I07-Surface & interface diffraction
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Cem
Ornek
,
Fan
Zhang
,
Alfred
Larsson
,
Mubashir
Mansoor
,
Gary S.
Harlow
,
Robin
Kroll
,
Francesco
Carla
,
Hadeel
Hussain
,
Dirk L.
Engelberg
,
Bora
Derin
,
Jinshan
Pan
Diamond Proposal Number(s):
[23388]
Open Access
Abstract: The passive film stability on stainless steel can be affected by hydrogen absorption and lead to microstructure embrittlement. This work shows that the absorption of hydrogen results in surface degradation due to oxide reduction and ionic defect generation within the passive film, which decomposes and eventually vanishes. The passive film provides a barrier to entering hydrogen, but when hydrogen is formed, atomic hydrogen infuses into the lattices of the austenite and ferrite phases, causing strain evolution, as shown by synchrotron x-ray diffraction data. The vacancy concentration and hence the strains increase with increasing electrochemical cathodic polarization. Under cathodic polarization, the surface oxides are thermodynamically unstable, but the complete reduction is kinetically restrained. As a result, surface oxides remain present under excessive cathodic polarization, contesting the classical assumption that oxides are easily removed. Density-functional theory calculations have shown that the degradation of the passive film is a reduction sequence of iron and chromium oxide, which causes thinning and change of the semiconductor properties of the passive film from n-type to p-type. As a result, the surface loses its passivity after long cathodic polarization and becomes only a weak barrier to hydrogen absorption and hence hydrogen embrittlement.
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Aug 2023
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[23975]
Abstract: The strength and fracture toughness of Additively Manufactured (AM) components are significantly influenced by the concentration and size of oxides and precipitate inclusions within the build powders. These features are highly sensitive to powder production parameters, as well as the number of times a powder has been reused. In this study synchrotron X-ray powder diffraction was performed in an inert atmosphere at room temperature and during in-situ heating, providing crucial insights into growth rates and distribution of oxides and precipitates as a function of temperature. From the high angular resolution data collected, the structural refinement showed that plasma wire arc atomisation shows lower residual strain than gas atomised powder samples at room temperature after atomisation likely due to lower temperatures achieved during the production process. Additionally, the results from the diffraction patterns collected during in-situ heating provide key insights to the four metal powders considered in this study, Ti-6Al-4 V, Ni718, AlSi10Mg, and Scalmalloy. This paper also highlights the potential that using synchrotron X-ray diffraction to study AM parts and constituent AM powder has to gain crucial insight into material properties and the build reliability of end use production quality parts from AM.
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Jun 2023
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I07-Surface & interface diffraction
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Cem
Ornek
,
Mubashir
Mansoor
,
Alfred
Larsson
,
Fan
Zhang
,
Gary S.
Harlow
,
Robin
Kroll
,
Francesco
Carla
,
Hadeel
Hussain
,
Bora
Derin
,
Ulf
Kivisäkk
,
Dirk L.
Engelberg
,
Edvin
Lundgren
,
Jinshan
Pan
Diamond Proposal Number(s):
[23388]
Open Access
Abstract: Various mechanisms have been proposed for hydrogen embrittlement of duplex stainless steel, but the causation of hydrogen-induced material degradation has remained unclear. This work shows that phase instability (decomposition) of the austenite phase and ductile-to-brittle transition of the ferrite phase precedes hydrogen embrittlement. In-situ diffraction measurements revealed that Ni-rich sites of the austenite phase decompose into metastable hydrides. Hydride formation is possible by increasing the hydrogen chemical potential during electrochemical charging and low defect formation energy of hydrogen interstitials. Our findings demonstrate that hydrogen embrittlement can only be understood if measured in situ and in real-time during the embrittlement process.
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Jun 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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A.
Koko
,
S.
Singh
,
S.
Barhli
,
T.
Connolley
,
N. T.
Vo
,
T.
Wigger
,
D.
Liu
,
Y.
Fu
,
J.
Réthoré
,
J.
Lechambre
,
J.-Y.
Buffiere
,
T. J.
Marrow
Diamond Proposal Number(s):
[12585]
Open Access
Abstract: The propagation rate of a fatigue crack in a nodular cast iron, loaded in cyclic tension, has been studied in situ by X-ray computed tomography and digital volume correlation. The semi-elliptical crack initiated from an asymmetric corner notch and evolved to a semi-circular shape, initially with a higher growth rate towards one edge of the notch before the propagation rate along the crack front became essentially independent of po-sition. The phase congruency of the displacement field was used to measure the crack shape. The three-dimensional stress intensity factors were calculated via a linear elastic finite element model that used the displacement fields around the crack front as the boundary conditions. Closure of the crack tip region was observed. The cyclic change in the local mode I opening of the crack tip determined the local fatigue crack propaga-tion rate along the crack front.
