I11-High Resolution Powder Diffraction
|
Henrik
Jacobsen
,
Hai L.
Feng
,
Andrew J.
Princep
,
Marein C.
Rahn
,
Yanfeng
Guo
,
Jie
Chen
,
Yoshitaka
Matsushita
,
Yoshihiro
Tsujimoto
,
Masahiro
Nagao
,
Dmitry
Khalyavin
,
Pascal
Manuel
,
Claire A.
Murray
,
Christian
Donnerer
,
James G.
Vale
,
Marco
Moretti Sala
,
Kazunari
Yamaura
,
Andrew T.
Boothroyd
Diamond Proposal Number(s):
[9839]
Abstract: We report on the structural, magnetic, and electronic properties of two new double-perovskites synthesized under high pressure,
Pb
2
CaOsO
6
and
Pb
2
ZnOsO
6
. Upon cooling below 80 K,
Pb
2
CaOsO
6
simultaneously undergoes a metal-to-insulator transition and develops antiferromagnetic order.
Pb
2
ZnOsO
6
, on the other hand, remains a paramagnetic metal down to 2 K. The key difference between the two compounds lies in their crystal structures. The Os atoms in
Pb
2
ZnOsO
6
are arranged on an approximately face-centered cubic lattice with strong antiferromagnetic nearest-neighbor exchange couplings. The geometrical frustration inherent to this lattice prevents magnetic order from forming down to the lowest temperatures. In contrast, the unit cell of
Pb
2
CaOsO
6
is heavily distorted up to at least 500 K including antiferroelectriclike displacements of the Pb and O atoms despite metallic conductivity above 80 K. This distortion relieves the magnetic frustration, facilitating magnetic order which, in turn, drives the metal-insulator transition. Our results suggest that the phase transition in
Pb
2
CaOsO
6
is spin driven and could be a rare example of a Slater transition.
|
Dec 2020
|
|
I16-Materials and Magnetism
|
C. D.
Dashwood
,
L. S. I.
Veiga
,
Q.
Faure
,
J. G.
Vale
,
D. G.
Porter
,
S. P.
Collins
,
P.
Manuel
,
D. D.
Khalyavin
,
F.
Orlandi
,
R. S.
Perry
,
R. D.
Johnson
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[23580]
Abstract: We show how complex modulated order can spontaneously emerge when magnetic interactions compete in a metal with polar lattice distortions. Combining neutron and resonant x-ray scattering with symmetry analysis, we reveal that the spin reorientation in
Ca
3
Ru
2
O
7
is mediated by a magnetic cycloid whose eccentricity evolves smoothly but rapidly with temperature. We find the cycloid to be highly sensitive to magnetic fields, which appear to continuously generate higher harmonic modulations. Our results provide a unified picture of the rich magnetic phases of this correlated, multiband polar metal.
|
Nov 2020
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[13284, 18786]
Abstract: Sr2CrO2Cr2As2 and Ba2CrO2Cr2As2 with Cr2+ ions in CrO2 sheets and in CrAs layers crystallize with the Sr2Mn3Sb2O2 structure (space group I4/mmm, Z = 2) and lattice parameters a = 4.00800(2) Å, c = 18.8214(1) Å (Sr2CrO2Cr2As2) and a = 4.05506(2) Å, c = 20.5637(1) Å (Ba2CrO2Cr2As2) at room temperature. Powder neutron diffraction reveals checkerboard-type antiferromagnetic ordering of the Cr2+ ions in the arsenide layers below TN1_Sr, of 600(10) K (Sr2CrO2Cr2As2) and TN1_Ba 465(5) K (Ba2CrO2Cr2As2) with the moments initially directed perpendicular to the layers in both compounds. Checkerboard-type antiferromagnetic ordering of the Cr2+ ions in the oxide layer below 230(5) K for Ba2CrO2Cr2As2 occurs with these moments also perpendicular to the layers, consistent with the orientation preferences of d4 moments in the two layers. In contrast, below 330(5) K in Sr2CrO2Cr2As2, the oxide layer Cr2+ moments are initially oriented in the CrO2 plane; but on further cooling, these moments rotate to become perpendicular to the CrO2 planes, while the moments in the arsenide layers rotate by 90° with the moments on the two sublattices remaining orthogonal throughout [behavior recently reported independently by Liu et al. [Liu et al. Phys. Rev. B 2018, 98, 134416]]. In Sr2CrO2Cr2As2, electron diffraction and high resolution powder X-ray diffraction data show no evidence for a structural distortion that would allow the two Cr2+ sublattices to couple, but high resolution neutron powder diffraction data suggest a small incommensurability between the magnetic structure and the crystal structure, which may account for the coupling of the two sublattices and the observed spin reorientation. The saturation values of the Cr2+ moments in the CrO2 layers (3.34(1) μB (for Sr2CrO2Cr2As2) and 3.30(1) μB (for Ba2CrO2Cr2As2)) are larger than those in the CrAs layers (2.68(1) μB for Sr2CrO2Cr2As2 and 2.298(8) μB for Ba2CrO2Cr2As2) reflecting greater covalency in the arsenide layers.
