Inelastic neutron scattering from solid krypton at 10 °K

The phonon dispersion of fcc krypton has been measured along high-symmetry directions at 10 \ifmmode^\circ\else\textdegree\fi{}K on a single crystal with an equilibrium lattice spacing of 5.646 \ifmmode\pm\else\textpm\fi{} 0.002 A. The data can be fitted with a general three-neighbor-force-constant 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 fourth- through eighth-nearest neighbors, the zero-sound elastic constants are determined to be ${c}_{11}=514\ifmmode\pm\else\textpm\fi{}5$, ${c}_{12}=284\ifmmode\pm\else\textpm\fi{}6$, and ${c}_{44}=268\ifmmode\pm\else\textpm\fi{}3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ dyn ${\mathrm{cm}}^{\ensuremath{-}2}$. The agreement of the measured dispersion curves with theoretical calculations by Barker etal. is excellent; the maximum deviation of \ensuremath{\cong}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.

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