HYDROGEN DIFFUSION STUDIES OF MICROCRYSTALLINE AND CRYSTALLINE LANI3.94SI0.54 FILMS

A comparison of the hydrogen diffusion behaviour in microcrystalline a nd crystalline LaNi3.94Si0.54 films was studied using an electrochemic al permeation technique. For the microcrystalline film, hydrogen diffu sion transient curves were found to be composed of two steps of transi ents, which might be ascribed to the transition from alpha phase to hy dride phase and the subsequent migration of the phase boundary. Such a behaviour, however, was absent for the crystalline counterpart within the time range of our investigation, and we attributed this to the sl ower diffusion as compared with the microcrystalline film. Hydrogen di ffusion coefficients in microcrystalline films increased evidently wit h increasing hydrogen concentration, whereas there was a negligible co ncentration dependence in the crystalline counterpart. Similar to an e arlier suggestion, the electrochemical permeation technique may be use ful in the investigation of hydride formation in solid state hydrogen storage materials in addition to providing hydrogen transport data.