I09-Surface and Interface Structural Analysis
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David A.
Duncan
,
Nicolae
Atodiresei
,
Simone
Lisi
,
Phil J.
Blowey
,
Vasile
Caciuc
,
James
Lawrence
,
Tien-lin
Lee
,
Maria Grazia
Betti
,
Pardeep Kumar
Thakur
,
Ada
Della Pia
,
Stefan
Blügel
,
Giovanni
Costantini
,
D. Phil
Woodruff
Diamond Proposal Number(s):
[13625]
Open Access
Abstract: Theoretical formulations capable of modeling chemical interactions over 3–4 orders of magnitude of bond strength, from covalent to van der Waals (vdW) forces, are one of the primary goals in materials physics, and chemistry. Development of vdW corrections for density-functional theory has thus been a major research field for two decades. While many of these corrections are semiempirical, more theoretically rigorous ab initio functionals have been developed. The ab initio functional vdW-DF2, when coupled with the reoptimized B86 exchange function (vdW-DF2-rB86), has typically performed as well, if not better than most semiempirical formulations. Here we present a system, Co intercalation of graphene on Ir(111), for which a semiempirical correction predicts local corrugation maxima in locations at which the vdW-DF2-rB86 functional predicts global minima. Sub-angstrom precision quantitative structural measurements show better agreement with the semiempirical correction. We posit that it is balancing the weak vdW interaction with the stronger, even covalent, interactions that proves a challenge for the vdW-DF2-rB86 functional.
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Dec 2019
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B16-Test Beamline
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Diamond Proposal Number(s):
[12472]
Open Access
Abstract: The distinct molecular architecture and thermomechanical properties of polyurethane block copolymers make them suitable for applications ranging from textile fibers to temperature sensors. In the present study, differential scanning calorimetry (DSC) analysis and macroscopic stress relaxation measurements are used to identify the key internal processes occurring in the temperature ranges between −10 °C and 0 °C and between 60 °C and 70 °C. The underlying physical phenomena are elucidated by the small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) study of synchrotron beams, allowing the exploration of the structure-property relationships as a function of temperature. In situ multiscale deformation analysis under uniaxial cyclic thermomechanical loading reveals a significant anomaly in the strain evolution at the nanoscale (assessed via SAXS) in the range between −10 °C and 0 °C owing to the ‘melting’ of the soft matrix. Furthermore, WAXS measurement of crystal strain within the hard regions reveals significant compressive residual strains arising from unloading at ∼60 °C, which are associated with the dynamic shape memory effect in polyurethane at these temperatures.
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Dec 2019
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[20892, 20650]
Abstract: Zeolite encapsulated metal nanoparticle catalysts hold great promise for several green and sustainable processes, ranging from environmental remediation to renewable energy and biomass conversion. In particular, the microporous zeolite framework keeps the nanoparticles in a firm grip that can control selectivity and prevent sintering at high temperatures. While progress in the synthesis of mesoporous zeolites continues, the encapsulation of metal nanoparticles remains a challenge that often requires complex procedures and expensive additives. Here, we report a general method to encapsulate both base and noble metal nanoparticles inside the internal voids of a compartmentalized mesoporous zeolite prepared by carbon templating and steam-assisted recrystallization. This results in a remarkable shell-like morphology that facilitates the formation of small metal nanoparticles upon simple impregnation and reduction. When the materials are applied in catalysis, we for instance demonstrate that zeolite encapsulated Ni nanoparticles are highly active, selective and stable catalysts for CO2 methanation (49% conversion with 93% selectivity at 450°C). A reaction where catalysts often suffer from sintering due to the high reaction temperatures. While the introduction of Ni nanoparticles prior to the steam-assisted recrystallization results in the formation of inactive nickel phyllosilicates, noble metals such as Pt do not suffer from this limitation. Therefore, we also demonstrate the synthesis of an active catalyst prepared by the formation of Pt nanoparticles prior to the shell synthesis. We tested the zeolite encapsulated Pt nanoparticles for hydrogenation of linear and cyclic alkenes with increased chain length. The catalysts are active for hydrogenation of oct-1-ene (66% conversion) and cyclooctene (79% conversion) but inactive for the large cyclododecane (<1% conversion), which show that this type of catalyst is highly selective in size selective catalysis. All catalysts are characterized by XRD, TEM, XPS and N2 physisorption.