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Oct 2020
|
|
I11-High Resolution Powder Diffraction
I19-Small Molecule Single Crystal Diffraction
|
Stephen P.
Argent
,
Ivan
Da Silva
,
Alex
Greenaway
,
Mathew
Savage
,
Jack
Humby
,
Andrew J.
Davies
,
Harriott
Nowell
,
William
Lewis
,
Pascal
Manuel
,
Chiu C.
Tang
,
Alexander J.
Blake
,
Michael W.
George
,
Alexander V.
Markevich
,
Elena
Besley
,
Sihai
Yang
,
Neil R.
Champness
,
Martin
Schroeder
Diamond Proposal Number(s):
[861, 11622, 15833, 9443]
Open Access
Abstract: Designing porous materials which can selectively adsorb CO2 or CH4 is an important environmental and industrial goal which requires an understanding of the host–guest interactions involved at the atomic scale. Metal–organic polyhedra (MOPs) showing permanent porosity upon desolvation are rarely observed. We report a family of MOPs (Cu-1a, Cu-1b, Cu-2), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. Thus, for Cu-1a, the void fraction outside the cages totals 56% with only 2% within. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analyses. The exceptional stability of Cu-1a enables a detailed structural investigation into the adsorption of CO2 and CH4 using in situ X-ray and neutron diffraction, coupled with DFT calculations. The primary binding sites for adsorbed CO2 and CH4 in Cu-1a are found to be the open metal sites and pockets defined by the faces of phenyl rings. More importantly, the structural analysis of a hydrated sample of Cu-1a reveals a strong hydrogen bond between the adsorbed CO2 molecule and the Cu(II)-bound water molecule, shedding light on previous empirical and theoretical observations that partial hydration of metal−organic framework (MOF) materials containing open metal sites increases their uptake of CO2. The results of the crystallographic study on MOP–gas binding have been rationalized using DFT calculations, yielding individual binding energies for the various pore environments of Cu-1a.
|
Oct 2020
|
|
B22-Multimode InfraRed imaging And Microspectroscopy
|
Thien D.
Duong
,
Sergey A.
Sapchenko
,
Ivan
Da Silva
,
Harry G. W.
Godfrey
,
Yongqiang
Cheng
,
Luke L.
Daemen
,
Pascal
Manuel
,
Mark D.
Frogley
,
Gianfelice
Cinque
,
Anibal J.
Ramirez-cuesta
,
Sihai
Yang
,
Martin
Schroeder
Diamond Proposal Number(s):
[14938]
Open Access
Abstract: Metal–organic frameworks (MOFs) functionalised with amine, amide and hydroxyl groups show great promise for CO2 binding due to their ability to form hydrogen bonds to CO2. Herein we report the adsorption and selectivity of CO2 in four iso-reticular MOFs adopting the NbO topology. Functionalisation of the parent MOF, MFM-102, with –NO2, –NH2 and alkyl groups leads to an enhancement of CO2 adsorption of up to 36% for the NO2-decorated MOF and with raised selectivity. MFM-102-NO2 shows the highest adsorption capacity for CO2 (184 cm3 g−1 at 273 K and 1.0 bar) within this series, comparable to the best-behaving iso-reticular MOFs. At 298 K and 1.0 bar, MFM-102-NO2 shows a CO2/CH4 selectivity of 5.0. In situ inelastic neutron scattering and synchrotron FT-IR micro-spectroscopy were employed to elucidate the host–guest interaction dynamics within CO2-loaded MFM-102-NO2. Neutron powder diffraction enabled the direct observation of the preferred binding domains in MFM-102-NO2, and, to the best of our knowledge, we report the first example of CO2 binding to a –NO2 group in a porous MOF. Synergistic effects between the –NO2 group and the open metal sites lead to optimal binding of CO2 molecules within MFM-102-NO2 via hydrogen bonding to C–H groups.
