. The anaharmonicity leads to phonons shifts and widths which can be seen as map intensity, FIGURE.6. They can be compared to the harmonic phonon dispersion curves, which intensities are in the similar scale as shown on FIGIRE. 2. The plots correspond to temperature T=2300K and pressure P=57GPa. Due to the paticular scattering cross section, form factor and orientation of the crystal the intensities arround Γ wavevector are not visible.
FIGURE.6. (Up) The map of intensities of anharmonic phonon dispersion bands for MgSiO3Pb at temperature T=2300K and pressure P=57GPa. (Down) The plot of harmonic phonon dispersion curves of MgSiO3, with intensities represented by colours. Similar map and dispersion bands can be obtained for the x-ray scattering form factor. The incoherent neutron scattering and the nuclear inelastic absorption data can be also ploted from anharmonic phonon density of states. .Light Spectroscopy FIGURE.7 (up) shows infrared absorption spectra for the harmonic phonons at Γ wavevector and at elevated temperature T=2300k and pressure P=57GPa. FIGURE.7 (down) present the infrared active modes with considerable widths which cause that the anharmonic modes overlap and the spectra contains less peaks. The absorption geometry correspond the polycrystal of unpolarized light. Similar analysis can be performed for the Raman spectra, although the Ranam tensor requires larger computational efford.
FIGURE.7. (Up) Infrared absorption spectra for the harmonic phonons, and
(Down) Spectra for anharmonic phonons for MgSiO3
at temperature T=2300K and pressure P=57GPa.
Last update: September 20, 2017 |
