I20-Scanning-X-ray spectroscopy (XAS/XES)
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Yuvraj
Vaishnav
,
Mohamad
Abou-Daher
,
Cristina I. Q.
Silva
,
Rohit K.
Rai
,
Walid
Al Maksoud
,
Marcell
Toth
,
Mohandoss
Viswanathan
,
Peng
Ren
,
Fumitaka
Takeiri
,
Shusaku
Hayama
,
Samy
Ould-Chikh
,
Mohamed Nejib
Hedhili
,
Maxim
Avdeev
,
Wen
Yin
,
Saburo
Hosokawa
,
Genki
Kobayashi
,
Isaac
Abrahams
,
Aamir
Farooq
,
Javier
Ruiz-Martinez
,
Yoji
Kobayashi
Diamond Proposal Number(s):
[31497]
Open Access
Abstract: High-entropy oxides are attracting attention for catalysis, but there are relatively few detailed studies on their precise structure, hampering true detailed studies on fundamental properties affecting their activities. In addition, diffusion has been often characterized as generally slow in high-entropy systems. Here, we determine the precise oxygen content and structure of the fluorite-like high-entropy oxide (La, Ce, Pr, Nd, Y)O1.68 and have identified a large oxygen storage capacity based on efficient Ce/Pr redox due to facile oxide diffusion pathways and suppression of sintering. The structure and composition were identified through a combined Rietveld refinement of X-ray and neutron diffraction data, and the oxidation state of Ce and Pr was investigated by high energy resolution fluorescence detected–X-ray absorption near edge spectra (HERFD–XANES). (La, Ce, Pr, Nd, Y)O1.68 utilizes the full redox range of Ce/Pr, resulting in a high oxygen storage cumulative capacity despite the lower content of Ce/Pr compared to other well-known ceria derivatives. Diffusion pathway analysis by bond valence site energy mapping shows decreased barriers for oxide anion diffusion through the bulk, also benefiting redox reactions. The high-entropy nature also suppresses sintering, resulting in better cycling performance. This results in a higher performance as a methane oxidation catalyst support. We also investigate its use as a NOx reduction catalyst support.
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Mar 2026
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I15-1-X-ray Pair Distribution Function (XPDF)
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B. A.
Kyffin
,
R.
Di Pasquale
,
D. M.
Pickup
,
F.
Foroutan
,
I.
Abrahams
,
N.
Kanwal
,
D. S.
Keeble
,
M.
Felipe-Sotelo
,
A.
Hoxha
,
Z.
Moghaddam
,
S. J.
Hinder
,
M. A.
Baker
,
E. T.
Nery
,
D.
Carta
Diamond Proposal Number(s):
[18923]
Open Access
Abstract: Phosphate-based glasses (PBGs) are bioresorbable materials that find application in the field of controlled drug delivery and tissue engineering. The structural arrangements of the phosphate units in PBGs, along with the knowledge of how therapeutic metallic ions are embedded in the phosphate network are important in understanding the degradation and targeted release properties of these materials. Using a combination of Raman spectroscopy, high-energy X-ray diffraction and 31P and 23Na solid-state magic angle spinning nuclear magnetic resonance, the atomic structure of coacervate PBGs in the system P2O5-CaO-Na2O-MOx (M = Cu or Zn) with loadings of 2, 10 and 15 mol % of M2+ have been studied as functions of composition and calcination temperature. After drying at room temperature, the structures of the phosphate network in PBG-Cu and PBG-Zn are quite similar, with that of PBG-Zn exhibiting slightly higher connectivity. Heating at 300°C causes degradation of the polyphosphate chains, even though Q2 species remain predominant. X-ray photoelectron spectroscopy demonstrates that Cu in calcined PBGs is present in both oxidation states +1 and +2, with a predominance of the +2 state. Cu and Zn ions release data after 24 h exposure of PBGs in deionized water and cell medium DMEM show that release is proportional to their loadings. Cytotoxicity MTT assays of dissolution products of PBG-Cu/ZnX calcined at 300 °C on human osteoblast cells (MG63) and on human skin cells (HaCaTs) showed good cellular response for all compositions, indicating that PBGs have great potential for both hard and soft tissue regeneration.
