I15-1-X-ray Pair Distribution Function (XPDF)
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Elsebeth J.
Pedersen
,
Theany
To
,
Søren S.
Sørensen
,
Rasmus
Christensen
,
Johan F. S.
Christensen
,
Lars R.
Jensen
,
Michal
Bockowski
,
Oxana V.
Magdysyuk
,
Maria
Diaz-Lopez
,
Yuanzheng
Yue
,
Morten M.
Smedskjaer
Diamond Proposal Number(s):
[30401]
Abstract: Methods to improve the fracture toughness of oxide glasses are needed since low fracture toughness is a major bottleneck for their applications. To overcome this, it is critically important to investigate the effect of both short- and medium-range structural features on fracture toughness. Recent work reported a record-high fracture toughness for a bulk lithium aluminoborate glass subjected to hot compression. Here, we further explore the structural origin of this high fracture toughness by subjecting different alkali aluminoborate glasses to hot compression. Through a combination of x-ray total scattering experiments and atomistic simulations, we find that hot compression causes significant changes to both the short- and medium-range order structure of the glasses, e.g., increased coordination numbers (CNs) of network forming species and decreased average size of ring-type structures. To this end, we reveal positive correlations between the pressure-induced increase in fracture toughness and (i) the increase in average CN of network forming species and (ii) the area of the first sharp diffraction peak in the structure factor. Our study thus improves the understanding of which structural features benefit intrinsic toughening of oxide glasses.
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May 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Open Access
Abstract: Membranes with ultrahigh permeance and practical selectivity could greatly decrease the cost of difficult industrial gas separations, such as CH4/N2 separation. Advanced membranes made from porous materials, such as metal–organic frameworks, can achieve a good gas separation performance, although they are typically formed on support layers or mixed with polymeric matrices, placing limitations on gas permeance. Here an amorphous glass foam, agfZIF-62, wherein a, g and f denote amorphous, glass and foam, respectively, was synthesized by a polymer-thermal-decomposition-assisted melting strategy, starting from a crystalline zeolitic imidazolate framework, ZIF-62. The thermal decomposition of incorporated low-molecular-weight polyethyleneimine evolves CO2, NH3 and H2O gases, creating a large number and variety of pores. This greatly increases pore interconnectivity but maintains the crystalline ZIF-62 ultramicropores, allowing ultrahigh gas permeance and good selectivity. A self-supported circular agfZIF-62 with a thickness of 200–330 µm and area of 8.55 cm2 was used for membrane separation. The membranes perform well, showing a CH4 permeance of 30,000–50,000 gas permeance units, approximately two orders of magnitude higher than that of other reported membranes, with good CH4/N2 selectivity (4–6).
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May 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[15895]
Open Access
Abstract: Flexible metal–organic frameworks (MOFs), showing a reversible phase change behavior in response to guest adsorption or temperature, provide unique opportunities for molecular separation or energy storage applications. Herein, we investigate the complex guest- and temperature-responsive behavior of a functionalized MOF-5 derivative. The material is characterized by a geometrically rigid network structure that is decorated with dispersion energy donating hexyloxy substituents. Distinguished by the phenomenon of frustrated flexibility, the functionalized MOF-5 derivative switches between a highly crystalline, cubic structure and a semi-crystalline, aperiodically distorted structure depending on guest adsorption and temperature. Via a combination of several variable temperature global and local structure techniques (x-ray diffraction, x-ray total scattering, and Fourier-transform IR spectroscopy), detailed insights into the complementary disorder–order transitions of the framework backbone and the dangling hexyloxy substituents are provided. Our results set the stage for the discovery of new responsive MOFs exhibiting a more complex phase change behavior interfacing periodic and aperiodic structural changes.
