X-ray diffraction studies of the spinel series Mg(CrxAl2-x)O4I. Lattice parameters and structure

Synthesis of nanoporous spheres of cubic gallium oxynitride and their lithium ion intercalation properties

Cubic spinel structured gallium oxynitride has been synthesized through the reaction of metallic gallium and water in the presence of organic ethylenediamine. The relative content of the mixed solvent of water and ethylenediamine controls the product morphology and structure. A novel well-defined nanoporous structure has finally been obtained, whose large surface area and peculiar surface chemistry will generate novel physical and chemical properties. As an example, lithium intercalation properties for prospective applications in lithium ion batteries are demonstrated in this work.

True space group of spinel-type chromium oxides and sulfides, and ternary lithium chlorides – band structure calculations

The results of band structure (extended Hückel procedure) and cohesive energy calculations of spinel-type chromium oxides and sulfides, and of lithium vanadium chloride were presented. They confirm that the D3dto C3vsymmetry reduction of the octahedrally coordinated metal ions (Cr, V) of the respective oxides and of Li2VCl4(space group F-43m instead of Fd-3m) is caused by relatively strong metal-metal bonds with crystal orbital overlap populations (COOP) up to 10% of those of the metal-oxygen bonds despite M-M distances ≅300pm. In the case of spinel-type chromium sulfides, the Cr-Cr interactions are antibonding in nature and, hence, no symmetry reduction occurs.

New symmetry and structure for spinel

The crystal structure of magnesium aluminate is conventionally described within a symmetry corresponding to the centrosymmetrical space group Fd3m but this has created difficulties for the interpretation of many of its physical properties. Therefore, extensive X-ray diffraction intensity data have been collected from a small spherical synthetic single crystal and used for a structure parameter refinement assuming F4̅3m symmetry as proposed by Grimes ( Phil. Mag . 26, 1217‒1226 (1972)), and also for refinement according to conventional symmetry. The F4̅3m assumption yields the first direct measurement of the suspected deviations from the centrosymmetrical structure, and is found to provide a significantly superior fit to the experimental data, especially at high angles and with reflexions having structure factors less than 10.0. The weak reflexions include nine that are forbidden under Fd3m symmetry and it is shown that there is satisfactory agreement between observed and calculated structure factors in these cases.