| 1. |
- Anker, Andy S., et al.
(författare)
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Extracting structural motifs from pair distribution function data of nanostructures using explainable machine learning
- 2022
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Ingår i: npj Computational Materials. - : Springer Science and Business Media LLC. - 2057-3960. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Characterization of material structure with X-ray or neutron scattering using e.g. Pair Distribution Function (PDF) analysis most often rely on refining a structure model against an experimental dataset. However, identifying a suitable model is often a bottleneck. Recently, automated approaches have made it possible to test thousands of models for each dataset, but these methods are computationally expensive and analysing the output, i.e. extracting structural information from the resulting fits in a meaningful way, is challenging. Our Machine Learning based Motif Extractor (ML-MotEx) trains an ML algorithm on thousands of fits, and uses SHAP (SHapley Additive exPlanation) values to identify which model features are important for the fit quality. We use the method for 4 different chemical systems, including disordered nanomaterials and clusters. ML-MotEx opens for a type of modelling where each feature in a model is assigned an importance value for the fit quality based on explainable ML.
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| 2. |
- Christensen, Christian Kolle, et al.
(författare)
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Beam damage in operando X-ray diffraction studies of Li-ion batteries
- 2023
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 30:Pt 3, s. 561-570
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Tidskriftsartikel (refereegranskat)abstract
- Operando powder X-ray diffraction (PXRD) is a widely employed method for the investigation of structural evolution and phase transitions in electrodes for rechargeable batteries. Due to the advantages of high brilliance and high X-ray energies, the experiments are often carried out at synchrotron facilities. It is known that the X-ray exposure can cause beam damage in the battery cell, resulting in hindrance of the electrochemical reaction. This study investigates the extent of X-ray beam damage during operando PXRD synchrotron experiments on battery materials with varying X-ray energies, amount of X-ray exposure and battery cell chemistries. Battery cells were exposed to 15, 25 or 35 keV X-rays (with varying dose) during charge or discharge in a battery test cell specially designed for operando experiments. The observed beam damage was probed by μPXRD mapping of the electrodes recovered from the operando battery cell after charge/discharge. The investigation reveals that the beam damage depends strongly on both the X-ray energy and the amount of exposure, and that it also depends strongly on the cell chemistry, i.e. the chemical composition of the electrode.
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| 3. |
- Christensen, Thorbjørn Erik Køppen, et al.
(författare)
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Flexible design in the stomatopod dactyl club
- 2023
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Ingår i: IUCrJ. - 2052-2525. ; 10:Pt 3, s. 288-296
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Tidskriftsartikel (refereegranskat)abstract
- The stomatopod is a fascinating animal that uses its weaponized appendage dactyl clubs for breaking mollusc shells. Dactyl clubs are a well studied example of biomineralized hierarchical structures. Most research has focused on the regions close to the action, namely the impact region and surface composed of chitin and apatite crystallites. Further away from the site of impact, the club has lower mineralization and more amorphous phases; these areas have not been as actively studied as their highly mineralized counterparts. This work focuses on the side of the club, in what is known as the periodic and striated regions. A combination of laboratory micro-computed tomography, synchrotron X-ray diffraction mapping and synchrotron X-ray fluorescence mapping has shown that the mineral in this region undergoes the transition from an amorphous to a crystalline phase in some, but not all, clubs. This means that this side region can be mineralized by either an amorphous phase, calcite crystallites or a mixture of both. It was found that when larger calcite crystallites form, they are organized (textured) with respect to the chitin present in this biocomposite. This suggests that chitin may serve as a template for crystallization when the side of the club is fully mineralized. Further, calcite crystallites were found to form as early as 1 week after moulting of the club. This suggests that the side of the club is designed with a significant safety margin that allows for a variety of phases, i.e. the club can function independently of whether the side region has a crystalline or amorphous mineral phase.
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| 4. |
- Grinderslev, Jakob B., et al.
(författare)
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Polymorphism and solid solutions of trimethylammonium monocarboranes
- 2022
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 51:41, s. 15806-15815
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Tidskriftsartikel (refereegranskat)abstract
- Metal closo-boranes have recently received significant attention as solid-state electrolytes due to their high thermal and electrochemical stability, and the weak interaction between the cat- and anion, facilitating fast ionic conductivity. Here we report a synthesis method for obtaining a novel mixed closo-carborane compound, [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08]. The crystal structures are investigated for [NH(CH3)3][CB9H10] and [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08], revealing that the latter forms a solid solution isostructural to [NH(CH3)3][CB9H10]. The compounds exhibit polymorphism as a function of temperature, and we report the discovery of four polymorphs of [NH(CH3)3][CB9H10] and four isostructural solid solution [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08], along with a high-temperature decomposition intermediate of the latter. The α-polymorph is an ordered structure, with increasing amounts of disorder for the β- and γ-polymorphs, while the high temperature δ- and ϵ-polymorphs at T > 476 K are fully disordered on both the cation and anion site. These new compounds may be used as precursors for new types of solid-state ionic conductors.
