Wu, HuiZhou, WeiUdovic, Terrence J.Rush, John J.Yildirim, TannerHuang, QingzhenBowman, Robert C.2023-05-232023-05-232007-02-092011-05-18https://repository.upenn.edu/handle/20.500.14332/42844ß-ZrNiD1-x (for x≈0.1, near the ß-γ phase boundary) was found to possess a triclinic P1(overline) structure as determined by high-resolution neutron power diffraction. This is very different from the widely accepted orthohombic and distorted orthorhombic Cmcm structures previously proposed. In contrast to the single type of D site associated with these latter structures, the true ß-ZrNiD1-x structure contains two crystallographically distinct interstitial D sites: "Zr4Ni2" octahedral sites and "Zr4" tetrahedral sites, alternately ordered along the a direction. From first-principles calculations, the total energy of the P1(overline) structure was found to be ≈0.24 eV per unit cell lower than Cmcm-symmetry ZrNiD and could be rationalized in terms of different D local-bonding configurations and metal-deuterium interactions. Resultant phonon calculations based on this structure were also consistnet with the measured neutron vibrational spectrum.Physical Sciences and MathematicsPhysicsArticle