Experimentelle Untersuchung der Ramanstreuung an Kristallpulvern

A comparison of the Raman spectra of single crystals with those made using their powder reveals the following differences: (1) The intensity of the Raman lines decreases with grain size. (2) The breadth of the lines increases with grain size. (3) The spectra of powder specimens show additional lines. The decrease in the intensity is mainly due to surface scattering, whereas the broadening of the lines can be caused by two different factors: (a) In the case of polar crystals different spectra overlap because of different orientations of the grains. (b) Additional interactions with `surface modes' of the individual crystals, which may also show a dispersion depending on the shape of the grains. Na<sub>2</sub>WO<sub>4</sub> with its higher symmetry and the weakly polar SiO<sub>2</sub> show the decrease in intensity, while the examples showing the interactions with `surface modes', are quartz and platy crystals of SiC. Anomalous broadening can be demonstrated using strongly polar KIO₃. The results of this study have been applied to determining the effect of such lamellar structures, as in labradorites, on Raman lines.