Laves phase compounds

Abstract. The interaction of hydrogen with ZrMn2 Laves phase compound at pressure up to 60 atm and temperature range from 100 to 305 °C has been investigated using reaction calorimetry. The obtained results allow us to propose the existence of two hydride phase in the ZrMn2-H2 system. 

Abstract. The interaction of hydrogen with nonstoichiometric Tio.9Zro.iMnL3Vo.5 Laves phase compound at pressure up to 60 atm and in temperature range from 150 to 190°C has been studied by means of calorimetric and P-X isotherm methods. The obtained results allow us to propose the existence of one hydride phase, 0-hydride, in the Ti0 9Zr0 jMnj 3V0 5 - H2 system in the temperature range 150-170°C. It has been found that temperature 190°C is close to critical temperature (182°C) above which hydride phases does not exist. 

For cubic Laves-phase compounds with RpJR > 1-35, the Z2/rj ratio becomes less than 1. In this case, each g site has only one nearest neighbor lying at the adjacent hexagon. Such a transformation of the g-site sublattice may lead to a qualitative change in the microscopic picture of H jump motion the faster jump process is expected to be transformed into the back-and-forth jumps within pairs of g sites belonging to adjacent hexagons. The results of recent QENS experiments... 

Jacob, 1. and Shaltiel, D., Hydrogen sorption properties of some AB2 Laves phase compounds. Journal of the Less-Common Met., 1979, 65 p. 117-128. 

Besnus et al. (1982) have performed magnetization, diffuse neutron scattering, 57Fe Mossbauer and NMR studies on these C15 Laves phase compounds over a wide range of composition. The Curie temperatures and average moments are reduced with increasing Mn content and it was concluded from the neutron and NMR data... 

Domyschev et al. (1974) have studied the system GdZn but were unable to produce the GdZna Laves phase compound. The authors thought this was due to the low electronegative ratio of these elements. 

Van Dongen, J.C.M., G.J. Nieuwenhuys, J.A. Mydosh, A.H. van der Kraan and K.H.J. Buschow, 1980, Magnetic Properties and Electrical Resistivity of Transition Metal Laves Phase Compounds Y(Coi iFei)2, Y(Iri, Fe,)2, and HfCCoi-jFexlz, in Rhodes, P., ed.. Physics of Transition Metals, 1980 (Conference Series Nr. 55. The Institute of Physics, Bristol and London) p. 275. 

Fig. 59. Left Angular dependence of the TF = 0.15T p.SR depolarization rate for a single crystal of CeAlj at temperatures well above 3.5 K). The crystal is rotated around the (110) axis. An angle of 90" corre nds to a field applied along (100). The top part shows the experimental result for two tenqieratures, die bottom part corresponding dipolar sum calculations for three different tetrahedral muon stopping sites. Right Tenqierature dependence of the muon spin depolarization rate in three CIS Laves-phase compounds. The step around 80K signals the onset of muon mobility (see text). From Hartmann et al. (1989, 1990b).

Properties of the paramagnetic state of R Laves-phase compounds from TF-p,SR ... 

Cannon et al. (1975) used the Jaccarino-Walker model for the transition-metal moment in some cubic Laves phase compounds. Specifically, they showed that in the Gd(COj Ni )2 system the Co moment appears to be criticaUy dependent on the number and type of its nearest neighbours. Ichinose (1987) measured the NMR of " Al, Mn, " Co and Gd in Gd(X, Coj2 for X = Al, Mn, Fe and Ni. He found from the analysis of the NMR spectra that the concentration dependence of the Co hyperfine field is proportional to the sum of the conduction electron polarization arising from nearest-neighbour transition atoms and that the Co atoms carry a magnetic moment induced by the neighbouring X atoms. 

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. 7.22 Schematic structure of a the Laves phase compound Ca(Al,Si)2, and b a structural view composed of truncated tetrahedral cages with Ca atoms in the center, CaOAleSie [60]...

As a property of anomalously high magnitude in cubic Laves phase compounds of rare earth metals such as Fe2(Tbo.3Dyo.7), which are the basis of magnetostrictive materials serving as magnetostrictive transducers and sensors [3.3]. 

The cubic Laves-phase compounds RT2 have been studied intensively in the last decade. The simple structure with a single crystallographic site for the R and T ions makes these compounds especially suited for an extensive analysis of the basic magnetic interaction as a function of the lanthanide elements and of the 3d partner. In RC02, a... 

Curie temperatures, low-temperature saturation moments, and lattice parameters of some Sm and Gd cubic Laves-phase compounds (Buschow et al., 1973a). 

---