R-Ni systems

The HFFP method is flee of any assumptions regarding the R-R interaction. However, because of the rather large difference of Mr-Mt in almost all the lanthanide intermetallics, it can be applied for the substituted alloys only. When R is replaced by Y, the 4d electrons are introduced to the system. Thus, besides the 3d-5d hybridization, one should taken into account the influence of the 3d-4d mixing on the magnetic behaviour. For the HFFP studies, the Y substitution is applied when Mr is larger than Mj. As consequence, in the Fe, Co compounds, this magnetic dilution appears only in the R-rich ones, whereas it is applied to all of the R-Ni systems. 

Fig. 13.6. Compound formation in the R-Ni systems. Notes 1) YNi also crystallizes with a monoclinic structure related to the FeB type. 2) EtjNi22 and Et4Ni,7 crystallize with structures derived from the CaCUj type. 3) The following compounds have been claimed to exist but no structural details are available Eu,Ni (Y, GdljNij (Y, Gd)Ni4.

Finally, in the R-Ni system the compounds of the type CrB and FeB are observed. These structures can be transformed into each other by changing the stacking sequence (Hohnke and Parthe, 1966). These structures can also be deduced from the cubic close packed structure. Only in the R-Co system are the hexagonally (P63/m) crystallizing R4C03 compounds of the so-called H04C03 type observed (Berthet-Colominas et al., 1968 Lemaire and Schweizer, 1967). In some specific R-Co and many R-Ni systems the orthorhombic structure of the type AhNi is observed. 

Fig. 2. Schematic representation of intermetallic compounds occurring in various R-Ni systems. This diagram was constructed using the compilation of compounds given in Buschow s review (1977a), the results published by Parthe and Moreau (1977) and those given by van Vucht and Buschow (1976).

Owing to their numerous actual and potential applications, several ternary and complex systems of these metals, especially of aluminium, have been investigated a few examples of the systematics of Al-Me-X alloys are presented in 5.18 and in Fig. 5.41. Recent contributions to this subject have been given with the study of the systems R-Al-Cu (Riani et al. 2005, and references there in). These rare earth alloys, characterized by the formation of several intermediate phases, are interesting also as raw materials for the preparation of amorphous alloys. Regularities in the trends of their properties have been underlined. The experimental and calculated data relevant to the binary systems Al-Fe, Al-Ni and Fe-Ni have been examined and discussed in a paper concerning the assessment of the ternary Al-Fe-Ni system (Eleno et al. 2006). 

R-Ni(Pd, Pt)-Sb. Interaction of the components in these systems is the most complicated and highly diversified (table 61). 

Bhattacharyya et al.100 and Mann and Dosi101 both observed a two-stage oxidation-reduction mechanism although with somewhat different kinetic expressions. Malinski et al.55 studied the catalytic activities of the vanadates of Fe, Co, and Ni. The highest yields of formaldehyde were obtained with atomic ratios V/Me = 1 and the catalyst with Ni was the most selective. I.r. spectra taken before and after methanol oxidation show different stabilities of the (V=0) bond, which is most constant in the V-Ni system. 

CuioSn3, and Cu6Sn5 (Villars and Calvert, 1991,1997) exist, no binary nickel and copper plumbides are known. This fact is transferred to the ternary R-Ni(Cu)-Pb systems. The plumbides systems contain fewer ternary compounds when compared to the stannide ones. To give an example, 15 stannides have been reported for the Gd-Ni-Sn system (Skolozdra, 1997), while only five plumbides exist in the related system with lead (Gulay, 2003b). This empirical rule is observed for many other ternary systems. 

G. Liang, 1. Huot, S. Boily, A. Van Neste, R. Schulz, Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2-Tm (Tm = Ti, V, Mn, Fe and Ni) systems, . /. Alloys Compd. 292 (1999) 247-252... 

This result should be, of course, consistent with the result for the conventional DFT of a spin-compensated (paramagnetic) system characterized by nf(r) = ni(r) — jn(r). From Eq. (135) its exchange energy can be written as... 

The increase in volume change for the Cr system is explained by the electronic change in the inner coordination sphere from the Jahn-Teller distorted coordination sphere of Cr to an octahedral one in Cr -R (56). Further increase for the Co system is due to change of the electronic configuration of high spin d for Co to low spin d for Co -R in this system (73). The largest volume of activation found in the Ni system is attributed to the change in coordination number of the central Ni ion from planar low spin d (Nicyclam) to octahedral d for the Ni-R complex (45). 

Sch2] Schultz, A., Chuang, Y.-Y, Chang, Y.A., Three-Dimensional Phase Diagram Representation , Bull. Alloy Phase Diagrams, 6(4), 304-316 (1985) (Calculation, Thermodyn., 20) [1985Spe] Spencer, R, Hack, K., Moser, Z., Zakulski, W., Calculation of the Fcc/Liquid Phase Equilibria in the Cu-Fe-Ni System , Calphad, 9(2), 191-198 (1985) (Thermodyn., Assessment, 31)... 

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