In-situ STM and XRD studies on Nb–H films: Coherent and incoherent phase transitions

Burlaka, Vladimir; Wagner, Stefan; Pundt, Astrid

doi:10.1016/j.jallcom.2014.12.103

Cited by 10 publications

(21 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Linear elastic theory predicts a similar value of 1.4 nm for this film thickness (Δc H = 0.4 H/Nb, d = 25 nm). This drastic change of morphology and distribution of hydrides compared to the thicker film is related to the different coherent state during the phase transformation 37 , 40 .…”

Section: Resultsmentioning

confidence: 99%

“…Hydrogen absorption of 1 H/Nb in epitaxial Nb (110) films on rigid substrates results in a strong out-of-plane expansion 30 , 33 , 37 , 38 and a considerable mechanical stress up to 10 GPa 39 . If the initial thickness of the Nb film is d Nb < 5 nm, stress release is not possible and an elastic stress evolution is measured up to a solubility of 1 H/Nb 39 .…”

Section: Introductionmentioning

confidence: 99%

“…However, above an initial Nb-film thickness of 10 nm, precipitation and growth of the hydride phase is observed and topography changes appear. The precipitation and growth mechanism depends on the film thickness 37 , 40 , as the coherency between the hydride and the α-matrix changes. Precipitates are coherent with the matrix for 10 nm < d 0 ≤ 37 nm 40 and incoherent for d 0 ≥ 40 nm 37 .…”

Section: Introductionmentioning

confidence: 99%

“…The precipitation and growth mechanism depends on the film thickness 37 , 40 , as the coherency between the hydride and the α-matrix changes. Precipitates are coherent with the matrix for 10 nm < d 0 ≤ 37 nm 40 and incoherent for d 0 ≥ 40 nm 37 . For coherent precipitates, the lattice planes between the hydride precipitates and the α-matrix match by local strain, while for incoherent precipitates dislocations are present to adjust for the mismatch between the lattice planes 41 .…”

Section: Introductionmentioning

confidence: 99%

“…For coherent precipitates, the lattice planes between the hydride precipitates and the α-matrix match by local strain, while for incoherent precipitates dislocations are present to adjust for the mismatch between the lattice planes 41 . The two states result in different surface topographies in the two-phase region of the Nb-H thin films system, with changes in lateral spreading as well as in the local topographical heights 33 , 37 .…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Defect generation in Pd layers by ‘smart’ films with high H-affinity

Burlaka

Roddatis

Bongers

et al. 2017

Sci Rep

Self Cite

View full text Add to dashboard Cite

In this paper, we demonstrate that the microstructure and the surface of a thin palladium (Pd) film can be intentionally altered by the presence of a subjacent niobium (Nb) film. Depending on the thickness of the Nb film and on the hydrogen gas pressure, defects in the Pd film can be healed or created. To demonstrate this effect, Pd/Nb/sapphire (Al 2 O 3 ) stacks are studied during hydrogen gas exposure at room temperature by using scanning tunneling microscopy (STM), X-ray diffraction (XRD) and environmental transmission electron microscopy (ETEM). STM shows that hydrogen-induced topography changes in the Nb films depend on the film thickness which affects the height of the Nb surface corrugations, their lateral size and distribution. XRD measurements show that these changes in the Nb hydride film influence the microstructure of the overlaying Pd film. ETEM reveals that the modifications of the Pd film occur due to the precipitation and growth of the Nb hydride phase. The appearance of new defects, interface and surface roughening is observed in the Pd film above locally grown Nb hydride grains. These results can open a new route to design 'smart' catalysts or membranes, which may accommodate their microstructure depending on the gaseous environment.Nano-sized metal films are widely used as a key element for hydrogen storage 1,2 , hydrogen gas sensors [3][4][5] , gas purification membranes 6, 7 and heterogeneous catalysts 8,9 . The surface morphology in such films plays an important role, especially for membrane applications and catalytic reactions, as edges and corners can work as active sites 10

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Defect generation in Pd layers by ‘smart’ films with high H-affinity

Burlaka

Roddatis

Bongers

et al. 2017

Sci Rep

Self Cite

View full text Add to dashboard Cite

show abstract

Structural Phase Transitions in Niobium Hydrogen Thin Films: Mechanical Stress, Phase Equilibria and Critical Temperatures

et al. 2019

Self Cite

View full text Add to dashboard Cite

Metal−hydrogen (M−H) systems offer grand opportunities for studies on fundamental aspects of thermodynamics and kinetics. When the system size is reduced to the nanoscale, microstructural defects as well as mechanical stress affect the systems’ properties. This is contemplated for the model system of epitaxial niobium−hydrogen (Nb−H) thin films. Hydrogen absorption in metals commonly leads to lattice expansion which is hindered when the metal adheres to a flat rigid substrate. Consequently, high mechanical stress of about −10 GPa for 1 H/Nb are predicted, in theory. However, metals cannot yield such high stresses and respond with plastic deformation, commonly limiting measured stresses to −2 to −3 GPa for 100 nm Nb−H films. It will be shown that the coherency state changes with film thickness reduction, shifting the onset of plastic deformation to larger hydrogen concentrations. Below critical film thicknesses, plastic deformation is fully absent. The system then behaves purely elastic and ultra‐high stress of about −10 (±2) GPa can be obtained. Arising stress controls the phase stability of M−H systems, and the coherency state strongly affects the nucleation and growth dynamics of the phase transition. In case of Nb−H thin films of less than 8 nm thickness the common phase transformation from the α‐phase solid solution to the hydride phase is completely suppressed at 300 K. Related effects can be utilised to optimise metal−hydrides used in applications.

show abstract