Silicides physical properties

Titanium Silicides. The titanium—silicon system includes Ti Si, Ti Si, TiSi, and TiSi (154). Physical properties are summarized in Table 18. Direct synthesis by heating the elements in vacuo or in a protective atmosphere is possible. In the latter case, it is convenient to use titanium hydride instead of titanium metal. Other preparative methods include high temperature electrolysis of molten salt baths containing titanium dioxide and alkalifluorosiUcate (155) reaction of TiCl, SiCl, and H2 at ca 1150°C, using appropriate reactant quantities for both TiSi and TiSi2 (156) and, for Ti Si, reaction between titanium dioxide and calcium siUcide at ca 1200°C, followed by dissolution of excess lime and calcium siUcate in acetic acid. 

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

A totally different but nevertheless exciting field is the solid state chemistry of silicides and of Zintl anions aimed on the optimization of the physical properties (e.g. conductivity) and their derivatization to give molecular species. 

Although the silicon atom has the same outer electronic structure as carbon its chemistry shows very little resemblance to that of carbon. It is true that elementary silicon has the same crystal structure as one of the forms of carbon (diamond) and that some of its simpler compounds have formulae like those of carbon compounds, but there is seldom much similarity in chemical or physical properties. Since it is more electro-positive than carbon it forms compounds with many metals which have typical alloy structures (see the silicides, p. 789) and some of these have the same structures as the corresponding borides. In fact, silicon in many ways resembles boron more closely than carbon, though the formulae of the compounds are usually quite different. Some of these resemblances are mentioned at the beginning of the next chapter. Silicides have few properties in common with carbides but many with borides, for example, the formation of extended networks of linked Si (B) atoms, though on the other hand few silicides are actually isostructural with borides because Si is appreciably larger than B and does not form some of the polyhedral complexes which are peculiar to boron and are one of the least understood features of boron chemistry. 

This Datareview has described the known surface phases which exist on both a- and P-SiC. Surface treatments by annealing in UHV, by ion bombardment and by laser irradiation are not suitable to prepare SiC surfaces for further study. Chemical reduction of surface oxides is the preferred route to surface preparation, particularly using a Si flux at temperatures < 1000°C. A distinction is drawn between ideal surfaces prepared in UHV and practical ones where substrates are chemically treated or ion bombarded prior to metallisation. Processes occurring during deposition of the first few monolayers of metal and subsequent treatments are discussed in terms of chemical and physical properties. A total of 15 metal-SiC combinations are reviewed and discussed in terms of silicide and carbide formation. 

The non-oxide ceramics comprise essentially borides, carbides, nitrides, and silicides. Like oxide ceramics they have two kinds of uses, which frequently overlap application of their physical properties and of their refractory high-temperature properties. Extensive accounts can be found in [2.1-3,8,10],... 

Table 3 2-25 Physical properties of silicides and silicide-based high-temperature refractories [2.4]...

Table 10.22. Selected physical properties of advanced ceramics (borides, carbides, nitrides, silicides, and oxides)... 

The history of ceramics is as old as civilization, and our use of ceramics is a measure of the technological progress of a civilization. Ceramics have important effects on human history and human civilization. Earlier transitional ceramics, several thousand years ago, were made by clay minerals such as kaolinite. Modem ceramics are classified as advanced and fine ceramics. Both include three distinct material categories oxides such as alumina and zirconia, nonoxides such as carbide, boride, nitride, and silicide, as well as composite materials such as particulate reinforced and fiber reinforced combinations of oxides and nonoxides. These advanced ceramics, made by modem chemical compounds, can be used in the fields of mechanics, metallurgy, chemistry, medicine, optical, thermal, magnetic, electrical and electronics industries, because of the suitable chemical and physical properties. In particular, photoelectron and microelectronics devices, which are the basis of the modern information era, are fabricated by diferent kinds of optical and electronic ceramics. In other words, optical and electronic ceramics are the base materials of the modern information era. 

Silicides have long been considered for high-temperature service because of their potentially high strength, certain attractive physical properties (including, for example, low density and good electrical and semi-... 

A metal silicide is a compoimd that has silicon with more electropositive metal elements. Metal silicides have been the subject of numerous studies because of their potential applications in Si-based microelectronics and optoelectronics. They can be classified into two groups metallic and semiconducting silicides. Some metallic silicides (VsSi, NbaSi, CoSi2, etc.) are superconductors. Table 4.1 summarizes some physical properties of metallic silicides. 

V. S. Neshpor. Investigation of the Production Conditions and Some Physical Properties of Silicides of the Transition Metals, author s abstract of dissertation, Kiev Polytech. Inst., Kiev, 1961. 

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