Effects of oxide additive on thermoelectricity of FeSi2
Thermoelectricity has been hot issue in these days, because of environmental problems and energy sources deficit. Moreover, material development for thermoelectricity is now busy in oxide and metal or alloy, basically. However, conclusive materials with good performance have not yet been found in application basis. We have studied oxide-added beta-FeSi2 for these years. Iron disilicide is well known and utilized in relatively higher temperature. In this report, we indicated our successful improvement of performance of beta-FeSi2 added with Ta2O5 showing the figure of merit almost 0.3 times 10-3/K This was obtained by reducing thermal conductivity and electrical resistivity (a half of standard FeSi2)
Large thermoelectric power in NaCo 2 O 4 single crystals
We measured and analyzed the transport properties of single-crystal ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$, which is a metallic transition-metal oxide consisting of a two-dimensional triangle lattice of Co. Reflecting the crystal structure, the resistivity is highly anisotropic between in- and out-of-plane directions, and the in-plane resistivity is as low as 200 $\ensuremath{\mu}\ensuremath{\Omega}$ cm at 300 K. Most strikingly, the in-plane thermoelectric power of ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ is about 100 $\ensuremath{\mu}$V/K at 300 K, which is nearly ten times larger than that of typical metals. The large thermoelectric power and the low resistivity suggest that ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ is a potential thermoelectric material.
Thermoelectric properties of transition-metal oxide NaCo/sub 2/O/sub 4/ system
A transition-metal oxide NaCo/sub 2/O/sub 4/ system has been synthesized by a standard solid-state reaction method, and the thermoelectric properties have been measured. The resistivity /spl rho/ and the thermoelectric power /spl alpha/ of the as-sintered NaCo/sub 2/O/sub 4/ is 2 m/spl Omega/cm and 100 /spl mu/V/K at room temperature, respectively. By hot-pressing, the electrical resistivity is reduced to about 60%, and by Ba- or Bi-substitution for Na, Cu- or Bi-substitution for Co, the thermoelectric power is enhanced up to 1.4 times. For all the samples, the figure-of-merit shows a flat temperature dependence over a wide range from 100 to 400/spl deg/C, and in the hot-pressed Na(Co/sub 0.95/Cu/sub 0.05/)/sub 2/O/sub 4/, the maximum value of 0.88/spl times/10/sup -3/ K/sup -1/ is achieved around 300/spl deg/C, with /spl rho/=2 m/spl Omega/cm, /spl alpha/=147 /spl mu/V/K, and the thermal conductivity /spl kappa/=1.3 W/mK. In spite of being a low carrier mobility material, NaCo/sub 2/O/sub 4/ system shows good thermoelectric performance. This indicates the possibility of applying low-mobility materials to thermoelectric devices, and thus the NaCo/sub 2/O/sub 4/ system will be a prospective candidate for thermoelectric materials.