Mg/Ti multilayers: Structural and hydrogen absorption properties

R.J. Wijngaarden, A. Baldi, G. K. Pálsson, M. Gonzalez-Silveira, H. Schreuders, M.J. Slaman, J.H. Rector, G. Krishnan, B.J. Kooi, G. S. Walker, M. W. Fay, B. Hjörvarsson, B. Dam, R.P. Griessen

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Abstract

Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a "spinodal-like" microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to H2 gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness Λ at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces. © 2010 The American Physical Society.
Original languageEnglish
Article number224203
Number of pages10
JournalPhysical Review B. Condensed Matter and Materials Physics
Volume81
Issue number228203
DOIs
Publication statusPublished - 8 Jun 2010

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