Investigation of nanocrystalline Gd films loaded with hydrogen

Hruška, Petr; Čı́žek, Jakub; Dobroň, Patrik; Anwand, W.; Mücklich, A.; Gemma, Ryota; Wagner, Stefan; Uchida, Helmut Takahiro; Pundt, Astrid

doi:10.1016/j.jallcom.2014.12.156

Cited by 5 publications

(3 citation statements)

References 20 publications

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“…In case of binary alloys, we determined pure Cu and GdH 2 ( = 0) or CaH 2 ( = 1) peaks. Formation of Gd hydride (Gd + H 2 → GdH 2 ) has already been observed by Hruška et al [22], whereas Ca reaction with hydrogen (Ca + H 2 → CaH 2 ) was investigated by Sturdy and Mulford [23], and Rittmeyer and Wietelmann [24]. Copper hydride has been previously found to form from elemental copper only under severe pressure around 20 GPa [25], so it is reasonable to assume that protons do not react with copper atoms in our alloys at given hydrogenation conditions.…”

Section: Hydrogenationsupporting

confidence: 53%

Solid Solubility in Cu₅Gd_1−xCa_x System: Structure, Stability, and Hydrogenation

Kocjan

Kelhar

Gradišek

et al. 2017

Advances in Materials Science and Engineering

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We report on synthesis and characterization of a novel group of compounds based on copper, gadolinium, and calcium. Cu-Ca and Cu-Gd binaries were previously studied while Ca and Gd are known to be immiscible themselves. The effects of substituting Gd with Ca in Cu5Gd1-xCax compounds (0≤x≤1) were studied by investigating the phase stability and crystal structure of the resulting new compounds in five specimens with x = 0, 0.33, 0.50, 0.66, and 1, respectively. The samples produced by melt-spinning had hexagonal P6/mmm structure, irrespective of Ca amount (x), where lattice parameters varied with x linearly. This is an indication of good solid solubility under the preparation conditions. A slower cooling upon arc-melting caused the liquid phase separation into Cu4.5Gd and Cu-Ca compounds. Using TEM, rapidly solidified ribbons (Cu5Gd0.5Ca0.5) were investigated and the formation of a homogeneous ternary phase with a nearly nominal stoichiometric composition and minor amounts of Cu-Ca secondary phase was observed. Using DSC and HT XRD, we found that these systems are stable at least up to 400°C. Upon a 16-hour hydrogenation at 1 bar and 300°C, all specimens absorbed about 0.5 wt.% of hydrogen. This caused changes in structure with the formation of pure Cu and H2Gd1-xCax solid solution.

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Section: Hydrogenationsupporting

confidence: 53%

Solid Solubility in Cu₅Gd_1−xCa_x System: Structure, Stability, and Hydrogenation

Kocjan

Kelhar

Gradišek

et al. 2017

Advances in Materials Science and Engineering

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“…If not, hexagonal crystal lattice would solely expand upon hydrogenation, which would appear as a shift of XRD peaks to lower angles. It is worth mentioning that Hruška et al [21] reported on the following phase transition as the hydrogen concentration increases in bulk Gd: α (hcp, Gd) → β (fcc, GdH 2 ) → γ (hcp, GdH 3 ). Despite the fact that all hydrides had the same crystal structure, Figure 8a, the corresponding H 2 mass-spectra, Figure 8b In general, when more calcium was in the alloy, higher temperatures were required for thermal hydrogen desorption, indicating that Ca-H has more negative formation enthalpy than Gd-H.…”

