Phonon dispersion of the bcc phase of group-IV metals. I. bcc titanium

The phonon dispersion has been measured on in situ grown bcc titanium at 1020°C. A band of low-frequency and strongly damped phonons extending along the Brillouin surface from T[110] 1/2(1,1,0) to L 2/3(1,1,1) is found. These strongly anharmonic phonons have been measured at various temperatures between the bcc-to-hcp transition temperature and the melting point. Geometrical considerations show how these large-amplitude lattice vibrations are related to the displacements which are necessary for the two martensitic phase transitions from bcc to (under pressure) and from bcc to hcp (upon lowering the temperature).