We calculate the lattice thermal conductivity in model ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ nanocomposites by molecular dynamics in a transient thermal conduction regime. Our simulations provide evidence that thermal transport depends only marginally on stoichiometry in the range $0.2\le x\le 0.8$, while it is deeply affected by the granulometry. In particular, we show that ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ nanocomposites have lattice thermal conductivity below the corresponding bulk alloy with the same stoichiometry. The main role in affecting thermal conduction is provided by grain boundaries, which largely affect vibrational modes with a long mean-free path.

• Received 24 July 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.065901