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13 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I19-Small Molecule Single Crystal Diffraction	LED-pump-X-ray-multiprobe crystallography for sub-second timescales Lauren E. Hatcher , Mark R. Warren , Jonathan M. Skelton , Anuradha R. Pallipurath , Lucy K. Saunders , David R. Allan , Paul Hathaway , Giulio Crevatin , David Omar , Ben. H. Williams , Ben A. Coulson , Chick C. Wilson , Paul R. Raithby Communications Chemistry 5 DOI: 10.1038/s42004-022-00716-1 Diamond Proposal Number(s): [17306, 19670] Open Access Show Abstract ▼ Abstract: The visualization of chemical processes that occur in the solid-state is key to the design of new functional materials. One of the challenges in these studies is to monitor the processes across a range of timescales in real-time. Here, we present a pump-multiprobe single-crystal X-ray diffraction (SCXRD) technique for studying photoexcited solid-state species with millisecond-to-minute lifetimes. We excite using pulsed LEDs and synchronise to a gated X-ray detector to collect 3D structures with sub-second time resolution while maximising photo-conversion and minimising beam damage. Our implementation provides complete control of the pump-multiprobe sequencing and can access a range of timescales using the same setup. Using LEDs allows variation of the intensity and pulse width and ensures uniform illumination of the crystal, spreading the energy load in time and space. We demonstrate our method by studying the variable-temperature kinetics of photo-activated linkage isomerism in [Pd(Bu4dien)(NO2)][BPh4] single-crystals. We further show that our method extends to following indicative Bragg reflections with a continuous readout Timepix3 detector chip. Our approach is applicable to a range of physical and biological processes that occur on millisecond and slower timescales, which cannot be studied using existing techniques.	Aug 2022
I09-Surface and Interface Structural Analysis	Ge 4s2 lone pairs and band alignments in GeS and GeSe for photovoltaics Matthew J. Smiles , Jonathan M. Skelton , Huw Shiel , Leanne A. H. Jones , Jack E. N. Swallow , Holly J. Edwards , Thomas Featherstone , Philip A. E. Murgatroyd , Pardeep K. Thakur , Tien-Lin Lee , Vinod R. Dhanak , Tim D. Veal Journal Of Materials Chemistry A DOI: 10.1039/D1TA05955F Diamond Proposal Number(s): [21431, 23160] Open Access Show Abstract ▼ Abstract: Germanium sulfide and germanium selenide bulk crystals were prepared using a melt growth technique. X-ray photoemission spectroscopy (XPS) was used to determine ionisation potentials of 5.74 and 5.48 eV for GeS and GeSe respectively. These values were used with the previously-measured band gaps to establish the natural band alignments with potential window layers for solar cells and to identify CdS and TiO2 as sensible choices. The ionisation potential of GeS is found to be smaller than in comparable materials. Using XPS and hard x-ray photoemission (HAXPES) measurements in conjunction with density-functional theory calculations, we demonstrate that stereochemically active Ge 4s lone pairs are present at the valence-band maxima. Our work thus provides direct evidence for active lone pairs in GeS and GeSe, with important implications for the applications of these and related materials, such as Ge-based perovskites.	Sep 2021
	Ca4Sb2O and Ca4Bi2O: two promising mixed-anion thermoelectrics Warda Rahim , Jonathan M. Skelton , David O. Scanlon Journal Of Materials Chemistry A 9, 20417 - 20435 DOI: 10.1039/D1TA03649A Open Access Show Abstract ▼ Abstract: The environmental burden of fossil fuels and the rising impact of global warming have created an urgent need for sustainable clean energy sources. This has led to widespread interest in thermoelectric (TE) materials to recover part of the ∼60% of global energy currently wasted as heat as usable electricity. Oxides are particularly attractive as they are thermally stable, chemically inert, and formed of earth-abundant elements, but despite intensive efforts there have been no reports of oxide TEs matching the performance of flagship chalcogenide materials such as PbTe, Bi2Te3 and SnSe. A number of ternary X4Y2Z mixed-anion systems, including oxides, have predicted band gaps in the useful range for several renewable-energy