Dispersion Relations for Phonons in KCl at 80 and 300°K

Abstract

Phonon dispersion relations in KCI at 80 O K have been determined using inelastic neutron scattering. The measurements have been performed mainly in the symmetry directions[loo], [110], and [lll], but also a t some other points in the reciprocal space. More than one third of the phonons in all branches were also studied a t 300 "K in order to obtain an estimate of the temperature dependence of their frequencies. A comparison is made with dispersion curves calculated by Niisslein and Schroder for their "breathing shell" variant of the shell model for ionic crystals. The agreement for the dispersion curves is quite satisfactory in the most cases.

Impurity-Induced Far-Infrared Absorption in KBr and KCl

“…With our assignment of the critical points the calculated frequencies appear 2% low in agreement with frequencies measured in the nearby region of the zone along the [111] direction by Copley et al (1969) using neutron spectroscopy. However more recent neutron results by Raunio and Almqvist (1969) in this region indicate that the unper turbed phonon energies tend to a higher value in agreement with the infrared results. It is interesting to note that these critical points correspond to similar features already seen in KBr.…”

Observation of nuclear wave packets in the excited state of the F-center in alkali halides

“…The phonon dispersion curves in Refs. [16,17] indicate that the highest frequency of the LO phonons, i.e., the frequency of LO mode at zone center (or G point) in the Brillouin zone, is 6.39 THz Ej and Wj are, respectively, the peak energy and the FWHM, where suffix j ¼ a, e denotes absorption or emission, and T is the sample temperature. The values of Ej and Wj are given by the empirical formulae of temperature dependence of the absorption (emission) peak and width, which are derived by Gebhardt and Kü hnert in Ref.…”

“…in a pure KCl crystal at 80 K. The 6.0 THz mode lies close to the zone center in the phonon dispersion curves and has a small reduced wave vector k of 0.2, i.e., corresponding to a wavelength of 5a, where a is the lattice constant [16,17]. In the Raman spectra [6], the enhancement of the LO modes around 6.0 THz is observed under excitation resonant with the higher excited states (3p, 4p,y) rather than the first excited state (2p state).…”

Lattice Dynamics of RbI at 80 °K

“…I n a series of earlier papers we have presented experimental results for phonon dispersion relations in NaCl [l], KC1 [2], RbF and RbCl [3]. These have recently been interpreted in terms of the shell model due to Woods et al Complete results on RbBr have also been obtained and will be published elsewhere [5].…”