Inelastic neutron scattering from solid krypton at 10 °K

Abstract

The phonon dispersion of fcc krypton has been measured along high-symmetry directions at 10'K on a single crystal with an equilibrium lattice spacing of 5.646 + 0.002 A. The data can be fitted with a general three-neighbor-forceeonstant model of nine parameters with only slight depatures from central force axially symmetric conditions. Utilizing theoretical estimates of the weak additional forces due to the fourththrough eighth-nearest neighbors, the zero-sound elastic constants are determined to be c "=514 + 5, c "=284 + 6, and c "=268 g 3 x 10' dyn cm '-. The agreement of the measured dispersion curves with theoretical calculations by Barker et af. is excellent; the maximum deviation of =3% occurs near the zone boundary. A broadening of the neutron response for zone-boundary modes was observed that was comparable to the energy itself when the sample was near its melting point.

Lattice dynamics for fcc rare gas solids Ne, Ar, and Kr fromab initiopotentials

“…The agreement between the calculated and the experimental temperature dependences of the specific heat at constant volume served in such study as a criterion to evaluate the calculated phonon densities. We recall that the Cauchy equality C 12 = C 44 , where C 12 and C 44 represent two of the three distinguishable elastic constants of a cubic solid, holds reasonably well for the RGS's of the elements mentioned above, at temperatures between 5 and 25 K, [3][4][5] and towards the zero-pressure limit ͑see predictions compared with experimental data in Ref. 6͒.…”

“…23 The largest differences between the phonon frequencies produced by the ELJ potential and the experimental values amount to 14% in the case of neon and 9% in the cases of argon and krypton. As a reference, the largest experimental uncertainties in the phonon energies are 7.1% in the case of neon at 6.5 K, 5 3.2% for argon at 10 K, 4 and 6.3% for krypton at 10 K. 3 Taking the predicted phonon frequencies as a criterion, the ab initio potentials perform as good as the pair potentials parametrized empirically, except for Kr. The model used here underestimates the phonon frequencies, and a more precise treatment requires the inclusion of three-body forces ͑especially for the heavier rare gases͒ and anharmonicity effects ͑especially for the lighter rare gases͒.…”

On the Distinction between Debye Bosons and Phonons

“…Under this condition lattice theories can give reasonable description of the phonon dispersions [3]. The rare gas solids [8][9][10][11] and CsCl [12] are examples of a vanishing Debye boson-phonon interaction. For these solids the acoustic phonons are perfectly described by sine functions of wave vector.…”

Generation of Coherent Zone Boundary Phonons by Impulsive Excitation of Molecules

“…We investigate electronic excitation of a diatomic molecule (I 2 ) embedded in the bulk of rare gas polycrystalline films. The fcc lattice of rare gas crystals has only acoustic phonons with very well characterized longitudinal and transversal phonon branches [3]. Our investigations result in a selection of phonons different from Refs.…”