The present work exhibits the possible interstitial sites for hydrogen occupation in the intermetallic lattice of ZrNi(CrB - structure type) by their Wyckoff notation and by the number of Zr and Ni atoms on the polyhedron vertices. In view of a previous model, predicting the relative interstitial occupancy in intermetallic hydrides, we propose a hydrogen location scheme for ZrNiHx. According to this scheme the 4c3 (4Zr) tetrahedral interstices are almost solely occupied by hydrogen atoms in ZrNiH. A small quantity of hydrogen is predicted to be located at this composition in (3Zr + 1Ni) tetrahedra. At x ≈ 2.6, 4c3 is completely and 8f1, 8g1 and 8g2 are partially occupied according to our model. The 8f1, 8g1 and 8g2 tetrahedral sites are crystallographically different one from the other but they are identical with regard to the metal atoms composing them -(3Zr + 1Ni); such sites are indistinguishable in our model. Above x ≈ 2.6 we predict that (2Zr + 2Ni) tetrahedra begin to be gradually populated. The agreement between our predictions and the analysis of the existing neutron diffraction data on ZrNiDx is only a partial one. We believe, however, that some experimental evidences from pressure-composition isotherms and inelastic neutron scattering may support our predictions. The use of a Boltzmann distribution function, previously employed in calculating the relative occupation numbers of various interstitial sites, is revised for few cases (e.g. ZrNiHx, Y6Mn23Hx), for which a Fermi distribution function must be used.
|Number of pages||5|
|Journal||Solid State Communications|
|State||Published - 1 Jan 1982|
ASJC Scopus subject areas
- Chemistry (all)
- Condensed Matter Physics
- Materials Chemistry