| 1. |
- Bylin, Johan, et al.
(författare)
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Hydrogen-induced volume changes, dipole tensor, and elastic hydrogen-hydrogen interaction in a metallic glass
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:10
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen and its isotopes, absorbed in metals, induce local stress on the atomic structure, which generates a global expansion in proportion to the concentration of hydrogen. The dipole force tensor and its interaction with the stress fields give rise to an effective attractive nonlocal potential between hydrogen atoms-the elastic hydrogen-hydrogen interaction-which is a key quantity governing the phase transitions of hydrogen in metals. While the dipole tensor and the elastic interaction have been researched in crystalline materials, they remain experimentally unexplored in metallic glasses and it is unclear how these quantities are affected by the lack of point group symmetries. Here, we investigate both experimentally and theoretically the volume changes, the components of the force dipole tensor, and ultimately the elastic hydrogen-hydrogen interaction in the metallic glass V80Zr20. In situ neutron reflectometry was used to determine the deuterium-induced volume changes as a function of deuterium concentration. The one-dimensional volume expansion is found to change by more than 14% without any structural degradation, up to concentrations of one deuterium atom per metal atom. From the expansion, we determine that the out-of-plane component of the elastic dipole tensor is remarkably similar to a composition weighted sum of the ones found in crystalline vanadium and zirconium. Via ab initio calculations of both free and biaxially constrained expanded metallic structures, we determine that the trace of the dipole tensor varies with hydrogen concentration and is essentially invariant of global elastic boundary conditions. As a consequence, the elastic hydrogen-hydrogen interaction energy is found to be concentration-dependent as well, illustrating that the disordered nature of a metallic glass does not impede the mediation of the elastic attraction, but rather allows it to vary with hydrogen content.
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| 2. |
- Bylin, Johan, et al.
(författare)
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One-shot pair distribution functions of thin films using lab-based x-ray sources
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate the feasibility of obtaining accurate pair distribution functions of thin amorphous films down to 80 nm, using modern laboratory-based x-ray sources. The pair distribution functions are obtained using a single diffraction scan (one-shot) without the requirement of additional scans of the substrate or of the air. By using a crystalline substrate combined with an oblique scattering geometry, most of the Bragg scattering of the substrate is avoided, rendering the substrate Compton scattering the primary contribution. By utilizing a discriminating energy filter, available in the latest generation of modern detectors, we demonstrate that the Compton intensity can further be reduced to negligible levels at higher wavevector values. We minimize scattering from the sample holder and the air by the systematic selection of pixels in the detector image based on the projected detection footprint of the sample and the use of a 3D printed sample holder. Finally, x-ray optical effects in the absorption factors and the ratios between the Compton intensity of the substrate and film are taken into account by using a theoretical tool that simulates the electric field inside the film and the substrate, which aids in planning both the sample design and measurement protocol.
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| 3. |
- Bylin, Johan, et al.
(författare)
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The influence of hydrogen on the electronic structure in transition metallic glasses
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the influence of hydrogen on the electronic structure of a binary transition metallic glass of V80Zr20. We examine the hybridization between the hydrogen and metal atoms with the aid of hard x-ray photoelectron spectroscopy. Combined with ab initio density functional theory, we are able to show and predict the formation of s-d hybridized energy states. With optical transmission and resistivity measurements, we investigate the emergent electronic properties formed out of those altered energy states, and together with the theoretical calculations of the frequency-dependent conductivity tensor, we qualitatively support the observed strong wavelength-dependency of the hydrogen-induced changes on the optical absorption and a positive parabolic change in resistivity with hydrogen concentration.
