Superconducting materials nitrides

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. 

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. 

Polymer and chain formation is another property of chalcogen-nitrogen compounds that distinguishes them from their oxygen analogues. In addition to the unique, superconducting poly(sulfur nitride) (SN) (1.24) (Section 14.2), a variety of poly(thiazyl) chains such as RS5N4R (1.25) (Section 14.3) have been characterized. Interest in these chains stems from their possible use as models for the behaviour of (SN) and as components in molecular materials, e.g., as molecular wires. 

Organometallic precursors are used in the synthesis of a variety of semiconducting materials and superconducting cuprates. Organoaluminium silicate precursors have been used for the synthesis of aluminosilicates [25], while polymeric methylsilyl-amines have been used to obtain SiC-Si3N4 fibres [26], Silicon nitride can also be made using organometallic precursors. 

There also exist structural similarities between the MeN clusters and the class of solid-state compounds known as transition metal nitrides. In these refractory compounds the nitrogen exists in either an octahedral or a trigonal prismatic array of transition metals 125). The interest in using transition metal nitrides for superconducting thin films as well as chemically inert coatings (i25) should promote studies in which nitrido clusters could be used as starting materials for the synthesis of new refractory materials. 

Niobium, discovered in 1801 and formerly called colum-bium, was a special favorite. A soft, ductile, gray-blue metal, it is present in several minerals, forms a number of compounds and complexes, and is used to strengthen welded joints and certain steels. In 1941, scientists reported superconductivity in niobium nitride with a Tc around 16° K, fairly high compared to earlier superconductors. Progress slowed after that until 1953, when John Hulm, of the University of Chicago, put together a material... 

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. 

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. 

Poly(sulfur nitride), [SN]X, possesses remarkable properties such as electrical conductivity at room temperature and superconductivity below 0.3 K see Labes MM, Love P, Nichols LF, (1979) Chem Rev 1 [SN]X is insoluble and has a polymeric structure in the solid state with interchain S—S interactions. As these interactions are crucial to the properties of the material, [SN]X is best regarded as a solid-state polymer rather than a polymeric material with discrete macromolecular chains of the type discussed in this section... 

The majority of metal phosphides have a metal arsenide analogue which they usually resanble in properties and structure (Table 8.2). Metal phosphides, arsenides and nitrides not infrequently exhibit properties similar to those of metal carbides, silicides and germanides. Some metal phosphides are very useful semiconductors, while others shew superconduction or a variety of magnetic properties. Light-emitting diodes (LEDs) and nanostructured materials are other modem applications (Chapter 12.19). 

In die sections that follow, we briefly discuss the synthesis of inorganic solids by various methods with several examples, paying attention to the chemical routes. While oxide materials occupy a great part of the monograph, other classes of materials such as chalcogenides, carbides, fluorides and nitrides are also discussed. Superconducting oxides, intermetallics, porous materials and intergrowlh structures have been discussed in separate sections. We have added a new section on nanomaterials. 

In this book, we briefly examine the different types of reactions and methods employed in the synthesis of inorganic solid materials. Besides the traditional ceramic procedures, we discuss precursor methods, combustion method, topochemical reactions, intercalation reactions, ion-exchange reactions, alkali-flux method, sol-gel method, mechanochemical synthesis, microwave synthesis, electrochemical methods, pyrosol process, arc and skull methods and high-pressure methods. Hydrothermal and solvothermal syntheses are discussed separately and also in sections dealing with specific materials. Superconducting cuprates and intergrowth structures are discussed in separate sections. Synthesis of nanomaterials is dealt with in some detail. Synthetic methods for metal borides, carbides, nitrides, fluorides, sili-cides, phosphides and chalcogenides are also outlined. 

Coordination compounds are found in new materials such as onedimensional conductors and are also utilized as volatile precursors for the deposition of metal oxides in thin superconducting films or deposition of metal carbides or nitrides for refractory protective coatings and other applications. Coordination compounds have also proven to be useful precursors for the deposition under relatively mild conditions of high purity thin metal films for microelectronic applications. Historically, we consider Ni(CO)4 as the prototypical example discovered by Mond in... 

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