Formation of crystalline and amorphous hydrides by hydrogenation of C15 Laves phase YFe2

Formation conditions of crystalline (c-) and amorphous (a-) YFe2Hx hydrides during thermal analysis of C15 Laves phase YFe2 in a hydrogen pressure (0.1–5.0 MPa) at heating rates of 0.17 and 0.33 K/s have been investigated by XRD, Ar-DSC, TEM and hydrogen analysis. Hydrogen absorption, hydrogen-induced amorphization (HIA), the precipitation of BiF3-type YH3 and the decomposition of the remaining amorphous hydride into α-Fe + YH3 occur exothermally with increasing temperature. The peak temperature Tp for hydrogen absorption, HIA, and the decomposition of the remaining amorphous hydride show the negative pressure dependence, but that for the precipitation of the hydride shows the positive one. As a consequence of such pressure dependence, HIA overlaps with the precipitation of YH3 at 0.1 MPa H2 and 0.33 K/s. Formation conditions of c- and a-YFe2Hx are compared with those of the other C15 Laves phases RFe2 and the mechanism of HIA in C15 Laves phases RFe2 is discussed.