PHONONS IN NANOCRYSTALLINE FE-57

We measured the phonon density of states (DOS) of nanocrystalline Fe b y resonant inelastic nuclear gamma-ray scattering. The nanophase mater ial shows large distortions in its phonon DOS. We attribute the high e nergy distortion to lifetime broadening. A damped harmonic oscillator model for the phonons provides a low quality factor, Q(u), averaging a bout 5, but the longitudinal modes may have been broadened most. The n anocrystalline Fe also shows an enhancement in its phonon DOS at energ ies below 15 meV. The difference in vibrational entropy of the bulk an d nanocrystalline Fe was small, owing to competing changes in the nano crystalline phonon DOS at low and high energies.