Raman Scattering in CdI₂ Polytypes and Dispersion of Optical Phonons

Abstract

Raman spectra of various CdI₂ polytypes have been measured at liquid He temperature. Several folded modes of the E symmetry optical branch have been observed in higher polytypes. The dispersion curve of the E symmetry branch in the [00ξ] direction has been obtained from the experimental frequencies of the folded modes. The pressure dependence of the Raman active modes has been also measured. These results are analyzed by using a linear chain model and a polarizable ion model. The analysis indicates that the long range forces contribute little to the interlayer forces and that the difference in long range forces as well as the short range forces among the polytypes is very small.