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Sep 2024
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[21476, 27911]
Open Access
Abstract: Hierarchical porous phosphate-based glasses (PPG) have great potential in biomedicine. Micropores (pore size < 2 nm) increase the surface area, mesopores (pore size 2 to 50 nm) facilitate the absorption and diffusion of therapeutic ions and molecules making them ideal controlled delivery systems, while macropores (pore size > 50 nm) facilitate the movement and diffusion of cells and fluids. In addition, the bioresorbability of PPG allows for their complete solubility in body fluid, alongside simultaneous formation of new tissue. Making PPG via the traditional melt-quenching (MQ) synthesis method used for phosphate-based glasses (PG), is not straightforward. Hence, we present here a route for preparing such glasses using a combination of sol-gel (SG) and templating methods. Hierarchical porous PPG in the P2O5-CaO-Na2O system with the addition of 1, 3 and 5 mol % of Zn2+ were prepared with pore dimensions ranging from the micro- to the macro scales using Pluronic 123 (P123) as a surfactant. The presence of micropores (0.30-0.46 nm), mesopores (1.75 to 9.35 nm) and macropores (163-207 nm) was assessed via synchrotron-based Small-Angle X-ray Scattering (SAXS), with the presence of the latter two confirmed by Scanning Electron Microscopy (SEM). Structural characterisation performed using 31P solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier Transform Infra-red (FT-IR) spectroscopies shows the presence of Q2, Q1 and Q0 phosphate species with a predominance of Q1 species in all compositions. Dissolution studies in deionised (DI) water confirm that controlled release of phosphates, Ca2+, Na+ and Zn2+ is achieved over a period of 7 days. In particular, the release of Zn2+ is proportional to its loading, making its delivery particularly easy to control.
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Jul 2024
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I15-1-X-ray Pair Distribution Function (XPDF)
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Haolai
Tian
,
Guanqun
Cai
,
Lei
Tan
,
He
Lin
,
Anthony E.
Phillips
,
Isaac
Abrahams
,
David A.
Keen
,
Dean S.
Keeble
,
Andy
Fiedler
,
Junrong
Zhang
,
Xiang Yang
Kong
,
Martin T.
Dove
Diamond Proposal Number(s):
[19378]
Open Access
Abstract: The lithium-ion conducting solid electrolyte Li7La3Zr2O12 has one crystalline phase that has the cubic garnet structure, and this phase has one of the highest room temperature lithium-ion conductivities of any oxide. Neutron and X-ray total scattering data, analysed by the Reverse Monte Carlo method, have been used to examine the distribution of lithium ions over a wide range of temperatures, and to explore aspects of the stability and flexibility of the basic oxide structure. We compare the results with those from supporting molecular dynamics simulations. Unlike previous work, our method requires no prior assumptions about the Li ion distribution. Using total scattering rather than solely Bragg scattering, we obtain much higher real-space resolution than previously available. The combination of X-ray and neutron scattering allows detailed characterisation of both the mobile and immobile sublattices. Only a small fraction of Li ions are mobile at any one time; diffusion occurs primarily by movement between Li2 sites via empty Li1 sites.
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Oct 2023
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Open Access
Abstract: Mesoporous glasses are a promising class of bioresorbable biomaterials characterized by high surface area and extended porosity in the range of 2 to 50 nm. These peculiar properties make them ideal materials for the controlled release of therapeutic ions and molecules. Whilst mesoporous silicate-based glasses (MSG) have been widely investigated, much less work has been done on mesoporous phosphate-based glasses (MPG). In the present study, MPG in the P2O5–CaO–Na2O system, undoped and doped with 1, 3, and 5 mol% of Cu ions were synthesized via a combination of the sol–gel method and supramolecular templating. The non-ionic triblock copolymer Pluronic P123 was used as a templating agent. The porous structure was studied via a combination of Scanning Electron Microscopy (SEM), Small-Angle X-ray Scattering (SAXS), and N2 adsorption–desorption analysis at 77 K. The structure of the phosphate network was investigated via solid state 31P Magic Angle Spinning Nuclear Magnetic Resonance (31P MAS-NMR) and Fourier Transform Infrared (FTIR) spectroscopy. Degradation studies, performed in water via Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), showed that phosphates, Ca2+, Na+ and Cu ions are released in a controlled manner over a 7 days period. The controlled release of Cu, proportional to the copper loading, imbues antibacterial properties to MPG. A significant statistical reduction of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacterial viability was observed over a 3 days period. E. coli appeared to be more resistant than S. aureus to the antibacterial effect of copper. This study shows that copper doped MPG have great potential as bioresorbable materials for controlled delivery of antibacterial ions.
