Quasi-three-dimensional conductor

Finally, a supramolecular three-dimensional network formed through - - secondary bonds has been described for the related tellurium compound (TMTTeN)2[Au(CN)2] (TMTTeN = (2,3,6,7-tetramethylnaphtho[l,8-cd 4,5-c d ]bis [l,2]ditellurole), a salt which is a quasi-three-dimensional conductor [76]. The donor molecules are stacked along the c-axis and take the same orientation with a short interplanar distance of about 3.4 A and a large slip distance of approximately 4 A. There are several intermolecular - - contacts, and a three-dimensional network through tellurium atoms is developed between the intracolumns and intercolumns. 

In the majority of quasi-one-dimensional compounds the superconducting transition is not observed, since at higher temperatures there takes place a phase transition into a dielectric state. It has been suggested that suppression of the dielectric transition by impurities may be beneficial for producing superconductivity. This concept is based on the absence of the non-magnetic impurity influence on the superconducting transition in three-dimensional conductors. 

Below it is shown that in quasi-one-dimensional conductors the impurities suppress both the dielectric and superconducting transitions. This is related to the fact that the BCS formula for the superconducting transition temperature cannot be applied to quasi-one-dimensional conductors. For the three-dimensional case the transition temperature is determined by the density of electron states, its dependence on the impurity concentration being weak. In contrast, in the quasi-one-dimensional case this temperature depends on the amplitude of the electron pair jump from one thread to another and from the type of the one-dimensional correlation function. 

We will see that it is the interactions between chains or sheets that is responsible for finite temperature transitions. That is the reason for labeling systems of chains or sheet as quasi-one- or two-dimensional. They exhibit one- or two-dimensional behavior until there occurs a crossover to higher dimensionality. Obviously, crystals do exist and as such must be three-dimensional. Binding forces are intrinsically three-dimensional. Let us then take for granted the existence of the crystalline backbone of organic conductors and concentrate on the electronic properties which are of interest to conduction. It is the strong anisotropy in these which is responsible for the stamp of quasi-one- or quasi-two-dimensional solids. 

A detailed discussion of charge transfer in quasi-one-dimensional organic conductors can be found in Refs. 114 and 142. According to the classification of Ref. 114, three methods can be used to evaluate the charge transfer ... 

Quasi-solid-state electrolytes include gel polymer electrolytes, ionic liquids, and plastic crystal systems. It is important to distinguish polymer electrolytes and gel polymer electrolytes. In polymer electrolytes, charged cationic or anionic groups are chemically bonded to a polymer chain, while gel polymer electrolytes are solvated by a high dielectric constant solvent and are free to move. In a classical gel electrolyte, polymer and salts are mixed with a solvent, usually having a concentration above 50 wt%, and the role of the polymer is to act as a stiffener for the solvent, creating a three-dimensional network, where cations and anions move freely in the liquid phase [88]. The solid polymer electrolyte includes poly(ethylene oxide) (PEO)-based lithium ion conductors that typically show conductivities of 10 S cm while the gel polymer electrolytes have semisolid character with much higher ionic conductivities of the order 10 —10 S cm . ... 

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