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Apr 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[21604]
Abstract: The liquid phase of metal–organic frameworks (MOFs) is key for the preparation of melt-quenched bulk glasses as well as the shaping of these materials for various applications; however, only very few MOFs can be melted and transformed into stable glasses. Here, the solvothermal and mechanochemical preparation of a new series of functionalized derivatives of ZIF-4 (Zn(im)2, where im– = imidazolate and ZIF = zeolitic imidazolate framework) containing the cyano-functionalized imidazolate linkers CNim– (4-cynanoimidazolate) and dCNim– (4,5-dicyanoimidazolate) is reported. The strongly electron-withdrawing nature of the CN groups facilitates low-temperature melting of the materials (below 310 °C for some derivatives) and the formation of microporous ZIF glasses with remarkably low glass-transition temperatures (down to only about 250 °C) and strong resistance against recrystallization. Besides conventional ZIF-4, the CN-functionalized ZIFs are so far the only MOFs to show an exothermic framework collapse to a low-density liquid phase and a subsequent transition to a high-density liquid phase. By systematic adjustment of the fraction of cyano-functionalized linkers in the ZIFs, we derive fundamental insights into the thermodynamics of the unique polyamorphic nature of these glass formers as well as further design rules for the porosity of the ZIF glasses and the viscosity of their corresponding liquids. The results provide new insights into the unusual phenomenon of liquid–liquid transitions as well as a guide for the chemical diversification of meltable MOFs, likely with implications beyond the archetypal ZIF glass formers.
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Apr 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Samuel W.
Coles
,
Viktoria
Falkowski
,
Harry S.
Geddes
,
Gabriel E.
Pérez
,
Samuel G.
Booth
,
Alexander G.
Squires
,
Conn
O'Rourke
,
Kit
Mccoll
,
Andrew L.
Goodwin
,
Serena A.
Cussen
,
Simon J.
Clarke
,
Saiful
Islam
,
Benjamin J.
Morgan
Diamond Proposal Number(s):
[27702]
Open Access
Abstract: Short-range ordering in cation-disordered cathodes can have a significant effect on their electrochemical properties. Here, we characterise the cation short-range order in the antiperovskite cathode material Li2FeSO, using density functional theory, Monte Carlo simulations, and synchrotron X-ray pair-distribution-function data. We predict partial short-range cation-ordering, characterised by favourable OLi4Fe2 oxygen coordination with a preference for polar cis-OLi4Fe2 over non-polar trans-OLi4Fe2 configurations. This preference for polar cation configurations produces long-range disorder, in agreement with experimental data. The predicted short-range-order preference contrasts with that for a simple point-charge model, which instead predicts preferential trans-OLi4Fe2 oxygen coordination and corresponding long-range crystallographic order. The absence of long-range order in Li2FeSO can therefore be attributed to the relative stability of cis-OLi4Fe2 and other non-OLi4Fe2 oxygen-coordination motifs. We show that this effect is associated with the polarisation of oxide and sulfide anions in polar coordination environments, which stabilises these polar short-range cation orderings. We propose similar anion-polarisation–directed short-range-ordering may be present in other heterocationic materials that contain cations with different formal charges. Our analysis also illustrates the limitations of using simple point-charge models to predict the structure of cation-disordered materials, where other factors, such as anion polarisation, may play a critical role in directing both short- and long-range structural correlations.
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Apr 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[19053]
Open Access
Abstract: A reverse Monte Carlo analysis of neutron and x-ray total scattering data from two ceria-zirconia samples of composition Ce0.75Zr0.25O2 is performed to analyze the distribution of cations and to examine the possibility of oxide-ion disorder. For the first material, heated in air under moderate conditions (800 °C), the structure is a single-phase solid-solution with the statistical distribution of cations, but a local tetragonal symmetry is found, consistent with the different coordination preferences of Ce and Zr. For the second material, heated under H2 at 1050 °C followed by reoxidation at 400 °C, the structure shows a considerable disorder, with evidence for oxygen interstitials (Frenkel-ion defects) and a non-statistical distribution of cations with significantly higher concentrations of like–like cation nearest neighbors, highlighting the existence of cation-rich nano-domains. The results highlight the dynamic nature of this solid-solution, with structural evolution upon thermal treatment, which is of relevance to understanding its stability under redox catalytic conditions in practical applications.
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Mar 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[28776]
Abstract: An anion doped aluminium chlorofluoride AlCl0.1F2.8(OTeF5)0.1 (ACF-teflate) was synthesized. The material contains pentafluoroorthotellurate (teflate) groups, which mimic fluoride ions electronically, but are sterically more demanding. They are embedded into the amorphous structure. The latter was studied by PDF analysis, EXAFS data and MAS NMR spectroscopy. The mesoporous powder is a Lewis superacid, and ATR-IR spectra of adsorbed CD3CN reveal a blue-shift of the adsorption band by 73 cm−1, which is larger than the shift for SbF5. Remarkably, ACF-teflate catalyzes dehydrofluorination reactions of monofluoroalkanes to yield olefins in C6D6. In these cases, no Friedel-Crafts products were formed.
