The Diffusion of H in Mg and the Nucleation and Growth of MgH<sub>
                     <sub>2</sub>
                  </sub> in Thin Films*

Spatz, P.; Aebischer, H. A.; Krozer, Anatol; Schlapbach, L.

doi:10.1524/zpch.1993.181.part_1_2.393

Cited by 95 publications

(65 citation statements)

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“…However, for pure Mg hydride thin film without any rare earth and nickel elements, the optical properties have not been sufficiently studied because it was quite difficult to load enough hydrogen into the Pd/Mg thin films previously reported. [4][5][6][7][8]14) Since we have found the optimizing sputtering condition to fully hydrogenate the Pd/Mg films at relatively low temperature, we carried out the experiments of the optical transmission in this work. 10) Figure 6 shows the photographs in transmitted light as a function of charging time under a H 2 gas pressure of 0.1 MPa at 393 K for the two-layered Pd(10 nm)/Mg(200 nm) film.…”

Section: Methodsmentioning

confidence: 99%

“…3) In this work, we will present our recent results of hydrogen storage, structural and optical properties in nano-composite multi-layered Pd/Mg thin films, that have been done for realizing the cooperative phenomena. Until now, several investigations of the two-layered Pd/Mg thin films for hydrogen storage materials have been carried out by Krözer et al, 4,5) Fischer et al 6,7) and Spatz et al 8) Various interesting features have been reported but no remarkable improvement in hydrogen storage properties has been reported. On the other hand, the results obtained in this work indicated that the advantageous hydrogen storage properties of Pd and Mg metals could be extracted in the multi-layered nano-composite Pd/Mg films by suitably controlling the strcture in nano-meter scales.…”

Section: Introductionmentioning

confidence: 99%

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Remarkable Hydrogen Storage, Structural and Optical Properties in Multi-layered Pd/Mg Thin Films

et al. 2002

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In this paper, we review our recent results on hydrogen storage, structural and optical properties in multi-layered Pd/Mg thin films. The thin films were prepared using a RF associated magnetron sputtering method, in which the structure in Mg layer was controlled into columnarlike textures with several tens nanometer in diameter by optimizing the sputtering conditions. The results obtained indicate that hydrogen of ∼ 5 mass% absorbs at 373 K in Mg under a hydrogen pressure of 0.1 MPa in multi-layered Pd/Mg films and the hydrogen desorbs at 360 K in vacuum. Such excellent hydrogen storage properties are explained by cooperative phenomena that hydrogen displays in nano-composite interface boundary regions between the Pd and Mg films. In addition, we experimentally confirmed at the first time that the rare earth and nickel free two-layered Pd/Mg film displayed optical transparency upon hydrogenation.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Remarkable Hydrogen Storage, Structural and Optical Properties in Multi-layered Pd/Mg Thin Films

et al. 2002

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“…6,7 The diffusional properties of hydrogen in magnesium have been investigated by Renner and Grabke, who determined a diffusion constant of D = 4.0ϫ 10 −13 m 2 / s at 300 K. 8 Using neutron scattering, Töpler et al found H-diffusion in MgH 2 to be three orders of magnitude lower than in Mg (at 350 K), 9 and Spatz et al have determined the overall hydrogen diffusion coefficient for the Mg-to-MgH 2 -transition (including nucleation and growth) to be as low as DЈ = 1.1 ϫ 10 −20 m 2 / s using XPS. 10 In the present work, a comprehensive investigation of the potential energy surface (PES) of hydrogen on the magnesium(0001) surface is presented. Rates of activated dissociative and diffusional processes are calculated using a combination of DFT calculations, path techniques and vibrational frequencies, enabling a direct determination of the ratelimiting processes.…”

Section: Introductionmentioning

confidence: 99%

Locating the rate-limiting step for the interaction of hydrogen withMg(0001)using density-functional theory calculations and rate theory

2004

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The dissociation of molecular hydrogen on a Mg͑0001͒ surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located using the nudged elastic band method, and rates of the activated processes are calculated within the harmonic approximation to transition state rate theory, using both classical and quantum partition functions based atomic vibrational frequencies calculated by DFT. The dissociation/recombination of H 2 is found to be rate-limiting for the ab-and desorption of hydrogen, respectively. Zero-point energy contributions are found to be substantial for the diffusion of atomic hydrogen, but classical rates are still found to be within an order of magnitude at room temperature.

