Nitrides, ternary properties

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. 

Although the distinction is not always clear, ternary nitrides (and nitrides in general) often are classified into two groups (1) intermetallic-type and (2) ionic/covalent-type. Intermetallic nitrides are those in which metal-metal (M-M) interactions are dominant and where the nitrogen atoms are interstitial within the metal array.3 Because these phases are stabilized by M-M interactions, the structure and physical properties are similar to those of many other metallic systems, such as alloys, metals, and... 

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. 

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. 

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

Metallic carbides, nitrides, and oxides are used industrially in many applications their physical properties are also of intrinsic interest. This section pinpoints various preparative techniques and reviews methods of crystal growth for this group of compounds. More detailed discussion is found in the reviews cited and in the references therein. The discussion is confined to binary compounds, M Xi, (M is a cation X = C, N, or O a and b are simple integers) that display metallic properties the very numerous ternaries MoMcXj, (M, M being different cations) cannot be described in this brief presentation. 

Another material of this kind is tungsten disulphide, originally developed by NASA for aerospace applications, now also applicable to specialty industries [58]. Ti3SiC2 is a thermodynamically stable, nano-layered, ternary carbide and part of a family of over 50 ternary carbides and nitrides, the MAX phases [62]. These phases are a new class of solids possessing unique combinations of properties they are readily machinable, relatively soft for ceramics, but elastically stiff, and electrically and thermally conductive. They combine the good properties of both metals and ceramics that could lead to this technology contributing to future lubricant developments. 

Chromium nitride layers (fabricated by, e.g. cathodic arc plasma deposition) are interesting because of their corrosion properties as well as because of their excellent adhesion properties and fine-grained structure. They are applied for die-casting moulds where excellent edge properties are necessary [115,116] some of these layer can have a multiphase character composed of Cr(N), Cr2N, and CrNi t [117]. Sputter deposited ternary chromium nitrides such as Cr fMe (N with Me = Ti, Nb, Mo, and W additions and with grain sizes of up to 25 nm have been found [118] to show either a hardness minimum (Me = Mo, Ti) or a maximum of up to 27GPa (Me-W, Nb). 

Ternary nitrides have recently been extensively studied, because they may display a wider variety of useful properties compared to the binary nitrides. The majority of reported ternary nitrides contain an electropositive element along with a transition metal or main-group metal [245]. The electropositive element (e.g., Ca, Sr, Ba, Mg) is included to increase the stabUity of the nitride, via the inductive effect [246]. 

Historically, the development of nitrides proceeded slowly until the emergence of silicon nitride during the late 1950s. From that time onwards, the intricacies of the relationship between the two forms of silicon nitride, combined with the observation that, when hot-pressed or sintered into dense products, silicon nitride displayed excellent mechanical properties at temperatures in excess of 1000 °C, propelled silicon nitride into a subject area of intense interest. As a result, it now resides in a well-defined niche as a stmctural material for wear parts and related applications. At the same time, this provided a catalyst for the development of other nitrides, both of a binary and ternary character. Increasing complexity was provided by the observation that, just as with mineral silicates, aluminum could replace silicon in... 

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