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Fig. 4 | Geochemical Transactions

Fig. 4

From: Cryptomelane formation from nanocrystalline vernadite precursor: a high energy X-ray scattering and transmission electron microscopy perspective on reaction mechanisms

Fig. 4

Scheme of vernadite layer and of atomic pairs involving Mn atoms. a Scheme of a vernadite layer, seen along c* with grey octahedra representing (MnO6)8− octahedra. The first three atomic shells formed by layer Mn around a given layer Mn (Mn–MnLX pairs, were X stands for the atomic shell) are highlighted with concentric circles. Green full circles with a “1” mark, red full circles with a “2” mark, orange full circles with a “3” mark, and “4” marks respectively schematize layer Mn belonging to the first, second, third and fourth (only partly represented) atomic shells. b Scheme of a layer seen perpendicular to c*. Blue octahedra are layer vacancies, which are capped on one side by TCMn3+ (purple octahedra). The first layer Mn to TCMn pair (Mn–TCMn1) as well as the first TCMn to TCMn pair, when the two atoms are on opposite sides of the layer (TCMn–TCMn1), are represented. “T” stands for “top” and means that a TCMn is located on the other side of the layer as compared to a TCMn labeled “B” (standing for “bottom”). c Scheme of a layer containing 1/4 vacancy (blue octahedra) per layer octahedron, vacancies being ordered. Purple octahedra are omitted for clarity, only the captions “T” and “B” are left to materialize TCMn. The first TCMn–TCMn pair is highlighted with arrows. d Same as c, but with a layer containing 1/3 vacancy per layer octahedron

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