Divalent ternary compounds

The sample with two phases has a quite different optical absorption.) The authors concluded that Tm is purely divalent, as confirmed by the study of TmTei jS c which has a nonvarying optical density up to x = 0.3. The lattice cell parameter of this ternary compound varies from 5.88 A up to 6.15 A (x = 0.3). 

No ternary phase diagram is established for the system Eu Al-Si the only data available were presented by Muravyova et al. (1972) and concern the existence of a ternary compound EuAljSij with the La202S-type of structure (space group P3ml) for sample preparation and atom parameters, see Sm-Al-Si. Lattice parameters were a = 4.18, c = 7.25 and suggest the presence of divalent Eu. 

From the results reviewed in this chapter, some common regularities of the interaction of rare-earth metals with iron and germanium can be drawn. The number of ternary compounds formed with light rare-earth elements, iron and germanium monotonously increases from lanthanum to samarium. No ternary compounds were found with europium, which is probably due to its divalent nature, compared to trivalency for the other rare earths. Among the heavy lanthanides, Tm forms the largest number of ternary compounds with iron and germanium. 

Ternary compounds formed by divalent rare earth elements... 

As a defined ternary B-C-N compound is not known, other starting materials are to be considered in order to synthesize one of the, yet unknown, La-B-C-N compounds. Solution chemistry routes were successfully performed with tetra-cyanoborates to synthesize the compounds A[B(CN)4] with monovalent A = Li, Ag, Cu cations, and M[B(CN)4]2 with divalent M = Hg, Cu, Zn, Mn cations [47]. 

In a classification of the compounds of the divalent metals, the following families of binary Me5X3 (and related ternary Me5X3H phases) were described (Corbett and Leon-Escamilla 2003) ... 

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. 

The same structure was independently fully redetermined for the synthetic ternary fluorides BaMnAlF7 and BaMnGaFv [14-16], in which the tervalent ions occupy the site of Al3+ in the natural usovite, whereas the manganese splits up between the octahedral site of Mg2+ and the 8-fold coordinated site of Ca2+ this initiated a successful quest for isostructural synthetic compounds Ba2MnM,IIM"I112Fi4 [15,17], where the different sizes of M11 and M,n would induce a selective repartition of the divalent ions between the square-antiprism site and the octahedral one. 

The composition of the various compounds can be understood by examining the upper section of the ternary phase diagram Me0-Fe203-Ba0, where Me is a divalent metal such as Ni, Mg, Co, Fe, Zn, Mn or Cu, Fig. 2.20. All the ferrites are found on the joins BaFei20i9-Me2Fe408 and BaFei20i9-Me2BaFei2022, or M-S and M-Y, respectively. M, S and Y are the end-members. 

Because the tripositive ions are the most stable for all the rare earth elements in almost all compounds, the thermochemistry of the solid (crystalline) rare earth sesquioxides dominates this chapter. Some rare earths have divalent or tetravalent states, so the chemistry of solid monoxides and dioxides are included. There are also many nonstoichiometric binary oxides of cerium, praseodymium, and terbium. As much as possible, the thermochemistry of these nonstoichiometric binary oxides is included. The stability, phase diagrams, and structures of ternary and polynary... 

Ternary I-III-VI QDs have attracted less research interest compared with binary III-V compounds (InP). The I-III-VI semiconductors composed of group I (Cu, Ag), III (AI, Ga, In, Tl), and VI (S, Se, Te) elements can be conceptually derived from II-VI binary compounds by replacing two divalent cations with one monovalent and one trivalent cation these elements are potentially less toxic. These compounds have a wide range of optical and electronic properties and depend on one another for their chalcopyrite structure (Fig. 1.17) [85]. 

Thus, the comparison of the R-Ni-Ge systems, carried out above, shows a similarity in the interaction of rare-earth metals with nickel and germanium wifii the exception of europium, which forms a considerably smaller number of compounds. This is consistent with europium s divalent character, and its similar behavior observed in the other Eu-3d element-Ge systems. At the same time, the type of interaction and the crystal structures of compoimds formed are different for the elements of the light and heavy lanthanides. The only two ternary germanides of scandium, which are isotypic with lanthanide-containing compounds, are ScNiGe (structure type TiNiSi) and Sc3NinGe4 (structure type Sc3NinGe4). 

In contrast, the divalent state is stabilized by the low electronegativity of the anions, with increasing stability as the anion electronegativity decreases. For instance, in the case of europium, for which the normal oxide is EU2O3, the corresponding EU2S3 sulfide does not exist. The normal sulfide is Eu(II)S, which is easily obtained by action of H2S on trivalent europium compounds (oxide, carbonate, etc). However the trivalence of europium is manifest in some chalcogenides, which may all be considered as ternary or quaternary compounds. 

In the case of selenides and tellurides, only divalent Eu is known in the binary chalcogenides. Among the ternary chalcogenides, almost all the compounds are formed by Eu(II), but some rare derivatives of Eu(III) are known, and especially Eu202Se and NaEuSc2. However, the selenides have not been so extensively studied as the sulfides. 

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