I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[28223]
Open Access
Abstract: The metal-organic framework MOF-808 contains Zr6O8 nodes with a high density of vacancy sites, which can incorporate carboxylate-containing functional groups to tune chemical reactivity. Although the postsynthetic methods to modify the chemistry of the Zr6O8 nodes in MOFs are well known, tackling these alterations from a structural perspective is still a challenge. We have combined infrared spectroscopy experiments and first-principles calculations to identify the presence of node vacancies accessible for chemical modifications within the MOF-808. We demonstrate the potential of our approach to assess the decoration of MOF-808 nodes with different catechol–benzoate ligands. Furthermore, we have applied advanced synchrotron characterization tools, such as pair distribution function analyses and X-ray absorption spectroscopy, to resolve the atomic structure of single metal sites incorporated into the catechol groups postsynthetically. Finally, we demonstrate the catalytic activity of these MOF-808 materials decorated with single copper sites for 1,3-dipolar cycloadditions.
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May 2022
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[20038]
Open Access
Abstract: The rational design of disordered frameworks is an appealing route to target functional materials. However, intentional realisation of such materials relies on our ability to readily characterise and quantify structural disorder. Here, we use multivariate analysis of pair distribution functions to fingerprint and quantify the disorder within a series of compositionally identical metal–organic frameworks, possessing different crystalline, disordered, and amorphous structures. We find this approach can provide powerful insight into the kinetics and mechanism of structural collapse that links these materials. Our methodology is also extended to a very different system, namely the melting of a zeolitic imidazolate framework, to demonstrate the potential generality of this approach across many areas of disordered structural chemistry.
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Apr 2022
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[8858, 9902]
Abstract: We studied in situ the local atomic structure evolution of an equiatomic
Zr
50
Cu
50
metallic glassy alloy under high pressure compression inside a diamond anvil cell using synchrotron x-ray total scattering. The empirical potential structure refinement method was used to reconstruct the three-dimensional atomic models at each pressure step, and to analyze the spatially averaged local atomic structure configurations. The interatomic distances of different atomic pairs are reduced at different rates with increasing pressure and the Cu-Cu pairs exhibit the highest percentage reduction. Between ambient pressure and 36.85 GPa, the atomic separation of the Cu-Cu pairs is reduced by ∼12% compared to ∼5% for Zr-Zr and Zr-Cu pairs. Such disproportional decrease in interatomic distance results in inhomogeneous atom reconfiguration in the short atomic range. With the increase of pressure, the Zr atoms move preferentially towards the Zr-Zr pairs, while the Cu atoms move preferentially towards the Cu-Cu pairs, creating inhomogeneous atom reconfiguration with positive short-range order coefficients of 0.0309 and 0.0464 for Zr-Zr and Cu-Cu respectively, but a negative value of −0.0464 for Zr-Cu pairs. Voronoi tessellation method was also used to study the evolution of the short-range atom packing versus pressure, elucidating the cause for the bimodal distribution of the bond angle distributions. The research sheds light on understanding of the atomic reconfiguration of equiatomic alloys under high pressure.
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Feb 2022
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I15-1-X-ray Pair Distribution Function (XPDF)
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Alice M.
Bumstead
,
Ignas
Pakamore
,
Kieran D.
Richards
,
Michael F.
Thorne
,
Sophia S.
Boyadjieva
,
Celia
Castillo-Blas
,
Lauren N.
Mchugh
,
Adam F.
Sapnik
,
Dean S.
Keeble
,
David A.
Keen
,
Rachel C.
Evans
,
Ross S.
Forgan
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038]
Abstract: Melt-quenched metal–organic framework (MOF) glasses have gained significant interest as the first new category of glass reported in 50 years. In this work, an amine-functionalized zeolitic imidazolate framework (ZIF), denoted ZIF-UC-6, was prepared and demonstrated to undergo both melting and glass formation. The presence of an amine group resulted in a lower melting temperature compared to other ZIFs, while also allowing material properties to be tuned by post-synthetic modification (PSM). As a prototypical example, the ZIF glass surface was functionalized with octyl isocyanate, changing its behavior from hydrophilic to hydrophobic. PSM therefore provides a promising strategy for tuning the surface properties of MOF glasses.
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Feb 2022
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[24348]
Abstract: Bi2MExlV1−xO5.5−(5−l)x/2−δ (BIMEVOX, ME = dopant, l = valency) systems are a family of fast oxide ion conductors that show very high ionic conductivity at low and intermediate temperatures. Despite being studied for almost 30 years, the extent of the disorder in these systems has meant that many questions about the detail of the local structure remain unanswered. In this work, reverse Monte Carlo analysis of a combination of synchrotron X-ray and neutron diffraction data has been used to examine the defect structure in the tetravalent-substituent system, Bi2V1−xGexO5.5−x/2−δ. Although the ordered α-phase is seen at room temperature over an extensive compositional range, the incommensurately ordered γ′-phase can be quenched to room temperature at x = 0.35, which on heating above 500 °C, undergoes a transition to the fully disordered tetragonal γ-phase. Germanium is suggested to mainly adopt a tetrahedral coordination environment in both these phases, while vanadium shows different local geometries including tetrahedral, pentacoordinate and octahedral, the relative proportions of which change with temperature. Oxygen vacancies are found to be mainly distributed in equatorial sites around Ge and V, with a higher concentration of apical vacancies in the γ′-phase. A non-random deficiency in next-nearest-neighbour vacancy pairs in the 〈100〉 tetragonal direction is identified, consistent with the known superlattice ordering seen in lower x-value compositions, suggesting short range ordering of oxide ions/vacancies. Such ordering is known to contribute to a lowering of oxide ion conductivity and may well be a factor in lowering the conductivity of the γ-phase BIMEVOXes. These data are supported by 51V solid state NMR results as well as Raman spectroscopic data, with electrical characterization by A.C. impedance spectroscopy.
