IR reflectance spectroscopy at 50–450 cm–1 was used to study homogeneous monocrystals of (FeIn2S3)x∙(In2S3)1–x grown by the method of direction melt crystallization (vertical Bridgman method). The frequencies of the transverse (ωTO) and longitudinal optical phonons (ωLO) as well as their damping coefficients were determined. Concentration dependence curves were constructed for these parameters and their behavior was established
