Electrical Properties at Low 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. 

Orientational disorder and packing irregularities in terms of a modified Anderson-Hubbard Hamiltonian [63,64] will lead to a distribution of the on-site Coulomb interaction as well as of the interaction of electrons on different (at least neighboring) sites as it was explicitly pointed out by Cuevas et al. [65]. Compared to the Coulomb-gap model of Efros and Sklovskii [66], they took into account three different states of charge of the mesoscopic particles, i.e. neutral, positively and negatively charged. The VRH behavior, which dominates the electrical properties at low temperatures, can conclusively be explained with this model. 

Recently, phosphane and phosphite copper(I) carboxylates have become favored over copper(I) / -diketonates, since these species produce copper films of high purity with excellent electrical properties at low temperatures. However, at the time this review is being written Cu(I) / -diketonates are commercially available, e.g. Cu(hfac)( -ViSiMe3) (lOo, CupraSelect ) and Cu(hfac)(mhy) (10k, Gigacopper ), making this class of metal enolate precursors still the most important in industrial applications. 

A characteristic change of the electrical properties at low temperatures is observed between 90 and 110 kbar, similar to that around 20 kbar in SmS (see Rare Earth Elements C7, 1983, p. 224), Holtzberg, Wittig [6], Wittig [7], which may be associated with a phase transition. The phase transition for SmSe (p-T diagram) and Smi xSe (p-x diagram) is discussed in terms of the existence of a critical point by Aptekar et al. [8]. 

Unsaturated resias based on 1,4-cyclohexanedimethanol are useful ia gel coats and ia laminating and molding resias where advantage is taken of the properties of very low water absorption and resistance to boiling water (6). Thermal stabiHty is imparted to molding resias, both thermoplastic (71,72) and thermoset (73—76), enabling retention of physical and electrical properties at elevated temperatures (77). Additionally, resistance to chemical and environmental exposure is characteristic of products made from these resias (78). 

The nylons are reasonably good electrical insulators at low temperatures and under conditions of low humidity but the insulation properties deteriorate as humidity and temperature increase. The effects of the amount of absorbed water on the volume resistivity of nylon 66 is shown in Figure 18.15. This effect is even greater with nylon 6 but markedly less with nylon 11. Some typical electrical properties of the nylons are given in Table 18.5. 

It is a well-known fact that, as the size of a metal particle is decreased, the overlap of the bands of valence electrons, with which we are mainly concerned, diminishes, and finally they are replaced by discrete energy levels characteristic of the isolated atom. This results in the loss of electrical conductivity and in the Mie plasmon resonance, an effect that has been noted with the AU55 and smaller clusters, on the basis of which they were described above as being molecular . The extent of band overlap is temperature-sensitive because of thermal excitation, i.e. bands tend to convert to levels as temperature falls thus metallic properties may be seen at high temperature and insulator properties at low temperature. As an approximate guide we may take the relation... 

Intense research has in recent years been devoted to noncrystalline materials. It was discovered also that the majority of semiconducting boron-rich borides display several properties that resemble those of the noncrystalline solids. Among the amorphous properties are the temperature and field dependencies of electrical conductivity at low temperature, the temperature dependence of thermal conductivity at high temperatures, and the temperature dependence of the magnetic susceptibility. In addition, the boron-rich semiconductors display crystalline properties, for example, the temperature dependence of the thermal condnctivity at low temperatures, the lattice absorption spectra and the possibility to change... 

III. In some instances, recent data on relevant properties at low temperatures are available, as in the NBS-ARPA-Battelle Handbook [% but more are needed. In particular, data on low-temperature properties of materials for very large loadcarrying welded or bolted structures are not available. Radiation damage at 4 K and the effect of thermal cycling on irradiated metals and organics are other areas where little information is available. The same is true of composite materials, both as structural elements and as thermal and electrical insulators. Furthermore, since very large quantities of material will be necessary, and the structures will probably be subject to close public scrutiny, attention must be paid to heat and product-form... 

Electrical Properties at Room Temperature and at Low Frequency of Some... 

Joule James Prescott (1818—1889) Brit, eng. who quantilled heat liberated upon the electric passage through resistance, unit joule named after him Kamerlingh-Onnes Heike (1853—1926) Dutch phys., obtained liquid helium, found uperconductivity of mercuiy, studied magnetic and optical properties at low temperatures... 

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