Investigation of nanocrystalline Gd films loaded with hydrogen

The present work reports on microstructure studies of hydrogen-loaded nanocrystalline Gd films prepared by cold cathode beam sputtering on sapphire (1 1 -2 0) substrates. The Gd films were electrochemically step-by-step charged with hydrogen and the structural development with increasing concentration of absorbed hydrogen was studied by transmission electron microscopy and in-situ X-ray diffraction using synchrotron radiation. The relaxation of hydrogen-induced stresses was examined by acoustic emission measurements. In the low concentration range absorbed hydrogen occupies preferentially vacancy-like defects at GBs typical for nanocrystalline films. With increasing hydrogen concentration hydrogen starts to occupy interstitial sites. At the solid solution limit the grains gradually transform into the beta-phase (GdH2). Finally at high hydrogen concentrations xH > 2:0 H/Gd, the film structure becomes almost completely amorphous. Contrary to bulk Gd specimens, the formation of the gamma-phase (GdH3) was not observed in this work.