Section: Hydrogenationmentioning

confidence: 97%

SOLID SOLUBILITY IN Cu5Gd1-xCax SYSTEM: STRUCTURE, STABILITY, HYDROGENATION AND CATALYSIS OF OXYGEN REDUCTION

Kocjan

Kelhar

Gradišek

et al. 2017

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We studied the effects of substituting gadolinium in the compound Cu5Gd with Ca by investigating the phase stability and crystal structure of the resulting new compounds. For rapidly quenched materials produced by melt spinning, the crystal structure was always hexagonal P6/mmm, irrespective of the Ca addition (x) in alloys with the formula Cu5Gd1-xCax, indicating good solid solubility under these conditions, which was additionally confirmed by Vegard’s law. Slower cooling upon arc-melting process caused the phase separation into Cu4Gd and CuCa. Using TEM, we investigated rapidly solidified ribbons of Cu5Gd0.5Ca0.5 and observed co-existence of Cu–Ca secondary phase with a matrix phase having the nominal stoichiometric composition. The oxygen level in this sample was found to be within 2–5 at. %, which was attributed to surface oxidation during or after TEM sample preparation. Upon hydrogenation, the crystal structure of all samples changed from hexagonal to cubic (F-43m), which is the thermodynamically stable polymorph of Cu5Gd compound. Strong catalytic activity of water formation from gaseous H2 and O2 was coincidentally discovered during dehydrogenation experiment, thus making this material as potential candidate for zero-platinum oxygen reduction catalyst.

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“…In the present study, we explore the thermodynamics of a highly strained Gd film with hydrogen, at moderate hydrogen concentrations (H/Gd ∼ 0.6) and at mesoscopic dimensions. At that concentration, metal and dihydride phases coexist in bulk Gd . However, in the highly strained Gd film, the phase transformation is prohibited.…”

Section: Introductionmentioning

confidence: 97%

Dynamics of H in a Thin Gd Film: Evidence of Spinodal Decomposition

Manassen

Realpe

Schweke³

2019

J. Phys. Chem. C

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Gd thin films react at room temperature with hydrogen to form hydrides, by nucleation and growth, even for very low H content (H/Gd > 0.01). This phase transformation can be destabilized and suppressed in highly stressed films. In the present study, a thin Gd layer was deposited on a W(110) substrate, leading to a highly strained film. Following exposure to hydrogen, the overall strain in the film is further increased. Hydrogen was found to dissolve in the metallic matrix without forming distinct hydride nuclei. However, the lateral distribution of H in the film evolved with time, from a rather homogeneous repartition to an inhomogeneous one, reflecting the process of spinodal decomposition of hydrogen in the film. The spinodal decomposition process was monitored using scanning tunneling microscopy. This process involves principally the diffusion of H in the film, but a slow change in shape of the Gd islands covering the wetting layer was also observed. These changes were used to monitor the evolution of the local strains and hydrogen concentrations with time and to draw strain and composition maps at different times, before and after hydrogenation. Numerical simulations of the process, using the chemical potential of H in the highly strained film and applying the Cahn–Hilliard equation, were shown to be in good agreement with the experimental observations, in both spatial and temporal scales. The present study shows that high tensile strains strongly affect the dynamics of the H distribution and the composition of the H-containing phases, opening the route for future studies of M–H systems on the nanometer scale.

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Investigation of nanocrystalline Gd films loaded with hydrogen

Cited by 5 publications

References 20 publications

Solid Solubility in Cu₅Gd_1−xCa_x System: Structure, Stability, and Hydrogenation

Solid Solubility in Cu₅Gd_1−xCa_x System: Structure, Stability, and Hydrogenation

SOLID SOLUBILITY IN Cu5Gd1-xCax SYSTEM: STRUCTURE, STABILITY, HYDROGENATION AND CATALYSIS OF OXYGEN REDUCTION

Dynamics of H in a Thin Gd Film: Evidence of Spinodal Decomposition

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Investigation of nanocrystalline Gd films loaded with hydrogen

Cited by 5 publications

References 20 publications

Solid Solubility in Cu5Gd1−xCax System: Structure, Stability, and Hydrogenation

Solid Solubility in Cu5Gd1−xCax System: Structure, Stability, and Hydrogenation

SOLID SOLUBILITY IN Cu5Gd1-xCax SYSTEM: STRUCTURE, STABILITY, HYDROGENATION AND CATALYSIS OF OXYGEN REDUCTION

Dynamics of H in a Thin Gd Film: Evidence of Spinodal Decomposition

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Solid Solubility in Cu₅Gd_1−xCa_x System: Structure, Stability, and Hydrogenation

Solid Solubility in Cu₅Gd_1−xCa_x System: Structure, Stability, and Hydrogenation