Synthesis of hexagonal C14/C36 and cubic C15 ZrCr2 Laves phases and thermodynamic stability of their hydrides

ZrCr₂ samples with well defined hexagonal (C14/C36) or cubic (C15) Laves phase structures have been synthesised by melting in an arc furnace followed by different treatments depending on the sample type. Hydrogen absorption capacity and thermodynamic stability of their respective hydrides have been investigated by solid–gas reaction. Pressure–composition–temperature (PCT) curves obtained for both structures at temperatures of 348, 373, 398 and 423 K, and H-pressures from 10¹ to 10⁶ Pa, showed that the cubic phase is less stable than the hexagonal ones. This result was related to Miedema's rule of reversed stability and also correlated to the volume of the interstitial hole for hydrogen.