Structural ternary Laves phases

A systematic analysis of structure and stability of binary and ternary Laves phases, or Friauf-Laves phases, has been performed by Stein et al. (2004, 2005). By reviewing a large number of experimentally determined phase diagrams with Laves phases, a number of general conclusions have been obtained. These may be summarized in the following points ... 

N. Hanada, S. Orimo, H. Fujii, Hydriding properties of ordered-/disordered-Mg-based ternary Laves phase structures, J. Alloys Compd. 356-357 (2003) 429-432. 

The partial substitution of the transition element M in MjSi by a second transition metal M leads to ternary silicides of approximate composition MM Si corresponding to (M,M )2Si. Such ternaries are primarily the Si-containing E phases and V phases (Jeitschko etal., 1969 Jeitschko, 1970) and the ternary Si-containing Laves phases (Bardos etal., 1961), which were discussed in Sec. 8, as well as many other phases, which all differ by composition and crystal structure (Nowotny, 1972 a). This is exemplified by the Fe-Nb-Si system with the ternary silicides E, V, Xj, Xj, Xj and the Laves phase Nb(Fe,Si)2 with up to 25 at.% Si (Raghavan, 1987), or the Co-Nb-Si system with the ternary silicides E, T, v, Ti, v i, and the ternary Laves phase Nb(Co,Si)2 with Si contents between about 10 and 20 at.% (Argent, 1984). Finally, it is noted that other phases - in particular a phases and A13 Mn-base phases - dissolve large amounts of Si by which these phases are stabilized (Gupta et al., 1960 Bardos et al., 1966). 

The ordered ternary Laves phases are discussed with the 6725 Sc2C03Si structure. The disordered Laves phases can be found with the 67(50) Sc(Ni 5Al 5)2 compound. A tendency toward a partial ordering of the non-rare-earth elements is found to be related to the T/M ratio. See for example Oesterreicher (1973a). 

Laves phases occurring in ternary systems, the binary subsystems of which contain no Laves phases, generally pertain to the hexagonal MgZn2-type structure. 

Structure data are summarized in Table 2. No ternary phase has been reported in the Cr-Fe-Zr system. However binary Laves phases show extended solubihty ranges along the ZrFc2-ZrCr2 quasibinary section. The variation of the lattice parameters with composition along the section are reported in Fig. 1 according to [1970Kan]. 

Fig. 16. The four ternary ordered Laves phase structure types showing the atom arrangement in or close to each side of the (1120) plane of the hexagonal or triple hexagonal cells. Of the atoms positioned away from the (1120) plane only B atoms are indicated which form a triangle with a B atom in the (1120) plane with the same z value.

Ste] Stein, R, Palm, M., Sauthoff, G., Structure and Stability of Laves Phases Part II - Structure Type Variations in Binary and Ternary Systems , Intermetallics, 13, 1056-1074 (2005) (Review, 249)... 

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