RAMAN-SCATTERING INVESTIGATION OF LEAD MIXED HALIDES, PBCL2XBR2(1-X), AS A FUNCTION OF THE PROPORTION-X IS-AN-ELEMENT-OF [0,1]

PbCl2xBr2(1 − x) single crystals for various compositions were studied by Raman spectroscopy at 14 K. It is shown that the phonons are of one‐ or two‐mode behaviour when the proportion x varies from 0 to 1. Lattice dynamic and group theory considerations related to structural data allow one to establish a mechanism for the substitutional filling of the anion sites and their participation in the lattice vibrations, the frequency of which has been measured as a function of x at 14 K. The maximum disorder given by the Raman line widths occurs for x = 0.25 and x = 0.75, in accordance with dielectric measurements. Copyright © 1990 John Wiley & Sons, Ltd.