Céline Darie

Effect of iron on delithiation in LixCo1−yFeyO2. Part 2:in-situ XANES and EXAFS upon electrochemical cycling

LixCo1−yFeyO2 solid solutions were examined in an in-situ electrochemical X-ray absorption spectroscopy study using a plastic battery configuration. XANES and EXAFS were applied to elucidate the evolution of local symmetry and oxidation states of iron and cobalt upon electrochemical cycling of three particular stoichiometries: LixCo0.9Fe0.1O2, LixCo0.8Fe0.2O2 and LixCo0.6Fe0.4O2. While the cobalt environment shows little variation, a distortion of the FeO6 octahedra occurs quite rapidly for all three samples with a decrease in the next neighbour numbers from six to four. This is ascribed to the Jahn–Teller effect which affects Fe4+ (a d4 system), that is formed upon delithiation. No distortion is observed for cobalt. Along the delithiation process a simultaneous increase in the edge energy occurs for cobalt and iron in the case of y = 0.1 and to a lesser extent for iron than for cobalt for y = 0.4. This means that the oxidation of Fe3+ occurs together with the oxidation of the cobalt matrix in the cobalt-rich samples but becomes more difficult for iron-rich samples. In the case of the cobalt-rich samples, the edge-energy for both elements shifts back down at the end of charge, in spite of the continuing oxidation of the cations. This effect is probably related to the appearance of a new lithium-poor phase, that is not formed for y = 0.4, and confirms the in-situ X-ray diffraction results published in the first part of this series.

InCuO2.5 and ScCuO2.5: new oxidized copper delafossites with triangular lattices of Cu2+ cations

New oxidized delafossite compounds of composition InCuO2.5 and ScCuO2.5 are synthesized and their structures are characterized by means of x-ray and neutron powder diffraction. Oxygen intake is accompanied by a small increase of the unit cell, and a complex superstructure attributed to oxygen ordering appears. Average structure refinements show the presence of additional oxygen close to the centres of Cu triangles, and an average copper valence of +2. The two compounds appear to be isostructural. Magnetic measurements show a non-linear thermal increase of the inverse magnetic susceptibility up to some maximum, soon followed by a minimum around 280 K.

Evidence for a spinon Fermi surface in the triangular S=1 quantum spin liquid Ba3NiSb2O9

Inelastic neutron scattering is used to study the low-energy magnetic excitations in the spin-1 triangular lattice of the 6H-B phase of Ba

Spin excitations in the antiferromagnet NaNiO2

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Structural and electrochemical properties of new nanospherical manganese oxides for lithium batteries

NiSb

Structural Study of a Doubly Ordered Perovskite Family NaLnCoWO6 (Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb): Hybrid Improper Ferroelectricity in Nine New Members

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Effect of magnesium doping on the orbital and magnetic order in LiNiO2

O

Oxygen doped S = 1/2 Cu delafossites: a muon spin rotation/relaxation study

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Effect of iron on delithiation in LiXCo1-yFeyO2. Part 1: in-situ electrochemical and X-ray diffraction study

. We study two powder samples: Ba

High magnetic field study of quasi-stoichiometric Li1-xNi1+xO2

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