Search for instability-induced amorphization in deuterated ErFe2.

Abstract

Experimental evidence--in the form of a specific-heat anomaly--for instability-induced amorphization of ${\mathrm{ErFe}}_{2}$ 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 ${\mathrm{ErFe}}_{2}$ below and above the reversible, endothermic, \ensuremath{\lambda}-shaped enthalpy signal that they found at \ensuremath{\sim}200 \ifmmode^\circ\else\textdegree\fi{}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.