B18-Core EXAFS
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Andrew M.
Beale
,
Miren
Agote-Aran
,
Rachel E.
Fletcher
,
Martha
Briceno
,
Anna B.
Kroner
,
Igor V.
Sazanov
,
Ben
Slater
,
María E.
Rivas
,
Andrew W. J.
Smith
,
Paul
Collier
,
Ines
Lezcano-Gonzalez
Diamond Proposal Number(s):
[11623]
Abstract: The structure and activity of Mo/Silicalite‐1 (MFI, Si/Al = ∞) were compared to Mo/H‐ZSM‐5 (MFI, Si/Al = 15), a widely studied catalyst for methane dehydroaromatisation (MDA). The anchoring mode of Mo was evaluated by in situ X‐ray absorption spectroscopy (XAS) and density functional theory (DFT). The results showed that in Mo/Silicalite‐1, calcination leads to dispersion of MoO3 precursor into tetrahedral Mo‐oxo species in close proximity to the microporous framework. A weaker interaction of the Mo‐oxo species with the Silicalite‐1 was determined by XAS and DFT. While both catalysts are active for MDA, Mo/Silicalite‐1 undergoes rapid deactivation which was attributed to a faster sintering of Mo species leading to the accumulation of carbon deposits on the zeolite outer surface. The results shed light onto the nature of the Mo structure(s) while evidencing the importance of framework Al in stabilising active Mo species under MDA conditions.
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Sep 2019
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[17193]
Open Access
Abstract: By tuning the A site cation size it is possible to control the degree of octahedral distortion and ultimately structural symmetry in the new perovskite solid solution La0.5Na0.5−xKxTiO3, affording a rhombohedral-to-cubic transition as x increases above 0.4. The La3+ and K+ cations are distributed randomly across the A site leading to significant phonon disorder in cubic La0.5K0.5TiO3 (Pm[3 with combining macron]m) which produces a phonon-glass with a thermal conductivity of 2.37(12) W m−1 K−1 at 300 K; a reduction of 75% when compared with isostructural SrTiO3. This simple cation substitution of Sr2+ for La3+ and K+ maintains the flexible structural chemistry of the perovskite structure and two mechanisms of doping for the introduction of electronic charge carriers are explored; A site doping in La1−yKyTiO3 or B site doping in La0.5K0.5Ti1−zNbzO3. The phonon-glass thermal conductivity of La0.5K0.5TiO3 is retained upon doping through both of these mechanisms highlighting how the usually strongly coupled thermal and electronic transport can be minimised by mass disorder in perovskites. Precise control over octahedral distortion in A site doped La1−yKyTiO3, which has rhombohedral (R[3 with combining macron]c) symmetry affords lower band dispersions and increased carrier effective masses over those achieved in B site doped La0.5K0.5Ti1−zNbzO3 which maintains the cubic (Pm[3 with combining macron]m) symmetry of the undoped La0.5K0.5TiO3 parent. The higher Seebeck coefficients of A site doped La1−yKyTiO3 yield larger power factors and lead to increased thermoelectric figures of merit and improved conversion efficiencies compared with the mechanism for B site doping.
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Jul 2018
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[17375, 13284]
Abstract: We report the nonaqueous synthesis of Cd(CN)2 by oxidation of cadmium metal with Hg(CN)2 in liquid ammonia. The reaction proceeds via an intermediate of composition Cd(NH3)2[Cd(CN)4], which converts to Cd(CN)2 on prolonged heating. Powder X-ray diffraction measurements allow us to determine the crystal structure of the previously-unreported Cd(NH3)2[Cd(CN)4], which we find to adopt a twofold interpenetrating PtS topology. We discuss the effect of partial oxidation on the Cd/Hg composition of this intermediate, as well as its implications for the reconstructive nature of the deammination process. Variable-temperature X-ray diffraction measurements allow us to characterise the anisotropic negative thermal expansion (NTE) behaviour of Cd(NH3)2[Cd(CN)4] together with the effect of Cd/Hg substitution; ab initio density functional theory (DFT) calculations reveal a similarly anomalous mechanical response in the form of both negative linear compressibility (NLC) and negative Poisson's ratios.
