Misfit layer compounds

The structures of all these phases are built up from TX2 layers consisting of sheets of octahedra, similar to those in the Cdl2 structure of TiS2 or sheets of trigonal prisms similar to those found in the (3-MoS2 structure of NbS2. These are separated by 

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Wiegers GA (1996) Misfit Layer Compounds Stmctures and Physical Properties. Prog SoUd State Chem 24 1-139... 

Figure 4.31 Idealized structures of misfit-layer compounds (a) (LaS)i.20CrS2 (b) (SnS)i.i7 NbS2 (c) (Ca2CoO3)0.62(CoO2) and (d) (Bi0.87SrO2)2(CoO2)i.s2. The shaded polyhedra represent sheets of MX6 octahedra (a, c, d) or trigonal prisms (b).

G. A. Wiegers, Misfit Layer Compounds Structures and Physical Properties, Prog. Solid State Chem., 24, 1-139 (1996). 

Misfit layered compounds of the type, (RX) (TX2) , where R is a rare earth, Pb or Bi, T = Ti, V, Nb or Ta and X = S or Se, are typical incommensurate phases that have been investigated in detail (Rouxel Meerschaut, 1994). The incommensuration here arises from a structural misfit between the rocksalt-like RX and layered TXj dichalcogenide units which are stacked alternately. The interplay of structure and electron-transfer from the RX to TXj units gives rise to novel electronic properties. For... 

Cario, L., Lefond, A., Palvadeau, A., Deudon, P., and Meerschault, C. (1999). Evidence of a mixed valence state for europium in the misfit layer compound [(EuS)i.5]i. i5NbS2 by means of a superspace structural determination, Mossbauer spectroscopy and magnetic measurements. /. Solid State Chem. 147, 58-67. 

Figure 52 (a) The MQ and TQ2 parts of a misfit layer compound, (b) Different stacking motifs between the so-called quadratic and hexagonal slabs... 

The misfit layer compounds are typified by materials with a formula MS +fiTS2)m, in which T is a transition metal atom, Ti, V, Cr, Nb, or Ta, and M is a large atom such as Sn, Pb, Bi, with stereochemically active electron lone pairs, or a lanthanide. The structures are built from S-T-S layers, in which the metal T takes trigonal-prismatic coordination. These layers are interleaved with layers of the halite structure, usually two or three atom layers in thickness, with composition MSx. This leads to a chemical formula of [MSx]n(71S 2)m, where n varies from approximately 1.08-1.24, and m takes values of 1-3, depending upon the nature of T and M. A typical example is the compound [(Lni/3Sr2/3S)i.5]i.i5 NbS2. In all of the misfit layer compounds, the lattice parameter of the interpolated halite layers fit one lattice parameter of the rS2 layer but not the other, so that in this direction, the... 

Exfoliation is also facilitated by mechanical methods such as the application of high-intensity ultrasound. High-intensity ultrasound is known to increase the rate of intercalation reactions. However, in recent studies on the exfoliation of the misfit layer compounds PbNb2S5 and SmNb2S5, some degree of dispersion was obtained by ultrasonic treatment in specific solvents such as ethanol and isopropanol. ° The solvents were not intercalated, but acted to stabilize the dispersions. The dispersions contained a substantial fraction of particles with fewer than 10 layers, but only a small fraction was exfoliated. Along with the ion exchange reaction under relatively severe conditions compared with other layered... 

The misfit layer compounds are typified by materials with a formula in which T is a transition metal... 

Fig. 7.4 The large supercell representing the (PbS)i.14X382 misfit layer compound containmg 296 atoms. In the TaS2 layer 4 Ta atoms are substituted by Pb and in the PbS double layers 12 Ta atoms substitute the corresponding Pb atoms leading to a strong relaxation. For further details see [32]...

Misfit layered compounds are ternary chalcogenides of the general formula (AX)MX2 (A = Pb, Bi, Sn, or rare earth M = Cr, Nb, Ta, or V X = S or Se). This class of compounds has a unique structure composed of alternate stacking of... 

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