Electrical conductivity superconductivity

In metals, the primary mechanisms of both thermal conductivity and electrical conductivity are the same. Accordingly, the mechanisms of electron-lattice interaction described in the previous section for thermal conductivity apply equally well to electrical conductivity. Superconductivity also depends upon the electron-lattice interaction, albeit in a much more subtle way. A brief discussion of superconductivity completes this section. 

Crystalline solids based upon molecular components exhibit numerous properties of fundamental scientific and technological interest, including electrical conductivity, superconductivity, nonlinear optical l havior, and ferromagnetism.(7) The principle... 

Bismuthides. Many intermetaUic compounds of bismuth with alkafl metals and alkaline earth metals have the expected formulas M Bi and M Bi, respectively. These compounds ate not saltlike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi . Both the alkafl and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particularly noteworthy as having extremely short bond distances between the alkafl metal atoms. 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Metals and semiconductors are electronic conductors in which an electric current is carried by delocalized electrons. A metallic conductor is an electronic conductor in which the electrical conductivity decreases as the temperature is raised. A semiconductor is an electronic conductor in which the electrical conductivity increases as the temperature is raised. In most cases, a metallic conductor has a much higher electrical conductivity than a semiconductor, but it is the temperature dependence of the conductivity that distinguishes the two types of conductors. An insulator does not conduct electricity. A superconductor is a solid that has zero resistance to an electric current. Some metals become superconductors at very low temperatures, at about 20 K or less, and some compounds also show superconductivity (see Box 5.2). High-temperature superconductors have enormous technological potential because they offer the prospect of more efficient power transmission and the generation of high magnetic fields for use in transport systems (Fig. 3.42). 

While on the topic on electrical conduction and resistance offered by an electrically conducting medium it is usual to extend to a phenomenon called superconductivity this has now been recognized as having a profound impact on the electrical field. Exciting possibilities exist. The phenomenon is exhibited by certain types of matter and is characterized by two fundamental properties ... 

Metallic electrical conductivity, in some cases also superconductivity at low temperatures (e.g. NbC, transition temperature 10.1 K). 

Carbon, as graphite, has strong electrical conductivity properties. It is an important component in electrodes used in a variety of devices, including flashhght cells (batteries). Amorphous carbon has some superconduction capabilities. 

Niobium is a very important metal in both ferrous and nonferrous metallurgy. As an additive to alloys or when alloyed with other metals niobium imparts high mechanical strength, high electrical conductivity, and ductihty to alloys. It enhances corrosion resistance of most alloys. The metal and several of its alloys exhibit superconductivity. Nobium is used as an additive in... 

This past decade has seen numerous controversial studies regarding electrical conduction of DNA. Some reported high conductivity [115, 116, 118] with Crt of at most lO" S cm [115] or even superconducting properties [119], while others claimed that the carefully deionized DNA molecules are insulating [117, 120] in agreement with the old reports [121, 122] with ctri- less than 10 S cm. The controversy seems to have settled on a wide consensus that, apart from ionic conduction by the sodium gegenions, double-stranded DNA is an electrical insulator. 

Crystals of (BEDT-TTF)2Re04 are lustrous metallic black in color and are superconducting at a temperature of 2 K at a pressure of 5 k bar.5 In the absence of applied pressure this material shows metallic behavior (increased electrical conductivity as the temperature is decreased) from room temperature to 81 K at which temperature a metal-insulator transition occurs. The crystallographic lattice parameters, for the triclinic unit cell, are5 a = 7.78 A, b = 12.59 A, c — 16.97 A, a = 73.0°, 0 = 79.89°, y = 89.06°, and unit cell volume, Vc = 1565 A3. 

The discovery of electrical conductivity and superconductivity in crystalline materials derived from conventional molecular species effectively introduces a new area of synthetic chemistry. The conductivity is associated with specific molecular arrays and synthesis of the materials requires the ability to conceive and implement the preparation of a particular crystalline state. Molecular conductors are derived from pairs of redox reagents, an area where heterocyclic systems are well established. Placement of heteroatoms of selected electronegativity at chosen positions in a delocalized electron system offers a subtle and effective means for altering the orbital energies which ultimately control the electron transfer properties of redox reagents. 

The electrical conductivity of a pure arsenic crystal has been measured 3 at temperatures down to 2-42° Abs. The resistance-temperature curve is similar to those of pure metals. There is evidence of definite residual resistance being maintained at low temperatures, but arsenic does not exhibit the abnormally high residual resistance shown by bismuth, nor does it show superconductivity. The resistance is by no means proportional to the absolute temperature. It has been estimated that the electrical resistance of liquid arsenic at the melting point is about 0-4 of that of the solid phase.4... 

The conference was opened with a speech by Lorentz on the theory of electrons he had developed about 20 years before, followed by papers by Joffe on the electrical conductivity of crystals, Kamerlingh Onnes on superconductivity, and Hall on the metallic conduction and the transversal effects of the magnetic field. This last speech was followed by a discussion in which Langevin and Bridgman injected a few interesting remarks. 

The electric conductivity of such organic materials makes them related to metals. This was the reason conductive ion radical salt were named organic metals or organic conductors. Some organic conductors can become superconductors under certain conditions. Superconductivity is a disappearance of electrical impedance that allows electric current to flow with no loss of energy. 

The search for new organic metals and superconductors has attracted a great deal of attention in synthetic chemistry and material science since the discovery of high electrical conductivity in conjugated polymers such as polyacetylene [1], Lots of theoretical studies have been carried out in order to understand the mechanism of conductivity and superconductivity in the conjugated polymers and related... 

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