Temperature Dependence of the Vibrational Properties of PbI2

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Abstract
Infrared reflectivity measurements are made from 20 to 600 cm−1 at temperatures ranging from 5 to 575 K for the layered semiconductor PbI2. The reflection spectra are analysed by means of a damped Lorentzian‐oscillator model and the calculated optical properties are presented. The infrared reflectivity of PbI2 shows a broad reststrahlen band, pointing to the significantly ionic character of this compound. Optical properties are compared with those of other layered semiconductors. The optical constants, long‐wavelength optical‐phonon frequencies (both TO and LO), and their half‐widths are obtained as functions of temperature. The temperature dependence is discussed using an anharmonic coupling model with a two‐phonon decay. The general behaviour of anharmonic effects in PbI2 agrees qualitatively with the theory of Maradudin and Fein.