Enhancement of the thermopower in Nax CoO2 in the large-x regime (x ≥ 0.75)

Minhyea Lee, Liliana Viciu, Lu Li, Yayu Wang, M. L. Foo, S. Watauchi, R. A. Pascal, Robert Joseph Cava, Nai Phuan Ong

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

We observe two distinct phases of Nax CoO2 in the large Na-doping region (x ≥ 0.75), a pure phase H2, and a mixed phase H2 + H3. The H2 phase is characterized by a steep increase of the Peltier conductivity α defined as J = α (- ∇ T), where J the thermoelectric current driven by the temperature gradient - ∇ T. The mixed-phase state H2 + H3 exhibits an unusual layered phase separation with conducting layers existing in parallel with insulating ones. At the critical doping xp ∼ 0.85, the figure-of-merit Z at 80 K is 40 times larger than that of the as-grown sample (x ∼ 0.7). The Hall coefficient and magnetoresistance are also reported.

Original languageEnglish (US)
Pages (from-to)1564-1568
Number of pages5
JournalPhysica B: Condensed Matter
Volume403
Issue number5-9
DOIs
StatePublished - Apr 1 2008

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering

Keywords

  • Figure-of-merit
  • Hall effect
  • Mixed phase
  • Thermopower

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