I11-High Resolution Powder Diffraction
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A. J. R.
Thom
,
D. G.
Madden
,
R.
Bueno-Perez
,
A.n.
Al Shakhs
,
C. T.
Lennon
,
R. J.
Marshall
,
C. A.
Walshe
,
C.
Wilson
,
C. A.
Murray
,
S. P.
Thompson
,
G. F.
Turner
,
D.
Bara
,
S. A.
Moggach
,
D.
Fairen-Jimenez
,
R. S.
Forgan
Diamond Proposal Number(s):
[22028]
Open Access
Abstract: To achieve optimal performance in gas storage and delivery applications, metal–organic frameworks (MOFs) must combine high gravimetric and volumetric capacities. One potential route to balancing high pore volume with suitable crystal density is interpenetration, where identical nets sit within the void space of one another. Herein, we report an interpenetrated MIL-53 topology MOF, named GUF-1, where one-dimensional Sc(μ2-OH) chains are connected by 4,4′-(ethyne-1,2-diyl)dibenzoate linkers into a material that is an unusual example of an interpenetrated MOF with a rod-like secondary building unit. A combination of modulated self-assembly and grand canonical Monte Carlo simulations are used to optimise the porosity of GUF-1; H2 adsorption isotherms reveal a moderately high Qst for H2 of 7.6 kJ/mol and a working capacity of 41 g/L in a temperature–pressure swing system, which is comparable to benchmark MOFs. These results show that interpenetration is a potentially viable route to high-performance gas storage materials comprised of relatively simple building blocks.
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Jun 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[24092]
Open Access
Abstract: Marine archaeological artefacts contain unexpected compounds due to prolonged exposure to the sea. These can remain dormant and embedded within materials until a change in their surrounding environment, such as exposure to oxygen, prompts a transformation. These changes can pose a problem, as acidic compounds are formed which disintegrate the material, or crystals form which physically break the artefact apart. The extent of these transformations is highly heterogeneous due to its dependence on the ability for oxygen to reach and catalyse these reactions. Additionally, these transformations are heavily dependent on the environment the artefact is exposed to, and the pathways available for ingress, either naturally or through previous degradation. This results in materials with a range of different compounds which are often co-located on the macro, micro and nano-scale. Trying to de-convolute these compounds is challenging, and usually requires a suite of complementary techniques to achieve. Here we report on damaging salts found within marine archaeological bricks and show how it is only possible to qualitatively and quantitatively understand what is present by employing a range of analytical techniques, such as XRD, SEM-EDS and SR-XPD. The marine archaeological bricks studied were found to contain a range of different sulfate-based salts, which had grown crystals in preferred orientations. This provides information which will guide further conservation strategies such as how these bricks are stored, conserved and protected in the future.
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May 2022
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I11-High Resolution Powder Diffraction
I15-Extreme Conditions
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Diamond Proposal Number(s):
[14061, 17673, 16390]
Open Access
Abstract: The similar electronic structures of Bi3+ and Pb2+ have motivated researchers to explore bismuth-based perovskite compounds, which in the past decade has been further fuelled by the demand for developing lead-free piezoceramics. The difficulty in stabilizing the perovskite phase in bismuth based compounds has directed most research activities towards exploring two main compounds - multiferroic BiFeO3 and relaxor ferroelectric Na1/2Bi1/2TiO3 and their derivatives. In recent years, quenching these materials from the sintering temperature or from the paraelectric phase (above the Curie temperature, Tc) has resulted in a plethora of fundamentally interesting and technologically relevant advances, including enhanced thermal depolarization temperature, high Tc, giant strain and control over the atomic structure and electrical conductivity at the domain wall. In this contribution, a brief overview of quenching piezoceramics is presented, with majority of the discussion encompassing salient features of quenching lead-free perovskite structured Na1/2Bi1/2TiO3- and BiFeO3- based materials. For each material system, the influence of quenching on phase transitions, domain switching behavior and electromechanical properties are presented, apart from outlining the current understanding of the underlying mechanisms. The review provides guidelines for further exploration of the quenching strategy for improving the functionality of Bi-based piezoceramics.
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May 2022
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I11-High Resolution Powder Diffraction
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Bernhard T.
Leube
,
Christopher M.
Collins
,
Luke M.
Daniels
,
Benjamin B.
Duff
,
Yun
Dang
,
Ruiyong
Chen
,
Michael W.
Gaultois
,
Troy D.
Manning
,
Frédéric
Blanc
,
Matthew S.
