Structure and high temperature thermoelectric properties of delafossite-type oxide CuFe1-xNixO2 (0 ≤ x ≤ 0.05)

Kei Hayashi, Tomohiro Nozaki, Tsuyoshi Kajitani

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We have investigated crystal structure of delafossite-type oxide CuFe 1-xNixO2 (0 ≤ x ≤ 0.05) and measured its thermoelectric properties at high temperatures ranging from 300 and 1100 K. The lattice parameter a of the Ni2+-doped samples is nearly equal to that of CuFeO2, while the lattice parameter c of the Ni 2+-doped samples increases. Nearly constant a-axis is due to the decrease of (Fe/Ni)-O distance and simultaneous increase of O-(Fe/Ni)-O angle. Increase of the c-axis is due to the increase of Cu-O distance in the Ni 2+-doped samples. The valence states of the Fe- and Cu-sites are calculated from bond valence summation. The valence state of the Fe-site in the Ni2+-doped samples is larger than that of CuFeO2, an indication of hole doping in the Fe-site. This increase of hole carriers enhances the electrical conductivity σ. The highest electrical conductivity is 18 S/cm. Although the Seebeck coefficient S decreased by Ni 2+ doping, the S is still high value (S > 250 μV/K). The thermal conductivity κ of CuFe1-xNixO2 is relatively high (κ > 4 W/mK). The maximum dimensionless figure of merit ZT = σS2T/κ = 0.14 is obtained with the sample of x = 0.01 at 1100K, being higher than that of the polycrystalline γ-Na 0.7CoO2. There is no significant evaporation of the constituent elements after the heat cycles.

Original languageEnglish
Pages (from-to)5226-5229
Number of pages4
JournalJapanese Journal of Applied Physics
Issue number8 A
Publication statusPublished - 2007 Aug 6


  • Delafossite
  • Thermoelectric properties
  • X-ray diffraction


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