NEUTRON-SCATTERING STUDY OF DEUTERIUM SHORT-RANGE ORDER IN VDX

The short-range order of the D interstitials in two (alpha' phase) VDx powder samples (x = 0.75 and 0.82) was investigated at room temperatu re by diffuse neutron scattering. The study demonstrates a (within exp erimental accuracy complete) blocking of interstitial sites in the two nearest shells around a given D atom, a reduced occupation probabilit y for the sites in the third shell and an increased occupation probabi lity of the sites in the fourth, fifth and sixth shells. These results prove directly the existence of a strong short-range repulsion betwee n the D atoms.