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Large enhancement of the thermopower in NaxCoO2 at high Na doping

Nature Materials volume 5, pages 537–540 (2006)Cite this article

Abstract

Research on the oxide perovskites has uncovered electronic properties that are strikingly enhanced compared with those in conventional metals. Examples are the high critical temperatures of the cuprate superconductors and the colossal magnetoresistance in the manganites. The conducting layered cobaltate NaxCoO2 exhibits several interesting electronic phases as the Na content x is varied1,2,3,4, including water-induced superconductivity4 and an insulating state3 that is destroyed by field5. Initial measurements1 showed that, in the as-grown composition, NaxCoO2 has moderately large thermopower S and conductivity σ. However, the prospects for thermoelectric cooling applications faded when the figure of merit Z was found to be small at this composition (0.6<x<0.7). Here we report that, in the poorly explored high-doping region x>0.75, S undergoes an even steeper enhancement. At the critical doping xp∼0.85, Z (at 80 K) reaches values ∼40 times larger than in the as-grown crystals. We discuss prospects for low-temperature thermoelectric applications.

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Figure 1: In-plane resistivity ρ versus T in log-linear scale.
Figure 2: The in-plane thermopower S and the figure of merit Z in NaxCoO2.
Figure 3: Curves of the Peltier conductivity α versus T and scaling of the α–T curves in selected samples.
Figure 4: Variation of α (50 K) and σ (300 K) versus x in NaxCoO2 at large x.

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Acknowledgements

We acknowledge support from the US Office of Naval Research (Contract N00014-04-1-0057) and by the National Science Foundation Grant DMR 0213706.

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Author notes

  1. Yayu Wang

    Present address: Department of Physics, University of California, Berkeley, California, 94720, USA

  2. M. L. Foo

    Present address: Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada

  3. S. Watauchi

    Present address: Division of Synthesis of Superconducting Materials, Yamanashi University, Yamanashi, 400-8511, Japan

Authors and Affiliations

  1. Department of Physics, Princeton University, Princeton, New Jersey, 08544, USA

    Minhyea Lee, Lu Li, Yayu Wang & N. P. Ong

  2. Department of Chemistry, Princeton University, Princeton, New Jersey, 08544, USA

    Liliana Viciu, M. L. Foo, S. Watauchi, R. A. Pascal Jr & R. J. Cava

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Correspondence to N. P. Ong.

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Supplementary information and figures S1, S2, S3 (PDF 380 kb)

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Lee, M., Viciu, L., Li, L. et al. Large enhancement of the thermopower in NaxCoO2 at high Na doping. Nature Mater 5, 537–540 (2006). https://doi.org/10.1038/nmat1669

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