Manganese dioxide structure

Sn-doped Mn02 oxide retained about 71 %, while undoped MnC>2 retained only 40.2% from their initial capacities at 40th cycle. The capacity loss observed in the first cycles in undoped Mn02 was attributed to the small amount of lithium ions inserted in the Mn02 electrode that could not be easily removed from the structure. Similar detrimental effect of cycling on the manganese dioxide structure, but with smaller amplitude, occurred in Sn-Mn02. The reason for a much smaller capacity fade in Sn-doped materials was the enhancement of the structural stability by the presence of the framework Sn ions, which contributed to the reduction of Jahn-Teller ions. 

Fig. 3. Crystal structure of manganese dioxides where ( ) represent Mn and (° ), and the lines define the octahedra hoUandite (6), psilomelane (7),...

R. G. Bums and V. M. Bums, Structural Relationships Between Manganese(IW) Oxides in The Manganese Dioxide Symposium, Vol. 1,1. C. Sample Office, 1975. 

Structural Chemistry of Manganese Dioxide and Related Compounds... 

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 ... 

The presence of the foreign cation stabilizes the crystal structure of a - Mn02 compounds. This manganese dioxide modification (more exactly it is not a real MnOz modification, since the structure contains a considerable proportion of foreign atoms) can be heated to relatively high temperatures (300 - 400 °C) without destruction of the lattice. Although Thackeray et al. reported the synthesis of cation-and water- free a - MnOz [49, 50J, which is reported to be stable up to 300 °C without destruction of the [2 x 2] tunnel structure, it is commonly believed that a small,... 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Shao-Hom Y., Hackney S. A., Comilsen B. C., Structural characterization of heat-treated electrolytic manganese dioxide and topotactic transformation of discharge products in the Li-Mn02 cells, J. Electrochem. Society, (1997) 144, 3147-3153. 

It is shown that electrolytic manganese dioxide, which has been obtained from fluorine-containing electrolytes differs from traditional types of Mn02 obtained by state-of-the-art synthesis methods. This material is characterized by the increased amount of structural defects. It is shown that crystalline structure with a large number of defects has a higher catalytic and electrochemical activity. 

Manganese dioxide has found wide use in different electrochemical power sources as cathode material. It is known that the structure and properties of manganese dioxide depend on the method of its synthesis. 

The observed higher rate of mass transfer in nonstoichiometric oxides makes it possible to operate at discharge current densities on the order of 2 - 5 mA/cm2, which is several times greater than that used with the conventional manganese dioxide. Thus, the purposeful disordering of structure of a cathode material of manganese dioxide allows to utilize such power sources in extreme conditions - for element discharge at a low... 

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