The electrical and thermal properties of metallic nanostructures have attracted considerable fundamental and technological interests. Recent studies confirmed a dramatic decrease in the electrical and thermal conductivities when the dimension is comparable or even smaller than the electron mean free path. However, the verification of the Wiedemann-Franz law in these nanostructures remains hotly debated. The Lorenz number obtained from the two-probe measurement is found to be much larger than that from the four-probe measurement. Here, we reported the electrical and thermal properties of the individual silver nanowires measured by the two-probe and four-probe configurations. The measured electrical contact resistance is found to be nearly temperature-independent, indicating a ballistic-dominant electronic transport at the contacts. When the effect of thermal contact resistance is diminished, the Lorenz number measured by the four-probe configuration is comparable to the Sommerfeld value, verifying that the Wiedemann-Franz law holds in the monocrystalline-like silver nanowire. Comparatively, the derived electrical conductivity becomes smaller and the thermal conductivity becomes larger in the two-probe measurement, confirming that the electrical contact resistance will introduce a large error. The present study experimentally demonstrates a reasonable explanation to the discouragingly broad span in the Lorenz number obtained from different metallic nanostructures.

Solid solution has been considered as an effective approach to advanced thermoelectrics. However, the benefit from the decrease in lattice thermal conductivity induced by the impurity scattering will be compensated by the reduction in carrier mobility, therefore suppressing the maximum figure of merit (zT). We demonstrate the characteristics of the fundamental properties, including the lattice thermal conductivity and carrier mobility, of undoped PbSe1−xSx solid solutions (0 < x < 1) at room temperature, which provide an efficient way to evaluate the maximum zT of the materials with optimum doping. The lattice thermal conductivity is found to decrease significantly after adding a small amount of PbSe into PbS matrix up to the composition of PbSe0.7S0.3 when the carrier mobility remains virtually unchanged, indicating the beneficial effect of impurity scattering to improve the thermoelectric performance.