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Crystalline solids superconductors

In 1991, scientists at AT T Bell Laboratories discovered a new class of high-temperature superconductors based on fullerene, the allotrope of carbon that contains Cgo molecules (Sections 10.10 and 19.6). Called "buckyballs," after the architect R. Buckminster Fuller, these soccer ball-shaped Cgo molecules react with potassium to give K3C6o- This stable crystalline solid contains a face-centered cubic array of buckyballs, with K+ ions in the cavities between the Cgo molecules (Figure 21.16). At room temperature, K3Q,o is a metallic conductor, but it becomes a superconductor at 18 K. The rubidium fulleride, Rb C o, and a rubidium— thallium-Cfio compound of unknown stoichiometry have higher Tc values of 30 K and 45M8 K, respectively. [Pg.932]

In this chapter, we start by introducing the most basic structural imit of a solid material — the unit cell. From there, we explain how crystalline solids form different shapes and are organized into different systems. At the end of the chapter, we explain some of the important and useful characteristics of solid materials, including their use as superconductors, and semiconductors. [Pg.287]

The behavior of hehum at low temperatures is quite different from that of all other materials. When cooled under atmospheric pressure, helium liquefies at 4.2 K, but it never solidifies, no matter how cold it is made. This behavior is inejqrlicable in terms of classical physics where, at a sufficiently low temperature, even the very weak interatomic forces that exist between helium atoms should be sufficient to draw the material together into a crystalline solid. Furthermore, the liquid in question has maity extraordinary properties. In particular, it undergoes a transition at 2 K to a state of superfluidity, such that it has zero viscosity and can flow without dissipation of energy, even through channels of vanishingly small dimensions. This frictionless flow of the liquid is closely analogous to the frictionless flow of the electrons in a superconductor. On Earth, superfluidity and superconductivity are exclusively low-temperature phenomena, but it is inferred that they probably also arise in the proton and neutron fluids within neutron stars. [Pg.40]

The citrate gel method was developed by Marcilly et al. (99) and can be illustrated by the synthesis of the ceramic superconductor YBa2Cu307 (100). Nitrate solutions of Y, Ba, and Cu were added to citric acid solution, and the pH was kept at 6 to prevent precipitation of barium nitrate. Heating the solution at 75°C in air produced a viscous liquid containing polybasic chelates. Further heating at 85°C in a vacuum produced an amorphous solid that was pyrolyzed in air at 900°C to produce a crystalline powder. [Pg.108]

In comparisons of muons with protons and of muonium with hydrogen atoms, pronounced quantum effects occur whenever dynamics are involved. In this way, muons have been utilized to probe a large variety of properties and materials insulators, semiconductors, metals, superconductors, insulators, gases, liquids, crystalline and amorphous solids, static and dynamic magnetic properties of all kinds, electron mobility, quantum diffusion, chemical reactivity and molecular structure and dynamics. The term adopted for the broad field of muon spin spectroscopy techniques, fiSR, emphasizes the analogy with other types of magnetic resonance for example EPR. juS represents muon spin , and R in a more general sense stands simultaneously for rotation , relaxation and resonance . [Pg.279]

It is a fundamental problem in solid-state physics, that due to a misleading many-body treatment the true nature of the crystalline structure beyond the B-O approximation was never revealed. This is the reason why the BCS theory, in spite of the fact that Frohlich was critical to it and disregarded it, survives more than a half of century up till now. The BCS theory is based on the naive belief that the structure of superconductors is the same as the structure of conductors, i.e. that it is defined through the B-0 approximation. As we have shown in our previous work [21], there is no mechanism, which could split the degenerate electronic spectrum of conductors and open an energy gap at the adiabatic level. [Pg.545]

Almost a decade ago the first molecular superconductors based on the transition metal complex molecule (TTF)[Ni(dmit)2]2 was discovered (TTF = tetrathiafiilvalene, dmit = isotrithionedithiolate) [ 1 ]. Since then several M(dmit)2 superconductors have been found. Although most of the molecular metals currently studied are systems based on multi-sulfur (or selenium) 71 molecules, the first example of a metallic molecular crystal was a partially oxidized platinum complex. The discovery of the partially oxidized platinum complex is very old, about 150 years ago, but the physical meaning of the system had not been noticed until the crystal structure (by Krogmann and Hausen) revealed the existence of the extended linear Pt-Pt metal bonds [2]. The diffuse X-ray scattering experiments on this system (K2[Pt(CN)4]Bro.3 3H2O) by Comes et al. [3] convinced many people, who were interested in conducting crystalline molecular solids at that time, of the existence of one-dimensional metal electrons in molecular crystals for the first time, and so a new era of metallic molecular systems had been bom. [Pg.250]


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See also in sourсe #XX -- [ Pg.236 , Pg.237 , Pg.238 ]




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Solids superconductors

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