applications, including as TEs, and some also show the complex crystal structures indicative of low lattice thermal conductivity. In this study, we use ab initio calculations to investigate the TE performance of two structurally-similar mixed-anion oxypnictides, Ca4Sb2O and Ca4Bi2O. Electronic-structure and band-alignment calculations using hybrid density-functional theory (DFT), including spin–orbit coupling, suggest that both materials are likely to be p-type dopable with large charge-carrier mobilities. Lattice-dynamics calculations using third-order perturbation theory predict ultra-low lattice thermal conductivities of ∼0.8 and ∼0.5 W m−1 K−1 above 750 K. Nanostructuring to a crystal grain size of 20 nm is predicted to further reduce the room temperature thermal conductivity by around 40%. Finally, we use the electronic- and thermal-transport calculations to estimate the thermoelectric figure of merit ZT, and show that with p-type doping both oxides could potentially serve as promising earth-abundant oxide TEs for high-temperature applications.	Sep 2021
B18-Core EXAFS	Use of interplay between a-site non-stoichiometry and hydroxide doping to deliver novel proton-conducting perovskite oxides Jin Goo Lee , Aaron B. Naden , Cristian D. Savaniu , Paul A. Connor , Julia L. Payne , Jonathan M. Skelton , Alexandra Gibbs , Jianing Hui , Stephen C. Parker , John T. S. Irvine Advanced Energy Materials 8 DOI: 10.1002/aenm.202101337 Diamond Proposal Number(s): [17198] Open Access Show Abstract ▼ Abstract: The magnitude of ionic conductivity is known to depend upon both mobility and number of available carriers. For proton conductors, hydration is a key factor in determining the charge–carrier concentration in ABO3 perovskite oxides. Despite the high reported proton mobility of calcium titanate (CaTiO3), this titanate perovskite has thus far been regarded as a poor proton conductor due to the low hydration capability. Here, the enhanced proton conductivity of the defective calcium titanate Ca0.92TiO2.84(OH)0.16 prepared by replacing lattice oxygens with hydroxyl groups via a solvothermal route is shown. Conductivity measurements in a humidified Ar atmosphere reveal that, remarkably, this material exhibits one order of magnitude higher bulk conductivity (10−4 Scm−1 at 200 °C) than hydrated stoichiometric CaTiO3 prepared by traditional solid-state synthesis due to the higher concentration of protonic defects and variation in the crystal structure. The replacement of Ca2+ by Ni2+ in the Ca1−xTi1O3−2x(OH)2x, which mostly exsolve metallic Ni nanoparticles along orthorhombic (100) planes upon reduction, is also demonstrated. These results suggest a new strategy by tailoring the defect chemistry via hydration or cation doping followed by exsolution for targeted energy applications.	Aug 2021
	Bulk and surface conformations in solid-state lovastatin: Spectroscopic and molecular dynamics studies Anuradha R. Pallipurath , Jonathan M. Skelton , Andrew Britton , Elizabeth A. Willneff , Sven Schroeder Crystals 11 DOI: 10.3390/cryst11050509 Open Access Show Abstract ▼ Abstract: Conformational flexibility in molecules can give rise to a range of functional group terminations at crystal surfaces and dynamic disorder in the bulk. In this work, we explore the conformational behavior of the drug molecule lovastatin in the crystallographically disordered solid and at crystal surfaces through a combination of computational modeling and spectroscopy. Gas-phase and periodic quantum-chemical calculations are used to study the potential energy surface associated with rotatable bonds to examine the disorder in bulk. These calculations are combined with vibrational and X-ray photoelectron spectroscopy measurements to obtain insight into the conformations in bulk and at the surface. Our MD simulations show that the bulk disorder is driven by cooperative motion of the butyl group on the S-butanoate moiety along one crystallographic direction beyond a unit cell. The calculations show that the O-H group can rotate relatively freely between two low-energy conformers in the gas phase but is locked in position by intermolecular H-bonding interactions in the bulk crystal, and we find tentative spectroscopic evidence for the second conformer being present at the surface. We also comment on the relative utility of these different techniques for studying molecular conformation in bulk and at surfaces and highlight possible areas for future developments.	May 2021
