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.