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May 2018
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[16778]
Abstract: Efficient chiral separation remains a very challenging task due to the identical physical and chemical properties of the enantiomers of a molecule. Enantiomers only behave differently from each other in the presence of other chiral species. Homochiral metal organ-ic frameworks have received much attention for their promising enantioseparation properties. However, there are still challenges to overcome in this field such as high enantiomeric separation. Structural defects play an important role in the properties of MOFs and can significantly change the pore architecture. In this work, we introduced missing linker defects into a homochiral metal or-ganic framework [Zn2(bdc)(L-lac)(dmf)] (ZnBLD) and observed an increase in enantiomeric excess for 1-phenylethanol of 35% with the defective frameworks. We adjusted the concentration of monocarboxylic acid ligand L-lactic acid by varying the ratio of Zn2+ to ligand from 0.5 to 0.85mmol. Additionally, a defective framework was synthesized with propanoic acid as modulator. In order to elucidate the correlation between defects and enantiomeric excess, four characterization techniques (FTIR, TGA, 1H NMR and PXRD) were employed. Full width at half maximum analysis (FWHM) was performed on the powder x-ray diffraction traces and showed that the higher concentration of monocarboxylic acid MOFs were isostructural but suffered from increased FWHM values.
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Nov 2017
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[12336, 17193]
Abstract: Phonon-glass electron-crystal (PGEC) behaviour is realised in La0.5Na0.5Ti1–xNbxO3 thermoelectric oxides. The vibrational disorder imposed by the presence of both La3+ and Na+ cations on the A site of the ABO3 perovskite oxide La0.5Na0.5TiO3 produces a phonon-glass with a thermal conductivity, κ, 80% lower than that of SrTiO3 at room temperature. Unlike other state-of-the-art thermoelectric oxides, where there is strong coupling of κ to the electronic power factor, the electronic transport of these materials can be optimised independently of the thermal transport through cation substitution at the octahedral B site. The low κ of the phonon-glass parent is retained across the La0.5Na0.5Ti1–xNbxO3 series without disrupting the electronic conductivity, affording PGEC behaviour in oxides.
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Aug 2017
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I11-High Resolution Powder Diffraction
I19-Small Molecule Single Crystal Diffraction
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Angeles
Pulido
,
Linjiang
Chen
,
Tomasz
Kaczorowski
,
Daniel
Holden
,
Marc A.
Little
,
Samantha Y.
Chong
,
Benjamin J.
Slater
,
David P.
Mcmahon
,
Baltasar
Bonillo
,
Chloe J.
Stackhouse
,
Andrew
Stephenson
,
Christopher M.
Kane
,
Rob
Clowes
,
Tom
Hasell
,
Andrew I.
Cooper
,
Graeme M.
Day
Diamond Proposal Number(s):
[8728, 12336]
Abstract: Molecular crystals cannot be designed in the same manner as macroscopic objects, because they do not assemble according to simple, intuitive rules. Their structures result from the balance of many weak interactions, rather than from the strong and predictable bonding patterns found in metal–organic frameworks and covalent organic frameworks. Hence, design strategies that assume a topology or other structural blueprint will often fail. Here we combine computational crystal structure prediction and property prediction to build energy–structure–function maps that describe the possible structures and properties that are available to a candidate molecule. Using these maps, we identify a highly porous solid, which has the lowest density reported for a molecular crystal so far. Both the structure of the crystal and its physical properties, such as methane storage capacity and guest-molecule selectivity, are predicted using the molecular structure as the only input. More generally, energy–structure–function maps could be used to guide the experimental discovery of materials with any target function that can be calculated from predicted crystal structures, such as electronic structure or mechanical properties.
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Mar 2017
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I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
I15-Extreme Conditions
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Matthew J.
Cliffe
,
Elizabeth
Castillo-Martinez
,
Yue
Wu
,
Jeongjae
Lee
,
Alexander C.
Forse
,
Francesca C. N.
Firth
,
Peyman Z.
Moghadam
,
David
Fairen-Jimenez
,
Michael W.
Gaultois
,
Joshua A.
Hill
,
Oxana V.
Magdysyuk
,
Ben
Slater
,
Andrew L.
Goodwin
,
Clare P.
