Investigation of the Phonon Dispersion Relations of Chromium by Inelastic Neutron Scattering

The phonon dispersion relations for chromium have been measured at room temperature in three symmetry directions using the triple-axis neutron diffractometer at the Missouri University Research Reactor. Careful consideration was given to focusing techniques associated with instrumental resolution. Consequently, the most appropriate experimental configuration, leading to the most favorable focusing criteria, was used for each phonon measurement. The experimentally determined phonon dispersion relations for chromium showed at least four regions of anomalous behavior not previously observed. The regions of anomalous behavior are shown to be related to the structure of the Fermi surface of chromium in agreement with recent band-structure calculations. A fourth-nearest-neighbor Born-von K\'arm\'an analysis of the dispersion relations has been used to calculate the frequency distribution function for chromium.