Far infrared properties of iron doped single crystal PbTe

Far infrared reflectivity spectra of single crystal PbTe samples doped with 0.2 at% Fe were measured in the temperature range between 10 K and 300 K. These spectra show very sharp and narrow dips below 120 cm-1. The experimental data were numerically analyzed using a fitting procedure based on the plasmon-phonon interaction model. Two local modes were observed. The first one was noted between 130 cm-1 and 170 cm-1 depending on the temperature and the second more frequency stable one was noted at about 230 cm-1