SEARCH FOR INSTABILITY-INDUCED AMORPHIZATION IN DEUTERATED ERFE2

Experimental evidence-in the form of a specific-heat anomaly-for instability-induced amorphization of ErFe2 by hydrogenation was recently reported by Fecht, Fu, and Johnson [Phys. Rev. Lett. 64, 1753 (1990)]. We have attempted to study this anomaly by in .situ elastic neutron diffraction and differential-scanning-calorimetry (DSC) measurements of deuterated ErFe2 below and above the reversible, endothermic, lambda-shaped enthalpy signal that they found at approximately 200-degrees-C. Our combined diffraction and DSC results reveal that the amorphization transition is irreversible, strongly exothermic and occurs only at a significantly higher temperature than that of the specific-heat anomaly. Rather than resulting from an underlying instability of the crystalline phase, amorphization occurs as a by-product of short-range clustering of the Er and Fe atoms, which is driven by the creation of energetically more favorable sites for the deuterium atoms.