Phase transitions in the Nb-D(H) system: Superlattice reflections near the α’-β phase transition

An experimental study of ${\mathrm{NbD}}_{\mathrm{x}}$(${\mathrm{H}}_{\mathrm{x}}$) alloys (0.70<x<0.85) in the vicinity of the α’-β phase transition was conducted using x-ray and elastic neutron scattering techniques in the temperature range 300<T<473 K. ‘‘Superlattice’’ reflections between the Bragg peaks of the bcc α’ phase were observed for both x-ray and neutron scattering but there were significant differences between observations carried out with the two types of radiation. The temperature dependence of these weak reflections was determined in the α’ phase. These superlattice reflections were interpreted as being due to periodic modulations of the metal lattice caused by the partial ordering of deuterium atoms in the α’ phase.