Marked effects of alloying on the thermal conductivity of nanoporous materials.

We show that porous alloys can display thermal conductivity reductions at considerably larger pore sizes than nonalloyed porous materials of the same nominal porosity. The thermal conductivity of Si0.5Ge0.5 alloy with 0.1 porosity becomes half the nonporous value at 1000 nm pore sizes, whereas pores smaller than 100 nm are required to achieve the same relative reduction in pure Si or Ge. Using Monte Carlo simulations, we also show that previous models had overestimated the thermal conductivity in the small pore limit. Our results imply that nanoporous alloys should be advantageous with respect to nanoporous nonalloys, for applications requiring a low thermal conductivity, such as novel thermoelectrics.