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Jan 2022
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[20038]
Open Access
Abstract: Four novel dicyanamide-containing hybrid organic-inorganic ABX3 structures are reported, and the thermal behaviour of a series of nine perovskite and non-perovskite [AB(N(CN)2)3] (A = (C3H7)4N, (C4H9)4N, (C5H11)4N; B = Co, Fe, Mn). Structure-property relationships are investigated by varying both A-site organic and B-site transition metal cations. In particular, increasing the size of the A-site cation from (C3H7)4N → (C4H9)4N → (C5H11)4N was observed to result in a decrease in Tm through an increase in ΔSf. Consistent trends in Tm with metal replacement are observed with each A-site cation, with Co < Fe < Mn. The majority of the melts formed were found to recrystallise partially upon cooling, though glasses could be formed through a small degree of organic linker decomposition. Total scattering methods are used to provide a greater understanding of the melting mechanism
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Jan 2022
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[23666, 23167]
Open Access
Abstract: Li-rich rocksalt oxides are promising candidates as high-energy density cathode materials for next-generation Li-ion batteries because they present extremely diverse structures and compositions. Most reported materials in this family contain as many cations as anions, a characteristic of the ideal cubic closed-packed rocksalt composition. In this work, a new rocksalt-derived structure type is stabilized by selecting divalent Cu and pentavalent Sb cations to favor the formation of oxygen vacancies during synthesis. The structure and composition of the oxygen-deficient Li4CuSbO5.5□0.5 phase is characterized by combining X-ray and neutron diffraction, ICP-OES, XAS, and magnetometry measurements. The ordering of cations and oxygen vacancies is discussed in comparison with the related Li2CuO2□1 and Li5SbO5□1 phases. The electrochemical properties of this material are presented, with only 0.55 Li+ extracted upon oxidation, corresponding to a limited utilization of cationic and/or anionic redox, whereas more than 2 Li+ ions can be reversibly inserted upon reduction to 1 V vs Li+/Li, a large capacity attributed to a conversion reaction and the reduction of Cu2+ to Cu0. Control of the formation of oxygen vacancies in Li-rich rocksalt oxides by selecting appropriate cations and synthesis conditions affords a new route for tuning the electrochemical properties of cathode materials for Li-ion batteries. Furthermore, the development of material models of the required level of detail to predict phase diagrams and electrochemical properties, including oxygen release in Li-rich rocksalt oxides, still relies on the accurate prediction of crystal structures. Experimental identification of new accessible structure types stabilized by oxygen vacancies represents a valuable step forward in the development of predictive models.
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Dec 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[18630]
Open Access
Abstract: The structures of Zr and Hf metal–organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.
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Nov 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[27222]
Abstract: The Protic Ionic Liquid (PIL) formed by neutralization of the super-strong base 1,7-diazabicyclo[5.4.0]undec-7-ene (DBU) with the super-strong acid bis(trifluoromethanesulfonyl)-imide (TFSI), indicated as [DBUH][TFSI], has been investigated. Its chemical physical properties and structural features have been explored using a synergy of experimental and computational tools. Molecular Dynamics-rationalised X-ray diffraction patterns highlight the major role played by hydrogen bonding (HB) in affecting morphology in this PIL. A comparison between HB features in this and in related PILs has been presented, on the base of far-IR experiments and DFT analysis. Indications of a weaker HB interaction in [DBUH][TFSI] in comparison with [DBUH][TfO], consistently with their ΔpKa difference, have been observed and rationalised in terms of geometrical properties of the main conformers contributing to the experimental spectra. In the liquid phase of [DBUH][TFSI] a particularly large conformational disorder is observed and the corresponding large dispersion of the frequencies of the HB stretching modes leads to a broad absorption band without a well defined peak. On the contrary, well detectable HB related absorptions are observable in the solid phase of [DBUH][TFSI] and at all temperatures in [DBU][TfO], where less configurational disorder occurs.
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Oct 2021
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[9902, 8858]
Abstract: The tensile fractured surfaces of ZrTi-based bulk metallic glass and composite samples were studied using synchrotron X-ray total scattering. The scanned areas contain different shear bands densities. The shear bands create localized atomic strains, which in turn cause more ordered atomic structures. Such structural changes were reflected in the scattering structure factor, i.e. the higher the density of the shear bands, the higher the scattering structure factor. Similar phenomenon was also found in the metallic glass composite.
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Aug 2021
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