|
May 2020
|
|
I11-High Resolution Powder Diffraction
|
Yuchao
Chai
,
Xue
Han
,
Weiyao
Li
,
Shanshan
Liu
,
Sikai
Yao
,
Chong
Wang
,
Wei
Shi
,
Ivan
Da Silva
,
Pascal
Manuel
,
Yongqiang
Cheng
,
Luke D.
Daemen
,
Anibal J.
Ramirez-cuesta
,
Chiu C.
Tang
,
Ling
Jiang
,
Sihai
Yang
,
Naijia
Guan
,
Landong
Li
Diamond Proposal Number(s):
[23483]
Open Access
Abstract: The efficient removal of alkyne impurities for the production of polymer-grade lower olefins remains an important and challenging goal for many industries. We report a strategy to control the pore interior of faujasite (FAU) zeolites by the confinement of isolated open nickel(II) sites in their six-membered rings. Under ambient conditions, Ni@FAU showed remarkable adsorption of alkynes and efficient separations of acetylene/ethylene, propyne/propylene, and butyne/1,3-butadiene mixtures, with unprecedented dynamic separation selectivities of 100, 92, and 83, respectively. In situ neutron diffraction and inelastic neutron scattering revealed that confined nickel(II) sites enabled chemoselective and reversible binding to acetylene through the formation of metastable [Ni(II)(C2H2)3] complexes. Control of the chemistry of pore interiors of easily scalable zeolites has unlocked their potential in challenging industrial separations.
|
May 2020
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[13284, 18786]
Open Access
Abstract: Mixed-valent transition metal compounds display complex structural, electronic and magnetic properties which can often be exquisitely tuned. Here the charge-ordered state of stoichiometric CaFe3O5 is probed using neutron powder diffraction, Monte Carlo simulation and symmetry analysis. Magnetic ordering is dominated by the formation of ferromagnetic Fe3+–Fe2+–Fe3+ trimers which are evident above the magnetic ordering transition. Between TN = 289 K and 281 K an incommensurate magnetically ordered phase develops due to magnetic frustration, but a spin Jahn-Teller distortion lifts the frustration and enables the magnetic ordering to lock in to a charge-ordered commensurate state at lower temperatures. Stoichiometric CaFe3O5 exhibits single phase behaviour throughout and avoids the phase separation into two distinct crystallographic phases with different magnetic structures and Fe valence distributions reported recently, which likely occurs due to partial Fe2+ for Ca2+ substitution. This underlines the sensitivity of the magnetism and chemistry of these mixed-valent systems to composition.
|
Dec 2019
|
|
I10-Beamline for Advanced Dichroism
|
Abstract: We present long-wavelength neutron diffraction data measured on both single crystal and polycrystalline samples of the skyrmion host material Cu2OSeO3. We observe magnetic satellites around the
(0
1
⎯
⎯
1)
(01¯1)
diffraction peak not accessible to other techniques, and distinguish helical from conical spin textures in reciprocal space. Our measurements show that not only the field-polarised phase but also the helical ground state are made up of ferrimagnetic clusters instead of individual spins. These clusters are distorted Cu tetrahedra, where the spin on one Cu ion is anti-aligned with the spin on the three other Cu ions.
|
Dec 2019
|
|
B22-Multimode InfraRed imaging And Microspectroscopy
|
Jack
Humby
,
Oguarabau
Benson
,
Gemma L.
Smith
,
Stephen P.
Argent
,
Ivan
Da Silva
,
Yongqiang
Cheng
,
Svemir
Rudic
,
Pascal
Manuel
,
Mark D.
Frogley
,
Gianfelice
Cinque
,
Lucy K.
Saunders
,
Inigo
Vitorica-yrezabal
,
George F. S.
