Dynamics of the cadmium-chloride-type layer structures
TL;DR: In this paper, a linear chain model with intralayer force constants was used to interpret the long wavelength lattice vibrations of the layer structures -CdBr 2, CdCl 2, MnCl 2 and CoCl 2.
About: This article is published in Solid State Communications.The article was published on 1975-03-15. It has received 9 citations till now.
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TL;DR: In this paper, it was shown that a thermally-induced 2H → 4H inter-polytype conversion in PbI2 has been observed via the appearance, in Raman scattering, of a shear-motion rigid-layer line at 14 cm-1 and a Davydov splitting of an intra layer line.
62 citations
TL;DR: In this paper, the polarizable ion model is used to explain the observed anisotropy of the lattice vibrations of layered compounds with the Cd(OH)2 or CdCl2 structure.
Abstract: The polarizable ion model is used to explain the observed anisotropy of the lattice vibrations of layered compounds with the Cd(OH)2 or CdCl2 structure. The electronic polarizabilities of the ions, the Szigeti effective charge, and the contribution of the short-range forces to the frequencies of the optical modes are deduced from optical data for the lattice vibrations of PbI2, CdI2, SnS2, and SnSe2. From the analysis it is found that the contribution of the short-range forces is rather isotropic. The large anisotropy of the optical modes is caused mainly by static dipoles of the anions induced by local electric fields. For the semiconductors SnS2 and SnSe2 the reduction of the ionic charges and static dipoles is larger than for the more ionic compounds PbI2 and CdI2.
Le modele d'ion polarisable est utilise afin d'expliquer l'anisotropie observee des vibrations des composes avec la structure de Cd(OH)2 ou CdCl2. Les polarisabilites electroniques des ions, ainsi que la charge effective de Szigeti et la contribution des forces a courte distance aux frequences des modes optiques sont deduites des donnees optiques pour les vibrations de PbI2, CdI2, SnS2 et SnSe2. On a decouvert que la contribution des forces a courte distance est assez isotropique. La grande anisotropie des modes optiques est cause principalement par les dipoles statiques des anions. Pour les composes semi-conducteurs SnS2 et SnSe2 la reduction des charges ioniques et des dipoles statiques est plus grande que pour les composes plus ionique PbI2 et CdI2.
26 citations
01 Jan 1979
TL;DR: The interest in the phonon energies of layered crystal structures has grown rapidly during the last decade as mentioned in this paper, due to fundamental considerations concerning low-dimensional systems to the utility of these materials as superconductors, lubricants, and thermoelectric elements.
Abstract: Research interest in the phonon energies of layered crystal structures has grown rapidly during the last decade. The reasons for the interest vary from fundamental considerations concerning low-dimensional systems to the utility of these materials as superconductors, lubricants, and thermoelectric elements. Infrared and Raman studies of layered materials were initiated long before the current phase of research activity. The first infrared spectrum was obtained on brucite [Mg(OH)2] in 1905 by Coblentz [1]; however, relatively few papers were reported in the literature before 1960. Krishnamurti’s work [2] on Mg(OH)2 and Ca(OH)2 appears to have been the first extensive Raman study of layered compounds. Current activity has also greatly benefited from instrumental developments in spectrometers and laser light sources. Infrared and Raman techniques are now mature, and they have been used to advantage in far-infrared and high-resolution work on layered structures. (The former experimental difficulties can be appreciated by reading the survey of the Raman effect in solids by Menzies [3], which was written a little over twenty years ago.)
17 citations
TL;DR: In this article, the Eu infrared active mode for CdBr2 was assigned at a frequency of 111.5+or 0.5 cm-1 for liquid air temperatures.
Abstract: Very thin samples of CdCl2 type crystals can be produced by stripping with sellotape. This allows the Eu infrared active mode to be observed by infrared absorption at a frequency of 111.5+or-0.5 cm-1 for CdBr2 at liquid air temperatures. This assignment of the Eu infrared mode for CdBr2 is in disagreement with the earlier assignment of Lockwood (1973).
10 citations
TL;DR: In this article, an atom-atom interaction force model has been used to calculate the frequencies of long-wavelength lattice vibrations in high-symmetry layer crystals-MoS2, PbI2, GaSe and GaS.
Abstract: An atom-atom interaction force model has been used to calculate the frequencies of long-wavelength lattice vibrations in high-symmetry layer crystals-MoS2, PbI2, GaSe and GaS. The weak interlayer force has been neglected. Assuming that each layer is electrically neutral we need to perform the lattice sums only in the two directions parallel to the layers. It is found that in the case of MoS2 and PbI2 crystals, good results obtained by expressing the lattice sums in terms of two nearest-neighbour forces only. In the case of GaSe and GaS crystals the lattice sums are evaluated in terms of four nearest-neighbour forces. The larger difference between the calculated and observed values in GaSe may be due to long-range electrostatic forces.
7 citations
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TL;DR: In this article, the observed degeneracy of mutually exclusive infrared and Raman-active modes in Mo$(S) was traced to the weak van der Waals interaction between layers.
Abstract: The observed degeneracy of mutually exclusive infrared- and Raman-active modes in Mo${\mathrm{S}}_{2}$ is traced by means of group theory to the weak van der Waals interaction between layers.
337 citations
TL;DR: Using a triple Raman spectrometer, the authors observed the rigid-layer E 2 g 2 mode in hexagonal MoS 2, and the interlayer forces were shown to be about 100 times weaker than the intralayer forces.
145 citations
TL;DR: In this article, the longwavelength lattice vibrations of MoS2 and GaSe are interpreted by means of a linear-chain model that includes both intralayer and interlayer force constants.
96 citations