Experimental observation of hydrogen ordering inTbD2+x

A neutron-scattering investigation gives evidence of deuterium ordering at lower temperatures in a superstoichiometric heavy-rare-earth dihydride, ${\mathrm{TbD}}_{2+\mathit{x}}$. The ordering occurs within the ensemble of deuterium atoms located on octahedral interstitial sites of the fcc lattice. The ordered state is described by an interstitial ${\mathit{DO}}_{22}$ (I4/mmm) structure revealing the presence of a repulsive deuterium-deuterium interaction.