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Dec 2019
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[8117]
Abstract: The crystallization of poly(3-hexylthiophene) (P3HT) to form nanowires has attracted considerable interest because this process significantly increases the hole mobility when compared to amorphous P3HT, leading to improved performance in photovoltaic and other organic electronic devices. However, full characterization of the crystallization self-assembly of the polymer chains in solution has not been achieved yet, due to limited use of
in−situ
not destructive techniques. Here, we investigate the ageing-driven formation and evolution of regioregular (rr) P3HT nanostructures in chlorobenzene solution using small angle neutron scattering (SANS) and UV–Vis spectroscopy. We have monitored how the shape of the rr-P3HT aggregates evolves. The initial states for rr-P3HT chains are the random coils, which straighten to form rods. These subsequently π - π stack to form 2D lamellae, which further stack to create nanowires. The formation of nanowires is promoted both by the length of ageing and by low temperatures (
4∘C
). Temperatures above
>40∘C
reverse the formation of nanowires. Additionally, atomic force microscopy (AFM) and grazing incidence wide angle x-ray scattering (GIWAXS) reveal that the nanowires can be successfully aligned during deposition by off-axis spin coating. Finally, the anisotropic conductivity of the aligned rr-P3HT nanowire films is reported. This is significant for applications such as gas sensing or organic thin film transistors, where increased conductivity and controlled nanostructure are desirable.
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Nov 2019
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I11-High Resolution Powder Diffraction
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S. A.
Barczak
,
R. J.
Quinn
,
J. E.
Halpin
,
K.
Domosud
,
R. I.
Smith
,
A. R.
Baker
,
E.
Don
,
I.
Forbes
,
K.
Refson
,
D. A.
Maclaren
,
J. W. G.
Bos
Diamond Proposal Number(s):
[14032]
Open Access
Abstract: We outline a strategy to improve the thermoelectric performance of n-type XNiSn based half-Heusler alloys through Cu doping into vacant tetrahedral sites. A comprehensive combination of structural characterisation and modelling is employed to discriminate the competing mechanisms for thermoelectric enhancement. During synthesis a mineralising effect occurs that improves the homogeneity of the alloying elements Ti, Zr and Hf, and promotes grain growth, leading to a doubling of the electron mobility. In the formed materials, Cu is a strong n-type dopant, like Sb, but occupies the interstitial site and strongly enhances phonon scattering without diminishing carrier mobility (in contrast to interstitial Ni). Simultaneous alloying with Ti, Zr and Hf serves to minimise the thermal conductivity via regular mass disorder and strain effects. A best electronic power factor, S2/ρ, of 3.6 mW m−1 K−2 and maximum ZT of 0.8 at 773 K were observed for a Ti0.5Zr0.25Hf0.25NiCu0.025Sn composition, enabling promising device power densities of ∼6 W cm−2 and ∼8% conversion efficiency from a 450 K gradient. These findings are important because they provide new insight into the mechanisms underpinning high ZT in the XNiSn system and indicate a direction for further improvements in thermoelectric performance.
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Nov 2019
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B22-Multimode InfraRed imaging And Microspectroscopy
I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Harry G. W.
Godfrey
,
Lydia
Briggs
,
Xue
Han
,
William J. F.
Trenholme
,
Christopher
Morris
,
Mathew
Savage
,
Louis
Kimberley
,
Oxana
Magdysyuk
,
Michael
Drakopoulos
,
Claire A.
Murray
,
Chiu C.
Tang
,
Mark D.
Frogley
,
Gianfelice
Cinque
,
Sihai
Yang
,
Martin
Schroeder
Diamond Proposal Number(s):
[11278]
Open Access
Abstract: Understanding the mechanism of assembly and function of metal-organic frameworks (MOFs) is important for the development of practical materials. Herein, we report a time-resolved diffraction analysis of the kinetics of formation of a robust MOF, MFM-300(Fe), which shows high adsorption capacity for CO2 (9.55 mmol g−1 at 293 K and 20 bar). Applying the Avrami-Erofe’ev and the two-step kinetic Finke-Watzky models to in situ high-energy synchrotron X-ray powder diffraction data obtained during the synthesis of MFM-300(Fe) enables determination of the overall activation energy of formation (50.9 kJ mol−1), the average energy of nucleation (56.7 kJ mol−1), and the average energy of autocatalytic growth (50.7 kJ mol−1). The synthesis of MFM-300(Fe) has been scaled up 1000-fold, enabling the successful breakthrough separations of the CO2/N2 mixture in a packed-bed with a selectivity for CO2/N2 of 21.6. This study gives an overall understanding for the intrinsic behaviors of this MOF system, and we have determined directly the binding domains and dynamics for adsorbed CO2 molecules within the pores of MFM-300(Fe).
