Structural investigation of hydrogen solubility in YyR1-y alloys (R=Tb and Gd)

We have studied the structure of hydrogen loaded YyTb1-y alloys, with y=0.2 and 0.9, by X-ray diffraction (XRD) techniques. The room-temperature XRD profiles of Y0.2Tb0.8Hx exhibit, in addition to the peaks of the h.c.p. metal lattice, those of the f.c.c. dihydride for all x>0. In the case of Y0.9Tb0.1Hx, the f.c.c. peaks show up only for x=0.20, indicating H-solubility for smaller hydrogen concentrations in this alloy. As for the two YyGd1-y (y=0.3 and 0.4) alloys, we observe in both cases precipitation of the dihydride for the smallest H concentrations. These results complement earlier resistivity measurements on the same systems, by presenting the evolution of the respective lattice parameters and their c/a ratios upon hydrogen addition and, in particular, specifying the influence of the metal lattice environment upon the state of the precipitating hydride