Phonon frequencies of copper have been measured at 80 K with a neutron crystal spectrometer at a large number of points—mainly in off-symmetry directions. The frequency distribution is calculated, and also the Debye temperature in the interval 0-300 K. The agreement with calorimetric measurements is very satisfactory. Several Born-von Kármán models were fitted to the experimental frequencies. The best fit was obtained using a model with general forces extending to eighth nearest neighbors. The conditions for axial symmetry of the interatomic forces are much better fulfilled in copper than, for instance, in aluminum. However, a general force model is preferable also for copper when a good fit in the whole zone is wanted.

• Received 15 November 1971

DOI:https://doi.org/10.1103/PhysRevB.7.2393