CRYSTAL-STRUCTURE OF HYDRIDE AND DEUTERIDE OF UNIAL

The hydrogen and deuterium absorption behaviour of UNiAl was examined at hydrogen isotope pressures below 10(5) Pa and temperatures up to 973 K. Under these conditions UNiAl absorbed hydrogen and deuterium up to UNiAlH0.8, and UNiAlD0.7 respectively. Neutron powder diffraction of UNiAlD0.7 revealed that each D atom occupies a 3U-2Ni site formed by three U atoms and two Ni atoms. It is at the centre of a triangle of U atoms which two SU-1Ni-type tetrahedral sites share. This occupation slightly changed the arrangement of metal atoms to enlarge the 3U triangle. Changes in X-ray diffraction pattern suggested the further movement of metallic atoms to form UNiAlH27.