Laves-phase intermetallics

Table 10. Magnetic properties of cubic AnX laves phases intermetallics with non-magnetic elements... 

Zhu] Zhu, J.H., Liu, C.T., Liaw, P.K., Phase Stability and Mechanical Behavior of NbCr2-based Laves Phases , Intermetallics, 7, 1011-1016 (1999) (Ciys. Structure, Phase Relations, Experimental, Electronic Structure, Meehan. Prop.,, 25)... 

This section presents a brief survey of metallic systems in which ESR of lanthanide ions have been studied. Only those host materials are included which may be classed as metals, alloys, or intermetallic compounds of the rare earths, in parallel with the survey of applications of ESR in insulators in section 4.1. The following subsections treat, respectively, rare-earth metals and alloys (especially those based on La, Y, Sc, and Lu), Laves phase intermetallic compounds, and the so-called Van Vleck para-magnetic compounds, of which many fall in the category of the rare earth mono-pnictides. The ESR of lanthanide ions in non-lanthanide host materials such as the noble metals is not included. Such systems are discussed in the extensive reviews by Orbach et al. (1974) and by Taylor (1975). 

The cubic CeMj Laves-phase intermetallic compounds (M = Fe, Co, Ni) have anomalously small lattice constants compared with those of the corresponding compounds of all other rare earths. This is illustrated in fig. 51, where we have plotted the lattice constants of the trivalent rare earth RMj compounds taking Gd and Pr... 

UPt3 is considerably less compressible than the AnBejs compounds studied. This parallels the situation found in the bulk moduli of the Laves-phase intermetallic compounds of uranium (see table 2). In both cases, the intermetallics with a transition metal (Fe, Co, Mn, Ir for the Laves phases, Pt for the heavy-fermion compounds) are considerably stiffer than those incorporating a metal of one of the main groups of the periodic table (Al for the Laves-type compounds, Be for the heavy-fermion compounds). In interpreting compression data of these types of compounds, one should think of a possible stiffening effect linked to the existence of partly filled shells. 

Considering then the phase composition as a significant parameter, we obtain the histogram shown in Fig. 7.1(a) for the distribution of the intermetallic phases according to the stoichiometry of binary prototypes. For instance, the binary Laves phases, the A1B2, Caln2, etc., type phases are all included in the number reported for the 66-67.99 stoichiometry range, even if the real stoichiometry of the specific phase is different, see Fig. 7.1(b). We may note the overall prevalence of phases and, to a certain extent, of structural types, which may be related to simple (1 2, 1 1, 1 3, 2 3, etc.) stoichiometric ratios. 

In essence, metal/intermetallic hydrides of AB, AB (Laves phases), AB, and A B have not been improved to any remarkable extent since the end of the 1990s. Nevertheless, there have been some efforts directed to either improvement of synthesis or properties of metal/intermetallic hydrides particularly by application of ball milling associated with nanostructuring. Some of these more recent efforts will be briefly discussed in the following sections. 

From an experimental point of view, it appears that the resonant f level is the best starting hypothesis for most U, Np and Pu compounds. Only in some cases of strong hybridization (particularly for Laves phase and AuCua-type structure intermetallics) it will broaden into true bands and we shall try to give criteria for itinerant magnetism. 

NpOs2 this intermetallic Laves phase is ferromagnetic below T = 7.5 K with p d = 0.4 Pb while p ff = 3.3 Pb - The magnetie entropy is 0.2 RLn2 while y = 205 mJ/mol j 238) y dditional evidence for itinerant magnetism comes from the very large superimposed susceptibility in the ordered state... 

There are several dozen metallic AB2 compounds called Laves phases that are superconducting they have either cubic or hexagonal crystal structures. Some have critical temperatures above 10 K and high upper critical magnetic fields Bc2- For example, Zri/2Hfi/2V2 has rc = 10.1K, B 2 = 24 T, and a compound with a different Zr/Hf ratio has similar and Bc2 values with the critical current density Jc 4 X 10 A/cm. These materials also have the advantage of not being as hard and brittle as some other intermetallics and alloys with comparable transition temperatures. 

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