Oxidation and annealing of thin FeTi layers covered with Pd

The hydrogen storage material FeTi has the disadvantage to lose its sorptio n capacity in contact with impurities such as O-2 and H2O. A possibility to overcome this problem is to coat it with an anti-corrosive layer which is permeable for hydrogen. In this study we prepared FeTi layers covered with a (4 or 20 MI) thin Pd layer. We used ion beam and sputter profiling techni ques, X-ray photoelectron spectrometry and scanning probe techniques to inv estigate the response of these bi-layers upon annealing up to 300 degrees C in vacuum, air and 10(-5) mbar O-2. The layered structure remains intact u p to 150 degrees C. At 200 degrees C in air and O-2, Fe and (some) Ti move towards the Pd surface where they form oxide regions. At higher temperature s thicker oxide regions, presumably along the Pd grains, are formed. These processes are more pronounced for the case of 4 nm Pd. A model is presented to explain the observed phenomena. We conclude that up to 150 degrees C 4 nm of Pd is sufficient to act as a protective layer. For a temperature of 2 00 degrees C, 20 nm Pd may still provide sufficient protection against oxid ation. (C) 1999 Elsevier Science B.V. All rights reserved.