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Nov 2019
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[18974]
Abstract: Potassium-ion (K-ion) batteries potentially offer numerous advantages over conventional lithium-ion batteries as a result of the high natural abundance of potassium and its lower positive charge density, compared with lithium. This introduces the possibility of using K-ion in fast charging applications, in which cost effectiveness is also a major factor. Unlike for sodium-ion batteries, graphite can be used as an anode in K-ion cells, for which an extensive supply chain, electrode manufacturing infrastructure, and knowledge already exists. However, the performance of graphite anodes in K-ion cells does not meet expectations, with rapid capacity fading and poor first cycle irreversible capacities often reported. Here we investigate the formation and composition of the solid electrolyte interphase (SEI) as well as K+ insertion in graphite anodes in K-ion batteries. Through the use of energy-tuned synchrotron-based X-ray photoelectron spectroscopy, we make a detailed analysis at three probing depths up to ~50 nm of graphite anodes cycled to various potentials on the first discharge-charge cycle. Extensive SEI formation from a KPF6/DEC:EC electrolyte system is found to occur at low potentials during the insertion of potassium into graphite. During the subsequent removal of potassium from the structure, the thick SEI is partially stripped from the electrode, demonstrating that the SEI layer is unstable and contributes to a significant proportion of the capacity on both discharge and charge. With this in mind, further work is required to develop an electrolyte system with stable SEI layer formation on graphite in order to advance K-ion battery technology.
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Nov 2019
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[17223]
Open Access
Abstract: Halide perovskites are emerging as valid alternatives to conventional photovoltaic active materials owing to their low cost and high device performances. This material family also shows exceptional tunability of properties by varying chemical components, crystal structure, and dimensionality, providing a unique set of building blocks for new structures. Here, highly stable self‐assembled lead–tin perovskite heterostructures formed between low‐bandgap 3D and higher‐bandgap 2D components are demonstrated. A combination of surface‐sensitive X‐ray diffraction, spatially resolved photoluminescence, and electron microscopy measurements is used to reveal that microstructural heterojunctions form between high‐bandgap 2D surface crystallites and lower‐bandgap 3D domains. Furthermore, in situ X‐ray diffraction measurements are used during film formation to show that an ammonium thiocyanate additive delays formation of the 3D component and thus provides a tunable lever to substantially increase the fraction of 2D surface crystallites. These novel heterostructures will find use in bottom cells for stable tandem photovoltaics with a surface 2D layer passivating the 3D material, or in energy‐transfer devices requiring controlled energy flow from localized surface crystallites to the bulk.
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Nov 2019
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Abstract: Mixed anion compounds in the Fm-3m vacancy ordered perovskite structure were synthesised and characterised experimentally and computationally with a focus on compounds where A = Cs+. Pure anion Cs2SnX6 compounds were formed with X = Cl, Br and I using a room temperature solution phase method. Mixed anion compounds were formed as solid solutions of Cs2SnCl6 and Cs2SnBr6 and a second series from Cs2SnBr6 and Cs2SnI6. Single phase structures formed across the entirety of both composition series, with no evidence of long range anion ordering observed by diffraction. A distortion of the cubic A2BX6 structure was identified in which the spacing of the BX6 octahedra changes to accommodate the A site cation without reduction of overall symmetry. Optical band gap values varied with anion composition between 4.89 eV in Cs2SnCl6 to 1.35 eV in Cs2SnI6, but proved highly non-linear with changes in composition. In mixed halide compounds it was found that lower energy optical transitions appeared that were not present in the pure halide compounds, and this could be attributed to lowering of the local symmetry within the tin halide octahedra. The electronic structure was characterised by photoemission spectroscopy, and Raman spectroscopy revealed vibrational modes in the mixed halide compounds that could be assigned to particular mixed halide octahedra. This analysis was used to determine the distribution of octahedra types in mixed anion compounds, which was found to be consistent with a near-random distribution of halide anions throughout the structure, although some deviations from random halide distribution were noted in mixed iodide-bromide compounds, where the larger iodide anions preferentially adopted trans configurations.
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Nov 2019
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B18-Core EXAFS
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Diamond Proposal Number(s):
[17243]
Abstract: Technetium and transuranic elements (TRUs) are long-lived radionuclides, produced as a result of nuclear power generation. Co-immobilisation of these radionuclides in a ceramic wasteform is attractive as they are problematic for vitrification and would reduce the demand on a future geological disposal facility. A range of zirconolite ceramics have been produced via an oxide route using the surrogates Mo and Ce with a view to the co-immobilisation of Tc and TRUs. The resultant materials were characterised by XRD, SEM-EDX, TEM and XAS. Final phase assemblage was found to be affected by target stoichiometry, the Ca precursor used, processing temperature and processing atmosphere. Through appropriate optimisation of processing conditions and target stoichiometry, the results of this study show co-immobilisation of Tc and TRUs is a promising approach.
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Nov 2019
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