doi:10.1016/S0167-2738(02)00570-2 We have prepared LiCo1−yAlyO2 and LiNi0.5−yAlyCo0.5O2 (0≤y≤0.3) powder samples by a low temperature sol–gel method using succinic acid as chelating agent. We have studied the details of their crystallographic and local structure by X-ray diffraction (XRD) and FTIR spectroscopy, respectively; we have analyzed their chemical composition by ICP and obtained information about the morphology of the polycrystalline particles by SEM. Also, we have studied the electrochemical performance of the as-prepared materials in the Li LiNi0.5−yAlyCo0.5O2 cells cycled in the potential range 2.5–4.2 V finding that the overall capacity of the oxides has been reduced due to the metal substitution. For example, at 4.2 V cut-off, the charge capacity of the Li LiNi0.35Al0.15Co0.5O2 cell is ca. 115 mA h/g. However, more stable charge–discharge cycling performances have been obtained as compared to those displayed by the native oxides. Finally, we have characterized the kinetics of Li-diffusion by the galvanostatic intermittent titration technique and, according to our results, Al substitution provides an increase in the chemical diffusion coefficients of Li ions in the LiNi0.5−yAlyCo0.5O2 matrix

Polycrystalline samples of the charge ordered mixed oxide LaMn 0.5 Co 0.5 O 3Ϫδ (T CO ϭ 400 K) have been prepared by the nitrate decomposition method. These samples are biphasic, according to XRPD, and except one, oxygen defficient (δ ϳ 0.04-0.05). The study of the dielectric properties of these samples reveal that LaMn 0.5 Co 0.5 O 3Ϫδ displays a high dielectric constant, specially at room temperature and low frequencies. This εЈ r is seen to be strongly dependent on the particle size and not so much on the oxygen defficiency and the best properties are found in the sample with biggest particle size (φ ϭ 7 μm) for which εЈ r (300 K) ϳ 10 5 up to

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We present in this paper a detailed investigation of the dielectric properties of the mixed oxide CaMn7O12 that shows a charge-ordering transition at TCO = 440 K. Surprisingly, this compound presents a high dielectric constant at room temperature. Data taken at several frequencies and temperatures point to relaxor dielectric behaviour, that can be attributed to the electronic inhomogeneities present in the material. Extrinsic Maxwell–Wagner effects make a significant contribution to this dielectric response, as revealed by the studies made on samples of different particle size and using different types of contact. The intrinsic dielectric constant of this material is εr (intrinsic)′∼30 at room temperature, a value that is relatively high for this type of compound and that we relate to the presence of the electronic process of charge ordering in this material.

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