Thermo-Electric Properties of Cu and Ni Nanoparticles Packed Beds

The hot-wire method and the four-probe resistivity method are applied to probe the thermal conductivity (k) and the electric conductivity (sigma) of Cu and Ni nanoparticle packed beds (NPBs). A fitting method based on classical physical theory is devised to separate k(e) (electronic thermal conductivity) and k(p) (phonon thermal conductivity) from k at room temperature. Results turn out that k(p) only accounts for a small proportion of k (4-20%); the proportion decreases with increasing porosity or temperature. Most importantly, this fitting method provides a simple way to separate k(e) and k(p) from k at room temperature. The Wiedemann-Franz law is checked and is found to be unsuitable for NPBs. The Lorenz number (L) is calculated from measurements of k(e), k, and sigma Results turn out that L is found to be 50-60 times that of the bulk. With a Seebeck coefficient (S) measured, the thermoelectric property of NPBs is also calculated. We find that the NPB possess an advantage in thermoelectric property than bulk, the thermoelectric figure of merit (ZT) of Ni (Cu) NPBs can be 20.17 (1.87) times that of bulk Ni (Cu). The effect of porosity on ZT is also discussed, and results show that a NPB with a small porosity is more preferable as a thermoelectric material. With a small porosity, ZT can be even 1.73 times that of a large porosity. Although metals are not good thermoelectric material, the method in this paper supplies a way to improve the thermoelectric property of other thermoelectric materials.