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| 5. |
- Gurzęda, Bartosz, et al.
(författare)
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Graphite oxide by “chlorate route” oxidation without HNO3 : Does acid matter?
- 2024
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Ingår i: Carbon. - 0008-6223 .- 1873-3891. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Very strong difference in many properties is well documented for graphite oxides (GtO) synthesized by Brodie (BGO) and Hummers (HGO) methods. The difference is typically assigned to the type of oxidant (chlorates or KMnO4, respectively). However, not only oxidants but also acids used in these methods are different. It is still unclear which of the different properties of GtO are dependent on the oxidant or acid used in the synthesis. Here we synthesized a new type of graphite oxide using an oxidation agent typical for the Brodie method (KClO3) in combination with acids so far used only in modified Hummers' method (H2SO4+H3PO4). The GtO synthesized by this method (MGO) demonstrates some properties similar to BGO (higher temperature of exfoliation and less defected structure) but also similarity to some other properties of HGO (absence of sharp swelling transitions). Comparing MGO, BGO, and HGO allows us to distinguish the effects of acids and oxidants on the properties of graphite oxides. The new procedure proposed in this study allows preparation of GtO nearly free from hole/vacancy defects (similarly to BGO) but avoids dangerous HNO3. MGO is suggested as a favorable precursor for the preparation of graphene films by thermal or chemical reduction methods.
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| 6. |
- Iakunkov, Artem, et al.
(författare)
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Effect of chain length on swelling transitions of Brodie graphite oxide in liquid 1-alcohols
- 2024
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Ingår i: Advanced Materials Interfaces. - : Wiley-VCH Verlagsgesellschaft. - 2196-7350. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Swelling is the most fundamental property of graphite oxides (GO). Here, a structural study of Brodie graphite oxide (BGO) swelling in a set of long chain 1-alcohols (named C11 to C22 according to the number of carbons) performed using synchrotron radiation X-ray diffraction at elevated temperatures is reported. Even the longest of tested alcohols (C22) is found to intercalate BGO with enormous expansion of the interlayer distance from ≈6Å up to ≈63Å, the highest expansion of GO lattice ever reported. Swelling transitions from low temperature α-phase to high temperature β-phase are found for BGO in all alcohols in the C11–C22 set. The transitions correspond to decrease of inter-layer distance correlating with the length of alcohol molecules, and change in their orientation from perpendicular to GO planes to layered parallel to GO (Type II transitions). These transitions are very different compared to BGO swelling transitions (Type I) found in smaller alcohols and related to insertion/de-insertion of additional layer of alcohol parallel to GO. Analysis of general trends in the whole set of 1-alcohols (C1 to C22) shows that the 1-alcohol chain length defines the type of swelling transition with Type I found for alcohols with C<10 and Type II for C>10.
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| 7. |
- Isakov, Matti, et al.
(författare)
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In-Situ X-ray Diffraction Analysis of Metastable Austenite Containing Steels Under Mechanical Loading at a Wide Strain Rate Range
- 2023
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 54:4, s. 1320-1331
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents and discusses the methodology and technical aspects of mechanical tests carried out at a wide strain rate range with simultaneous synchrotron X-ray diffraction measurements. The motivation for the study was to develop capabilities for in-situ characterization of the loading rate dependency of mechanically induced phase transformations in steels containing metastable austenite. The experiments were carried out at the DanMAX beamline of the MAX IV Laboratory, into which a custom-made tensile loading device was incorporated. The test setup was supplemented with in-situ optical imaging of the specimen, which allowed digital image correlation-based deformation analysis. All the measurement channels were synchronized to a common time basis with trigger signals between the devices as well as post-test fine tuning based on diffraction ring shape analysis. This facilitated precise correlation between the mechanical and diffraction data at strain rates up to 1 s−1 corresponding to test duration of less than one second. Diffraction data were collected at an acquisition rate of 250 Hz, which provided excellent temporal resolution. The feasibility of the methodology is demonstrated by providing novel data on the kinetics of the martensitic phase transformation in EN 1.4318-alloy following a rapid increase in strain rate (a so-called jump test).
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| 8. |
- Juelsholt, Mikkel, et al.
