Compounding ternary-phase

As with the pnictates, a quasi-ternary phase diagram can be developed to map out possible compounds in this composition phase space using key chalcotetre-late building blocks. We have begun to make use of the peritectic nature of the starting materials, as this has facilitated reactions between phases. 

Figure 25 shows the ternary phase diagram (solubility isotherm) for an unsolvated racemic compound. Examples of this type include benzylidenecamphor in methanol, or /V-acetylvaline in acetone [141]. In Fig. 25, A and A represent the...

Many binary inorganic phases with a significant composition range can be listed1 (Table 4.3). Apart from binary compounds, ternary and other more complex materials may show nonstoichiometry in one or all atom components. 

Figure 2.29. Isothermal sections of ternary phase diagrams (a) Al-Er-Mg system at 400°C, Saccone et al. (2002) and, (b) Al-Cu-Ti system at 540°C from Villars et al. (1995). A number of single-phase regions (dark grey) may be noticed, both extending from binary compounds and as ternary intermediate phases (r) in the Al-Er-Mg system and the four phases Tj t2 t3 and t4 in the Al-Cu-Ti system. The three-phase fields are marked by an asterisk, in the Al-Er-Mg system a few tie-lines are indicated in the two-phase fields.

Typically, binary Laves compounds AM2 are formed in several systems of A metals such as alkaline earths, rare earths, actinides, Ti, Zr, Hf, etc., with M = Al, Mg, VIII group metals, etc. Laves phases are formed also in several ternary systems either as solid solution fields extending from one binary phase (or possibly connecting the binary phases of two boundary systems) or as true ternary phases, that is forming homogeneity fields not connected with the boundary systems. 

Considering for instance the formation of compounds, several variants may be observed due to the possible existence of binary (point or line) phases and/or of ternary, stoichiometric or solid solutions phases. Notice that true ternary phases may be formed (that is phases corresponding to homogeneity regions placed inside the diagram and not connected with the components or any binary phases). However within the ternary composition fields, phases are observed which contain all the... 

Figure 5.41. Schemes of ternary compound formation in ternary alloys. For a few metal pairs (Al-Cu, Al-Fe, etc.) the third elements are indicated (defined by their position in the Periodic Table) with which true ternary phases are formed that is, phases are formed which are homogeneous in internal regions of the composition triangle not connected with the corners or edges. Compare these data with those shown for the formation of binary compounds in the figures relevant to the involved metals.

These problems have of course different weights for the different metals. The high reactivity of the elements on the left-side of the Periodic Table is well-known. On this subject, relevant examples based on rare earth metals and their alloys and compounds are given in a paper by Gschneidner (1993) Metals, alloys and compounds high purities do make a difference The influence of impurity atoms, especially the interstitial elements, on some of the properties of pure rare earth metals and the stabilization of non-equilibrium structures of the metals are there discussed. The effects of impurities on intermetallic and non-metallic R compounds are also considered, including the composition and structure of line compounds, the nominal vs. true composition of a sample and/or of an intermediate phase, the stabilization of non-existent binary phases which correspond to real new ternary phases, etc. A few examples taken from the above-mentioned paper and reported here are especially relevant. They may be useful to highlight typical problems met in preparative intermetallic chemistry. 

Synthesis in liquidAl Al as a reactive solvent Several intermetallic alu-minides have been prepared from liquid aluminium very often the separation of the compounds may be achieved through the dissolution of Al which dissolves readily in several non-oxidizing acids (for instance HC1). For a review on the reactions carried out in liquid aluminium and on several compounds prepared, see Kanatzidis et al. (2005) binary compounds are listed (Re-Al, Co-Al, Ir-Al) as well as ternary phases (lanthanide and actinide-transition metal aluminides). Examples of quaternary compounds (alumino-silicides, alumino-germanides of lanthanides and transition metals) have also been described. As an example, a few preparative details of specific compounds are reported in the following. 

Notice, moreover, that for a family of binary and complex phases such as the Laves phases (Cu2Mg, MgZn2, Ni2Mg types) an overall number of about 1400 has been estimated. The restriction of the phase concentration to a limited number of stoichiometric ratios is also valid (and, perhaps, more evident) for the ternary phases. We may notice in Fig. 7.2, adapted from a paper by Rodgers and Villars (1993), that seven stoichiometric ratios (1 1 1, 2 1 1, 3 1 1, 4 1 1, 2 2 1, 3 2 1, 4 2 1) are the most prevalent. According to Rodgers and Villars they represent over 80% of all known ternary compounds. 

Binary representatives of this structure are found among the Mn, Cr, Fe, Ru, Rh, Os monosilicides and germanides, Zr and Hf monoantimonides, AuBe and A1 (or Ga) compounds with Pd and Pt. Ternary phases such as CrMnSi2, CrFeSi2, CrCoSi2, FeMnSi2 have been described. 

Figure 5 BaO-CuO-YOj 6 ternary phase diagram (1) ( 950-1000°C). Various compounds and compositions require various oxygen activities so that a complete rigorous representation of the diagram should include an additional dimension related to Poz.

Recall that we can take vertical slices of the ternary phase diagrams, as well as isothermal (horizontal) slices. If we take, for example, a slice that begins at the tenarite composition (CuO) and extends across to the hematite composition (Fc203), we would end up with a pseudobinary phase diagram, which, when plotted on the appropriate temperature-composition axes, would look like Figure 2.22. Note that the compound CuFc204 is present, here labeled as spinel (see Section 1.2.2.3), but there is much more phase and temperature information available to us. This is, in fact, how many metal oxide phase diagrams are presented. The most stable forms of the... 

Chemical deposition is not limited to binary compounds. Ternary (and higher) compounds can be deposited by this technique. For the same reason as for the non II-VI and IV-VI compounds in Section 2.9.3, this section will suffice with a table of ternary compounds reported up to now, with two additions. The first is a brief consideration of the principles involved in the deposition of materials containing three or more elements. The second is to identify, in the table, which deposits have been clearly demonstrated to be a true single-phase solid solution rather than a mixture of two or more phases. 

Two factors combine to lend a greater diversity in the stereochemistries exhibited by bivalent germanium, tin and lead compounds, the increased radius of Mn compared with that of Mw and the presence of a non-bonding pair of electrons. When the non-bonding pair of electrons occupies the isotropic valence level s orbital, as in, for example, the complex cations Pb[SC(NH2)2]6+ and Pb[antipyrine]6+, or when they are donated to conductance band levels, as in the binary tin and lead selenides or tellurides or the perovskite ternary phases CsMX3 (M = Sn, Pb X = Cl, Br, I), then the metal coordination is regular. However, in the majority of compounds an apparent vacancy in the coordination sphere of the metal is observed, which is usually ascribed to the presence of the non-bonding pair of electrons in a hybrid orbital and cited as evidence for a stereochemically active lone pair . 

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