Dyer
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[17193]
Open Access
Abstract: A tetragonal argyrodite with >7 mobile cations, Li7Zn0.5SiS6, is experimentally realized for the first time through solid state synthesis and exploration of the Li–Zn–Si–S phase diagram. The crystal structure of Li7Zn0.5SiS6 was solved ab initio from high-resolution X-ray and neutron powder diffraction data and supported by solid-state NMR. Li7Zn0.5SiS6 adopts a tetragonal I4 structure at room temperature with ordered Li and Zn positions and undergoes a transition above 411.1 K to a higher symmetry disordered F43m structure more typical of Li-containing argyrodites. Simultaneous occupation of four types of Li site (T5, T5a, T2, T4) at high temperature and five types of Li site (T5, T2, T4, T1, and a new trigonal planar T2a position) at room temperature is observed. This combination of sites forms interconnected Li pathways driven by the incorporation of Zn2+ into the Li sublattice and enables a range of possible jump processes. Zn2+ occupies the 48h T5 site in the high-temperature F43m structure, and a unique ordering pattern emerges in which only a subset of these T5 sites are occupied at room temperature in I4 Li7Zn0.5SiS6. The ionic conductivity, examined via AC impedance spectroscopy and VT-NMR, is 1.0(2) × 10–7 S cm–1 at room temperature and 4.3(4) × 10–4 S cm–1 at 503 K. The transition between the ordered I4 and disordered F43m structures is associated with a dramatic decrease in activation energy to 0.34(1) eV above 411 K. The incorporation of a small amount of Zn2+ exercises dramatic control of Li order in Li7Zn0.5SiS6 yielding a previously unseen distribution of Li sites, expanding our understanding of structure–property relationships in argyrodite materials.
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Apr 2022
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: Zeolites have found tremendous applications in the chemical industry. However, it is unclear about the dynamic nature of their active sites under the flow of adsorbate molecules for adsorption and catalysis, especially in operando conditions, which could be different from the as-synthesized structures. In the present study, we report a structural transformation of the adsorptive active sites in SAPO-34 zeolite by using acetone as a probe molecule under various temperatures. The combination of solid-state nuclear magnetic resonance, in-situ variable-temperature synchrotron x-ray diffraction, and in-situ diffuse-reflectance infrared Fourier-transform spectroscopy allow a clear identification and quantification that the chemisorption of acetone can convert the classical Brønsted acid site adsorption mode to an induced Frustrated Lewis Pairs adsorption mode at increasing temperatures. Such facile conversion is also supported by the calculations of ab-initio molecular-dynamics simulations. This work sheds new light on the importance of the dynamic structural alteration of active sites in zeolites with adsorbates at elevated temperatures.
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Apr 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[11237]
Abstract: Stainless steel hardfacing alloys are being developed for wear and corrosion resistant applications in pressurised water reactor environments. Two examples of this, the austenitic Tristelle 5183 and triplex RR2450 were produced by gas-atomisation before undergoing consolidation using hot isostatic pressing. The phase evolution of these alloys during simulated hot isostatic pressing cycles was observed in-situ, using synchrotron x-ray diffraction. During these cycles, the metastability of the gas-atomised powders is revealed, which influences the rate of high-temperature transformation within the RR2450 alloy. Additionally, a high-strength silicide phase, named π-ferrosilicide, forms within these alloys. It decomposes by a eutectoid transformation, demonstrating a high carbon solubility within this phase. The observations of this study demonstrate the need to carefully consider the process parameters during hot isostatic pressing for such complex alloys, since alloy phase transformation rates are heavily influenced by the starting condition of the gas-atomised powder.
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Apr 2022
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I11-High Resolution Powder Diffraction
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Tianxiang
Chen
,
Yong
Wang
,
Qi
Xue
,
Ching Kit Tommy
Wun
,
Pui Kin
So
,
Ka Fu
Yung
,
Tai-Sing
Wu
,
Yun-Liang
Soo
,
Keita
Taniya
,
Sarah
Day
,
Chiu C.
