Hostname: page-component-78c5997874-g7gxr Total loading time: 0 Render date: 2024-11-05T03:00:12.727Z Has data issue: false hasContentIssue false

Electromagnetic and Thermoelectric Characteristics of NaxCoO2 of Precisely Controlled Na Nonstoichiometry

Published online by Cambridge University Press:  11 February 2011

Teruki Motohashi
Affiliation:
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226–8503, Japan
Maarit Karppinen
Affiliation:
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226–8503, Japan
Hisao Yamauchi
Affiliation:
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226–8503, Japan
Get access

Abstract

Electromagnetic and thermoelectric characteristics of a sodium-cobalt oxide, NaxCoO2, were investigated. A precise control of Na nonstoichiometry was successfully facilitated by an unusual synthesis method named “rapid heat-up” technique. With increasing x, the absolute value of resistivity (ρ) monotonically decreased, while the value of thermoelectric power (S) increased, giving rise to a drastic enhancement in the thermoelectric power factor, i.e. S2 / ρ. Simultaneously enhanced thermoelectric power and reduced resistivity of the present compound are difficult to be understood within the framework of a conventional band picture. Moreover, for samples with the solubility limit Na content, i.e. x = 0.75, we discovered an unconventional electronic transition at Tm = 22 K, which may be induced by the strong-correlation effect of 3d electrons.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Terasaki, I., Sasago, Y., and Uchinokura, K., Phys. Rev. B 56, R12685 (1997).Google Scholar
2. Terasaki, I., in Proceedings of the 18th International Conference on Thermoelectrics (IC T'99), Baltimore, MD, Aug. 29 - Sept. 2, 1999 (IEEE, Piscataway, 2000) pp. 569 - 576.Google Scholar
3. Fouassier, C., Matejka, G., Reau, J.-M, and Hagenmuller, P., J. Solid State Chem. 6, 532 (1973).Google Scholar
4. Motohashi, T., Naujalis, E., Ueda, R., Isawa, K., Karppinen, M., and Yamauchi, H., Appl. Phys. Lett. 79, 1480 (2001).Google Scholar
5. Motohashi, T., Karppinen, M., and Yamauchi, H., in Oxide Thermoelectrics (Research Signpost, India, 2002) pp. 7381.Google Scholar
6. Jansen, V.M. and Hoppe, R., Z. Anorg. Allg Chem. 408, 104 (1974).Google Scholar
7. Tojo, T., Kawaji, H., Atake, T., Yamamura, Y., Hashida, M., and Tsuji, T., Phys. Rev. B 65, 052105 (2002).Google Scholar
8. Kawata, T., Iguchi, Y., Ito, T., Takahata, K., and Terasaki, I., Phys. Rev. B 60, 10584 (1999).Google Scholar
9. Motohashi, T., Ueda, R., Naujalis, E., Tojo, T., Terasaki, I., Atake, T., Karppinen, M., and Yamauchi, H., Phys. Rev. B, submitted; J. Low Temp. Phys. (2003) in press.Google Scholar