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Updated: May 31, 2026
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Modulated and unmodulated structures, and the transport mechanisms in the triangular lattice system Na(x)CoO(2) with
Masashige Onoda1, Tomohiro Ikeda
1Institute of Physics, University of Tsukuba, Tennodai, Tsukuba 305-8571, Japan.
Abstract:
The crystal structures of the triangular lattice system γ-phase Na(x)CoO(2) with compositions of [Formula: see text], 0.58 and 0.65 have been determined by means of x-ray four-circle diffraction. Na(0.58)CoO(2) has lattice constants of a(h) = 2.8180(5) and c(h) = 11.005(9) Å with space group P6(3)/mmc and does not exhibit structural modulation. On the other hand, Na(0.65)CoO(2) has a P6(3)/mmc-type superlattice with a doubled unit cell of a(sh) = 5.6527(5) and c(sh) = 10.9356(10) Å, and Na(0.48)CoO(2) indicates a Pmmn-type superlattice with a(so) = 5.6261(5), b(so) = 11.1406(10) and c(so) = 4.8723(5) Å. The structural modulation for [Formula: see text] is attributed to the incomplete order of Na ions without an order for Co valence, while that for [Formula: see text] results in almost complete Na order and partial valence order for Co. For [Formula: see text], the metal-poor metal transition occurs at about 50 K. The electrical resistivities for [Formula: see text] and 0.65 follow a T(3/2) dependence below 200 and 80 K, respectively, which may be due to antiferromagnetic spin fluctuations in three dimensions. At higher temperatures, the resistivities for the CoO(2) plane have a T(1) dependence, likely due to an enhancement of two dimensionality. For [Formula: see text], the resistivity maximum appears at about 250 K, which may be attributed to the renormalization effect of the Fermi surface by the fluctuations.
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