Protection of FeTi thin films using palladium coatings

Abstract

The use of FeTi as a hydrogen storage material is hindered by surface decomposition of the alloy when exposed to hydrogen charging gases containing PPM levels of O2/H2O impurities. This study investigates the application of palladium coatings as barrier materials against these impurities in order to increase the effective lifetime of the alloy over numerous charge-discharge cycles. Palladium was chosen because it has excellent hydrogen transport properties and it is impermeable to impurities containing oxygen at the temperatures and pressures of interest. Two 10 nm FeTi thin-film specimens were prepared, one coated with an additional 5 nm Pd overlayer, and both samples exposed to identical annealing and reduction treatments. Conversion electron Mossbauer spectroscopy (CEMS) was used along with other analytical techniques (i.e. XPS and SIMS) to obtain chemical, magnetic and electronic information at the buried and exposed interfaces. CEMS demonstrated that the Pd coating prevented subsurface decomposition of FeTi.