PHONON-DISPERSION OF BETA-SC

The phonon dispersion has been measured in the high-temperature bcc phase of a group-III metal (one d electron). In spite of its simple monatomic Bravais lattice the vibrational behavior of beta-Sc is very anisotropic: a valley of low-energy and strongly damped phonons extends along the Brillouin-zone surface. These large-amplitude vibrations displace the lattice towards the stacking sequence of the low-temperature hcp phase and the hitherto unobserved omega structure, and are interpreted as dynamical precursor fluctuations towards the reconstructive phase transitions.