  Inelastic neutron scattering measurements are utilized to explore relative
changes in the generalized phonon density of states of nanocrystalline Si1xGex
thermoelectric materials prepared via ball milling and hot-pressing techniques.
Dynamic signatures of Ge clustering can be inferred from the data by
referencing the resulting spectra to a density functional theoretical model
assuming homogeneous alloying via the virtual-crystal approximation.
Comparisons are also presented between as-milled Si nanopowder and bulk,
polycrystalline Si where a preferential low-energy enhancement and lifetime
broadening of the phonon density of states appear in the nanopowder. Negligible
differences are however observed between the phonon spectra of bulk Si and hot
pressed, nanostructured Si samples suggesting that changes to the single phonon
dynamics above 4 meV play only a secondary role in the modified heat conduction
of this compound.
