Amorphization of Laves phase hydride

Crystalline GdFe2 Laves phase are formed at relatively low temperatures; for example GdPe2H4.8 is formed at room temperature, which is reversible, with a H/M ratio of 1.6. However, at this temperature desorption of all the hydrogen is difficult because of slow kinetics. An amorphous GdFeHx phase forms at intermediate temperatures and pressures. The absorption isotherm is quite unusual, as the crystal-to-amorphous transformation is accompanied by either a gain or a loss of hydrogen and is temperature depended. Absorption isotherms taken below 475K showed that there is an abrupt decrease in the hydrogen capacity of the alloy during the crystalline-to-amorphous hydride phase transformation. Whereas the absorption isotherms taken above 475K showed that there is an abrupt increase in the hydrogen capacity during amorphization. At temperatures above 525 K, hydrogen absorption causes to the disproportionation of the GdFe2 crystal into a two-phase mixture of GdH2 and bcc □-Fe. The formation of the crystalline and amorphous GdFe2Hx phases, phase stability regions, disproportionation of the hydride will be presented.