	Watching photochemistry happen: Recent developments in dynamic single-crystal X-ray diffraction studies Lauren E. Hatcher , Mark R. Warren , Anuradha R. Pallipurath , Lucy Saunders , Jonathan M. Skelton DOI: 10.1007/430_2020_78 Show Abstract ▼ Abstract: Photoresponsive materials are an important contemporary research area with applications in, for example, energy and catalysis. Mechanistic information on solid-state photochemical reactions has traditionally come from spectroscopy and modelling, with crystallography limited to snapshots of endpoints and long-lived intermediates. Recent advances in X-ray sources and detectors have made it possible to follow solid-state reactions in situ with dynamic single-crystal X-ray diffraction (SCXRD) methods, allowing a full set of atomic positions to be determined over the course of the reaction. These experiments provide valuable structural information that can be used to interpret spectroscopic measurements and to inform materials design and optimisation. Solid-state linkage isomers, where small-molecule ligands such as NO, NO2−, N2 and SO2 show photo-induced changes in binding to a transition metal centre, have played a leading role in the development of dynamic SCXRD methodology, since the movement of whole atoms and the predictable temperature dependence of the excited-state lifetimes make them ideal test systems. The field of “photocrystallography”, pioneered by Coppens in the late 1990s, has developed alongside advances in instrumentation and computing and can now provide the 3D structures of species with lifetimes down to femtoseconds. In this chapter, we will review the development of photocrystallography experiments against linkage isomer systems, from the early identification of metastable species under continuous illumination, through measuring kinetics at low temperature, to recent experiments studying species with sub-second lifetimes. We will discuss the advances in X-ray sources and instrumentation that have made dynamic SCXRD experiments possible, and we will highlight the role of kinetic modelling and complementary spectroscopy in designing experiments. Finally, we will discuss possible directions for future development and identify some of the outstanding challenges that remain to be addressed.	Oct 2020
	Chemical trends in the lattice thermal conductivity of Li(Ni, Mn, Co)O2 (NMC) battery cathodes Hui Yang , Christopher N. Savory , Benjamin J. Morgan , David O. Scanlon , Jonathan M. Skelton , Aron Walsh Chemistry Of Materials DOI: 10.1021/acs.chemmater.0c02908 Show Abstract ▼ Abstract: While the transport of ions and electrons in conventional Li-ion battery cathode materials is well understood, our knowledge of the phonon (heat) transport is still in its infancy. We present a first-principles theoretical investigation of the chemical trends in the phonon frequency dispersion, mode lifetimes, and thermal conductivity in the series of layered lithium transition-metal oxides Li(NixMnyCoz)O2 (x + y + z = 1). The oxidation and spin states of the transition metal cations are found to strongly influence the structural dynamics. Calculations of the thermal conductivity show that LiCoO2 has highest average conductivity of 45.9 W·m–1·K–1 at T = 300 K and the largest anisotropy, followed by LiMnO2 with 8.9 W·m–1·K–1 and LiNiO2 with 6.0 W·m–1·K–1. The much lower thermal conductivity of LiMnO2 and LiNiO2 is found to be due to 1–2 orders of magnitude shorter phonon lifetimes. We further model the properties of binary and ternary transition metal combinations to examine the possible effects of mixing on the thermal transport. These results serve as a guide to ongoing work on the design of multicomponent battery electrodes with more effective thermal management.	Aug 2020
