  We present neutron inelastic scattering measurements of the low-energy
phonons in single crystal BiFeO3. The dispersions of the three acoustic phonon
modes (LA along [100], TA1 along [010] and TA2 along [110]) and two low energy
optic phonon modes (LO and TO1) have been mapped out between 300 K and 700 K.
Elastic constants are extracted from the phonon measurements. The energy
linewidths of both TA phonons at the zone boundary clearly broaden when the
system is warmed toward the magnetic ordering temperature TN = 640 K. This
suggests that the magnetic and low-energy lattice dynamics in this multiferroic
material are coupled.
