Elastic Laves phases

Density functional theory is used for band structure calculations of hydrogen storage materials. This method has been applied to a variety of hydrides such as ABs [77-79], AB [77], transition metals [53, 80], Laves phases [81], and complex hydrides [82[. Theoretical investigation is not only useful for the prediction of the heat of formation but it could also assess the elastic and mechanical properties of these materials, properties which are usually difficult to measure in the case of hydrides [78[. 

The correlation between the total phase enthalpy and the Young s modulus, which is one of the three elastic moduli, is shown in Fig. 6 for various cubic phases, i.e. for the f.c.c. elements Al and Ni (Al), the f.c.c.-ordered NijAl (LI 2), the b.c.c. ordered FeAl, NiAl and CoAl (B2), and the cubic Laves phases CaAlj, YAI2, LaAl2, NbCr2, ZrLaves phases, i.e. there seems to be a common scatter band and the data of some other phases are near this scatter band. It has to... 

The other examples of MV compounds are less spectacidar in their electron-phonon effects. Both YbAl2 and CePdj do not show very anomalous behaviour in Cg and V. This is probably related to the particular crystal structure (Laves phase for YbAl2 CujAu structure for CePdj). Simple elastic force constant effects may overshadow the anomalous elastic behaviour in these cases. 

Figures (A) Scattering at 0=0.87 A- and 360K from ZrTijHjg. The fit (soiid iine) to the data ( ) is the sum of the quasieiastic scattering with a Lorentzian line shape, (dashed line) and elastic scattering from the metal atoms (dotted line). (B) Line width of the Lorentzian component as a function of Q for T = 295, 330 and 360 K. The solid lines are fits from the Chudley-Elliott model (Eqn [8]) with / = 2.8 A. (Data recorded with IN10 at the ILL). Reproduced with permission from Fernandez JF, Kemali M, Johnson MR and Ross DK (1997) Quasieiastic neutron scattering measurements on the ZrTi2H3e C-15 Laves phase compound. P/ij4s/ca 6234-236 903-905.

The temperature dependence of the elastic moduli has been investigated from 4.2 to 300 K for various polycrystalline rare earth-cobalt (Klimker et ah, 1979), rare earth-iron (Klimker et al., 1974) Laves-phase... 

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