Borides superconductivity

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. 

Nickel atoms in BajNi B form distorted, puckered 3.6.3.6-kagome nets stacked in six layers perpendicular to the c axis. The densely packed framework of trigonal-Ni prisms again result in boron-pair formation, although Ba atoms are too large to be sandwiched between two Ni layers, and only four Ba can be accommodated within six Ni layers. Superconductivity is found for ( a, Sr, Ba)2pt9Bg borides with a structure related to Ba2Ni9Bfi and e o,B2 however, with respect to crystal chemistry and boron coordination, only the subcell is derived so far. 

Because they exhibit interplay of magnetic and superconducting properties, the formation and crystal chemistry of MRgMy4B4 compounds have been examined. Ternary rare-earth and actinide (Th, U, Pu)-transition metal borides of the approxi-... 

Solid borides have high melting points, exceptionally high hardness, excellent wear resistance, and good immunity to chemical attack, which make them industrially important with uses as refractory materials and in rocket cones and turbine blades. Some metal borides have been found to exhibit superconductivity. 

Superconductivity in the multiphase quaternary borocarbide system Y-Ni-B-C has been recently reported [141,142], Earlier work on valence fluctuations in ternary borides RENiaB were studied and in the case of YNi4B, a weak but reproducible signal of superconductivity at Tc of 12 K was observed. This is the first report or discovery of a ternary superconducting phase of the elements Y, Ni and B with a high Tc value (Fig. 12.27). 

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

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. 

Some selected superconducting carbides, nitrides, borides, and sulfides are presented in Table 1 with their values. Among these superconducting ceramics, the most influential factor was the crystal structure. Many of the important superconductors were based on the NaCl-type structure (also referred to as the B1 structure by metallurgists) and the... 

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

In the fifteen years since publication of the first edition of Comprehensive Coordination Chemistry (CCC, 1987), group 5 chemistry has been part of the intensive development of ceramic, optical, and magnetic materials based upon metal borides, nitrides, phosphides, oxides, and sulfides. A major impetus came from the discovery of the high-temperature superconducting oxides. In addition, the search for new routes to these materials via sol-gel or chemical vapor deposition techniques has spurred growth in metal amido, oxo, alkoxo, thio, and carboxylato chemistry. 

Graham, Sarah. Scientists Develop New Method of Manufacturing Superconducting Magnesium Boride. Scientific American, 4 September 2002. Available online. URL www.scientificamerican. com/article.cfm id=scientists-develop-new-me. Accessed on June 24, 2009. A brief description of MgB2 manufacture. 

This book summarizes the research on many different types of conducting materials in the field of CVD. In Chapter 2, Schulz and Marks report on superconducting films and Krauter and Rees, Jr. report on borides, silicides and nitrides in Chapter 8. In the present chapter we will focus on two classes of conducting materials, nitrides and transparent conducting oxides. It is possible that some aspects can also be found in other chapters of this book, e.g., CVD of Sn02. Nevertheless, they will be discussed in detail to give a consistent description on the state of the art. 

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