Grey
Diamond Proposal Number(s):
[9940, 15118, 12554, 13681, 13843]
Open Access
Abstract: We report a hafnium containing MOF, hcp UiO-67(Hf), which is a defective layered analogue of the face-centered cubic fcu UiO-67(Hf). hcp UiO-67 accommodates its low- ered ligand:metal ratio compared to fcu UiO-67 through a new structural mechanism: the formation of a condensed ‘double cluster’, analogous to the condensation of coor- dination polyhedra in oxide frameworks. In oxide frameworks variable stoichiometry can lead to more complex defect structures, e.g. crystallographic shear planes or mod- ules with differing compositions, which can be the source of further chemical reactivity; likewise the layered hcp UiO-67 can react further to form two-dimensional nanosheets. Delamination of hcp UiO-67 occurs through the cleavage of strong hafnium-carboxylate bonds and is effected under mild conditions suggesting that defect ordered MOFs could be a productive route to porous two-dimensional materials.
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Mar 2017
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I11-High Resolution Powder Diffraction
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Hongjun J.
Niu
,
Michael J.
Pitcher
,
Alex J.
Corkett
,
Sanliang
Ling
,
Pranab
Mandal
,
Marco
Zanella
,
Karl
Dawson
,
Plamen
Stamenov
,
Dmitry
Batuk
,
Artem M.
Abakumov
,
Craig L.
Bull
,
Ronald I
Smith
,
Claire A.
Murray
,
Sarah J.
Day
,
Ben
Slater
,
Furio
Cora
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[12336]
Abstract: The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long range magnetic ordering of high spin d5 cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray and electron diffraction methods. In-situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A3+/Fe3+ cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations that indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetisation are coupled in this system, with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.
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Dec 2016
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[6192, 7722]
Abstract: The influence of simple framework inorganic anions on the thermoresponsive behavior of the isostructural MIL-53 type metal–organic frameworks [AlF(bdc)] and [Al(OH)(bdc)] has been determined using a combination of diffraction and computational techniques. [AlF(bdc)] has an orthorhombic large pore structure from 500 to ∼175 K at which point it undergoes a subtle distortion to form a monoclinic large pore structure that remains stable to 11 K. The orthorhombic large pore form of [AlF(bdc)] exhibits negative thermal expansion from 175–500 K. [Al(OH)(bdc)] has an orthorhombic large pore structure from 500 to 125 K at which point it undergoes a displacive phase transition, a breathing effect, to form a nonporous monoclinic structure. The orthorhombic large pore form of [Al(OH)(bdc)] exhibits positive thermal expansion from 150 to 500 K. The presence of a breathing effect in [Al(OH)(bdc)], and not [AlF(bdc)], is related to the additional contributions to attractive interactions across the shortest dimension of the pore provided by the presence of the hydroxide groups. The display of positive or negative thermal expansion of the orthorhombic large pore structure of either material is related to the rigidity of the constituent corner-sharing chain of AlO4X2 octahedra with the more rigid AlO4F2 octahedra favoring one type of static or dynamic displacement and the less rigid AlO4(OH)2 octahedra favoring a different type of static displacement. Formation of metal–organic frameworks with controlled expansion and displacive phase transition properties, or simultaneously containing mixed thermoresponsive properties, is predicted through control of the identity and amount of the simple inorganic anions in this family of material. The work indicates the importance of considering the simplest species when designing the thermo-mechanical properties of metal–organic frameworks.
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Dec 2014
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I11-High Resolution Powder Diffraction
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Man-rong
Li
,
Umut
Adem
,
Sean R. C.
Mcmitchell
,
Zhongling
Xu
,
Chris I.
Thomas
,
John
Warren
,
Duong V.
Giap
,
Hongjun
Niu
,
Xinming
Wan
,
Robert G.
Palgrave
,
Florian
Schiffmann
,
Furio
Cora
,
Ben
Slater
,
Tim L.
Burnett
,
Markys G.
Cain
,
Artem M.
Abakumov
,
Gustaaf
Van Tendeloo
,
Michael F.
Thomas
,
Matthew J.
Rosseinsky
,
John B.
Claridge
Open Access
Abstract: Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K—this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3.
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Feb 2012
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