The layered double hydroxide (LDH) of Co with Al decomposes to yield an oxide residue with the spinel structure below 250°C. The decomposition reaction is preceded by the formation of an intermediate hydroxide in which the metal hydroxide layers are regularly stacked about the 𝑐-crystallographic axis, but the layers themselves are aperiodic. Aperiodicity is modeled by locating randomly chosen Co2+ ions in tetrahedral sites in the interlayer region. This phase is characterized by a single strong basal reflection in its powder diffraction pattern. All other reflections are extinguished on account of
turbostratic disorder which destroys all ℎ𝑘𝑙 reflections and
layer aperiodicity, which destroys all two dimensional ℎ𝑘 reflections.
Given its topochemical relationship with the spinel structure, such an intermediate is a necessary precursor to spinel formation.
Volume 42 | Issue 6
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