Electrical properties superconductors

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... 

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. 

The situation is very similar in the Chevrel phases. These are ternary molybdenum chalcogenides A,.[Mo6Xg] (A = metal, X = S, Se) that have attracted much attention because of their physical properties, especially as superconductors. The parent compound is PbMo6Sg it contains Mo6Sg clusters that are linked with each other in such a way that the free coordination sites of one cluster are occupied by sulfur atoms of adjacent clusters (Fig. 13.9). The electric properties of Chevrel phases depend on the number of valence electrons. With 24 electrons per cluster (one electron pair for each edge of the... 

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

Figure 6.9 The energy-momentum curve for seven electrons in a superconductor with (a) no applied electric field and (b) an applied electric field. Reprinted, by permission, from L. Solymar and D. Walsh, Lectures on the Electrical Properties of Materials, 5th ed., p. 428. Copyright 1993 by Oxford University Press.

On the basis of the electrical properties, it is advisable to divide these transitions into three general classes and to consider these classes in the following order semiconductor-to-semiconductor transitions in the present chapter, and metal-to-semiconductor and metal-to-superconductor transitions in Chapters 9 and 10. The case of polymers is treated separately in Chapters 11, 12, and 13. 

Interest in the crystalline polymer derived from SjNj, that is poly(sulfur nitride), was stimulated by M.M. Labes emd coworkers who have given a comprehensive review (56). This polymer has the electrical properties of a metal and provided the first example of a superconductor which lacked a metal atom. 

This chapter is intended as a convenience to those readers actively engaged in the investigation of high Tc superconductors by transmission electron microscopy (TEM). A future possible application of the newly discovered high Tc superconductors is their use in electronic devices. The electrical properties of a device strongly depend on their microstructure, since grain boundaries in these materials can behave as weak links as reported by Dimos et al. [4.1], Therefore, TEM is an important tool in the study of the relationship between the microstructure and the electrical properties. 

Figure 2-4. Magnetization versus applied magnetic field for a type II superconductor. The flux starts to penetrate the specimen at a field Wei lower than the thermodynamic critical field The specimen is in a vortex state between Wei and Wc2 and it has superconducting electrical properties up to We2. (From Kittel [18].)...

We analyze theoretically the phenomenon of photon-assisted quantum transport in superconductor(S)- semiconductorfN) mesoscopic system. Sub-gap structures in the I-V characteristics could be explained by multiple Andreev reflections. The electrical properties are strongly determined by the interface between superconductor and semiconductor. The current - voltage characteristics were found to be very sensitive to the photon frequency. 

Electrical properties of junctions formed between superconducting material, S, and a non-superconducting metallic material, N, which may be a metal or a degenerate semiconductor, are determined by special boundary conditions. If we consider a superconductor-semiconductor (S-N) interface with high transparency, a proximity effect is observed due to injection of electron pairs (Cooper pairs) from the superconductor into the semiconductor where they decay over a characteristic length, the induced coherence length. 

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