Group 13 elements nitrides

IV. POLYMERIC ROUTES TO MAIN GROUP ELEMENT NITRIDES... 

Another main group element nitride with considerable hardness is aluminum nitride, AIN. It is important as a ceramic insulator with high thermal conductivity. It has the hexagonal wurtzite type structure (h-ZnS) [111]. In contrast to the high-pressure compound c-BN, it is prepared by various methods at ambient pressure [22,112]. 

Main-group elements X such as monovalent F, divalent O, and trivalent N are expected to form families of transition-metal compounds MX (M—F fluorides, M=0 oxides, M=N nitrides) that are analogous to the corresponding p-block compounds. In this section we wish to compare the geometries and NBO descriptors of transition-metal halides, oxides, and nitrides briefly with the isovalent hydrocarbon species (that is, we compare fluorides with hydrides or alkyls, oxides with alkylidenes, and nitrides with alkylidynes). However, these substitutions also bring in other important electronic variations whose effects will now be considered. 

For carbides and nitrides containing more than one transition metal, or a transition metal and another element, the compositions and structures are more varied and complex. Plate 1.3 shows examples where the secondary component is a metal or main group element. Figure 1.2 shows examples where one of the secondary components is an alkali or alkaline earth... 

Main group element analysis was carried out with a Perkin-Elmer CHN elemental analyzer, while molybdenum analysis was performed using atomic absorption spectroscopy. The content of Mo and O on the surface of the catalysts was obtained by X-ray photoelectron spectroscopy (XPS) using a Shimazu ESCA-850 spectrometer with monochromatic MgKa. Since Mo 3p3/2 spectra overlapped with the N Is spectra for the nitrided catalysts, the degree of nitriding (N IsfMo 3d ratio) had to be obtained from a combination of elemental analysis and XPS. 

Starting with nitrides of the alkaline and alkaline earth group elements no elemental boron is formed and the c-BN produced is yellow and transparent. Both the quality and the yield of c-BN are increased. 

The crystal structures adopted by the binary carbides and nitrides are similar to those found in noble metals. The resemblance is not coincidental, and has been explained using Engel-Brewer valence bond theory [5]. Briefly, the main group elements C and N increase the metal s effective s-p electron count, so that structures and chemical properties of the early transition metals resemble those of the Group 8 metals. This idea was first introduced by Levy and Boudart [6] who noted that tungsten carbide had platinum-like properties. 

ELEMENTS (Metals and intermetallic alloys metalloids and nonmetals carbides, silicides, nitrides, phosphides) l.A Metals and Intermetallic Alloys l.AA. Copper-cupalite family TAB. Zinc-brass family l.AC. Indium-tin family l.AD. Mercury-amalgam family l.AE. Iron-chromium family l.AF. Platinum group elements l.AG. PGE-metal alloys... 

In the first and third of our groups of nitrides the formulae usually correspond to the normal valences of the elements and this is also true of some transition-metal compounds (e.g. Sc, Y, and 4f nitrides MN, Zr3N4) and of some of the molecular nitrides (e.g. P3N5) others, such as N4S4, have formulae and structures which are not understood. The molecular nitrides are few in number, and if their structures are known they are described under the structural chemistry of the appropriate element. 

Write out complete electron configurations for the atoms of the Group VA elements nitride ion, N and phosphide ion,... 

Toward the end of 1995, we identified a new class of solids best described as machinable, thermodynamically stable polycrystalline nanolaminates (Fig. 1.4a). These solids are ternary layered hexagonal carbides and nitrides with the general formula, M + AX , where = 1 to 3, M is an early transition metal, A is an A-group element (mostly IlIA and IVA) and X is C and or... 

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