The crystal chemistry of hydrotalcite-like compounds is investigated by powder diffraction methods such as Rietveld structure refinement, radial distribution function analysis, atom-specific radial distribution analysis obtained from anomalous diffraction data, and EXAFS spectroscopy. The topology of the brucite-type layer as well as the layer stacking arrangement and the intralayer bonding are determined for Mg,Al, Mg,Ga, and Ni,Al systems. The occurrence of long-range cation ordering in materials with M(II)/M(III) cation ratios close to 2.0 is observed only for systems with similar cation radii, and it is associated with a corrugation of the octahedral layer. The lack of ordering for systems with highly different cation radii is ascribed to the layer compression exhibited by these compounds, which prevents the layer distortion. The stacking arrangement is random for the solids investigated, except for the Mg,Al system which shows a preference for the rhombohedral polytype. It is proposed that this behavior is related to the extent of local directional bonds between the oppositely charged layers.

The structure of the phases obtained upon dehydration and decomposition of hydrotalcite-like compounds is investigated by several experimental techniques. A reaction mechanism is proposed encompassing a change in coordination of the M(III) cations during the dehydration step. The formation of a 3-dimensional structure occurs upon the subsequent decomposition of the interlayer anions and dehydroxylation of the octahedral layers. In the decomposed material the cations are trapped in the interstices of a regular oxygen cubic close packed lattice and exhibit a considerable disorder. Strains develop during the decomposition, which are likely related to the observed increase of surface area. The thermal stability of the decomposed materials is connected to the reduced cation diffusivity in the oxygen lattice.

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