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Jun 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Yajun
Yue
,
Aleksandra
Dzięgielewska
,
Man
Zhang
,
Stephen
Hull
,
Franciszek
Krok
,
Richard M.
Whiteley
,
Harold
Toms
,
Marcin
Malys
,
Xuankai
Huang
,
Marcin
Krynski
,
Ping
Miao
,
Haixue
Yan
,
Isaac
Abrahams
Diamond Proposal Number(s):
[24348]
Open Access
Abstract: The BIMEVOXes are among the best oxide ion conductors at low and intermediate temperatures. Their high conductivity is associated with local defect structure. In this work, the local structures of two BIMEVOX compositions, Bi2V0.9Ge0.1O5.45 and Bi2V0.95Sn0.05O5.475, are examined using total neutron and X-ray scattering methods, with both compositions exhibiting the ordered α-phase at 25 °C and the disordered γ-phase at 700 °C. While the diffraction data for the α-phase do not allow for the polar (C2) and nonpolar (C2/m) structures to be readily distinguished, measurements of dielectric permittivity suggest the α-phase is weakly ferroelectric in character, consistent with calculations of spontaneous polarization based on a combination of density functional calculations and machine learning methodology. Reverse Monte Carlo (RMC) analysis of total scattering data reveals Ge preferentially adopts tetrahedral geometry at both temperatures, while Sn is found to predominantly adopt octahedral coordination in the α-phase and tetrahedral coordination in the γ-phase. In all cases, V polyhedra are found to consist of tetrahedral, pentacoordinate, and octahedral geometries, as also predicted by the crystallographic analysis and confirmed by 51V solid state NMR spectroscopy. Although similar long-range structures are observed at room temperature, the oxide ion vacancy distributions were found to be quite different between the two studied compositions, with a nonrandom deficiency in vacancy pairs in the second-nearest shell along the ⟨100⟩ tetragonal direction for BIGEVOX10, compared with a long-distance (>8.0 Å) ordering of equatorial vacancies for BISNVOX05. This is attributed to the differences in the preferred coordination geometries of the substituent cations in the two systems. Impedance spectroscopy measurements reveal both compositions show high conductivity in the order of 10–1 S cm–1 at 600 °C.
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Dec 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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B18-Core EXAFS
I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[18595, 18923, 21525]
Open Access
Abstract: Phosphate-based glasses (PBGs) are traditionally prepared using the high-temperature melt-quenching (MQ) route or via the more recent sol–gel (SG) method that requires the use of organic solvents. The coacervation method represents an excellent inexpensive and green alternative to MQ and SG, being performed in aqueous solution and at room temperature. Coacervation is particularly applicable for the production of PBGs designed for biomedical applications because it allows for the inclusion of temperature-sensitive molecules and does not require the use of toxic solvents. Whereas the atomic structure of the MQ and SGPBGs is known, the atomic structure of those prepared via coacervation has yet to be investigated. In this study, a comprehensive advanced structural characterization has been performed on phosphate-based glasses in the system P2O5–CaO–Na2O–Ag2O (Ag2O mol % = 0, 1, 3, 5, 9, and 14) prepared via the coacervation method. Glasses within this system should find application as bioresorbable biomaterials thanks to their ability to release bioactive ions in a controlled manner. In particular, they possess antibacterial properties, inferred by the release of Ag+ over time. High-energy X-ray diffraction (HEXRD), 31P and 23Na solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), and X-ray absorption Spectroscopy (XAS) at the Ag K-edge were used to probe the atomic structure of the glasses after drying in vacuum and after calcination at 300 °C. The length of the polyphosphate chains in the solid state appears to be independent of silver concentration; however, significant degradation of these chains is seen after calcination at 300 °C. Atomic-scale characterisation results indicate that the structure of these glasses is akin to that of other silver-doped phosphate glasses prepared using the MQ and SG methods. This suggests that phosphate-based glasses prepared using milder and greener conditions may have similar chemical and physical properties such as solubility, biocompatibility, and antibacterial properties.
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May 2021
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