Hydrogenation behavior on 30 nm vanadium thin films with two different adhesion conditions

Tyagi, Anshu; Döring, Florian; Krebs, Hans‐Ulrich; Pundt, Astrid

doi:10.1016/j.ijhydene.2017.04.011

Cited by 3 publications

(1 citation statement)

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“…As a drawback, palladiums’ adhesion to many substrate materials is considerably low, limiting the study of stress effects. For epitaxial vanadium−hydrogen films the influence of elastic stresses on site occupancy, H solubility and H−H interaction was investigated, utilising the geometric anisotropy of interstitial lattice sites . The anisotropy causes a switchover of the energies of tetrahedral and octahedral interstitial sites.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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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.

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Section: Introductionmentioning

confidence: 99%