E. Chappel

Interlayer magnetic frustration in quasistoichiometric Li1-xNi1+xO2

Susceptibility, high-field magnetization, and submillimeter-wave electron spin resonance measurements of layered quasistoichiometric Li 1 - x Ni 1 + x O 2 are reported and compared to isomorphic NaNiO 2 . A mechanism of magnetic frustration induced by the excess Ni ions always present in the Li layers is proposed. We finally comment on the possible realization of an orbital liquid state in this controversial compound.

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

Structural changes occurring upon electrochemical delithiation in LixCo1−yFeyO2 solid solutions have been examined using in-situ electrochemical X-ray diffraction on plastic batteries, for y = 0.1, 0.2, 0.4 and 0.7. Two key points are emphasised in this study: (i) the influence of partial iron substitution on the LixCoO2 phase diagram, especially regarding the multiple phase transitions present for 0 ≤ x ≤ 1, (ii) the redox behaviour of iron along with cobalt during the electrochemical process. The y = 0.1 and y = 0.2 samples could be totally delithiated and resemble unsubstituted LixCoO2: these systems are two-phase in the range 0.6 < x < 0.9, where two distinct rhombohedral phases coexist, and a specific phase exists in the highly delithiated region. However no ordered analog to Li0.5CoO2 is found. The symmetry of the completely delithiated phases is trigonal (O1, CdI2-type, Pm1 space group) and monoclinic (O3, CdCl2-type, C2/m space group) for y = 0.1 and 0.2, respectively. For LixCo0.6Fe0.4O2, the two-phase regime is maintained down to x = 0.4, and no new phase is detected down to x = 0.18. The electrochemical capacities obtained show that iron is involved in the oxidation process. This will be confirmed by EXAFS and XANES measurements, the results of which are published in the second part of this series.

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

The high-field magnetization of quasi-stoichiometric Li1−xNi1+xO2 and NaNiO2 samples is measured. A new mechanism of magnetic frustration is proposed for Li1−xNi1+xO2. Finally, we comment on recent proposals of quantum spin orbital liquid.

On the metamagnetic state in Er1−xTxCo2 (T=Y, Tm) compounds

In ErCo2, owing to the substitution of Y or Tm for Er, a reduction of the exchange field HfdCo inducing an itinerant magnetic moment on the Co sites is observed. Close to the critical concentration for a collapse of the itinerant d moment inverse itinerant-electron metamagnetism is studied as a function of both external magnetic field and pressure.

Magnetic structure of Li1-xNi1+xO2

Abstract To describe the magnetic properties of the layered Li 1−x Ni 1+x O 2 compounds we use a mean field model with a weak ferromagnetic coupling J 2 F within the Ni planes between Ni 3+ ions, an interlayer antiferromagnetic interaction J AF between Ni 2+ present in the Li layers and their Ni 3+ nearest neighbours and an intraplane ferromagnetic interaction J 1 F between Ni 2+ and Ni 3+ ions in the Ni planes. The hierarchy ∣J 1 F ∣>∣J AF ∣> J 2 F ∣ is deduced from experimental data.

Magnetic structure of S=1/2 triangular Li1−xNi1+xO2

Abstract The sign and the hierarchy of the magnetic interactions in Li 1− x Ni 1+ x O 2 have been the subject of controversy for long and renewed recently by its promising properties for batteries. Here, based on a systematic experimental study performed on carefully characterized samples, a new theoretical scheme is proposed: well oriented ferromagnetic clusters are progressively formed with increasing doping x . Therefore, the cluster magnetization M C increases up to a critical value, and then, for x > x c , M C decreases due to excess Ni 2+ –Ni 3+ interplane antiferromagnetic interactions.