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“…22,23 The rate is increased by the presence of nickel 24,25 or oxide 26 on the Mg surface, or by decreased crystallinity. 27 We observed faster switching in film areas with higher nickel content, and gradual improvement with time and switching cycle, especially in the more Mg-rich regions.…”

mentioning

confidence: 99%

Switchable mirrors based on nickel–magnesium films

Richardson¹,

Slack²,

Armitage³

et al. 2001

Applied Physics Letters

342

198

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An electrochromic mirror electrode based on reversible uptake of hydrogen in nickel magnesium alloy films is reported. Thin, magnesium-rich Ni-Mg films prepared on glass substrates by cosputtering from Ni and Mg targets are mirror-like in appearance and have low visible transmittance. Upon exposure to hydrogen gas or on cathodic polarization in alkaline electrolyte, the films take up hydrogen and become transparent. When hydrogen is removed, the mirror properties are recovered. The transition is believed to result from reversible formation of Mg 2 NiH 4 and MgH 2 . A thin overlayer of palladium was found to enhance the kinetics of hydrogen insertion and extraction, and to protect the metal surface against oxidation.Devices capable of switching between mirror and transparent states may find applications in architectural and transportation energy conservation, lighting and displays, aerospace insolation control, and optical communications systems. Switchable mirrors based on rare earth hydrides were discovered by Huiberts et al., 1 who observed a reversible metal-to-insulator transition when a thin film (150 to 500 nm) of yttrium or lanthanum coated with a thin layer of palladium was exposed to hydrogen gas. The transition accompanies conversion of a metallic dihydride phase to a semiconducting trihydride. Rare earth-magnesium alloy films 2 were subsequently found to be superior to the pure lanthanides in maximum transparency and mirror-state reflectivity. Phase separation appears to occur when these alloys take up hydrogen, giving transparent MgH 2 and LnH 2-3 , both of which may participate in the switching mechanism. 3 Because the rare earths are highly vulnerable to oxidation, a Pd overlayer at least 5 nm thick is required for films exposed to air or to an alkaline electrolyte. Although the Pd catalyzes the uptake and removal of hydrogen, it limits the maximum transparency of the composite film to about 50%. 4 The influence of the Pd layer and of a Pd/AlO x composite cap layer on hydrogen uptake by rare earth-based films have been studied extensively by van Gogh et al. 5 and by van der Molen et al. In the case of nickel, a stoichiometric alloy phase, Mg 2 Ni, with the same Mg-Ni ratio as in the hydride, can be prepared from the elements. In Mg 2 Ni (Fig. 1a), there are Ni-Ni bonds (shown as hollow rods), two types of Ni-Mg bonds (solid rods) and three types of Mg-Mg bonds (not shown).10 The Ni-Ni bonds and Mg-Mg bonds are shorter in the alloy than in the pure elements. The alloy absorbs hydrogen without structural rearrangement up to a composition of Mg 2 NiH 0.3 .7 This phase has metallic properties similar to those of the pure alloy. Further introduction of hydrogen produces Mg 2 NiH 4 (Fig. 1b) Ni-Mg films were deposited by DC magnetron co-sputtering from 2 in diameter Ni and Mg (99.98%) targets onto glass substrates with and without transparent conductive coatings. The base pressure was 1.4 x 10 -7 Torr, process pressure 2 mTorr, Ni power 20 W, Mg power 22 W, target-tosubstrate distance 7.5 cm. Dep...

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The Diffusion of H in Mg and the Nucleation and Growth of MgH_₂ in Thin Films*

Cited by 95 publications

References 2 publications

Remarkable Hydrogen Storage, Structural and Optical Properties in Multi-layered Pd/Mg Thin Films

Remarkable Hydrogen Storage, Structural and Optical Properties in Multi-layered Pd/Mg Thin Films

Locating the rate-limiting step for the interaction of hydrogen withMg(0001)using density-functional theory calculations and rate theory

Switchable mirrors based on nickel–magnesium films

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The Diffusion of H in Mg and the Nucleation and Growth of MgH 2 in Thin Films*

Cited by 95 publications

References 2 publications

Remarkable Hydrogen Storage, Structural and Optical Properties in Multi-layered Pd/Mg Thin Films

Remarkable Hydrogen Storage, Structural and Optical Properties in Multi-layered Pd/Mg Thin Films

Locating the rate-limiting step for the interaction of hydrogen withMg(0001)using density-functional theory calculations and rate theory

Switchable mirrors based on nickel–magnesium films

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Product

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The Diffusion of H in Mg and the Nucleation and Growth of MgH_₂ in Thin Films*