FAR INFRARED REFLECTIVITY OF SBSI

Far infrared reflectivity of SbSI bulk crystals in a polarized light was measured in the temperature region between −185 and 80 °C and frequency from 400 up to 15 cm−1. The optical constants and dielectric constant were calculated using Kramers‐Kronig analysis. The experimental data were compared with the results of the group‐theoretical analysis of normal vibrations. Soft mode behaviour was observed in the lowest frequency region (below 100 cm−1) and parameters of the corresponding oscillator were calculated. The mode frequency shifts from 32 cm−1 at 60 °C to 22 cm−1 at 25 °C. The oscillator strength is not high enough to explain the whole value of the static dielectric constant so that still another lower frequency resonance as observed by Grigas and Karpus in the centimetre region or a relaxation as observed by Vu Huy Dat in megacycle region should exist. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim