Mechanical Grinding of TFe2 (T=Hf, Zr) Compounds

The structural changes produced during the mechanical grinding of the crystalline compounds ZrFe 2 and HfFe 2 (Laves phases) were analyzed by means of Mossbauer effect spectroscopy on 57 Fe , perturbed angular correlations of gamma rays on 181 Hf and X-ray diffraction. For the starting crystalline compounds the hyperfine interaction at both sites (T and Fe) is mainly magnetic with a weak electric quadrupole perturbation. The Mosssbauer spectra in both systems rapidly evolves with grinding time showing an increasing fraction of nuclei experiencing a pure quadrupole interaction. On the other hand, the nuclear spin precession curve changes monotonically and the fitted hyperfine parameters show that while the quadrupole perturbation increases the magnetic one remains nearly unchanged at Hf sites. The results show that after a severe grain size reduction partial amorphization and Fe segregation occurs probably as a consecuence of the surface energy accumulation and/or ambient contamination.