Ramsdellite structure

Figure 3 3D view of the pyrolustite structure Figure 4 3D view of the ramsdellite structure (reproduced from [1]) (reproduced from [1])... 

Ramsdellite is thermodynamically unstable toward a transformation into the stable ft -modification. Hence, it is rarely found in natural deposits. Natural ramsdellite has a stoichiometry close to the composition of Mn02 and can be considered another true modification of manganese dioxide. Attempts to synthesize ramsdellite in the laboratory usually lead to materials of questionable composition and structural classification. It is very likely that synthetic ramsdellite materials are more or less well-crystallized samples of the y-modification that will be described in more detail below. 

Further improvements on the previously discussed models were proposed in the latest model for y - and e - Mn02 by Chabre and Pannetier [12, 43, 44], Starting from De Wolff s model they developed a structural description of manganese dioxides that accounts for the scattering function of all y - and e - Mn02 materials and provides a method of characterizing them quantitatively in terms of structural defects. All y — and e - Mn02 samples can be described on the basis of an ideal ramsdellite lattice affected by two kinds of defects ... 

Figure 1. The structures of (a) a - Mn02, (b) P MnOj, Mn02, and (d) ramsdellite -Mn02 Hatched regions represent MnOfi octahedra...

The structure of the lithiated ramsdellite- Mn02 product after reaction with LiOH at 300 °C is shown in Fig. 3(d) [6]. The overall ideal reaction, which is similar to that when LiOH is used as a lithiating agent, can be written as ... 

In this case, lithiation of ramsdellite occurs by incorporation of Li20 into the Mn02 structure, which is analogous to the situation for the stabilization of a - MnOz (see Sec. 1.2.2) the reaction... 

Fig. 7.4 Tunnel structures based on rutiles, (a) Rutile-like chains, showing alternately short and long metal-metal distances, as in MoOj. (h)-(

Structure-type corundum spinel ramsdellite hollandite lepidocrocite smectite jarosite... 

Bystrom, A. M. (1949) The crystal structure of ramsdellite, an orthorhombic modification of Mn02. Acta Chem. Scand., 3,163-73. 

During the synthesis of OMS-1 and OL-1, several other phases can be produced. In particular, psilomelane, pyrolusite and ramsdellite can be formed. Pyrolusite has a composition of Mn02 which has a simple tetragonal rutile structure... 

The monoxides are known for all of the rare earth metals. They are all crystallizing at low temperatures isostructural to the NaCl-type. EU3O4 crystallizes orthorhombic [45, 46] with space group Pnam. This mixed valent compound contains Eu + and Eu + in the cation sublattice with a distorted octahedral coordination around Eu + and a coordination number of eight around Eu +. Fig. 3-19 shows the projection of the structure down [010]. The octahedral framework around Eu + can be related by a twinning operation (glide reflection) to the structure of ramsdellite (hep). 

---