Hydrogen solubility and diffusivity in amorphous La14Ni86 films

Hydrogen solubility and diffusivity in Pd-coated amorphous La14Ni86 films have been studied by thermal desorption spectroscopy (TDS). The TDS spectra were analyzed according to the statistical Harris and thermodynamic Kirchheim. models. For H-loading pressures up to 100 mbar, hydrogen essentially occupies La2Ni2 and LaNi3 tetrahedral sites at room temperature. Only hydrogen in LaNi3 sites can be thermally desorbed before crystallization of the films takes place. Progressive filling of LaNi3 sites with increasing hydrogen pressure occurs in agreement with the thermodynamic model. The density of LaNi3 sites is well characterized by a Gaussian distribution with a mean energy of -0.44 eV. As regards diffusivity, hydrogen atoms jump from mean energy LaNi3 sites with an activation enthalpy of 0.47 +/- 0.03 eV. Nonetheless, discrepancies in the width of the site energy distribution were found when it was independently evaluated from solubility and diffusivity analyses. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.