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

Abstract

The phonon dispersion has been measured on in situ--grown bcc titanium at 1020 \ifmmode^\circ\else\textdegree\fi{}C. A band of low-frequency and strongly damped phonons extending along the Brillouin surface from ${\mathrm{T}}_{[11\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}0]}$ 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 \ensuremath{\omega} (under pressure) and from bcc to hcp (upon lowering the temperature).