Chainlike hydrogen ordering inα-ScDxsystems

Hydrogen ordering is investigated in the α-${\mathrm{ScD}}_{\mathrm{x}}$ system for two concentrations x=0.19 and x=0.33 by diffuse neutron-scattering techniques. The results reveal the formation of chains, consisting of pairs of hydrogen atoms located on second-neighbor tetrahedral interstitial sites along the hexagonal direction. The results are similar to those found previously in α-${\mathrm{LuD}}_{\mathrm{x}}$. The differences between α-${\mathrm{ScD}}_{\mathrm{x}}$ and α-${\mathrm{LuD}}_{\mathrm{x}}$ give evidence for a chain formation due to a lowering of coherency stresses.