The β-ZrNiD1-x (for x ≈ 0.1, near to the β-γ phase boundary) was found to possess a triclinic P¯1 structure as determined by high-resolution neutron powder diffraction. This was very different to the widely accepted orthorhombic and distorted orthorhombic Cmcm structures proposed previously. In contrast to the single type of D site associated with these latter structures, the true β-ZrNiD1-x structure contained 2 crystallographically distinct interstitial D sites: so-called Zr4Ni2 octahedral sites and so-called Zr4 tetrahedral sites, alternately ordered along the a-direction. From first-principles calculations, the total energy of the P¯1 structure was found to be some 0.24eV/unit-cell lower than Cmcm-symmetry ZrNiD and could be rationalized in terms of different D local-bonding configurations and metal-D interactions. Resultant phonon calculations based upon this structure were also consistent with the measured neutron vibrational spectrum.

Structure and Interstitial Deuterium Sites of β-Phase ZrNi Deuteride. H.Wu, W.Zhou, T.J.Udovic, J.J.Rush, T.Yildirim, Q.Huang, R.C.Bowman: Physical Review B, 2007, 75[6], 064105 (7pp)