Ternary transition-metal elements

Figure 1. Formation of ternary borides MreMj3B2 and different structure types (Mre = rare-earth element, M-p = transition-metal element). , CeCo3B2 type ErIr3B2 type O, URujBj type El, Ndo7,Rh3 29B2 type IS, YOS3B2 type B, Laofi3Rh3B2 type , compound formation observed, but structure type unknown. Refs a , b , c , d e , f g , h , i , j ", k , 1 , m , r, s - , t u = 45 see also ref. 62.

Since the transition metal elements in these ternary Laves phases can substitute for each other freely, and since the distribution of Laves phase can be controlled by thermomechanical treatments there are possibilities for optimizing such NiAl alloys with Laves phases with respect to creep resistance and the brittle-to-ductile transition temperature (BDTT) by controlling the composition and phase distribution, and this is being studied presently... 

By introducing a third kind of transition-metal element, Pt ternary alloy catalysts attract considerable interests since the possibility of fine-tuning the geometric/ electronic stmctures for further improved catalytic activity [58, 59]. Here, we show that the deaUoying concept can be further applied in Pt ternary alloy catalysts, demonstrating a powerful approach to optimize the structure and activities of Pt alloy catalysts. 

Ternary J-Al-C compounds (Figs 9.2(e)-(g)) can be viewed as the intergrown structures consisting of two kinds of layers. One is the (T-C) (m = 1, 2 or 3) slab in the NaCl-type structure and the other consists of an Al-C unit in an arrangement similar to that of the binary aluminum carbide AI4C3. Wang etal. [12] identified the close relationships between the atomic radii of transition metal elements and lattice mismatch, as well as the strain... 

Figure 2. Formation of ternary borides MREMT4B4 (Mre = rare-earth element, Mj = transition metal) and different structure types. B, CeCo4B4 type B, LURU4B4 type a, NdCo4B4 type H, YOS4B4 type 8, Sm,4.eFe4B4 type MRcRe4B4 type , LuRh4B4type. Refs b, c , d", e, f , g , h, il l ...

The relative stabilities of the dioxides, sesquioxides and monoxides for first period transition metals are given in Figure 7.11(c). The stability of the higher oxidation state oxides decreases across the period. As we will discuss later, higher oxidation states can be stabilized in a ternary oxide if the second metal is a basic oxide like an alkaline earth metal. The lines in Figure 7.11(c) can in such cases be used to estimate enthalpies of formation for unstable oxidation states in order to determine the enthalpy stabilization in the acid-base reactions see below. Finally, it should be noted that the relative stability of the oxides in the higher oxidation states increases from the 3d via 4d to the 5d elements, as illustrated for the Cr, Mo and W oxides in Figure 7.11(d). 

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... 

The thiomolybdites are a class of molybdenum-sulfur compounds which contain molybdenum in a low oxidation state, usually +3. Two main types of such materials exist. The first type has the formula MMoS2 where M is a monovalent cation, usually an alkali metal. The second type has the formula MMo2S4 where M is a divalent cation, usually a transition metal. There are other thiomolybdite species, of composition other than that described above, which have been identified in ternary phase studies involving the M-Mo-S system (M = a transition element), but these have not been well characterized. 

One ubiquitous ternary structure is that of PbFCl (ZrSiS, BiOCl, Co2Sb, Fe2As).16,71 We ll call it MAB here because in the phases of interest to us the first element is often a transition metal and the other components, A and B, are often main group elements. Diagram 91 shows one view of this structure, 92 another. 

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