Carbides superconductivity

Other unusual additives include oxetanes, vinylic macromono-mers, silicon carbide, superconductive carbon blacks, silver-coated fly ash, metal oxides, Tb for green emission, antibacterial agents, and organic-inorganic hybrid copolymer fibers. In an interesting reversal, transition element acetylacetonate salts were decomposed in a PDMS matrix to give membranes with catalytic activity. ... 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Permonosulfuric acid (PMS), 26 392 Permselective diaphragms, 9 656-657 Permutations, in Latin hypercube sampling, 26 1009-1010 Pernicious anemia, vitamin B12 and, 25 804 Perovskite carbides, 4 692 Perovskite ferrites, 22 55, 56t, 57 Perovskite material, mercury-base superconducting, 23 801 Perovskites, 5 590-591 22 94-96, 97 ... 

Vanadium is added to steel for high resistance to oxidation and to stabilize carbide. Vanadium foil is used for cladding titanium to steel. Vanadium-gallium alloy is used in making superconductive magnets. An important compound of vanadium is pentoxide which has many commercial uses (See Vanadium Pentoxide). 

Here again certain trends were observed, and the most influential factor was the crystal structure which the superconducting material adopted. The most fruitful system was the NaCl-type structure (also referred to as the B1 structure by metallurgists). Many of the important superconductors in this ceramic class are based on this common structure, or one derived from it. Other crystal structures of importance for these ceramic materials include the Pu2C3 and MoB2 (or ThSi2) prototypes. A plot of transition temperature versus the number of valence electrons for binary and ternary carbides shows a broad maximum at 5 electrons per atom, with a Tc maximum at 13 K. 

Ashcroft, N.W., 1968, Phys. Rev. Lett. 21,1748. Baggio-Saitovitch, E.M., D.R. Sanchez and H. Mick-litz, 2001, in Rare Earth Transition Metal Boro-carbides (Nitrides) Superconducting, Magnetic and Normal State Properties, eds K.-H. Mailer and... 

There is an interesting analogy between the anomalous behavior of Pr in boro-carbides with the well-known anomalous properties of Pr-containing cuprates (Lynn, 1997, see Section 1.3). For PrBa2Cu30 -, e.g., it is widely accepted that the absence of superconductivity and the anomalously high Tn are connected with the increased hybridization of 4f levels with planar oxygen-derived states being important for superconductivity of doped holes. 

Borides Sohd-state Chemistry Carbides Transition Metal Solid-state Chemistry Electronic Structure of Sohds Quasicrystals Structure Property Maps for Inorganic Solids Superconductivity Zintl Compounds. 

Alloys Borates Solid-state Chemistry Carbides Transition Metal Solid-state Chemistry Chalcogenides Solid-state Chemistry Diffraction Methods in Inorganic Chemistry Electronic Structure of Solids Fluorides Solid-state Chemistry Halides Solid-state Chemistry Intercalation Chemistry Ionic Conductors Magnetic Oxides Magnetism of Extended Arrays in Inorganic Solids Nitrides Transition Metal Solid-state Chemistry Noncrystalline Solids Oxide Catalysts in Solid-state Chemistry Oxides Solid-state Chemistry Quasicrystals Semiconductor Interfaces Solids Characterization by Powder Diffraction Solids Computer Modeling Superconductivity Surfaces. 

The phenomenon of superconductivity is common in several particular types of compounds. Thus more than two dozen binary compounds with the fee sodium chloride (NaCl) stracture are superconducting. The carbides AC and nitrides AN, such as NbN with Tc = 17 K, have the highest transition temperatures of this group, and the metallic A atoms with values above 10 K were Nb, Mo, Ta, W, and Zr. The NaCl-type superconductors are compositionally stoichiometric but not structurally so. hi other words, these compounds have a small to moderate concentration of vacancies in the lattice. For example, YS has 10% vacancies, which means that its chemical formula should properly be written 0,980.9. Nonstoichiometric NaCl-type compounds such as Tai.oCo.ye also exist. Ordinarily the vacancies are random, but sometimes they are ordered. 

Following the discovery of superconductivity in Hg in 1911, physicists, chemists, material scientists, metallurgists, electrical engineers, and others have found superconductivity in thousands of materials with values from a few millikelvin to 164 K [current record T, obtained in HgBa2Ca2Cu309 (Flg-1223) under high pressure see 17.3,10.2.5], These materials include elements, alloys, carbides, nitrides, borides, sulfides, organics, and oxides. 

Searching for higher transition superconductors was not limited to the A15 alloys. Many carbides, nitrides, borides, sulfides, etc. were also found to be superconducting. 

Table 1. Selected Superconducting Carbides, Nitrides, Borides, and Sulfides with Their T- Values...

The superconductivity and structure of some ternary molybdenum sulphides 258 the non-stoicheiometry of ZrS2 259 and the phase systems ZnCd-S, ZnHg-S, and CdHg-S260 have all been investigated. The reaction of carbon disulphide with the metals of the transition groups IV, V, and VI, has been studied.261 In most cases, the product of the reaction at 800—1000 °C is a sulphide (or more rarely a mixture of two sulphides), but in the case of the metals niobium and tantalum a mixture of carbides is produced. 

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