Tunnel manganese dioxide

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,... 

Figure 2. Representation of the Psilomelane structure (treble chains of MnO6 octahedra joined to double chains of same, resulting in extended tunnel structure) of manganese dioxide. In aqueous media the terminal groups may have coordinated H2O or OH (or their dissociated equivalents, OH- or O ) present.

The crystal structure of romanechite (or psilomelane) is closely related to that of a-MnO,. Where as the or-modification of manganese dioxide consists of cornersharing double chains of MnO octahedra connected trough common edges, the romanechite structure is build up by crosslinking of chains of double and triple octahedra, as shown in Fig. 7(b). The resulting [2 X 3] tunnels, extending in the h direction of the monoclinic cell, are partially... 

Stability of tunnel structure of various forms of a-Mn02 upon repeated insertion and removal of lithium ions from manganese dioxides. 

Nanomaterials can also be tuned for specific purposes through doping. Specifically, the effect of the presence of manganese oxides on photocatalysis involving primarily titanium dioxide will be considered in this section. Titanium dioxide is a well-known photocatalyst and will be considered separately. K-OMS-2, which has a cryptomelane structure, is illustrated in Figure 8.4. Not all the literature discussed in this section, however, involves OMS tunnel structure materials. For example, amorphous manganese oxide (AMO) is also discussed as a photocatalyst. Manganite (MnOOH) is also included in battery applications. 

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