Raman scattering measurements have been made on the long-period polytypes of ${\mathrm{CdI}}_2$ whose structure has been identified by x-ray diffraction analysis. In addition to the principal phonon modes, we have observed new shear-type Raman modes which result from zone-folding effects. It is found that the relative Raman intensities of these folded modes depend strongly on the structure of the polytypes. A simple model is presented to explain the Raman intensity profiles of these polytypes. Model calculations of the relative Raman intensity show a qualitative agreement with the observations. The absence of folded modes of the compressional type is also explained by the model. It is shown that the Raman intensity profiles can be used to identify the structure of ${\mathrm{CdI}}_2$ polytypes. Finally, the model and the results of the analysis are discussed.

• Received 26 November 1984

DOI:https://doi.org/10.1103/PhysRevB.31.6531