Surface analysis of polycrystalline and nanocrystalline LaNi5-type alloys

Abstract The chemical composition and the cleanness of the surface of polycrystalline and nanocrystalline LaNi 5 , LaNi 4.2 Al 0.8 , and LaNi 3 AlCo alloys were studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Results showed that the surface segregation under UHV conditions of lanthanum atoms in the mechanically alloyed nanocrystalline samples is significantly stronger compared to that of polycrystalline powders obtained from arc-melted ingots. On the other hand, the level of oxygen impurities trapped in the mechanically alloyed powder during the processing is practically the same as in the arc-melted ingots. Furthermore, we have estimated an average native oxide layer thickness of nanocrystalline LaNi 4.2 Al 0.8 as ∼5 nm. A strong segregation of the Fe impurities to the surface could be responsible for the observed slightly lower hydrogen storage capacity of the mechanically alloyed nanocrystalline LaNi 4.2 Al 0.8 compared to that of polycrystalline sample.