Hydrogen-induced and A-site substitution-dependent structural properties of AB_2-type (Ho_(1-x)A_x)Co_2-hydrogen system (A = Mm and Ti)

摘要

The structural changes of the Laves phases pseudo-binary (Ho_(1-x)A_x)Co_2 alloys (A=Mm and Ti) uponhydrogen absorption have been investigated by means of powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The hydrogenation of alloys at different hydrogenation pressure and temperature has been performed using Sieverts-type apparatus. The effect of dehydrogenation and formation of hydride phases on the structural properties have been studied and results are interpreted with respect to their unhydrogentaed alloys. The pressure and temperature-dependent hydrogen-induced transformation from crystalline to amorphous and decomposition into constituents have been studied and discussed. The preferential occupancy of tetrahedral interstitial sites for hydrogen and relative stability of crystalline, amorphous and elemental hydrides have been reported. Further, the effect of Mm and Ti substitution upon amorphization conditions has been discussed.