The technique of inelastic scattering of thermal neutrons was used to study the temperature dependence of lattice vibrations in Cu in the range 23 °C to 1063 °C, i.e. up to 20 °C below the melting point, and in the various symmetry directions accessible in a (001) scattering plane. Resolution effects were taken into account in the determination of intrinsic phonon frequencies and linewidths. The results indicate a general softening of the lattice as the temperature is raised, the vibrations of transverse polarization being more strongly affected than those of longitudinal polarization. Even close to the melting point, most phonon lifetimes were sufficiently long to allow the unambiguous observation of one-phonon line profiles. A high resolution study at small wave vectors was also performed in order to determine the temperature variation of the zero-sound elastic constants. Among the points of particular interest is the fact that the frequency of the T1 branch was found to manifest a peculiar behaviour around the reduced wave vector [Formula: see text]; a careful examination did not reveal any corresponding distinctive behaviour in the linewidth (lifetime). A search for possible manifestations of the Kohn effect at high temperature was also performed along the [00ζ]T and [00ζζ]L branches.

Larose, A., & Brockhouse, B. N. (1976). Lattice vibrations in copper at elevated temperatures studied by neutron scattering. Canadian Journal of Physics, 54(19), 1990–2009.