NQR and X-ray investigation of the structure of Na${}_{2/3}$CoO${}_2$ compound

Abstract

We have synthesized various samples of the $x=2/3$ phase of sodium cobaltate Na${}_x$CoO${}_2$ and performed X-ray powder diffractions spectra to compare the diffraction with the structure proposed previously from NMR/NQR experiments [H. Alloul \emph{et al.}, EPL \textbf{85}, 47006 (2009)]. Rietveld analysis of the data are found in perfect agreement with those, and confirm the concentration x=2/3 obtained in the synthesis procedure. They even give indications on the atomic displacements of Na inside the unit cell. The detailed NQR data allow us to identify the NQR transitions and electric field gradient (EFG) parameters for 4 cobalt sites and 3 Na sites. The spin-lattice and spin-spin relaxation rates are found much smaller for the non-magnetic Co${}^{3+}$ sites than for the magnetic sites on which the holes are delocalized. The atomic ordering of the Na layers is therefore at the source of this ordered distribution of cobalt charges. The method used here to resolve the Na ordering and the subsequent Co charge order can be used valuably for other concentrations of Na.

10 figures, 7 tables. Submitted to Phys. Rev. B

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• Patterning of sodium ions and the control of electrons in sodium cobaltate
• Coupling between electronic and structural degrees of freedom in the triangular lattice conductor NaxCoO2
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• 59Co NMR study of the Co states in superconducting and anhydrous cobaltates
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• Spin correlations and cobalt charge states: A new phase diagram of sodium cobaltates
• Na ordering imprints a metallic kagome lattice onto the Co planes of Na2/3CoO2
• Direct link between low temperature magnetism and high temperature sodium order in NaxCoO2
• Na atomic order, Co charge disproportionation and magnetism in Na${}_x$CoO${}_2$ for large Na contents

Cited by in corpus (13)

• 59Co NMR evidence for charge and orbital order in the kagome like structure of Na2/3CoO2
• Magnetic fluctuations and specific heat in NaxCoO2 near a Lifshitz topological transition
• Na order and Co charge disproportionation in Na${}_x$CoO${}_2$
• 23Na NMR study of sodium order in NaxCoO2 with 22K Neel temperature
• Oxygen non-stoichiometry and the origin of Na ion ordering in P2-NaxCoO2
• Evolution of Co charge disproportionation with Na order in Na${}_x$CoO${}_2$
• Dynamic characterization of crystalline and glass phases of deuterated 1,1,2,2 Tetrachloroethane
• Synthesis of sodium cobaltate Na${}_x$CoO${}_2$ single crystals with controlled Na ordering
• Phase segregation in NaxCoO2 for large Na contents
• Origin of the electron disproportionation in the metallic sodium cobaltates
• Interplay between strong correlations and electronic topology in the underlying kagome lattice of Na2/3CoO2
• Hall effect evidence for an interplay between electronic correlations and Na order induced electronic bands topology in NaxCoO2
• Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53