Special pleochroism in the far-infrared spectra of ferroelectric triglycine sulfate.
A special dichroism is observed in the far-infrared spectra of triglycine sulfate crystals. The absorption of a few peculiar lines is dependent on the orientation of the sample surface while, indeed, the infrared electric vector is kept in a constant direction. A significant broadening of some lines in a plate cut perpendicular to the axis is explained by a heterogeneous electric field in the surface layer. New lines appearing only in a plate cut parallel may be interpreted either by a loss of symmetry in the surface parallel to the binary C2 axis or by more classic arguments derived from the complexity introduced by a high absorption index in a very anisotropic crystal. This dichroism is observed in reflectivity and, when transmission is considered, for some lines the dichroism is limited to very thin samples in good accordance with a surface layer explanation, while for other lines it is still observed for thick samples.
Hadni
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University of Nancy I, Far Infrared Laboratory, 54506 Vandoeuvre les Nancy, France.
Gerbaux
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