Neutron diffraction study of the β1-β2 transformation in Ta2D

The β1-β2 phase transformation in Ta2D was studied by neutron diffraction using the pulsed source at the Tohoku Linac and the Intense Pulsed Neutron Source, Argonne National Laboratory. It was found that the hh0 reflections almost disappear in the β2 phase, whereas the 001 reflections are the same as those in the β1 phase. The diffraction data show that the β2 phase has an orthorhombic unit cell which is identical with that of the β1 phase and contains four tantalum and two deuterium atoms in a volume which is approximately 212 × 1 × 212 that of the b.c.c. host lattice. The deuterium atoms fractionally occupy the tetrahedral sites in alternate (002)orth planes.