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The compound NiCo 2 O 4 , with spinel-related structure, has been prepared by thermal decomposition of metal nitrates and its bulk structural properties examined by means of magnetic measurements, neutron diffraction, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results suggest a delocalised electron distribution on the octahedral sites with average oxidation states of z3.5 and z2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo 2 O 4 of {Ni 3z 0.1 Co 2z 0.9 } tet [Ni 3.5z 0.9 Co 2.5z 1.1 ] oct O 4 . This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co 3z and Ni 3z . The surface of NiCo 2 O 4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co 2z , Co 3z , Ni 2z , Ni 3z and, probably, Ni 4z .

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Nanometric mixed iron-titanium oxides were prepared by mechanical milling with a view to determining their ability to act as anodic materials in lithium cells. At a TiO 2 /Fe 2 O 3 mole ratio of 0.4, a solid-state reaction occurs that leads to the formation of Fe 5 TiO 8 , which possesses a spinel-like structure; at lower ratios, however, the structure retains the hematite framework. Li/g-Fe 2 O 3 cells exhibit poor electrochemical reversibility; by contrast, Ti-containing electrodes possess improved cycling properties. Changes in the electrodes upon cycling were examined by X-ray photoelectron spectroscopy ͑XPS͒. XPS data confirm the participation of electrolyte in the electrochemical reaction and the different type of electrochemical reversibility exhibited by samples. Both processes were influenced by the presence of titanium. Titanium dioxide, in the presence of iron oxides, seems to be inactive to the electrochemical process. Based on the step potential electrochemical spectroscopy ͑SPES͒ curves and photoelectron spectra obtained, the presence of Ti increases the reversibility of the redox reactions undergone by the electrolyte during discharge/charge processes. The increased active-material/electrolyte/inactive-material interaction which is reported here offers new perspectives for the use of well-known transition oxides as anode materials in Li-ion batteries.

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Abstract-We present a method that combines Mˆssbauer spectroscopy and X-ray diffraction to quantify the modal mineralogy of unequilibrated ordinary chondrites (UOCs). Despite being a fundamental tool in the interpretation of geological systems, there are no modal mineralogical data available for these meteorites. This is due to their fine-grained nature, highly heterogeneous silicate mineralogy, and the presence of poorly characterized phases. Consequently, it has not been possible to obtain accurate modal mineralogy by conventional techniques such as point counting.Here we use Mˆssbauer spectroscopy as a preliminary identification technique and X-ray diffraction provides the quantification for a suite of recent UOC falls. We find the most primitive UOCs to contain a significant amount of phyllosilicate material that was converted during metamorphism to form ferromagnesian silicates. A complete suite of Antarctic samples is analyzed by each method to observe mineralogical trends and these are compared with trends shown by recent falls. The fact that mineralogical relationships shown by finds and falls are in agreement allows us to be confident that we are observing the products of pre-terrestrial alteration.Mˆssbauer spectroscopy reveals evidence of steadily increasing reduction with metamorphism in the UOCs. Because this technique allows comparisons to be made between UOCs and EOCs, our reduction sequence can be combined with other evidence showing progressive oxidation in the EOCs. This yields an integrated model of changing redox conditions on equilibrating ordinary chondrite parent bodies.

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