Properties of Superconductors

In electrochemical terms, one of the expected employment of superconductors is as electrode materials. However, before considering the eventual benefits offered to electrochemistry by such materials we must introduce the physical, physico-chemical and structural properties of superconductors.1... 

Before studying the properties of superconductors one must have efficient electrodes of these materials available. However, their fragile, porous and chemically non-inert nature makes them unsuitable in principle for use as electrodes. 

The classical tunneling experiment of Giaever (1960) provided unambiguous proof of the BCS theory of superconductivity. The STM as a local tunneling probe is certainly suitable to probe the local properties of superconductors, such as the local structure of the Abrikosov flux lattice. The work of Hess and co-workers (1989, 1990, 1990a, 1991) is a prominent example. 

Figure 6.9 Properties of superconductors (a) resistivity-temperature curve for a pure (solid) and an impure (broken) superconductor (b) magnetization as a function of external field for type I superconductor (c) magnetization curve for a type II superconductor.

By Ohm s law, the resistance of the conducting medium vanishes, and the medium becomes a superconductor. The Higgs mechanism and spontaneous symmetry breaking were derived using the properties of superconductors. 

An interesting property of superconductors is their ability to create a mirror image of a magnetic field within themselves. As a result, they are repelled by magnetic fields and can even be levitated above them (see Fig. 1.53). This property has led to research on the possibility of levitating railroad trains and other vehicles fitted with superconductors over magnetic tracks (see Fig. 3.43). 

Until now we have been discussing the properties of superconductors in general, and the examples that we have given were usually classical types with transition temperatures Tc below 24 K, and which usually were studied with liquid helium (at 4.2 K) as the refrigerant. The discovery of the cuprate materials that superconduct above 77 K raises the possibility of commercial applications using liquid nitrogen as the cooling fluid. This considerably reduces... 

In parallel studies, an even more interesting physical property, the superconductivity of organic materials, has been discovered. For example, 1 1 charge-transfer complexes of tetrathiafulvalene 81 (Scheme 1.24) and tetracya-noquinodimethane 82 were shown to display not only metal-like conductivity at ambient temperature but also properties of superconductors at low temperatures. Numerous compounds of this and other types were synthesized and tested. Especially promising results were obtained with charge-transfer salts of bis(ethylenedithio)tetrathiafulvalene 83 with simple inorganic anions. Some of... 

In the case of superconductors, although the structures are macroscopic they have to be described by quantum mechanics. It is a unique property of superconductors to show quantum structures on a macroscopic scale. (For instance the magnetic flux trapped in the vortices mentioned in this section is given by the expression, = -j -. The dimension of the core of such a... 

FIGURE 1. Physical properties of superconductors, (a) Resistivity vs. temperature for a pure and perfect lattice (solid line) impure and/or imperfect lattice (broken line), (b) Magnetic-field temperature dependence for Type-I or soft superconductors, (c) Schematic magnetization curve for hard" or Type-II superconductors. 

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