Phase transitions and thermally activated hydrogen dynamics in ZrV2Hx (0 ≤ x ≤ 1) intermetallic compounds

A detailed study of the relaxation process occurring in polycrystalline ZrV2Hx (0 ≤ x ≤ 1) below room temperature has been carried out by means of acoustic spectroscopy. At low H concentrations the main effect is due to the well known martensitic phase transformation around 120 K. Moreover a H-related thermally activated peak is detected around 240 K, at a vibration frequency of about 3.5 kHz. The peak features and the relaxation parameters are discussed in terms of the possible kinds of H dynamic giving rise to the anelastic effect.For the highest values of x a clear effect due to H ordering is visible around 200 K. In addition, a new thermally activated process is detected around 140 K and the experimental data can be satisfactorily fitted with the superposition of two broad peaks with activation energies of 0.14 and 0.17 eV. These processes are due to the jumps of H atoms, likely among tetrahedral interstitial sites in the lattice of the Laves phase.