X-ray absorption spectroscopy of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Na</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mi mathvariant="normal">Co</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>layered cobaltates

Kröll, Thomas; Knupfer, M.; Geck, J.; Heß, Christian; Schwieger, T.; Krabbes, G.; Sekar, C.; Batchelor, David; Berger, H.; Büchner, B.

doi:10.1103/physrevb.74.115123

Cited by 33 publications

(22 citation statements)

References 49 publications

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“…Likewise, the extrinsic character of Curie tails can be verified. Indeed, thanks to numerous hyperfine couplings through Na-O-Co superexchange paths, 27,28,29 the sodium nuclei are directly probing the average intrinsic cobalt planes spin susceptibility χ spin , as was clearly shown in previous NMR studies. 6,14,26 In practice, this is measured through the shift 23 K of the sodium nuclear resonance line:…”

Section: Doping-dependence Of Spin Susceptibilitymentioning

confidence: 70%

Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates

et al. 2008

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Using 23 Na NMR measurements on sodium cobaltates at intermediate dopings (0.44≤x≤0.62), we establish the qualitative change of behavior of the local magnetic susceptibility at x * =0.63-0.65, from a low x Pauli-like regime to the high x Curie-Weiss regime. For 0.5≤x≤0.62, the presence of a maximum T * in the temperature dependence of the susceptibility shows the existence of an x-dependent energy scale. T1 relaxation measurements establish the predominantly antiferromagnetic character of spin correlations for xx * . It is suggested that at a given x the ferromagnetic correlations might dominate the antiferromagnetic ones above T * . From 59 Co NMR data, it is shown that moving towards higher x away from x=0.5 results in the progressive appearance of nonmagnetic Co 3+ sites, breaking the homogeneity of Co states encountered for x≤0.5. The main features of the NMR-detected 59 Co quadrupolar effects, together with indications from the powder x-ray diffraction data, lead us to sketch a possible structural origin for the Co 3+ sites. In light of this ensemble of new experimental observations, a new phase diagram is proposed, taking into account the systematic presence of correlations and their x-dependence.

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Section: Doping-dependence Of Spin Susceptibilitymentioning

confidence: 70%

Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates

et al. 2008

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“…The O K -edge spectrum of pristine O-Na 2 RuO 3 ( t 2g 4 e g 0 ) shows a large peak at 534 eV, which is ascribed to the unoccupied hybridized orbital of O 2 p –Na 3 p , and its peak intensity simply reflects the amount of Na in the lattice30. The calculated density of states for O-Na 2 RuO 3 (Fig.…”

Section: Resultsmentioning

confidence: 99%

Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

et al. 2016

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Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g−1 (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g−1 (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

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“…In models having alkali-metal ion vacancies (namely Li 0.5 CoO 2 , Na 0.5 CoO 2 , and K 0.5 CoO 2 ), some Co 3+ ions were replaced with Co 4+ to maintain charge neutrality in accordance with results from first-principles calculations 18 and experiments. [19][20][21][22] The positions of the smaller Co 4+ ions were determined by measuring Co-O bond lengths in the initial structure; Co 3+ ions were assigned to positions with longer Co-O bond lengths and Co 4+ ions to shorter Co-O bond lengths, 23,24 and their positions were fixed during the course of the molecular dynamics simulation. A Buckinghamtype potential function was used to describe interactions between pairs of ions.…”

Section: Computational Proceduresmentioning

confidence: 99%

Effect of Ionic Radius and Resultant Two-Dimensionality of Phonons on Thermal Conductivity in M x CoO2 (M = Li, Na, K) by Perturbed Molecular Dynamics

Tada

Yoshiya

Yasuda

2010

Journal of Elec Materi

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Phonon thermal conductivity calculations for Li x CoO 2 , Na x CoO 2 , and K x CoO 2 (x = 1, 0.5) have been carried out by perturbed molecular dynamics to clarify the dependence of thermal conductivity on alkali-metal vacancy concentration in these materials. While thermal conductivity decreased for all compounds upon introduction of alkali-metal vacancies, the magnitude of the decrease is strongly dependent on the size of the alkali-metal ion. Further numerical analyses using fictitious physical parameters reveal that, with increasing ionic radius, the two-dimensionality of the phonons in the CoO 2 layers, which are responsible for overall thermal conductivity, is enhanced, resulting in lower thermal conductivity in vacancy-free compounds as well as ineffectiveness of alkali-metal vacancies in lowering thermal conductivity. In contrast, for systems with smaller alkali-metal ionic radius, even though higher thermal conductivity is predicted when no vacancies are present, vacancies are quite effective in significantly lowering thermal conductivity by modifying phonon states in the CoO 2 layers, more so than in systems with larger alkali-metal vacancies.

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X-ray absorption spectroscopy ofNaxCoO2layered cobaltates

Cited by 33 publications

References 49 publications

Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates

Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates

Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

Effect of Ionic Radius and Resultant Two-Dimensionality of Phonons on Thermal Conductivity in M x CoO2 (M = Li, Na, K) by Perturbed Molecular Dynamics

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