I09-Surface and Interface Structural Analysis	Sn 5s2 lone pairs and the electronic structure of tin sulphides: A photoreflectance, high-energy photoemission, and theoretical investigation Leanne A. H. Jones , Wojciech M. Linhart , Nicole Fleck , Jack E. N. Swallow , Philip A. E. Murgatroyd , Huw Shiel , Thomas J. Featherstone , Matthew J. Smiles , Pardeep K. Thakur , Tien-Lin Lee , Laurence J. Hardwick , Jonathan Alaria , Frank Jaeckel , Robert Kudrawiec , Lee A. Burton , Aron Walsh , Jonathan M. Skelton , Tim D. Veal , Vin R. Dhanak Physical Review Materials 4 DOI: 10.1103/PhysRevMaterials.4.074602 Diamond Proposal Number(s): [21431] Open Access Show Abstract ▼ Abstract: The effects of Sn 5 s lone pairs in the different phases of Sn sulphides are investigated with photoreflectance, hard x-ray photoemission spectroscopy (HAXPES), and density functional theory. Due to the photon energy-dependence of the photoionization cross sections, at high photon energy, the Sn 5 s orbital photoemission has increased intensity relative to that from other orbitals. This enables the Sn 5 s state contribution at the top of the valence band in the different Sn-sulphides, SnS, Sn 2 S 3 , and SnS 2 , to be clearly identified. SnS and Sn 2 S 3 contain Sn(II) cations and the corresponding Sn 5 s lone pairs are at the valence band maximum (VBM), leading to ∼ 1.0 –1.3 eV band gaps and relatively high VBM on an absolute energy scale. In contrast, SnS 2 only contains Sn(IV) cations, no filled lone pairs, and therefore has a ∼ 2.3 eV room-temperature band gap and much lower VBM compared with SnS and Sn 2 S 3 . The direct band gaps of these materials at 20 K are found using photoreflectance to be 1.36, 1.08, and 2.47 eV for SnS, Sn 2 S 3 , and SnS 2 , respectively, which further highlights the effect of having the lone-pair states at the VBM. As well as elucidating the role of the Sn 5 s lone pairs in determining the band gaps and band alignments of the family of Sn-sulphide compounds, this also highlights how HAXPES is an ideal method for probing the lone-pair contribution to the density of states of the emerging class of materials with n s 2 configuration.	Jul 2020
	Highly anisotropic thermal transport in LiCoO2 Hui Yang , Jia-Yue Yang , Christopher N. Savory , Jonathan M. Skelton , Benjamin J. Morgan , David O. Scanlon , Aron Walsh The Journal Of Physical Chemistry Letters DOI: 10.1021/acs.jpclett.9b02073 Show Abstract ▼ Abstract: LiCoO2 is the prototypical cathode in lithium-ion batteries. Its crystal structure consists of Li+ and CoO2– layers that alternate along the hexagonal ⟨0001⟩ axis. It is well established that the ionic and electronic conduction are anisotropic, but little is known regarding the heat transport. We analyze the phonon dispersion and lifetimes using anharmonic lattice dynamics based on quantum-chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ∼6 times higher than that along the c axis. An upper limit to the average thermal conductivity at T = 300 K of 38.5 W m–1 K–1 is set by short phonon lifetimes associated with anharmonic interactions within the octahedral face-sharing CoO2– network. Observations of conductivity <10 W m–1 K–1 can be understood by additional scattering channels including grain boundaries in polycrystalline samples. The impact on thermal processes in lithium-ion batteries is discussed.	Sep 2019
I19-Small Molecule Single Crystal Diffraction	Monitoring photo-induced population dynamics in metastable linkage isomer crystals: a crystallographic kinetic study of [Pd(Bu4dien)NO2]BPh4 Lauren E. Hatcher , Jonathan M. Skelton , Mark R. Warren , Clare Stubbs , Estelina Lora Da Silva , Paul R. Raithby Physical Chemistry Chemical Physics DOI: 10.1039/C7CP05422J Diamond Proposal Number(s): [8567, 9734, 13698] Open Access Show Abstract ▼ Abstract: We present a detailed kinetic study of photo-induced solid state linkage isomerism in the compound [Pd(Bu4dien)NO2]BPh4 (Bu4dien = N,N,N’,N’-tetrabutyldiethylenetriamine) using in-situ photocrystallographic techniques. We explore the key variables that influence the photoconversion and develop a detailed kinetic model for the excitation and decay processes and the temperature dependence of the conversion rates. We show that by varying the temperature the lifetime of the excited state can be varied over orders of magnitude, making these systems ideal test cases for the development of new time-resolved X-ray diffraction methods. The kinetic model is used to build a numerical-simulation tool, which we use to explore the practicalities of pump-probe single-crystal diffraction experiments with minute and second time-resolution.	Jan 2018

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