Ternary transition metal nitrides

Figure 8.8 Structure of FeWN2. An example of a ternary transition metal nitride containing octahedral iron and trigonal prismatic tungsten. Small white = Iron, Black = Tungsten, Large...

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... 

Figure 8.9 Structure of MnMoN2 and j3-MnWN2. Examples of ternary transition metal nitrides containing octahedral manganese and trigonal prismatic molybenum/tungsten. Small white = Manganese, Black = Molybenum/Tungsten, Large white = Nitrogen.

Kumta and co-workers [20] have used a three-step sol-gel-based procedure to prepare ternary transition metal nitrides involving heat treatment under ammonia of a metal organic hydroxide precursor. This route consists in the hydrolysis of a polymeric liquid precursor to form a metal-organic hydroxide. Thermochemical decomposition of the metal-organic hydroxide precursor under ammonia leads to ternary nitrides such as NijMOjN, FeWN and Ti AIN. DiSalvo and co-workers incorporated alkaU metal ions to increase the stability of the nitrides compared to binary compounds. They used a sol-gel-based route to prepare ternary alkali and alkaline-earth metal nitrides such as NaTaN, KTaN and NaNbN [21, 22]. 

Although there are several hundred biaary nitrides, only a relative few ternary bimetallic metal nitrides are known (6). A group of ternaries of the composition where M is an alkah, alkaline-earth, or a rare-earth metal and M is a transition or post-transition metal, have been synthesized (6). 

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. 

Binary transition metal nitrides can form ternary solid solntions with each other if they are isostmctural and if their lattice parameters differ by no more than abont 10-15%. 5-VNi-x and 5-ZrNi x do not form extensive solid solntions with each other and the intersolubility of 5-VNi x and 5-HfNi-x is not complete. 

Ternary phases with structures different from those of the phases of the binary boundary systems are more the exception than the rule. Such phases have been reported in the systems Nb-Mo-N, Ta-Mo-N, Nb-Ta-N, Zr-V-N, Nb-Cr-N, and Ta-Cr-N. Information about ternary transition metal-nitrogen systems is often available for specific temperatmes only. This is even more the case for quaternary nitride systems, which play a role in the production of carbonitride cermets where quaternary compounds of the types (Ti,Mo)(C,N) and (Ti,W)(C,N) are of interest (see Carbides Transition Metal Solid-state Chemistry), as well as in layer technology where titanium nitride-based coatings of the type Ti(C,B,N) are prepared by magnetron sputtering. Layers consisting of ternary compounds of the type (Ti,Al)N and (Ti,V)N also have favorable properties with respect to abrasion resistance. 

We have included not only pure nitride materials but also many amides, azides, oxynitrides (but not nitrates and nitrites), nitride chalcogenides, and nitride halides. Specifically excluded are polymeric compounds (e.g. SxNy), cluster compounds (e.g. Sc2C12N), coordination compounds (e.g. [Pd(NS3)2]), ternary azides and amides, as well as ternary interstitial transition-metal nitrides. We have attempted to include all important structures and all type compounds. This review is also unique in that we attempt to evaluate the... 

We suspect that the lack of alkali nitrides on the one hand and of transitional metal nitrides on the other hand led to the neglect, until recently, of a very rich ternary nitride chemistry. We have recorded here some remarkable nitrides (mostly reported rather recently) containing transition metal and alkali metals. We suspect that some of them were made serendipitously, as crucibles of elements like iron are often used to contain alkali-rich materials (such as Li, N). We observe that many ternary etc. oxides of elements such as Pt were similarly discovered as products of reactions in precious metal crucibles. 

Holleck, H., Ternary Carbide Systems of Actinoids wifli Transition Metals of Other Groups (in German), in Binary and Ternary Transition Metal Carbide and Nitride Systems , Petzow, G. (Ed.) Gebraeder Bomtraeger Berlin, Stuttgart, 92-111 (1984) (Crys. Structure, Phase Diagram, Phase Relations, Review, 91)... 

Until recently, the synthesis of ionic/covalent nitrides was relatively unexplored except for the pioneering work of Juza on ternary lithium nitrides.11 However, within the last decade, several groups have begun to explore ternary nitride systems, many of which have relied on the inductive effect. The inductive effect is based on the donation of electron density from an electropositive element to an adjacent metal-nitrogen bond, thereby increasing the covalency and stability of that bond and of the nitride material itself. The success of this method is illustrated by the fact that almost all of the known ionic/covalent ternary nitrides contain electropositive elements. Only recently has a small number of transition metal ternary nitrides been synthesized in the absence of the inductive effect at moderate temperatures, by taking advantage of low temperature techniques, such as the ammonolysis of oxide precursors and metathesis reactions.6,12-17... 

Upon additional alloying ternary carbonitrides quaternary carbonitrides are obtained. The group 4 and 5 transition metal carbides and nitrides are completely miscible except TiN-VC and ZrN-VC. Thus, modified material properties can be obtained (see also Section 9.2). Information on the properties of these carbides are still scarce," a few data are given in Figure 13 and Table 4. 

Metallic nitrides, sometimes termed interstitial compounds, are formed from combinations of N with transition metals of groups IVA, VA, and VIA. As the name implies, they exhibit electrical conductivity and most of the general characteristics associated with standard metals. They are also refractory and hard, and usually depart from the ideal stoichiometry ratios displayed above (see 17.3.9, Table 1). They readily form solid solutions with carbides and oxides, which gives rise to problems when it is necessary to obtain nitrides in pure form. Included in this category are numerous ternary nitrides of a transition metal with a group B metal. 

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... 

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... 

The nitrogen exchange between lithium and several transition metals gives rise to the formation of binary or ternary nitrides, which show analogies with the ternary oxides formed in Na—O—Me systems . In the lithium-nitrogen-stainless steel system, nitrogen is picked-up by the stainless steel due to the getter reaction of the... 

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