(författare)
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Size-induced amorphous structure in tungsten oxide nanoparticles
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:47, s. 20144-20156
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Tidskriftsartikel (refereegranskat)abstract
- The properties of functional materials are intrinsically linked to their atomic structure. When going to the nanoscale, size-induced structural changes in atomic structure often occur, however these are rarely well-understood. Here, we systematically investigate the atomic structure of tungsten oxide nanoparticles as a function of the nanoparticle size and observe drastic changes when the particles are smaller than 5 nm, where the particles are amorphous. The tungsten oxide nanoparticles are synthesized by thermal decomposition of ammonium metatungstate hydrate in oleylamine and by varying the ammonium metatungstate hydrate concentration, the nanoparticle size, shape and structure can be controlled. At low concentrations, nanoparticles with a diameter of 2-4 nm form and adopt an amorphous structure that locally resembles the structure of polyoxometalate clusters. When the concentration is increased the nanoparticles become elongated and form nanocrystalline rods up to 50 nm in length. The study thus reveals a size-dependent amorphous structure when going to the nanoscale and provides further knowledge on how metal oxide crystal structures change at extreme length scales.
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| 9. |
- Magnard, Nicolas P.L., et al.
(författare)
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Control of H-Related Defects in γ-MnO2 in a Hydrothermal Synthesis
- 2023
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Ingår i: Inorganic Chemistry. - 0020-1669. ; 62:32, s. 13021-13029
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Tidskriftsartikel (refereegranskat)abstract
- Manganese dioxide is a good candidate for effective energy storage and conversion as it possesses rich electrochemistry. The compound also shows a wide polymorphism. The γ-variety, an intergrowth of β- and R-MnO2, has been extensively studied in several types of batteries (e.g., Zn/MnO2, Li-ion) and is a common electrode material for commercial batteries. It is well known that the insertion of protons thermodynamically stabilizes γ-MnO2 with respect to β-MnO2. Protons can enter the structure either by forming groups of 4 hydroxyls around a Mn4+ vacancy, called a Ruetschi defect, or by forming a hydroxyl group near a Mn3+ ion, called a Coleman defect. These defects differently affect the electrochemistry of manganese oxide, and tailoring their amount in the structure can be used to tune the material properties. Previous studies have addressed the proton insertion process, but the role of the synthesis pathway on the amount of defects created is not well understood. We here investigate how the parameters in a hydrothermal synthesis of γ-MnO2 nanoparticles influence the amount and type of H-related defects. Structural investigations are carried out using Pair Distribution Function analysis, X-ray absorption spectroscopy, thermogravimetric analysis, and inelastic neutron scattering. We demonstrate the possibility to control the amount and type of defects introduced during the synthesis. While the amount of Ruetschi defects increases with synthesis temperature, it decreases with extended synthesis time, along with the amount of Coleman defects. Moreover, we discuss the arrangement of the defects in the γ-MnO2 nanoparticles.
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| 10. |
- Nordenström, Andreas, et al.
(författare)
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Temperature dependent intercalation of molten 1-hexadecanol into Brodie graphite oxide
- 2023
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 203, s. 770-784
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Tidskriftsartikel (refereegranskat)abstract
- Intercalation of very long molecules into the structure of multi-layered graphene oxide (GO) was studied using example of 1-hexadecanol (C16), an alcohol molecule with 16 carbon atoms. Brodie graphite oxide (BGO) immersed in excess of liquid C16 just above the melting point shows expansion of c-unit cell parameter from ∼6 Å to ∼48.76 Å forming a structure with two densely packed layers of C16 molecules in a perpendicular orientation relative to the GO planes (α-phase). Heating of the BGO-C16 α-phase in excess of C16 melt results in reversible phase transition into β-phase at 336–342K. The β-phase shows much smaller unit cell parameter of 29.83 Å (363K). Analysis of data obtained using vacuum-driven evaporation of C16 from the β-phase provides evidence for structure of β-phase consisting of five layers of C16 molecules in parallel to GO plane orientation. Therefore, the transition from α-to β-phase corresponds to change in orientation C16 molecules from perpendicular to parallel relative to GO planes and decrease in the amount of intercalated solvent. Cooling of the β-phase in absence of C16 melt is found to result in the formation of γ-phase with inter-layer distance of ∼26.5 Å corresponding to one layer of C16 molecules intercalated perpendicularly relative to the GO planes. Structures with one and two layers of C16 molecules parallel to GO planes were identified in samples with rather small initial loading of C16. Surprisingly rich variety of structures revealed in the BGO-C16 system provides opportunities to create materials with precisely controlled GO inter-layer distance.
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