Tang
,
Zehao
Li
,
Bolong
Huang
,
Shik Chi Edman
Tsang
,
Kwok-Yin
Wong
,
Tsz Woon Benedict
Lo
Diamond Proposal Number(s):
[26404]
Open Access
Abstract: The large-scale synthesis of supported multinuclear catalysts with controllable metal nuclearity and constituent composition remains a formidable challenge. We report the stepwise assembly of supported atom-precise bimetallic ligand-mediated metal ensembles (LMMEs) by exploiting the underlying principles of coordination chemistry and solid-state chemistry. Lewis di-basic 2-methylimidazole is used to bridge multiple Cu2+ and M2+ (M = Co, Ni, Cu, and Zn) ions within ZSM-5 zeolites. We observe the metal constituent composition of the LMMEs by mass spectroscopy. The adjacent metal nuclei in the LMMEs offer substantial synergistic effects that enhance the catalytic performance by at least an order of magnitude in the model catalytic “click” reaction. It is envisaged that this stepwise assembly approach to develop supported multinuclear catalysts with atom precision could effectively bridge homogeneous and heterogeneous catalysis.
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Apr 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[29466]
Open Access
Abstract: Magnetic bistability in single-molecule magnets (SMMs) is a potential basis for new types of nanoscale information storage material. The standard model for thermally activated relaxation of the magnetization in SMMs is based on the occurrence of a single Orbach process. Here, we show that incorporating a phosphorus atom into the framework of the dysprosium metallocene [(CpiPr5)Dy(CpPEt4)]+[B(C6F5)4]− (CpiPr5 is penta-isopropylcyclopentadienyl, CpPEt4 is tetraethylphospholyl) leads to the occurrence of two distinct high-temperature Orbach processes, with energy barriers of 1410(10) and 747(7) cm–1, respectively. These barriers provide experimental evidence for two different spin–phonon coupling regimes, which we explain with the aid of ab initio calculations. The strong and highly axial crystal field in this SMM also allows magnetic hysteresis to be observed up to 70 K, using a scan rate of 25 Oe s–1. In characterizing this SMM, we show that a conventional Debye model and consideration of rotational contributions to the spin–phonon interaction are insufficient to explain the observed phenomena.
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Apr 2022
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I11-High Resolution Powder Diffraction
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Abstract: The Heisenberg pyrochlore antiferromagnet
Gd
2
Pt
2
O
7
is one of a series of gadolinium pyrochlore compounds with a variety of B-site cations. Despite the expected simplicity of a spin-only
Gd
3
+
Heisenberg interaction model, the gadolinium pyrochlore series exhibits various complex magnetic ground states at low temperature.
Gd
2
Pt
2
O
7
displays the highest temperature magnetic order of the series with
T
N
=
1.6
K, which has been attributed to enhanced superexchange pathways facilitated by empty
5
d
e
g
Pt orbitals. In this study, we use various neutron scattering techniques on an isotopically enriched polycrystalline
160
Gd
2
Pt
2
O
7
sample to examine the magnetic structure and spin-wave excitation spectrum below
T
N
in order to extract the dominant exchange interactions. We find that the ground-state magnetic structure is the Palmer-Chalker state previously seen in
Gd
2
Sn
2
O
7
with an associated gapped excitation spectrum consistent with enhanced exchange interactions between further near-neighbor
Gd
3
+
ions. We confirm this exchange model with analysis of the magnetic diffuse scattering in the paramagnetic regime using polarized neutrons.
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Mar 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[28349]
Abstract: Frustrated lanthanide oxides with dense magnetic lattices are of fundamental interest for their potential in cryogenic refrigeration due to a large ground state entropy and suppressed ordering temperatures but can often be limited by short-range correlations. Here, we present examples of frustrated fcc oxides, Ba2GdSbO6 and Sr2GdSbO6, and the new site-disordered analogue Ca2GdSbO6 ([CaGd]A[CaSb]BO6), in which the magnetocaloric effect is influenced by minimal superexchange (J1 ∼ 10 mK). We report on the crystal structures using powder X-ray diffraction and the bulk magnetic properties through low-field susceptibility and isothermal magnetization measurements. The Gd compounds exhibit a magnetic entropy change of up to −15.8 J/K/molGd in a field of 7 T at 2 K, a 20% excess compared to the value of −13.0 J/K/molGd for a standard in magnetic refrigeration, Gd3Ga5O12. Heat capacity measurements indicate a lack of magnetic ordering down to 0.4 K for Ba2GdSbO6 and Sr2GdSbO6, suggesting cooling down through the liquid 4-He regime. A mean-field model is used to elucidate the role of primarily free-spin behavior in the magnetocaloric performance of these compounds in comparison to other top-performing Gd-based oxides. The chemical flexibility of the double perovskites raises the possibility of further enhancement of the magnetocaloric effect in the Gd3+fcc lattices.
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Mar 2022
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