Fundamental Cluster and Hydrogen Sites in Ti-Zr-Ni Quasicrystals

Abstract

AbstractA Rietveld refinement confirmed by ab initio calculations [1] has shown that the structure of the related W-phase [2] 1/1 approximant consists of Bergman clusters connected by “glue” sites. To investigate if the quasicrystal structure contains the same cluster we construct two constrained icosahedral glass models using the Bergman or Mackay cluster, respectively. A comparison with neutron diffraction data yields better agreement if the Bergman cluster is used, suggesting that this is a frequently occurring element in the quasicrystalline structure. Since absorbed hydrogen is known to locate preferentially in tetrahedral interstitial sites in many metals, the tetrahedral sites in the constrained glass were filled with hydrogen. The calculated powder neutron diffraction spectra are similar to the experimental data. It was not possible, however, to differentiate between possible tetrahedral sites where the hydrogen atoms sit. Hydrogen site energies from ab initio calculations indicate preferences that are consistent with fillings of non-Ni bearing tetrahedral sites.