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May 2023
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B18-Core EXAFS
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Open Access
Abstract: New and exotic ground states of magnetic materials are highly sought after and are extensively studied for the insights they provide into the thermodynamics of disorder and fundamental magnetic interactions. By controlling the crystal structure of an appropriate magnetic lattice, it is possible to cause the strong magnetic exchange interactions to sum to zero and so be frustrated. Due to the presence of this frustration, the lowest energy configuration that results may be crucially dependent on the tiniest of energy differences between a multitude of states that have (almost) the same energy. The keen interest in these materials arises from the fact that these finely balanced systems offer a way of probing classical or quantum mechanical interactions that are of fundamental importance but are too weak to be observed in non-frustrated systems. Here, we combine local and crystallographic probes of the cation-ordered double perovskite Ba2MnMoO6 that contains a face-centered cubic lattice of S = 5/2 Mn2+ cations. Neutron diffraction measurements below 9.27(7) K indicate that a fourfold degenerate non-collinear antiferromagnetic state exists with almost complete ordering of the Mn2+ spins. Muon spin relaxation measurements provide a local probe of the magnetic fields inside this material over the t1/2 = 2.2 µs lifetime of a muon, indicating a slightly lower Néel transition temperature of 7.9(1) K. The dc susceptibility data do not show the loss of magnetization that should accompany the onset of the antiferromagnetic order; they indicate that a strongly antiferromagnetically coupled paramagnetic state [θ = −73(3) K] persists down to 4 K, at which temperature a weak transition occurs. The behavior of this material differs considerably from the closely related compositions Ba2MnMO6 (M = W, Te), which show collinear ordering arrangements and well defined antiferromagnetic transitions in the bulk susceptibility. This suggests that the Mo6+ cation leads to a fine balance between the nearest and next-nearest neighbor superexchange in these frustrated double perovskite structures.
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May 2023
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I14-Hard X-ray Nanoprobe
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Diamond Proposal Number(s):
[20420, 28521]
Open Access
Abstract: All-perovskite tandem solar cells beckon as lower cost alternatives to conventional single-junction cells. Solution processing has enabled rapid optimization of perovskite solar technologies, but new deposition routes will enable modularity and scalability, facilitating technology adoption. Here, we utilize 4-source vacuum deposition to deposit FA0.7Cs0.3Pb(IxBr1–x)3 perovskite, where the bandgap is changed through fine control over the halide content. We show how using MeO-2PACz as a hole-transporting material and passivating the perovskite with ethylenediammonium diiodide reduces nonradiative losses, resulting in efficiencies of 17.8% in solar cells based on vacuum-deposited perovskites with a bandgap of 1.76 eV. By similarly passivating a narrow-bandgap FA0.75Cs0.25Pb0.5Sn0.5I3 perovskite and combining it with a subcell of evaporated FA0.7Cs0.3Pb(I0.64Br0.36)3, we report a 2-terminal all-perovskite tandem solar cell with champion open circuit voltage and efficiency of 2.06 V and 24.1%, respectively. This dry deposition method enables high reproducibility, opening avenues for modular, scalable multijunction devices even in complex architectures.
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May 2023
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I11-High Resolution Powder Diffraction
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Aizhamal
Subanbekova
,
Varvara I.
Nikolayenko
,
Andrey A.
Bezrukov
,
Debobroto
Sensharma
,
Naveen
Kumar
,
Daniel J.
O'Hearn
,
Volodymyr
Bon
,
Shi-Qiang
Wang
,
Kyriaki
Koupepidou
,
Shaza
Darwish
,
Stefan
Kaskel
,
Michael J.
