Thermal conductivity of bulk and nanowire Mg 2 Si x Sn 1 − x alloys from first principles

The lattice thermal conductivity ($\ensuremath{\kappa}$) of the thermoelectric materials, Mg${}_{2}$Si, Mg${}_{2}$Sn, and their alloys, are calculated for bulk and nanowires, without adjustable parameters. We find good agreement with bulk experimental results. For large nanowire diameters, size effects are stronger for the alloy than for the pure compounds. For example, in 200 nm diameter nanowires $\ensuremath{\kappa}$ is lower than its bulk value by 30$%$, 20$%$, and 20$%$ for Mg${}_{2}$Si${}_{0.6}$Sn${}_{0.4}$, Mg${}_{2}$Si, and Mg${}_{2}$Sn, respectively. For nanowires less than 20 nm thick, the relative decrease surpasses 50$%$, and it becomes larger in the pure compounds than in the alloy. At room…

• NS
  National Science Foundation

  Awards: 1066634, OCI-105357, 1066406, OCI-1053575, 1053575
• UD
  U.S. Department of Energy

  Awards: OCI-1053575, DE-FG, DE-FG02-09ER46577, DE-FG02-, 66406, DE-FG02
• AN
  Agence Nationale de la Recherche
• DA
  Defense Advanced Research Projects Agency
• OO
  Office of Science

  Awards: OCI-1053575, S3TEC, DE-FG02-09ER46577
• SS
  Solid-State Solar Thermal Energy Conversion, Massachusetts Institute of Technology

  Award: DE-FG02-09ER46577
• BE
  Basic Energy Sciences

  Awards: OCI-1053575, DE-FG02, DE-FG02-09ER46577