Structural changes of thin MgAl films during hydrogen desorption

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. We used neutron reflectometry (NR) to study the structural changes of thin Pd-capped Mg 0.7 Al 0.3 and Mg 0.6 Al 0.4 alloy films after hydrogen absorption and during hydrogen desorption. NR enabled us to determine the hydrogen content and hydrogen distribution in these thin MgAl alloy films along with the structural changes associated with the desorption process. The thin films expand by about 20% during the hydrogen absorption and the hydrogen is stored only in the MgAl layer with no hydrogen content in the Pd layer. The Mg 0.7 Al 0.3 films are fully desorbed at 448 K, whereas for the Mg 0.6 Al 0.4 films a temperature of 473 K is needed to fully desorb the hydrogen. Our NR measurements show that the higher annealing temperature needed to desorb the hydrogen from the Mg 0.6 Al 0.4 films led to an interdiffusion of the Pd layer into the MgAl layer. This Pd interdiffusion was also observed in a Mg 0.7 Al 0.3 film after a 9 h annealing at 473 K. So, the Pd interdiffusion into a MgAl film that has been charged with hydrogen is a common feature of the Pd/Mg 0.7 Al 0.3 and Pd/Mg 0.6 Al 0.4 alloy system. In contrast, for the as-prepared hydrogen-free Pd/Mg 0.7 Al 0.3 film the Pd layer stays intact and only a small interdiffusion zone occurs at the Pd/MgAl interface. Crown

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

“…The exact reason why the hysteresis expands when the Mg/Pd interface is present remains unclear. Baldi et al [46] have proposed an explanation based on the elastic clamping of Mg layer by means of Pd, having affinity to form an alloy with Mg. This model suffers from explaining the complete (de-)hydrogenation behavior of Mg films, still, we think that the formation of Mg-Pd alloy at the interface is the main reason for the destabilization, observed in Pd capped Mg films.…”

Hydrogen storage in binary and ternary Mg-based alloys: A comprehensive experimental study

“…Mg-Al-Ti, Mg-Fe-Ti and Mg-Fe-Al. Because of encouraging results on Mg 70 Al 30 films [23][24][25], this Mg content was chosen as the starting point for the ternary alloys.…”

Surface oxide on thin films of yttrium hydride studied by neutron reflectometry

“…Later, Munter et al showed how deuterium absorption could be monitored in-situ during loading experiments on thin Pd films 9,10 . More recently, a series of studies has been published by Fritzche et al, showing how NR can be used to investigate the thermodynamics of hydrogen uptake process in Pd-capped metal alloy films [11][12][13][14][15] . NR has also proved an efficient way to characterize deviations in the hydrogen stoichiometry in very thin interface layers 9,16 , and can be used to determine inter-diffusion of elements at the interfaces of metal hydride films 11,12 .…”