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arXiv 0911.5666cond-mat.mtrl-sci
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Mg/Ti多层膜的结构、光学和吸氢性能

Mg/Ti multilayers: structural, optical and hydrogen absorption properties

A. Baldi, G. K. Palsson, M. Gonzalez-Silveira, H. Schreuders, M. Slaman, J. H. Rector, G. Krishnan, B. J. Kooi, G. S. Walker, M. W. Fay, B. Hjorvarsson, R. J. W… 展开作者

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

摘要:

Mg-Ti合金具有不寻常的光学和吸氢性能,源于原子分布中具有小程度的化学短程有序的“类亚稳”微观结构。在本研究中,我们人工工程师的短程有序沉积Pd盖帽的Mg/Ti多层膜具有不同的周期性,并表征它们的结构和光学。尽管Mg和Ti之间的晶格参数失配较大,但沉积的金属多层膜显示出良好的结构一致性。在暴露于H2气体时,发生两步氢化过程,其中Ti层在Mg之前形成氢化物。从原位测量的双层厚度L在不同的氢气压力,我们观察到大的Mg和Ti层氢化后的面外膨胀,表明强烈的塑性形变的膜和随之而来的相干长度缩短。当在室温下在空气中卸载时,由于动力学约束,氢原子保持被捕获在Ti层中。这种加载/卸载序列可以解释在Mg和Ti中的氢的不同的热力学性质,如所示的模型多层系统上的扩散计算。氢谱法测得的吸附等温线可以解释为强结合的Mg/Pd和破碎的Mg/Ti界面所产生的弹性夹紧的结果。

英文摘要:

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 atoms distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities and characterize them both structurally and optically. Notwithstanding the large lattice parameter mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. Upon 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 L at different hydrogen pressures, we observe large out-of-plane expansions of the Mg and Ti layers upon hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. Upon 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.

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