Correlation of the thermal and electrical conductivities of nanoporous gold.

We measured the thermal and electrical conductivities of nanoporous Au thin foils in the temperature range 93-300 K. Resulting from the nanoscale microstructure, the two types of conductivities are both temperature dependent and significantly lower than those of bulk Au. However, the corresponding Lorenz number is strikingly similar to that of bulk Au, indicating that the Wiedemann-Franz law holds perfectly well for nanoporous metals in this temperature range. Compared to the bulk value, the Debye temperature of nanoporous Au is decreased. We predict the theoretical Debye temperature of nanoporous Au by its relation to the elastic constants. The present results indicate that the nanoporous Au foils should be comprised of macroscopic, single-crystalline porous grains rather than nanocrystals.