Letter abstract

Nature Materials 5, 537 - 540 (2006)
Published online: 11 June 2006 | doi:10.1038/nmat1669

Subject Categories: Ceramics | Electronic materials

Large enhancement of the thermopower in NaxCoO2 at high Na doping

Minhyea Lee1, Liliana Viciu2, Lu Li1, Yayu Wang1,3, M. L. Foo2,4, S. Watauchi2,5, R. A. Pascal Jr2, R. J. Cava2 & N. P. Ong1


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 sigma. 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 xpapprox0.85, Z (at 80 K) reaches values approx40 times larger than in the as-grown crystals. We discuss prospects for low-temperature thermoelectric applications.

  1. Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
  2. Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
  3. Present address: Department of Physics, University of California, Berkeley, California 94720, USA
  4. Present address: Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
  5. Present address: Division of Synthesis of Superconducting Materials, Yamanashi University, Yamanashi 400-8511, Japan

Correspondence to: N. P. Ong1 e-mail: npo@princeton.edu


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