Thermoelectric properties of Li-doped Cu 0.95-x M 0.05 Li x O (M=Mn, Ni, Zn)
- PDF / 330,829 Bytes
- 5 Pages / 432 x 648 pts Page_size
- 109 Downloads / 211 Views
Thermoelectric properties of Li-doped Cu0.95-xM0.05LixO (M=Mn, Ni, Zn) N. Yoshida, T. Naito and H. Fujishiro* (* corresponding author: [email protected]) Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, Japan. ABSTRACT Thermoelectric properties of the Li-doped Cu0.95-xM0.05LixO (M=divalent metal ion; Mn, Ni, Zn) were investigated at the temperature up to 1273 K. In the doped divalent metal ions, Zn2+ ion was the most effective to reduce the thermal conductivity, and the Ni2+ substitution was preferable to decrease the electrical resistivity. For the Cu0.95-xNi0.05LixO sample at x=0.03, the maxima of the dimensionless thermoelectric figure of merit ZT and the power factor P at 1246 K were 4.2×10-2 and 1.6 ×10-4 W/K2m, respectively. The enhancement of the thermoelectric properties of the Li-doped Cu0.95-xM0.05LixO system was discussed. INTRODUCTION The thermoelectric technology using a waste heat for electric power generation devices has been revised because of recent energy crisis besides other renewable energy sources. Since the discovery of NaCo2O4 in 1998 [1], oxide thermoelectric materials have been intensively studied using Ca-Co-O and NaCo2O4 systems with layered Co-O octahedron [2,3], as a substitute for the conventional semiconductors such as Bi2Te3. However, the thermoelectric performance has been still low. In material researches for thermoelectricity, we focus on the possibility of a conventional CuO system, because it is inexpensive, plentiful and non-toxic resources. CuO is known to be a metal deficient p-type semiconductor with a band gap of 1.2 eV with monoclinic crystal structure, and many studies were reported for the physical properties [4,5]. High-purity CuO has a large positive Seebeck coefficient S, but shows both a high electrical resistivity ρ and a high thermal conductivity κ. If the doping or substitution of univalent or trivalent ions is possible for the Cu site, the electrical resistivity and the thermal conductivity might be decreased. In this case, the thermoelectric efficiency may be enhanced, if the Seebeck coefficient is not deteriorated so much. Similarly to the CuO system, ZnO is a plentiful and promising material for the n-type thermoelectricity with a simple wurtzite structure [6]. The electrical resistivity ρ drastically decreases by the doping of a small amount of Al3+ and/or Ga3+, and the dimensionless thermoelectric figure of merit ZT (=S2T/ρκ) reaches 0.3 and 0.65 at 1273 K for Zn0.98Al0.02O and Zn0.96Al0.02Ga0.02O, respectively [7,8]. For the CuO system, the electric conductivity σ (=1/ρ) and Seebeck coefficient S were reported for the Li and Al doping, in which the Li-doping enhances the p-type electrical conductivity [9]. However, a systematic investigation has not been performed as a thermoelectric material of CuO as for the doping species and the optimum doping concentration. Recently, we have reported the alkali metal substitution for the Cu-site in CuO, in which Li+ is the most promising ion to enhance the thermoelectric performance. The ZT
Data Loading...
