Optical Spectra and Electronic Structures of Forsterite (α-Mg_2SiO_4) Single Crystals(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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Reflectivity spectra of forsterite (α-Mg_2SiO_4) single crystals for the polarization parallel to the a-axis (E‖α) and c-axis (E‖c) have been measured in the energy region up to 25 eV using synchrotron radiation. Optical constants have been derived from reflectivities through the Kramers-Kronig analysis. The absorption spectra exhibit sharp exciton bands at 8.89 (E‖α), 8.70 and 9.56 eV (E‖c). The electronic states of an embedded [Mg_9SiO_4] cluster have been calculated by the DV-Xα method in order to understand the optical properties of forsterite. The present calculation indicates that the top of the valence band is almost composed of the 2p orbitals of O atoms, and the bottom of the conduction band mainly of the 3s orbitals of Mg atoms. Therefore, the lowest exciton bands are attributed to the O 2p → Mg 3s transitions. The polarization dependence of the exciton bands is discussed on the basis of the results in the present calculation.
社団法人日本物理学会の論文
2002-11-15