Dichalcogenides layered

As an indication of the types of infonnation gleaned from all-electron methods, we focus on one recent approach, the FLAPW method. It has been used to detennine the band stmcture and optical properties over a wide energy range for a variety of crystal stmctures and chemical compositions ranging from elementary metals [ ] to complex oxides [M], layered dichalcogenides [, and nanoporous semiconductors The k p fonnulation has also enabled calculation of the complex band stmcture of the A1 (100) surface... 

Layered dichalcogenides, such as sulfides or selenides of Ti, Mo, W, Zr, Ta, Nb, V, and Cr, are able to dissolve certain alkali metal ions and in some cases posttransition (pseudo-alkali) metal ions (Cu, Ag ), via a mechanism in which the guest is inserted between the dichalcogenide layers. Lithium ion intercalation into TiS2, which among layered dichalcogenides has been one of the most prominent cathode... 

Surprisingly the layered oxides with the same structures as the layered dichalcogenides were not studied in that time period. The thought was presumably that oxides toward the right of the periodic table would be of little interest, and it was not considered that lithium could be readily removed... 

Fig. 3 Comparison of the structures of (a) graphite and inorganic layered compounds such as (b) NbS2/TaS2 (c) MoS3 (d) BN, In the layered dichalcogenides, the metal is in trigonal prismatic (TaS3) or octahedral coordination (MoSjX...

The disproportionation reactions with graphite of oxidants that are also strong Tewis acids parallel the intercalation of molecular species into the layered dichalcogenides, which are reductants and Tewis bases (see Section 3.2.1). 

Fig. 5.1 Surface structure of various semiconductors a) Ge b) TiO2 c) ZnO d) layered dichalcogenides (MX2)...

The structure is related to that of CdCl, with M(II) ions and P—P pairs occupying the Cd positions and sulfur atoms (close packed) occupying the chloride positions. This structure is very similar to that encountered in the wide class of the layered dichalcogenides MX. Each MPSj layer can also be described as a polymetallic complex, which consists of an array of M(II) cations coordinated to the sulfur atoms of (PjSg) - bridging ligands. This coordination chemist s view turns to be very useful to understand the reactivity of these peculiar materials. 

Layered dichalcogenides are typically two-dimensional compounds. Their structure is built up with [XMX] slabs (X = S, Se, Te) structural units. Within these units are strong ionocovalent or metallic bonds, whereas they are separated by rather large distances (generally of the order of the radii of closest approach) in agreement with weak interslab bondings. 

Table 1 shows the elements that form layered dichalcogenides. In addition a few other elements such as Ni, Co, Ir, Rh, and Pd give only ditellurides derivatives. The structures can be classified with respect to the nature of the slabs and the way they are stacked. 

Table 1. Formation of Layered Dichalcogenides with Octahedral or Trigonal Prismatic Coordination...

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