A study on hydrogen-induced amorphization in C15 Laves phase DyNi2 under different hydrogen pressures

Hydrogen pressure dependence of structural changes in C15 Laves phase DyMn2 studied by pressure differential scanning calorimetry

“…As the hydrogen pressure increases, T p for the simultaneous formation of cand a-DyMn 2 H x , and the simultaneous occurrence of HIA and the precipitation of DyH 3 shift to the low temperature side, i.e., they show a negative pressure dependence. Here, it is worth noticing that T p for the precipitation of DyH 3 shows a negative temperature dependence in contrast to that of DyFe 2 [22], DyCo 2 [26], and DyNi 2 [27]. Fig.…”

“…It is worth noticing that T p for the precipitation of DyH 3 shows a negative pressure dependence in contrast to that for the precipitation of RH 3 (DyNi 5 ) in RFe 2 (R = Dy, Ce, Tb, and Er) [20][21][22] and DyNi 2 [27]. Even if HIA and the precipitation of RH 3 (DyNi 5 ) occur simultaneously in RFe 2 (R = Dy, Tb, and Er) [20][21][22] and DyNi 2 [27], single-phase amorphous hydrides are formed at the higher hydrogen pressure, because T p for the precipitation shows a positive pressure dependence. That is, the positive pressure dependence of T p for the precipitation of DyH 3 (DyNi 5 ) is the key to form the single-phase amorphous hydride.…”

“…DyMn 2 absorbs hydrogen forming c-and a-DyMn 2 H x at the first exothermic peak in the same way as DyCo 2 [26] and DyNi 2 [27] but in contrast to DyFe 2 [22] and RFe 2 (R = Y, Sm, Gd, Tb, Dy, Ho, and Er) [14]. Hydrogen is usually absorbed in C15 Laves phases RM 2 without a structural change at room temperature, because the diffusion of R and M is very sluggish.…”

“…5(b)). From hydrogen analysis, XRD, Ar-DSC and TEM, we can see that the first exothermic peak of DyMn 2 results from the simultaneous formation of crystalline (c-) and amorphous (a-) DyMn 2 H x in the same way as DyCo 2 [26] and DyNi 2 [27]. Here, we must take care of the fact that the formation of a-DyMn 2 H x is not detected by XRD, but is detectable by Ar-DSC and TEM.…”

“…For instance, it has been reported that the C15 Laves phases AB 2 compounds having an atomic size ratio larger than 1.37 amorphize by hydrogenation [15], while those having a smaller one do not amorphize. Structural changes of C15 Laves phases RFe 2 in a hydrogen atmosphere have extensively been investigated [8][9][10][11][12][13][14][16][17][18][19][20][21][22], but those of C15 Laves phases RM 2 (M = Co, Ni, and Mn) have slightly been done [2,[23][24][25][26][27]. Recently, the present authors have systematically investigated structural changes of C15 Laves phases DyM 2 (M = Fe, Co, and Ni) having an atomic size ratio above 1.37 by the thermal analysis in a hydrogen atmosphere and showed the formation of the single-phase amorphous hydrides a-DyM 2 H x [22,26,27].…”