Binary nitrides

Kernforschungsanlage Julich Jiilich, Federal Republic of Germany 

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Reaction (2) is also used with a plasma at a deposition temperature of200-800°C.[ l Reaction (1) in combination with TiC will produce a binary nitride, (Ti j xAl )N, al so in a plasma at low temperature. I l... 

In the last decade, numerous compounds of these types have been the subject of detailed CVD studies, demonstrating their potential for the deposition of the corresponding binary materials. Most of the work has concentrated on binary nitrides and phosphides, while the deposition of binary MSb films has been studied to a far lesser extent. The lack of potential precursors has been the major problem for the deposition of group 13-antimonide films for many years. Only a very few group 13-Sb compounds have been known until we and Wells established general synthetic pathways as was shown in Sections 2 and 3. Consequently, detailed investigations concerning their potential to serve for the deposition of the desired materials... 

NO Removal. - A number of studies have investigated the potential of nitrides as catalysts for NO removal. NO reduction with hydrogen has been reported in a series of papers by Au and co-workers. Of the binary nitrides, the activities of VN, M02N and W2N have been compared. VN was found to be the least active and rapidly deactivated as a consequence of bulk oxidation, whereas both M02N and W2N were observed to possess activity with... 

Recent developments in the synthesis, structures, and properties of ionic/covalent ternary nitrides are reviewed. A description, including synthetic conditions, is given of preparative methods reported in the literature. Solid state synthetic reactions from binary nitrides as well as novel synthetic approaches such as amide synthesis and ammonolysis of ternary oxides are described. Examples of common structure types as well as electronic and magnetic properties are discussed. 

Alkaline earth-containing ternary nitrides make up the second largest group of ternary phases. Because the alkaline earth metals form stable binary nitrides, most alkaline earth containing ternary nitrides have been synthesized by the reaction of a binary nitride with a metal or by the reaction of two binary nitrides. This synthesis has resulted in a number of new ternary nitrides with a variety of structures. For example, the reaction of calcium nitride with Group 14 or 15 metals or metalloids forms a series of structurally related ternary nitrides with the anti-perovskite type structure. In Ca3MN (M = P, As, Sb, Bi, Ge, Sn, Pb) (Figure 8.5) the... 

The synthesis of ternary transition metal nitrides through the reaction of two binary nitrides (Table 8.1, Reaction 1) or by nitriding two metals (Table 8.1, Reaction 2) has been relatively unsuccessful. Consequently, until recently, there was little or no information concerning the synthesis and structures of these phases. Lately, several transition metal ternary nitrides have been made through other synthetic routes, such as metathesis reactions and ammonolysis. For example, the ternary nitride CuTaN217... 

Molybdenum metal was also detected when the amount of CaCl2 was not large enough. So, it is clear that the CaCl2 molten salt medium directs the reaction to the formation of the Mo2N binary nitride. 

TABLE 2 Lattice and elastic stiffness constants ol binary nitride compounds. 

The imide is a clear yellow sohd which is mnch more resistant to hydrolysis than the amide and which possesses greater thermal stability. At 250 °C it evolves ammonia and converts to the binary nitride (equation 33), which is a red-orange solid that decomposes violently on heating. 

Because of the evident structmal similarities between transition metal carbides and transition metal nitrides the carbon atoms in group 4 and 5 carbides can be replaced completely by nitrogen without changing the structme of the binary phases. So far only one distinct ternary phase Cr2 (C,N)2 has been reported. Intersolubihty between the binary nitrides and carbides in the group 6 carbonitride systems Cr-C-N and Mo-C-N is not complete because of the differences in the crystal structmes of the carbide and nitride phases. 

No direct evidence has been reported for the existence of a simple binary nitride. The formation of explosive P04N4 has been postulated in studies of the thermal decomposition of (NIL,)2PoBr6. 

For the development of new high-performance materials it is particularly interesting to search for new covalent nitrides with highly cross-linked structures. The binary nitrides P3N5 and Si3N4 are now well known but what about ternary nitrides in the system Si-P-N ... 

In the past, attempts to prepare such ternary nitrides by reaction of the respective binary nitrides always have failed because the binary nitrides do not melt congruently and also because of the low self-diffusion coefficients of these materials. However, for the synthesis of SiPNj a molecular precursor Cl3SiNPCl3 has been proven to be specifically useful [5]. In this compound the required structural element of two vertex sharing tetrahedra centered by phosphorus and silicon and connected via a common nitrogen atom is pre-organized on a molecular level. The precursor compound is obtained (Scheme 3) in a three-step synthesis starting from ((CH3)3Si)2NH which is commercially available. 

In addition to the binary nitrides described here, some ternary nitrides have been prepared, for example, Li5TiN3, Li7NbN4, and Li9CrNs, all with the fluorite type of structure (superstructures in most cases), and alkaline-earth compounds with Re, Os, Mo, or W(e.g. Sr9Re3Nio, CasMoNs). ... 

By far the largest class of ternary lithium nitrides are those with the antifluorite structure, prepared largely by Juza, and reviewed by him [42], The ternaries are more thermally stable than the binaries which would seem to indicate a relaxation of the internal strain (both cation- cation and anion-anion repulsions) of binary nitrides. Many of these compounds are in fact ordered superstructures of antifluorite and it is remarkable that most of the transition metals are observed in high oxidation states--much higher than those in the binaries (e.g. Li7Mn + N4 vs Mn5 + N2). They are Li+ conductors at elevated... 

Rubidium forms no binary nitride. Like potassium, its amide forms with the cubic rocksalt structure (above 40 C) which distorts to monoclinic symmetry as it is cooled [88, 95], Its azide forms with the KHF, structure, analogous to NaN3 and KN, [77, 85],... 

Cesium also forms no binary nitride. Its azide forms with the KHF, structure [85], and its low-temperature amide (below 50 C ) [95] forms with a tetragonal distortion of the CsCl structure. The high-temperature form (above 35 C) of CsNH, has the cubic CsCl structure with a rotationally-disordered NH, group. The hydrogen atoms have not been located for the amides. CsTaN, has been reported with a disordered structure resembling (i-cristobalite [82], Yellow CsOsO, N has the BaS04 structure [96]. 

Air-sensitive Ca3CrN3 can be made from reaction of the binary nitrides at 1350 C in sealed Mo tubes [131], The structure contains planar CrN, groups and CaNj square pyramids N atoms center Ca5Cr octahedra. The anion-centered description of the structure begins from the rocksalt structure viewed down a 4-fold axis. If one removes 1 /4 of the octahedra in a layer and then shears the layers, one obtains a layer of the Ca3CrN, structure. The layers are joined by edge-sharing as shown in Fig. 17. 

As already mentioned, synthesis of multinary silicon boron nitrides or carbon nitrides cannot be achieved via the well-known powder route, including mixing, milling, and sintering of binary nitride/carbide powders, because the interdiffiision of the covalent nitrides, and carbides, proceeds... 

In a second step, the absolute stabilities of the MFesN family of compounds are studied by theoretically determining the total electronic energies of all participating phases. In the present case, the educts must also include the binary nitride FeN adopting the zinc-blende type (see Section 3.2). Theory clearly indicates that FeN is enthalpically more stable than the elements, in accordance with independent calorimetric measurements [402] because the phase designated FeNo.91 is the most exothermic iron nitride (AHf -50 kJ/mol). Given the simple chemical reaction... 

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