Dynamics and charge transfer of hydrogen interstitials in ZrCrFe0.5Co0.5

Pressure–composition hydrogen absorption isotherms of ZrCrFe0.5Co0.5 have been obtained in the ranges 0.001⩽P⩽30 bar and 30⩽T⩽100°C. The dynamics of hydrogen interstitials and the diffusion coefficients have been determined from the kinetics of hydrogen absorption studies. The structural and electrical properties, and 57Fe Mössbauer spectroscopy characterization of ZrCrFe0.5Co0.5 hydrides have been studied at room temperature. The growth of the β phase at the expense of the α phase in the plateau region, as shown from powder X-ray diffractograms of the alloy hydrides, is used to explain the resistivity and Mössbauer spectroscopy results. The variation of resistivity with hydrogen content supports the random occupation of hydrogen atoms in the interstitial sites in the single phases (α and β) and cluster formation in the two-phase region (α+β). While the Mössbauer spectrum of the parent alloy shows a quadrupole doublet with an isomer shift (δ) in the negative scale, the δ value increases monotonically with hydrogen content (r) up to +0.20mms−1 for r=2.83. While the small splitting is indicative of near-cubic symmetry, the small δ value suggests iron metal in a high oxidation state. The change in the δ value upon hydrogen uptake is attributed to a volume effect and also suggests a possible chemical link between the metal and hydrogen atoms, through partial charge transfer from iron atoms to hydrogen atom interstitials.