Evidence for H (D) Ordering in $\mathrm{Pd}{\mathrm{H}}_x$ ($\mathrm{Pd}{\mathrm{D}}_x$)

Resistivity, annealing, and neutron-diffraction studies of $\mathrm{Pd}{\mathrm{H}}_x$ and $\mathrm{Pd}{\mathrm{D}}_x$ provide evidence for ordering of the H and D atoms on the octhaderal interstitial sublattice. Neutron diffraction results on a Pd${\mathrm{D}}_{0.76}$ single crystal indicate that the D atoms order on the fcc interstitial lattice with every fifth (4,2,0) plane vacant and all others filled, corresponding to the ${\mathrm{Ni}}_4$Mo structure.