These qualities stem from a short-range-ordered distribution of the Mg and Ti atoms. In order to study the influence of short-range order on the hydrogen sorption properties of Mg-Ti systems, we artificially engineered chemical segregation by depositing a Ti/Mg multilayer with 10 repetitions of Ti(2 nm)/Mg(4.4 nm). On exposure to H2, a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. In-situ neutron reflectometry allows an accurate determination of the out-of-plane expansion associated with each hydrogenation step. The volume expansion expected for the hydrogenation of both Ti and Mg is transferred completely along the vertical direction, indicating that large plastic deformations have to occur upon hydrogen uptake. Owing to the large negative neutron scattering length of hydrogen, neutron reflectometry proves to be an excellent technique for the in situ characterisation of the hydrogen absorption properties of thin films.
A Baldi, H Schreuders, B Dam, R Griessen (Delft University of Technology, The Netherlands), PC Aeberhard (Oxford University), C Kinane, WIF David, M Skoda, R Fan, S Langridge (ISIS)
Research date: November 2009
Contact: Dr A Baldi, A.Baldi@tudelft.nl; Dr C Kinane, firstname.lastname@example.org
Further reading: A Baldi et al., Phys Rev B 81 (2010) 224203