Observation of precursory phonons of an F.C.C.-H.C.P. transition

A study of the phonon dispersion relation in a Co0.65Ni0.35 alloy shows some novel features, which may be connected to the transition from the f.c.c. to the h.c.p. phase, which is expected at lower temperatures. In fact, in the study of the [ζζζ] T branch in the f.c.c. phase the presence of extra phonon peaks is observed at intermediate q-values, though the static f.c.c. phase cannot allow for the presence of a new branch. It is believed that a softened optical branch of the h.c.p. phase which interacts with the acoustic branch of the f.c.c. phase may cause the observed phonon structure.