Exp 166 Er Moessbauer and X-Ray Diffraction Study of ErMn sub 2 Hydrides

摘要

The pressure-composition isotherm at 22 exp 0 C for ErMn sub 2 H/sub x/ between 1 and 10 exp 4 torr shows the formation of two hydride phases with composition x = 4.6 and x = 4.0, and with equilibrium H sub 2 pressures of 15 torr and less than 1 torr, respectively. Both hydrides are expanded versions of the C14 hexagonal Laves structure of ErMn sub 2 with volume expansions of 23% and 37% for the lower and higher order phases, respectively. A slight preferential expansion parallel to the C sub 0 axis is observed. The exp 166 Er Moessbauer results show that Er magnetic moment in both hydride phases is reduced from the free-ion value measured in ErMn sub 2 . The ferromagnetic ordering present in ErMn sub 2 and ErMn sub 2 H sub 4 is absent in ErMn sub 2 H sub 4 sub 6 down to 1.5 K. Two Er sites are detected in ErMn sub 2 H sub 4 instead of one expected for the C14 structure. The origin of these sites is discussed in terms of possible hydrogen site occupancy configurations. (ERA citation 06:015847)