Structural destabilisation of MgH2 obtained by heavy ion irradiation

MgH2 powder samples have been irradiated with 120 keV Ar+8 ions with different ion fluencies ranging from 1012 to 1016 ions/cm2. Irradiation effects are estimated by SRIM calculations, and investigated experimentally using Raman spectroscopy and X-ray diffraction (XRD) analysis. The observed changes of structure and vibrational spectra are elaborated, their consequences on hydrogen bonding in MgH2 discussed, and influence on H-desorption properties investigated by Temperature Programmed Desorption (TPD) and Differential Scanning Calorimetry (DSC) techniques. It has been established that near-surface defects have a predominant influence on decreasing the H-desorption temperature. Variations of Raman, TPD and DSC spectra with irradiation conditions suggest that there are several mechanisms of dehydriding, and that they depend on defect concentration, interaction and ordering.