Superconducting intermetallic compounds

This suggestion theoretically explains the metal and intermetallic compound superconductivity phenomenon (J. Bardin, L.N. Cooper and R. Schrieffer, Nobel Prize 1972), discovered earlier by H. Kamerling-Onnes (Nobel Prize, 1913). This phenomenon occurs only at very low temperatures (—20 K). However, superconductivity has been discovered in nonmetalhc, oxide-type chemical compounds with critical points of superconductivity up to ==140 K (in hquid nitrogen region) (so-called high-temperature super conductors, HTSC) (J.G. Bednorz and K.A. Muller, Nobel Prize, 1987). Intensive attempts to synthesize new materials of this kind are in progress. 

Nevertheless deviations from eq. (9.19) have been observed for the intermetallic compound Auln2 [108,109] and for T1 [110,111], Requirements for the validity of eq. (9.19) are the absence of changing internal fields due to nuclear magnetic or electronic magnetic ordering in the relevant temperature range, the absence of nuclear electronic quadrupole interactions and no superconductive transition. 

Perhaps the Mg intermetallic compound which attracted most interest in the past 10 years is MgB2. The reason for this lies in its superconductivity below 39 K, which is an unusually high value for a phonon-mediated... 

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. 

Based on their difference in reacting to magnetic flux, superconducting material can be differentiated into Type-I and Type-II. The Type-11 superconductors are usually associated with intermetallic compounds instead of elements and their superconductivity is not easily affected even with a high magnetic field. 

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. 

These, therefore, constitute the guidelines for finding superconductors or how to raise the superconducting temperature. Since Covalon conduction is a nucleus to superconductivity and covalent bond is a poor conductor at room temperature, a good conductor at room temperature implies a poor covalent bond and therefore will not be a superconductor or will be a poor superconductor at best at low temperature. Inasmuch as a good covalent bond can come from compound formation, good superconductors, particularly Type-II, shall be expected to come from intermetallic compounds or special type of ceramic oxides and nitrides. 

P. Thalmeier and G. Zwicknagl, Unconventional superconductivity and magnetism in lanthanide and actinide intermetallic compounds 135... 

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. 

Superconductivity has been observed in the intercalated layered nitride halides of general composition MNX (M = Zr, Hf X = Cl, Br, I). On intercalation, jS-ZrNCl and /3-HfNCl, become superconductors with transition temperatures of 13 and 25.5 K, respectively. The transition temperature of the electron doped /3-HfNCl is higher than that observed in any intermetallic compound. 

The quest for superconductivity at always higher temperature has been a constant motivation in the material science research over the past quarter of the century. A well known example is the huge amount of work which has been invested in the synthesis, measurements and processing of intermetallic compounds belonging to the A-15 family of type II superconductors. These compounds V,Si [I] and NbjSn [2] are still at present the materials mostly used when superconductivity comes to applications [3]. 

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... 

Much attention was paid to slruelures, superconducting properties, magnetic susceptibilities, Knight shifts, and specific heats of intermetallic compounds of technetium. Their structure types and lattice constants arc presented in Table 9.3. A. 

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