Electricity superconductors

Niobium has special cryogenic properties. It can withstand very cold temperatures, which improves its abihty to conduct electricity. This characteristic makes it an excellent metal for low-temperature electrical superconductors. 

Table 8.5 Selected Electrical Superconductors. Structural Details for Some Entries are Given in Section 12.3...

In this analysis the transition is defined as a step change in the heat capacity of the sample as a function of temperature. By far the most important transition that is generally considered to be second order is the glass transition, Tg. However, for completeness, other examples of second-order transitions include Curie point transitions where a ferromagnetic material becomes paramagnetic, the transition from an electrical superconductor to a normal conductor, and the transition in helium from being a normal liquid to being a superfluid at 2.2 K. 

Conductors are nearly always metals, copper being a particularly good conductor, and are usually in wire form but they can be gases or liquids, water being a particularly good conductor of electricity. Superconductors is a term given to certain metals which have a very low resistance to electricity at low temperatures. 

Thus far the importance of carbon cluster chemistry has been in the discovery of new knowl edge Many scientists feel that the earliest industrial applications of the fullerenes will be based on their novel electrical properties Buckminsterfullerene is an insulator but has a high electron affinity and is a superconductor in its reduced form Nanotubes have aroused a great deal of interest for their electrical properties and as potential sources of carbon fibers of great strength... 

CERAMCS-ELECTRONIC PROPERTIES AND MATERIALSTHUCTURE] (Vol5) -in superconductors [CERAMICS AS ELECTRICAL MATERIALS] (Vol5)... 

Electrically Functional. Refractory coatings are used in semiconductor devices, capacitors, resistors, magnetic tape, disk memories, superconductors, solar ceUs, and diffusion barriers to impurity contamination from the substrate to the active layer. 

Electrical and Electronic Applications. Silver neodecanoate [62804-19-7] has been used in the preparation of a capacitor-end termination composition (110), lead and stannous neodecanoate have been used in circuit-board fabrication (111), and stannous neodecanoate has been used to form patterned semiconductive tin oxide films (112). The silver salt has also been used in the preparation of ceramic superconductors (113). Neodecanoate salts of barium, copper, yttrium, and europium have been used to prepare superconducting films and patterned thin-fHm superconductors. To prepare these materials, the metal salts are deposited on a substrate, then decomposed by heat to give the thin film (114—116) or by a focused beam (electron, ion, or laser) to give the patterned thin film (117,118). The resulting films exhibit superconductivity above Hquid nitrogen temperatures. 

Electrical Properties at Low Temperatures The eleciiical resistivity of most pure metalhc elements at ambient and moderately low temperatures is approximately proportional to the absolute temperature. At very low temperatures, however, the resistivity (with the exception of superconductors) approaches a residual value almost independent of temperature. Alloys, on the other hand, have resistivities much higher than those of their constituent elements and resistance-temperature coefficients that are quite low. The electrical resistivity of alloys as a consequence is largely independent of temperature and may often be of the same magnitude as the room temperature value. 

Superconductivity The physical state in which all resistance to the flow of direct-current electricity disappears is defined as superconductivity. The Bardeen-Cooper-Schriefer (BCS) theoiy has been reasonably successful in accounting for most of the basic features observed of the superconducting state for low-temperature superconductors (LTS) operating below 23 K. The advent of the ceramic high-temperature superconductors (HTS) by Bednorz and Miller (Z. Phys. B64, 189, 1989) has called for modifications to existing theories which have not been finahzed to date. The massive interest in the new superconductors that can be cooled with liquid nitrogen is just now beginning to make its way into new applications. 

Some of the alkali metal-group 15 element systems give compounds of stoichiometry ME. Of these, LiBi and NaBi have typical alloy stmc-tures and are superconductors below 2.47 K and 2.22 K respectively. Others, like LiAs, NaSb and KSb, have parallel infinite spirals of As or Sb atoms, and it is tempting to formulate them as M+ (E )" in which the (E )" spirals are iso-electronic with those of covalently catenated Se and Te (p. 752) however, their metallic lustre and electrical conductivity indicate at least some metallic bonding. Within the spiral chains As-As is 246 pm (cf. 252 pm in the element) and Sb-Sb is 285 pm (cf. 291 pm in the element). 

Many metal sulfides have important physical properties.They range from insulators, through semiconductors to metallic conductors of electricity, and some are even superconductors. 

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). 

Superconductivity is the loss of all electrical resistance when a substance is cooled below a certain characteristic transition temperature (Ts). It is thought that the low temperatures are required to reduce the effect of the vibrations of the atoms in their crystalline lattice. Superconductivity was first observed in 1911 in mercury, for which Ts = 4 K. Over the years, many other metallic superconductors were identified, some having transition temperatures as high as 23 K. However, low-temperature superconductors need to be cooled with liquid helium, which is very expensive. To use superconducting devices on a large scale, higher transition temperatures would be required. 

All metals conduct electricity on account of the mobility of the electrons that bind the atoms together. Ionic, molecular, and network solids are typically electrical insulators or semiconductors (see Sections 3.f3 and 3.14), but there are notable exceptions, such as high-temperature superconductors, which are ionic or ceramic solids (see Box 5.2), and there is currently considerable interest in the electrical conductivity ol some organic polymers (see Box 19.1). 

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