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Mar 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
I15-Extreme Conditions
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Ge
Wang
,
Tengfei
Hu
,
Wenxuan
Zhu
,
Zhilun
Lu
,
Annette
Kleppe
,
Maria
Diaz Lopez
,
Antonio
Feteira
,
Derek C.
Sinclair
,
Zhengqian
Fu
,
Houbing
Huang
,
Dawei
Wang
,
Ian M.
Reaney
Diamond Proposal Number(s):
[21714, 27500]
Abstract: For the first time, the origin of large electrostrain in pseudocubic
BiFeO
3
-based ceramics is verified with direct structural evidence backed by appropriate simulations. We employ advanced structural and microstructural characterizations of
BiFeO
3
-based ceramics that exhibit large electrostrain (
>
0.4
%
) to reveal the existence of multiple, nanoscale local symmetries, dominantly tetragonal or orthorhombic, which have a common, averaged direction of polarization over larger, meso- or microscale regions. Phase-field simulations confirm the existence of local nanoscale symmetries, thereby providing a new vision for designing high-performance lead-free ceramics for high-strain actuators.
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Feb 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[20339]
Open Access
Abstract: Industries transporting CO2 gas-saturated fluids have infrastructures made of carbon steel. This is a good material with great mechanical properties but prone to corrosion and potential failure. Corrosion in sweet environments involves the formation of FeCO3 as a corrosion film, which is recognized to play a protective role under certain conditions. This work on the dissolution of corrosion films in sweet environments, under acidic and undersaturated conditions, demonstrates that the effects on the integrity of steel are far more significant than the damage observed on the surface of the corrosion film. Our results prove that dissolution of FeCO3 involved the presence of an amorphous phase, the intermediate formation of FeCl2 or FeCl+, and the presence of a phase with short distance atom–atom correlations. The amorphous phase was identified as a mixture of retained γ-Fe and Fe3C. Partially broken α-Fe and Fe3C structures were identified to prove the damage on the material, confirming the interface zone without evident damage on the corrosion film. Dissolution affected both the α-Fe and FeCO3, with the lattice [102̅] from the FeCO3 crystalline structure being the fastest to dissolve. The damage of steel at the molecular scale was evident at the macroscale with pit depths of up to 250 μm. The impact on the integrity of steel can be, therefore, more drastic than frequently reported in industrial operations of CO2 transport industries that use cleaning procedures (e.g., acid treatment, pigging) as part of their operational activities.
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Feb 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Mohamed. A.
Ali
,
Wessel M. W.
Winters
,
Moushira A.
Mohamed
,
Dezhi
Tan
,
Guojun
Zheng
,
Rasmus S. K.
Madsen
,
Oxana V.
Magdysyuk
,
Maria
Diaz-Lopez
,
Biao
Cai
,
Nan
Gong
,
Yijue
Xu
,
Ivan
Hung
,
Zhehong
Gan
,
Sabyasachi
Sen
,
Hong-Tao
Sun
,
Thomas D.
Bennett
,
Xiaofeng
Liu
,
Yuanzheng
Yue
,
Jianrong
Qiu
Diamond Proposal Number(s):
[30401]
Abstract: Glassy metal coordination compounds (MCC) [e.g., metal-organic framework (MOF), coordination polymer, and metal inorganic-organic complex (MIOC)] are emerging members of the hybrid glass family. So far, a limited number of crystalline MCCs can be converted into glasses by the melt-quenching. Here, we report a universal wet-chemistry method, by which the super-sized supramolecular MIOC glasses can be synthesized from non-meltable MOFs. Alcohol and acid were used as agents to inhibit crystallization. The MIOC glasses demonstrate unique features including high transparency, shaping capability, and anisotropic network. Directional photoluminescence with a large polarization ratio (~47%) was observed from samples doped with organic dyes. This crystallization-suppressing approach enables fabrication of MCC glasses, which cannot be achieved by conventional vitrification methods, and thus allows for exploring new MCC glasses possessing photonic functionalities.
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Feb 2023
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