Crystal structure and transport properties of γ-NaxCoO2 (x=0.67 - 0.75)

Yasuhiro Ono, Nobuhiko Kato, Yoshinobu Ishii, Yuzuru Miyazaki, Tsuyoshi Kajitani

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

Crystal structure and transport properties of γ-NaxCoO2 have been studied in the range of x=0.67 - 0.75. Single-phase samples were prepared by sintering mixture of raw materials, Na2CO3 (99.5%) and Co3O4 (99.9%). Na/Co composition ratio (x) was determined by inductively coupled plasma (ICP) analysis. The crystal structure parameters were refined by Rietveld analysis of powder neutron diffraction intensities, assuming P63/mmc type space symmetry. Little changes in the crystal structure are noticed, except for Na contents. Electric resistivity ρ and Seebeck coefficient S were measured at temperatures between 380 K and 1000 K by the standard four-probe method and temperature-gradient method, respectively. The ρ-T curves exhibit the thermal hysteresis in the initial measurement. But, in the following measurement, the thermal hysteresis is significantly suppressed. The S was slightly higher in the sample with x=0.75 than in the others at any temperatures. Power factor (S2/ρ) reaches its maximum value at x = 0.75 (5.3 × 10-4 W/mK2 at 980 K). Hot pressing technique is effective in removing the thermal hysteresis of ρ as well as increasing the power factor.

Original languageEnglish
Pages (from-to)469-474
Number of pages6
JournalFuntai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy
Volume50
Issue number6
DOIs
Publication statusPublished - 2003 Jun

Keywords

  • Hot press
  • Layered cobaltite
  • Neutron diffraction
  • Rietveld analysis
  • Transport properties

ASJC Scopus subject areas

  • Mechanical Engineering
  • Industrial and Manufacturing Engineering
  • Metals and Alloys
  • Materials Chemistry

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