Whitehead
,
Timothy L.
Easun
,
William
Lewis
,
Alexander J.
Blake
,
Anibal J.
Ramirez-cuesta
,
Sihai
Yang
,
Martin
Schroeder
Diamond Proposal Number(s):
[13666]
Open Access
Abstract: In order to develop new porous materials for applications in gas separations such as natural gas upgrading, landfill gas processing and acetylene purification it is vital to gain understanding of host-substrate interactions at a molecular level. Herein we report a series of six isoreticular metal-organic frameworks (MOFs) for selective gas adsorption. These materials do not incorporate open metal sites and thus provide an excellent platform to investigate the effect of the incorporation of ligand functionality via amide and alkyne groups on substrate binding. By reducing the linker length of our previously reported MFM-136, we report much improved CO2/CH4 (50:50) and CO2/N¬2 (15:85) selectivity values of 20.2 and 65.4, respectively (1 bar and 273 K), in the new amide-decorated MOF, MFM-126. The CO2 separation performance of MFM-126 has been confirmed by dynamic breakthrough experiments. In situ inelastic neutron scattering and synchrotron FT-IR microspectroscopy were employed to elucidate dynamic interactions of adsorbed CO2 molecules within MFM-126. Upon changing the functionality to an alkyne group in MFM-127, the CO2 uptake decreases but the C2H2 uptake increases by 68%, leading to excellent C2H2/CO2 and C2H2/CH4 selectivities of 3.7 and 21.2, respectively. Neutron powder diffraction enabled the direct observation of the preferred binding domains in MFM-126 and MFM-127, and, to the best of our knowledge, we report the first example of acetylene binding to an alkyne moiety in a porous material, with over 50% of the acetylene observed within MFM-127 displaying interactions (<4 Å) with the alkyne functionality of the framework.
|
Oct 2018
|
|
B22-Multimode InfraRed imaging And Microspectroscopy
I11-High Resolution Powder Diffraction
|
Lei
Li
,
Ivan
Da Silva
,
Daniil I.
Kolokolov
,
Xue
Han
,
Jiangnan
Li
,
Gemma
Smith
,
Yongqiang
Cheng
,
Luke L.
Daemen
,
Christopher G.
Morris
,
Harry G. W.
Godfrey
,
Nicholas
Jacques
,
Xinran
Zhang
,
Pascal
Manuel
,
Mark D.
Frogley
,
Claire A.
Murray
,
Anibal J.
Ramirez-cuesta
,
Gianfelice
Cinque
,
Chiu C.
Tang
,
Alexander G.
Stepanov
,
Sihai
Yang
,
Martin
Schroder
Diamond Proposal Number(s):
[14564, 15970]
Open Access
Abstract: Modulation of pore environment is an effective strategy to optimize guest binding in porous materials. We report the post-synthetic modification of the charge distribution in a charged metal-organic framework, MFM-305-CH3, [Al(OH)(L)]Cl, [(H2L)Cl = 3,5-dicarboxy-1-methylpyridinium chloride] and its effect on guest binding. MFM-305-CH3 shows a distribution of cationic (methylpyridinium) and anionic (chloride) centers and can be modified to release free pyridyl N-centres by thermal demethylation of the 1-methylpyridinium moiety to give the neutral isostructural MFM-305. This leads simultaneously to enhanced adsorption capacities and selectivities (two parameters that often change in opposite directions) for CO2 and SO2 in MFM-305. The host-guest binding has been comprehensively investigated by in situ synchrotron X-ray and neutron powder diffraction, inelastic neutron scattering, synchrotron infrared and 2H NMR spectroscopy and theoretical modelling to reveal the binding domains of CO2 and SO2 in these materials. CO2 and SO2 binding in MFM-305-CH3 is shown to occur via hydrogen bonding to the methyl and aromatic-CH groups, with a long range interaction to chloride for CO2. In MFM-305 the hydroxyl, pyridyl and aromatic C-H groups bind CO2 and SO2 more effectively via hydrogen bonds and dipole interactions. Post-synthetic modification via dealkylation of the as-synthesised metal-organic framework is a powerful route to the synthesis of materials incorporating active polar groups that cannot be prepared directly.
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Oct 2018
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