Temperature and Doping Effect on Thermal Conductivity of Copper-Gold Icosahedral Bimetallic Nanoclusters and Bulk Structures

Molecular dynamics simulations based on analytic potentials are performed to investigate the coefficient of thermal conductivity (CTC) of gold copper (Au-Cu) nanoclusters with 55 atoms and icosahedral (Ih) structure at different compositions via a Green-Kubo formalism, and the results are compared with the corresponding quantities for bulk systems. The temperature dependence of CTC is considered for both AuCu nanoclusters and bulk systems in the 40 K < T < 273 K temperature range. For bulk systems, our results are in excellent agreement with the experiment and show that thermal conductivity decreases with temperature in the range of 40 K < T < 273 K, whereas it increases with temperature in the same range for Au-Cu alloys. The dependence of CTC for bulk AuCu on Cu mole fraction at 273 K is investigated, and a plateau is found as a function of copper doping. Heat transfer for pure copper and gold bulk systems occur mostly via a phonon mechanism, whereas for bulk copper gold alloys a diffusion mechanism is prevalent, explaining the difference in behavior as a function of temperature. For the 55 atom Ih AuCu nanoclusters, the CTC as a function of temperature and copper doping exhibits a nonmonotonous peak at about 80% Cu molar content, with the CTC value for the pure copper nanopartides in good agreement with the experiment. The CTC values for Au, Cu, and Au Cu alloys in nanoform tend to be much lower than the corresponding values in bulk structures with heat transfer occurring also via a convection mechanism that is absent in the bulk.