Germanium silicides

Silicon (3), which resembles metals in its chemical behavior, generally has a valence of +4. In a few compounds it exhibits a +2 valence, and in silicides it exists as a negative ion and largely violates the normal valency rules. Silicon, carbon, germanium, tin, and lead comprise the Group 14 (IVA) elements. Silicon and carbon form the carbide, SiC (see Carbides). Silicon and germanium are isomorphous and thus mutually soluble in all proportions. Neither tin nor lead reacts with silicon. Molten silicon is immiscible in both molten tin and molten lead. 

While interactions of alkali metals or magnesium with elemental silicon and germanium (or their oxides) can give various silicides or germanides, most of these products do not contain true anions and some are semiconductors. However, in Li12Si7 there are Si5 rings and trigonal planar Si-centered Si, units in the lattice. 

The remaining work discusses two techniques in thin film analysis, Rutherford backscattering spectrometry (RBS) and X-ray diffractrometry with emphasis on strain measurements. Rutherford backscattering spectrometry is illustrated with analysis of silicide formation as an example of thin film reactions. Silicon-germanium-carbon films serve as an example of strain calculations. 

Cockeram and Rapp have evaluated the kinetics of silicide coatings on Ti [103] and have used a halide-activated pack-cementation method to form boron- and germanium-doped silicide coatings on orthorhombic alloy substrates [104]. The coatings greatly decreased the cyclic oxidation kinetics and microhardness measurements did not indicate diffusion of oxygen into the substrate. 

B. V. Cockeram, R. A. Rapp Oxidation Resistant Boron- and Germanium-Doped Silicide Coatings for Refractory Metals at High Temperature to appear in Mater. Sci. and Eng. 

Table 1. Conditions of Formations of Silicon and Germanium Clathrates by Thermal Decomposition of Alkali Silicides and Germanides MSi and MGe (From Ref. 6) ...

Fig. 274. Filling (transfer) apparatus for preparing alkali metal silicides and germanides b—iron bomb d—silicon or germanium /—ampoule containing alkali metal.

Sensitive to moisture, but less reactive than the silicides. Decompose in air into alkali hydroxide and brown germanium monohydride (GeH)x- Decompose rapidly, with occasional Igniting in water, dilute acids or dilute alkalies. 

B. V. Cockeram and R. A. Rapp, Boron-modified and germanium-doped silicide diffusion coatings for Ti-Al-Nb, Nb-Ti-Al, Nb-Cr and Nb-base alloys. In Processing and Design Issues in High Temperature Materials, eds. N. S. Stoloff and R. H. Jones, Warrendale, PA, Mining, Metallurgy and Meterials Society, 1996, p. 391. 

The tantalum carbides and silicides and tungsten carbides cited above are used for their hardness, corrosion resistance in hot environment and their semiconducting properties, while niobium alloys (niobium-germanium, niobium-aluminium...) receive much attention for their properties of superconductivity. 

Cockeram B and Rapp R A (1996), Isothermal and cyclic oxidation resistance of boron-modified and germanium-doped silicide coatings for titanium alloys , Oxid Met, 45 (5/6), 427 68. 

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