Stabilization, superconductors

On the other hand, aluminum-stabilized superconductors are desirable because aluminum has excellent low-temperature electrical conductivity, low magnetoresistance, low heat capacity during cooldown, and low density. The great differences in mechanical properties between high-purity aluminum and NbTi alloys, however, make it very difficult to fabricate an aluminum-stabilized multifilamentary superconductor. 

Fig. 2. Cross section of an Al-stabilized superconductor containing 121 NbTi filaments in an 1100 Al matrix sheathed in high-purity aluminum.

The Al-stabilized, 0.91-mm wire containing 121 NbTi filaments was tensile-tested in an Instron machine with a clip-on extensometer. The crosshead speeds were 8 nm/sec until the 0.2% yield strength and 40 nm/sec until wire fracture. The mechanical properties are compared in Table I with those of a Cu-stabilized superconductor tested in a similar manner. Although the yield stress and ultimate strength of the A1 conductor were lower than those of the Cu conductor, the A1 content may not have been causing the weakness. The lower proportion of NbTi in... 

The nematic to smectic A phase transition has attracted a great deal of theoretical and experimental interest because it is tire simplest example of a phase transition characterized by tire development of translational order [88]. Experiments indicate tliat tire transition can be first order or, more usually, continuous, depending on tire range of stability of tire nematic phase. In addition, tire critical behaviour tliat results from a continuous transition is fascinating and allows a test of predictions of tire renonnalization group tlieory in an accessible experimental system. In fact, this transition is analogous to tire transition from a nonnal conductor to a superconductor [89], but is more readily studied in tire liquid crystal system. 

Ceramic materials are typically noncrystalline inorganic oxides prepared by heat-treatment of a powder and have a network structure. They include many silicate minerals, such as quartz (silicon dioxide, which has the empirical formula SiO,), and high-temperature superconductors (Box 5.2). Ceramic materials have great strength and stability, because covalent bonds must be broken to cause any deformation in the crystal. As a result, ceramic materials under physical stress tend to shatter rather than bend. Section 14.22 contains further information on the properties of ceramic materials. 

Rankine cycle, 23 231—234 Thermodynamic stability, of MgB2 superconductors, 23 833 Thermodynamic state variables,... 

It has now become apparent that f-band superconductors can be understood in a normal way, like d-band ones" we have just to think about density of states, bandwidth lattice unstabilities and electron correlations to interpret it. This was clearly summarized by Smith after the discovery of superconductivity of Pa and Am. Superconductivity of Am is made by the J = 0 ground state of its six 5 f electrons as was stressed by Johansson , this could also be the case for stabilized trivalent europium metal. The importance of lattice instabilities (like in A-15 high Tc superconductors) was put forward by Fournier who showed that the very large 6T/8p slope for U was mainly due to a very targe change in the electron-phonon coupling associated with the low temperature phase transition. 

Many of the oxide superconductors have relatively limited thermal stability. Strategies for the successful synthesis of such phases include the use of oxide precursors such as nitrates which react at relatively low temperatures, and the use of small particle size precursors and extensive grinding steps to promote reaction rates. These strategies have been important in the successful solid state syntheses of the superconducting phases, Ba2YCu4Og (2)(3) and BaPbj. bjPa (4). 

The second difference between the nickel and copper compounds is that La2Cu04 is a superconductor, being the first of the Cu02 layer compounds in which superconductivity was observed. The lattice-induced strain is a necessary condition for superconductivity since it stabilizes the higher oxidation state needed to provide the superconducting carriers as discussed in Section 13.3.2. 

Ever since the polymer (SN)X was shown to be metallic and to represent the first example of a polymeric superconductor (78JA1235), compounds that contain the NSN group have come under close scrutiny. For instance, the compound naphtho[l,8-corganic solvents. However, despite this apparent stability, the half-wave polarographic potentials of the compound clearly show it is readily oxidized and reduced in acetonitrile. 

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