Laves-phase compound superconductivity

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. 

CeRu2. The compound (cubic Laves phase) was originally used as a nonmagnetic host for R doping in early studies of the interaction of magnetism and superconductivity (see for example Matthias et al. 1958, Hillenbrand and Wilhelm 1972). In recent years, it has been established that the superconducting properties of CeRua itself are most unusual. 

Under a much higher pressure of 15 GPa, CaAl2Si2 decomposed to Ca(Al,Si)2 with the Laves phase structure [60]. The Laves phase compounds with transition metals are well known for superconductors with the C15 structure, which also belongs to space group Fd3m isotypic with the type II silicon clathrate compounds. Solid solutions Ca(Ali cSi c)2 (0.35 < x < 0.75) can be directly prepared under HPHT conditions of 1,000 °C and 13 GPa. The stoichiometric Laves phase compound CaAlSi shows superconductivity at = 2.6 K. This is the hrst Laves phase compound composed of only commonly found elements. The compound can... 

Fig. 26. Superconducting critical temperature versus (a) number of valence electrons per atom, (b) mean volume and (c) electron density for C14(MgZn2) type Laves phase compounds (after Roberts...

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