Thermal and Electrical Properties of gamma-NaxCoO2 (0.70 < x < 0.78)

Abstract

We have performed specific heat and electric resistivity measurements of Na${}_x$CoO${}_2$ ($x=0.70$-0.78). Two anomalies have been observed in the specific heat data for $x=0.78$, corresponding to magnetic transitions at $T_c=22$ K and $T_k\simeq 9$ K reported previously. In the electrical resistivity, a steep decrease at $T_c$ and a bending-like variation at $T_b$(=120K for $x=0.78$) have been observed. Moreover, we have investigated the $x$-dependence of these parameters in detail. The physical properties of this system are very sensitive to $x$, and the inconsistent results of previous reports can be explained by a small difference in $x$. Furthermore, for a higher $x$ value, a phase separation into Na-rich and Na-poor domains occurs as we previously proposed, while for a lower $x$ value, from characteristic behaviors of the specific heat and the electrical resistivity at the low-temperature region, the system is expected to be in the vicinity of the magnetic instability which virtually exists below $x=0.70$.

4 pages (3 figures included) and an extra figure (gif), to be published in J. Phys. Soc. Jpn. 73 (9) with possible minor revisions

References in corpus (8)

• Charge-ordering, commensurability and metallicity in the phase diagram of layered Na(x)CoO(2)
• Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy
• Giant electron-electron scattering in the Fermi-liquid state of Na_0.7CoO_2
• Bulk antiferromagnetism in $\mathbf{N}{\mathbf{a}}_{0.82}\mathbf{Co}{\mathbf{O}}_2$ single crystals
• Static magnetic order in Na${}_{0.75}$CoO${}_2$ detected by muon spin rotation and relaxation
• Mesoscopic phase separation in Na${}_x$CoO${}_2$ ($0.65\le x\le 0.75$)
• Mass-Enhanced Fermi Liquid Ground State in Na${}_{1.5}$Co${}_2$O${}_4$
• Synthesis, Characterization, and Magnetic Properties of gamma-NaxCoO2 (0.70 < x <0.84)

Cited by in corpus (8)

• Investigation of the Spin Density Wave in NaxCoO2
• 17-O NMR studies of a triangular-lattice superconductor Na{x}CoO{2}yH{2}O
• Spin fluctuations, magnetic long-range order and Fermi surface gapping in NaxCoO2
• Considerable non-local electronic correlations in strongly doped Na${}_x$CoO${}_2$
• NaxCoO2: Enhanced low-energy excitations of electrons on a 2D triangular lattice
• Interplay between mesoscopic phase separation and bulk magnetism in the layered NaxCoO2
• The magnetic field and pressure dependence of the magnetic ordering transition in NaxCoO2 (0.6<x<0.72)
• Thermopower enhancement from engineering the Na${}_{0.7}$CoO${}_2$ interacting fermiology via Fe doping