Layered compounds, electrical conductivity

Titanium disulfide has a Cdl2 structure (see Chapter 1). The solid is golden-yellow and has a high electrical conductivity along the titanium layers. Forming intercalation compounds with electron donors can increase the conductivity of titanium disulfide, the best example being with lithium, LLTiS2. This compound is synthesized in the cathode... 

It is evident from the studies carried out by Wesseling (34) on other polymer compounding systems that the electrical conductivity in such cases is of a complex percolation type which is primarily confined to the thin surface layer of the graphite coating the large, globular insulating polymer... 

The pronounced anisotropy of the electrical conductivity in layered compounds (8,15) suggests that the charge carriers move, on their way to the surface, predominantly within the layers, i.e. parallel to the main surface as shown in Fig. 14 (in which the relative path of the charge carriers within the layers is compressed). The random character of interlayer charge transport due to extrinsic conduction leads to a variety of possible paths, two of which are represented in Fig. 14. 

In recent years a set of interesting compounds known as graphitic compounds have been developed. In these compounds different atoms have been fitted in between the layers of carbon atoms to produce a substance with a greater electrical conductivity than pure graphite. Graphite is also used as a component in certain sports equipment, such as tennis and squash rackets. 

Polymer nanotubes composites are now extensively studied. Indeed, one may associate the properties of the polymer with those of nanotubes. This is the case of the mechanical reinforcement of standard polymer for example, but also one can take advantage of the specific electronic properties of the nanotubes. Therefore, we prepared composites with either saturated polymers like polymethylmethacrylate and MWNTs [27]. The electrical conductivity of these compounds as a function of the nanotube content exhibits for example a very low percolation threshold, (a few % in mass) and therefore they can be used as conducting and transparent layers in electronic devices such as Light Emitting Diodes (LEDs). Another type of composite that we have studied is based on the use of a conjugated polymer, polyphenylene-vinylene (PPV) known for its photoluminescence properties and SWNTs. We prepared this composite by mixing SWNTs to the precursor polymer of PPV. The conversion into PPV was subsequently performed by a thermal treatment at 300°C under dynamical vacuum [28],... 

The formation of vacancy rows in the layers of ionic compounds must result in the occurrence of strong electrical fields, especially at low temperatures when their electrical conductivity is insufficiently high. These fields will undoubtly affect the process of layer growth and may even lead to its arrest. The value of this effect may be estimated following N.F. Mott and R.W. Gurney.180... 

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