ZR2FEHX SYSTEM HYDRIDED AT LOW-TEMPERATURES - STRUCTURAL ASPECTS BY MOSSBAUER AND X-RAY-DIFFRACTION STUDIES

The first successful hydriding of the high-temperature phase of Zr2Fe, which has a C-16 CuAl2-type structure, is reported. The intermetallic compound could be hydrided at temperatures down to about 250 K and hydrogen pressures less than about 0.5 atm to a composition Zr2FeHx (x congruent-to 4.5) without changing its structure. The hydrides with x < 4.5 could be prepared in the desorption mode only; they are also found to have the C-16 structure. Mossbauer studies and X-ray cell parameter determination were carried out for some hydride compositions, and H-atom occupancies inferred from them. It is argued that, for low hydrogen concentration, H atoms occupy five-coordinated interstitial sites formed by Zr atoms only. At higher hydrogen concentration, tetrahedral sites formed by Fe as well as Zr atoms are the preferred sites.