Zaworotko
Diamond Proposal Number(s):
[30456]
Open Access
Abstract: In this work, we report the synthesis, structural characterisation and sorption properties of an 8-fold interpenetrated diamondoid (dia) metal–organic framework (MOF) that is sustained by a new extended linker ligand, [Cd(Imibz)2], X-dia-2-Cd, HImibz or 2 = 4-((4-(1H-imidazol-1-yl)phenylimino)methyl)benzoic acid. X-dia-2-Cd was found to exhibit reversible single-crystal-to-single-crystal (SC–SC) transformations between four distinct phases: an as-synthesised (from N,N-dimethylformamide) wide-pore phase, X-dia-2-Cd-α; a narrow-pore phase, X-dia-2-Cd-β, formed upon exposure to water; a narrow-pore phase obtained by activation, X-dia-2-Cd-γ; a medium-pore CO2-loaded phase X-dia-2-Cd-δ. While the space group remained constant in the four phases, the cell volumes and calculated void space ranged from 4988.7 Å3 and 47% (X-dia-2-Cd-α), respectively, to 3200.8 Å3 and 9.1% (X-dia-2-Cd-γ), respectively. X-dia-2-Cd-γ also exhibited a water vapour-induced structural transformation to the water-loaded X-dia-2-Cd-β phase, resulting in an S-shaped sorption isotherm. The inflection point occurred at 18% RH with negligible hysteresis on the desorption profile. Water vapour temperature-humidity swing cycling (60% RH, 300 K to 0% RH, 333 K) indicated hydrolytic stability of X-dia-2-Cd and working capacity was retained after 128 cycles of sorbent regeneration. CO2 (at 195 K) was also observed to induce a structural transformation in X-dia-2-Cd-γ and in situ PXRD studies at 1 bar of CO2, 195 K revealed the formation of X-dia-2-Cd-δ, which exhibited 31% larger unit cell volume than X-dia-2-Cd-γ.
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May 2023
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B18-Core EXAFS
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Open Access
Abstract: The Fischer–Tropsch (FT) synthesis is traditionally associated with fossil fuel consumption, but recently this technology has emerged as a keystone that enables the conversion of captured CO2 with sustainable hydrogen to energy-dense fuels and chemicals for sectors which are challenging to be electrified. Iron-based FT catalysts are promoted with alkali and transition metals to improve reducibility, activity, and selectivity. Due to their low concentration and the metastable state under reaction conditions, the exact speciation and location of these promoters remain poorly understood. We now show that the selectivity promoters such as potassium and manganese, locked into an oxidic matrix doubling as a catalyst support, surpass conventional promoting effects. La1–xKxAl1–yMnyO3−δ (x = 0 or 0.1; y = 0, 0.2, 0.6, or 1) perovskite supports yield a 60% increase in CO conversion comparable to conventional promotion but show reduced CO2 and overall C1 selectivity. The presented approach to promotion seems to decouple the enhancement of the FT and the water–gas shift reaction. We introduce a general catalyst design principle that can be extended to other key catalytic processes relying on alkali and transition metal promotion.
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May 2023
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20198]
Open Access
Abstract: Intentionally disordered metal–organic frameworks (MOFs) display rich functional behaviour. However, the characterisation of their atomic structures remains incredibly challenging. X-ray pair distribution function techniques have been pivotal in determining their average local structure but are largely insensitive to spatial variations in the structure. Fe-BTC (BTC = 1,3,5-benzenetricarboxylate) is a nanocomposite MOF, known for its catalytic properties, comprising crystalline nanoparticles and an amorphous matrix. Here, we use scanning electron diffraction to first map the crystalline and amorphous components to evaluate domain size and then to carry out electron pair distribution function analysis to probe the spatially separated atomic structure of the amorphous matrix. Further Bragg scattering analysis reveals systematic orientational disorder within Fe-BTC’s nanocrystallites, showing over 10° of continuous lattice rotation across single particles. Finally, we identify candidate unit cells for the crystalline component. These independent structural analyses quantify disorder in Fe-BTC at the critical length scale for engineering composite MOF materials.
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May 2023
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Qi
Xue
,
Ching Kit Tommy
Wun
,
Tianxiang
Chen
,
Shogo
Kawaguchi
,
Sarah
Day
,
Chiu C.
Tang
,
Tai-Sing
Wu
,
Yun-Liang
Soo
,
Cong
Lin
,
Yung-Kang
Peng
,
Jun
Yin
,
Tsz Woon Benedict
Lo
Abstract: Supported bimetallic dual-atom catalysts (DACs) have been regarded as a promising class of materials for small molecule activation, but their syntheses remain challenging. Here, we report the controlled synthesis of supported Cu,Fe DACs on the ZrO6O4 secondary building units of UiO-66-NH2 which allows the efficient activation of O2. Remarkably high product selectivity (>92%) towards benzaldehyde over our model photocatalytic styrene oxidation reaction has been achieved. The superior reactivity has been attributed to the well-balanced synergy between the electronic and steric characteristics, which enables efficient O2 activation by the sterically restrained Cu and Fe sites in proximity for the formation of the bridging peroxy group. This bridging peroxy group facilitates the selective oxidation of styrene akin to many peroxide-based oxidants. The confined microporous environment allows the control of the electronic and geometric properties of the DACs, which subsequently sheds light towards more precise atomistic engineering that approaches the conventional inorganic metal(s)-complex counterparts.
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May 2023
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