Germanium intermetallic compounds

A semiconductor is a crystalline material with a conductivity between that of a conductor and an insulator. There are many types of semiconducting materials, including elemental silicon and germanium intermetallic compounds, such as silicon carbide and gallium arsenide and a variety of organic compounds. Two semiconducting maferial.s that have found widest application for electronic devices are crystalline silicon and germanium. Here, we limit our discussions to these substances. 

The systems obtained when gallium is in the presence of bismuth, cadmium, germanium, mercury, lead, silicon, or thallium present miscibility gaps. No intermetallic compounds are formed. 

The most commonly measured property for these types of molecules is their dissociation energy or atomization energy. According to a recent review ( ) these have been experimentally determined for approximately 50 homonuclear diatomic metal molecules, 15 polyatomic metal molecules (including germanium but excluding silicon and antimony), 110 diatomic intermetallic compounds and more than 20 polyatomic intermetallic molecules. 

In the case of semiconductors, it was first shown in this laboratory that the arrangements of the atoms in the surface monolayers of (100) and (111) germanium and silicon are not the same as those for these planes in the bulk (25). The altered arrangements were revealed by the presence of fractional order beams for the surface gratings in certain azimuths. This was later found to be the case for all crystals tested which have a diamond-type lattice, including semiconducting diamond and several of the intermetallic compounds. The surface structure of silicon was observed to be much more complex than that of germanium. In some azimuths, several fractional orders less than one-half were observed. 

The tin intermetallic compounds are very closely related to those of germanium. FcaSn is similar to FesGe and shows two hyperfine fields [110]. 

In a companion chapter (174) P.S. Salamakha describes in detail the various structure types that have been adopted by the rare-earth-germanium ternary intermetallic compounds. The correlations, crystal chemistry and interrelationships of the 135 structure types are discussed. Two distinct behaviors are found depending on the nature of the outer bonding electrons the p elements behave differently from the s and d elements, which behave similarly. When the third component is a p element the compounds maintain the same R to Ge ratio as found in the binary R cGey phases, e.g. RGc2 and RsGes, where R is a rare earth metal. As one might expect many of the compounds have variable composition at a constant R content. For the s and d metals the compounds tend to fall on lines... 

With germanium the compound with the highest melting temperature has the composition RGc2 for La, Ce and Pr, and the composition R5Gc3 or An5Gc3 for all the other rare-earth elements, as well as for uranium. There is a large number of intermetallic... 

Germanium appears to form no carbide, but it alloys with many metals and metalloids. A complete tabulation of intermetallic compounds (as of 1968)1 fists 152 compositions, from which the representative metal germanides of Table 5 have been abstracted. The relation of Ge with Si is unique a continuous series of solid solutions is formed, and the two liquids also form ideal mixtures. About eighty ternary intermetallic compounds are known, and phase diagrams for many of the binary and ternary systems have been reportedly. 

This chapter is dedicated to ternary intermetallic rare earth-transition metal-lead phases (plumbides). Compared to related compounds with silicon (see Rogl in chapter 51, volume 7), germanium (Salamaha, Sologub and Bodak, chapters 173... 

Intermetallic clathrates were first discovered in the coiu se of investigations on the thermal decomposition of the binary compounds hltTti [48,49], where M = alkali metal and Tt = group 14 element. Systematic investigations carried out in the seminal work by Cros et al. [1-3,50-52] demonstrated that a variety of alkali metal silicon and germanium-based compositions are prepared via this route, which continues to be employed for preparation of clathrate materials in contemporary investigations [53-64]. 

One of the many families of intermetallic systems, which turned out to be particularly interesting, consists of compounds exhibiting the tetragonal BaAl type of crystal structure and its modifications. A few hundred of these compounds have been synthesized up to now and their properties investigated. Their general chemical formula is RT2X2, where R is a rare earth, T is a transition 3d, 4d, or 5d metal and X is silicon or germanium. 

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