Nitrides, ternary preparation

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. 

In another recent study, amorphous phosphorus nitride imide (HPN2), a ternary inorganic polymer, has also been prepared via a benzene-thermal reaction of PCI5 and NaN3 under mild conditions [40], The products have interesting morphologies (Fig. 10) of microtubes, hollow balls and square frameworks. Their potential use for industrial application is now under investigation. 

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. 

A further group of ternary nitrides are of the type R2Fei7Nx where R is a rare earth element such as Sm, Ce or Nd, and x indicates the variable nitrogen content. These phases have been prepared, by nitridation at relatively low temperatures and up to 15 MPa N2, under which conditions the nitrogen content can reach x = 3. They are closely related to borides and carbides with the similar formula and have attracted considerable... 

In the last few years we began our efforts to develop new inorganic solid materials with the synthesis and structure determination of the phosphorus nitrides [2]. Based on the synthesis of pure, defined, and crystalline P3N5 [3] we started a systematic preparative and structural investigation of ternary and multinary phosphorus nitrides. 

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. 

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. 

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). ... 

Binary and Ternary Compounds with Elements of Groups II, III, and V. 2f-ray electron spectroscopy has been used to probe the electronic structures of tungsten borides, nitrides and also some carbides and oxides. Enthalpies of formation AH°298.i5 the tungsten borides WB and W2B have been determined by fluorine calorimetry and are — 66.5 and — 68.2 kJ mol respectively. The theoretical possibilities of preparing M02B, a-MoB, MO2B5, WjB, a-WB, and W2B5 by chemical vapour deposition is discussed and MoXj (X = B or Be) have been prepared and examined by X-ray methods. ... 

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... 

Plutonium nitride. Unlike the corresponding uranium-nitrogen system, only the one plutonium nitride PuN exists. It is prepared by heating plutonium hydride in nitrogen at 250 to 400 C, by reacting plutonium metal with a hydrogen-ammonia mixture at 600°C, or by direction reaction of molten plutonium with nitrogen at 1000 C. Plutonium nitride forms solid solutions with UN. However, because of the appreciable volatility and dissociation of PuN at temperatures at about 1600 C and above, the ternary (U, Pu)N is less attractive as a nuclear fuel than pure UN [K2, S4]. 

Only a few ternary silicon nitrides have been prepared in a pure form and characterized. The isotypic compounds MSiN2 (M = Be, Mg, Mn, Ca, Zn), with the same valence electron concentration of 4, can be considered as ternary substitution variants of AlN [247]. These compounds contain three-dimensional (3-D) infinite network structures, with SiN4 tetrahedra linked through all four vertices by comer-sharing, which forms condensed [SieNe] twelve-membered rings in MgSiN2 [248]. 

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]. 

Cr, Mn, Co), from the nitridation of bimetallic oxide precursors with ammonia via TPR at the final reaction temperatures of 890-1110 K (70). The oxide precursors were prepared by conventional solid-state reactions. All the synthesized oxynitrides have face-centered cubic structures and large surface areas of 45-118 m /g. In addition, bimetallic and ternary-metallic oxynitrides were prepared by ammonolysis of metal salt precursors and NH3 gas in the various temperatures from 973 to 1023 K (71). 

The subsequently discussed ternary nitrides are mostly high-temperature materials. Preparation reactions of multicomponent Th-N-X mixtures must allow for very slow chemical interdiffusion coefficients in solids. Many preparations can be made by powder metallurgical techniques involving multiple comminution, mixing, and elevated-temperature annealing, e.g., formation of (Th,U) N solid solutions from the binary compounds. 

Synthetic routes derived from molecular and non-molecular precursors have expedited the development of technologically important 2- and 3- dimensional materials. Such approaches have often proved superior to conventional ceramic techniques in that high purity bulk samples or thin films can be prepared at lower temperatures much more rapidly. Predominant among the precursor methods are those based on decomposition reactions. These either involve gaseous species, such as those used in chemical vapor deposition (CVD), or solids. Examples include the pyrolysis of the gas-phase precursor [(CH3)2A1(NH2)]3 to produce aluminum nitride (i) and the thermal decomposition of solid state carbonate precursors of calcium and manganese (Cai j,Mn C03, 0 < x < 1) to produce several of the known ternary compounds in the Ca-Mn-O system (2). Single-displacement reactions are also common as precursor methods. These approaches usually involve gas-phase reactions and are also used in CVD techniques. Examples here include the formation oi... 

Such a reaction can probably be written for all rare earths. The same idea was successfully exploited by these authors to prepare a ternary lanthanum chromium nitride, identified by Broil and Jeitschko (1995) as LasCrio xNn, from a mixture of lanthanum and chromium binary oxides according to... 

Klesnar and Rogl (1992) have also studied phase relations and phase stabilities at T = 1400°C in the ternary systems R-B-N where R is Nd, Sm or Gd in this case ternary compounds are found to be stable. Three different stoichiometries were observed with these early lanthanides RBN2, R3B2N4 and Ri5Bg(N,0)25. In addition, Kikkawa et al. (1997) have recently reported the preparation under high pressure of another orthorhombic La-B-N phase. All these ternary lanthanide boron(oxy)nitrides are rather unstable under moist conditions. 

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