An experimental study of NbD(,x)(H(,x)) alloys (0.70 < x < 0.85) in the vicinity of the (alpha)'-(beta) phase transition was conducted using x-ray and elastic neutron scattering techniques in the temperature range 300 < T < 473 K. Diffuse scattering close to the Bragg peaks of the BCC (alpha)' phase was measured. The temperature dependence of the scattering was determined in the (alpha)' phase and the changes in the diffuse scattering were determined upon cooling through the (alpha)'-(beta) phase transition.

Calculations of the diffuse scattering were carried out using the distortion field around the hydrogen solutes and taking correlations between the interstitial solutes into account. Our interpretation of the diffuse scattering data leads to a qualitative picture of the interactions between the hydrogen interstitial atoms and the niobium host lattice atoms.

We have also observed "superlattice" reflections between the Bragg peaks of the BCC (alpha)' phase, resulting from static displacements of the niobium lattice. These have been interpreted as being due to the partial ordering of deuterium atoms on octahedral interstitial sites. Because these reflections were not observed for Nb-H alloys in this composition range, an interpretation based on D-D interactions is presented.