Inelastic neutron scattering study of phonon density of states in nanostructured Si1xGex thermoelectrics

TL;DR

This study uses inelastic neutron scattering to analyze phonon density of states in nanostructured Si1xGex thermoelectrics, revealing insights into phonon behavior and Ge clustering effects relevant to thermal conductivity.

Contribution

It provides a detailed comparison of phonon spectra in nanostructured and bulk Si1xGex, highlighting the limited impact of phonon dynamics above 4 meV on heat conduction.

Findings

Ge clustering signatures inferred from spectra

Nanopowder shows low-energy phonon enhancement

Minimal differences between bulk and nanostructured Si spectra

Abstract

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.