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| 4. |
- Bylin, Johan
(författare)
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The interaction of hydrogen with metallic glass
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Combining theoretical ab initio calculations with high-purity thin film sample synthesis and in situ measurements is a compelling way to bridge the gap in our understanding concerning hydrogen in metallic glasses, which is the primary work of this dissertation thesis. The main emphasis has been on how hydrogen affects the structure of metallic glasses, and how those changes influence not only the electronic properties of the amorphous metals but also their thermal stability. The real-space correlations in the form of the pair distribution functions in thin metallic films have primarily only been accessible through synchrotron radiation. An effective methodological procedure using laboratory-based x-ray sources is here brought forth, which, for the first time, can produce accessible and accurate pair distribution functions from thin films down to a thickness of 80 nm. The underpinning mechanisms behind the hydrogen-induced volume expansion of metallic glasses in the form of the dipole force tensor and an elastic hydrogen-hydrogen interaction were examined using in situ neutron reflectometry and first-principles calculations of expanding V80Zr20 amorphous structures. The dipole force tensor was concluded to be similar in magnitude to a mole-fraction-weighted sum of the ones found in hydrogen-contained vanadium and zirconium crystals, and the theoretical calculations demonstrated that it and the interaction energy varies with hydrogen concentration. The electronic structure of the metallic glass V80Zr20 was determined via hard x-ray photoemission spectrometry and confirmed by first-principles calculations to be modified by the presence of hydrogen, in which a collection of s-d hybridized states 7 eV below the Fermi level was formed. The changes closer to the Fermi level, together with the volume expansion, were via experiments and ab initio calculations established to cause a parabolic change in resistance and a strong wavelength dependence on the optical transmission. The thermal stability of amorphous VxZr1-x metals, investigated via ab initio calculations of the thermodynamic driving force towards crystallization, was found to affirm the observed hydrogen-induced enhancement in thermal stability.
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| 5. |
- Kaplan, Maciej, 1991-, et al.
(författare)
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Hydrogen-induced enhancement of thermal stability in VZr(H) metallic glasses
- 2022
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 24
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Tidskriftsartikel (refereegranskat)abstract
- Prediction of crystallization temperatures in metallic glasses is still an open question. Investigations of multi component alloys are common in the literature, however, binary and ternary alloys are more suitable for funda-mental studies due to their simplicity. Here, we show that a low thermodynamic driving force for crystallization can be associated with a high crystallization temperature. The driving force is determined by calculating - for the first time in metallic glasses - the temperature dependent Gibbs free energies of the alloys using ab initio density functional theory, in combination with the stochastic quenching method. The crystallization tempera-tures of VxZr100-x and VxZr67-xH33 have been determined using simultaneous in-situ x-ray scattering techniques and resistivity measurements. The onset of crystallization is found to exhibit a parabolic dependence throughout the composition range, whereas alloying with hydrogen increases the thermal stability up to 150 K close to the amorphous-crystalline boundaries. These findings suggest that hydrogen acts as an alloying element with the ability to dynamically tune the intrinsic properties of the material. Lastly, temperature-dependent descriptions of the Gibbs free energy and kinetic considerations of a metallic glass are necessary for a complete characterization of the crystallization process.
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| 6. |
- Ravensburg, Anna Lena, 1994-, et al.
(författare)
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GENL: An extensible fitting program for Laue oscillations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- GENL is a flexible program that can be used to simulate and/or fit x-ray diffraction data from epitaxial thin films exhibiting Laue oscillations. It utilizes differential evolution within a genetic algorithm for the fitting of data and is based on the kinematic theory of diffraction. Effects of polarization, absorption, the Lorentz factor, as well as instrumental resolution and vibrations are taken into account. Useful parameters that can be extracted after fitting include: atomic interplanar spacings, number of coherently scattering atomic planes, strain profiles along the film thickness, and crystal roughness. The program has been developed in MATLAB and employs a graphical user interface. The deployment strategy is twofold whereby the software can either be obtained in source code form and executed within the MATLAB environment, or as a pre-compiled binary for those who prefer not to run it within MATLAB. Finally, GENL can easily be extended to simulate multilayered film systems, superlattices, and films with atomic steps. The program is released under the GNU General Public Licence.
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