Mode localization and suppressed heat transport in amorphous alloys

Glasses usually represent the lower limit for the thermal conductivity of solids, but a fundamental understanding of lattice heat transport in amorphous materials can provide design rules to beat such a limit. Here we investigate the role of mass disorder in glasses by studying amorphous silicon-germanium alloy (a-Si1-xGex) over the full range of atomic concentration from x = 0 to x = 1, using molecular dynamics and the quasiharmonic Green-Kubo lattice dynamics formalism. We find that the thermal conductivity of a-Si1-xGex, as a function of x exhibits a smoother U shape than in crystalline mass-disordered alloys. The main contribution to the initial drop of thermal conductivity at low Ge concentration stems from the localization of otherwise extended modes that make up the lowest 8% of the population by frequency. Contributions from intermediate frequency modes are decreased more gradually with increasing Ge to reach a broad minimum thermal conductivity between concentrations of Ge from x = 0.25 to 0.75. Modal analysis unravels the correlations among localization, line broadening, and the contribution to thermal transport of modes within different frequency ranges.

Automated summary

Studying amorphous silicon-germanium alloy revealed the impact of mass disorder on the thermal conductivity of glasses, showing that Ge concentration affects the thermal conductivity and contributions from different frequency modes. The analysis unraveled correlations among localization, line broadening, and the contribution to thermal transport of modes within different frequency ranges.