Polytypism and the Vibrational Properties of PbI₂

Abstract

<p>The vibrational properties of polytypes of PbI₂ crystals have been studied experimentally by means of the techniques of Raman spectroscopy, X-ray diffraction and low temperature calorimetry. The crystals were prepared by three different methods: gel growth, thermal annealing and growth from the melt.</p> <p>The Raman spectra are used to determine features of the phonon dispersion curves, in the crystallographic c-direction, that are common to all of the polytypes. The results are correlated with existing information obtained from measurements of Brillouin spectra and inelastic scattering of neutrons.</p> <p>Both the heat capacity and the thermal conductivity were determined from the calorimetric measurements in the region 0.5</p> <p>All of the results are analysed within the framework of a 6-parameter force constant model. Bounds are placed on the magnitudes of anharmonic and 2-dimensional contributions to the vibrational properties.</p>