Superconductivity, metals/intermetallics

Surface fluorination in various fluorinated media are currently used nowadays as processes that allow the modifications of many classes of materials, such as metals, intermetallics, semiconductors, carbons, superconductors, oxide ceramics. The above selected examples have illustrated some physical properties that can be drastically modified, including conduction, adhesion, passivation, superconductivity, hy drophobicity / wettability. 

This volume of the Handbook on the Physics and Chemistry of Rare Earths adds five new chapters to the science of rare earths, compiled by researchers renowned in their respective fields. Volume 34 opens with an overview of ternary intermetallic systems containing rare earths, transition metals and indium (Chapter 218) followed by an assessment of up-to-date understanding of the interplay between order, magnetism and superconductivity of intermetallic compounds formed by rare earth and actinide metals (Chapter 219). Switching from metals to complex compounds of rare earths, Chapter 220 is dedicated to molecular stmctural studies using circularly polarized luminescence spectroscopy of lanthanide systems, while Chapter 221 examines rare-earth metal-organic frameworks, also known as coordination polymers, which are expected to have many practical applications in the future. A review discussing remarkable catalytic activity of rare earths in site-selective hydrolysis of deoxyribonucleic acid (DNA) and ribonucleic acid, or RNA (Chapter 222) completes this book. 

Only two superconducting metallic phases are used routinely in superconducting wires for applications the Nb—Ti solid solution phase and the NbsSn intermetallic phase. Due to the difference of their intrinsic superconducting properties Tc and 5c2. they have different ranges of application as indicated in Table 4.2-8. 

As mentioned above in the intermetallic Section, beta-tungsten, which is chemically WsO, is the prototype of the A-15 structure. The interest in WsO, or Ws01 x, is not only structural but is also based on the fact that this material is superconducting Further surprising is that, for the first time, this oxide superconductor has a higher transition temperature than that of the metal itself. Pure tungsten metal has a Tc of 15.4 mK, whereas the oxide WsO has a reported Tc of 3.35 K. Other oxide compounds such as CrsO and "MosO", which are isostructural with WsO, do not superconduct above 1.02 K. 

Bismuthides. Many intermetallic compounds of bismuth with alkali metals and alkaline earth metals have the expected formulas M3Bi and M3Bi2, respectively. These compounds are not salt ike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi3 . Both the alkali and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particulady noteworthy as having extremely short bond distances between the alkali metal atoms. 

Superconductivity has been found in metallic elements and intermetallic compounds and within their solid-solution-range. But, superconductivity has not been found in an alloy with an arbitrary composition. 

Since 1911 superconductivity has been observed in many metallic elements and intermetallics, principal among them being tin (3.7K), tantalum (4.5K), lead (7.2K), niobium (9.3K), Nb3Sn (18K) and Nb3Ge (20.9K). 

A review of the unsynchronized-resonating-covalent-bond theory of metals in presented. Key concepts, such as unsynchronous resonance, hypoelectronic elements, buffer elements, and hyperelectronic elements, are discussed in detail. Application of the theory is discussed for such things as the atomic volume of the constituents in alloys, the structure of boron, and superconductivity. These ideas represent Linus Pauling s understanding of the nature of the chemical bond in metals, alloys, and intermetallic compounds. 

For the heavier elements As, Sb, and Bi, further diversity in structure and stoichiometry is found. The ionic bond model becomes less useful as these species may be thought of as intermetallics, possessing metallic luster, and conduction or semiconduction properties. Typical examples include Na3Bi and NaBi, which becomes superconducting at low temperatures (<2.5 K). Further details will be found in the relevant article for each element, As, Sb, and Bi. Zintl anions of these elements are also known. ... 

Bismuth with a formal oxidation state of -3 is found in solid-state phases MsBi (M = alkali metal) and M)Bi2 (M = alkaline-earth metal). The compoundNasBi is metallic. Less reduced intermetallic phases with the alkali metals and alkaline-earth metals are also known. Examples inclnde MBi (M = Li, Na), MBi2 (M = K, Rb, Cs), and M Bk (M = Mg, Ca, Sr, Ba). The compounds M Bis (M = Ca, Sr, or Ba) superconduct at low temperatures. Some of these intermetallic phases have been extracted with amine solvents to yield anionic bismuth clusters in solntion (see Section 2.8.2). 

There are several dozen metallic AB2 compounds called Laves phases that are superconducting they have either cubic or hexagonal crystal structures. Some have critical temperatures above 10 K and high upper critical magnetic fields Bc2- For example, Zri/2Hfi/2V2 has rc = 10.1K, B 2 = 24 T, and a compound with a different Zr/Hf ratio has similar and Bc2 values with the critical current density Jc 4 X 10 A/cm. These materials also have the advantage of not being as hard and brittle as some other intermetallics and alloys with comparable transition temperatures. 

Over the next 60 years, superconductivity was observed in many alloys, metallic elements and intermetallic compounds with T values in... 

Intermetallic compounds composed of metal/metal or metal/non-metal form another group of superconducting compounds. The most... 

Superconducting materials can be divided into two general categories—brittle and ductile. The brittle superconductors consist of the intermetallic compounds such as columbium-tin (CbaSn) and vanadium-gallium (VsGa). The ductile superconductors consist of most of the elemental metals as well as alloys such as niobium-zirconium. 

The nature and origin of superconductivity was described in 1957 by John Bardeen, Leon Neil Cooper, and John Robert Schrieffer. Together they created the Bardeen Cooper Schrieffer (BCS) model. It occurs for many metals, alloys, intermetallic compounds, and doped semiconductors. The transition temperatures range from 92.5 K for Ybc CUjOg j, down to 0.001 K for the element Rh. And there are some materials that become superconducting only under high-pressure conditions. These materials all have to be extremely pure, even just one impurity in 10,000 atoms can severely affect the superconducting property. 

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