Hydrogen solubility and diffusivity in Pd-coated amorphous Ni86La14 films were studied by thermal desorption spectroscopy. The thermal desorption spectra were analyzed according to the statistical Harris and thermodynamic Kirchheim models. For H-loading pressures up to 100mbar, H essentially occupied La2Ni2 and Ni3La tetrahedral sites at room temperature. Only H in Ni3La sites could be thermally desorbed before crystallization of the films took place. Progressive filling of Ni3La sites with increasing H pressure occurred in agreement with the thermodynamic model. The density of Ni3La sites was well characterized by a Gaussian distribution with a mean energy of -0.44eV. During diffusion, the H atoms jumped from mean energy Ni3La sites with an activation enthalpy of 0.47eV. Discrepancies in the width of the site energy distribution were found when it was independently evaluated from solubility and diffusivity analyses.
F.Cuevas, M.Hirscher: Acta Materialia, 2003, 51[3], 701-12
Table 199
Diffusivity of Ni in NiGa
Ni (at%) | Sample | Temperature (C) | D (m2/s) |
51.2 | monocrystalline | 990 | 1.12 x 10-12 |
51.2 | monocrystalline | 1060 | 2.31 x 10-12 |
51.2 | monocrystalline | 1130 | 5.12 x 10-12 |
52.5 | monocrystalline | 1060 | 2.32 x 10-12 |
57.2 | polycrystalline | 1130 | 5.44 x 10-12 |
61.9 | polycrystalline | 1040 | 3.14 x 10-12 |
61.9 | polycrystalline | 1150 | 7.42 x 10-12 |