B18-Core EXAFS
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Open Access
Abstract: New and exotic ground states of magnetic materials are highly sought after and are extensively studied for the insights they provide into the thermodynamics of disorder and fundamental magnetic interactions. By controlling the crystal structure of an appropriate magnetic lattice, it is possible to cause the strong magnetic exchange interactions to sum to zero and so be frustrated. Due to the presence of this frustration, the lowest energy configuration that results may be crucially dependent on the tiniest of energy differences between a multitude of states that have (almost) the same energy. The keen interest in these materials arises from the fact that these finely balanced systems offer a way of probing classical or quantum mechanical interactions that are of fundamental importance but are too weak to be observed in non-frustrated systems. Here, we combine local and crystallographic probes of the cation-ordered double perovskite Ba2MnMoO6 that contains a face-centered cubic lattice of S = 5/2 Mn2+ cations. Neutron diffraction measurements below 9.27(7) K indicate that a fourfold degenerate non-collinear antiferromagnetic state exists with almost complete ordering of the Mn2+ spins. Muon spin relaxation measurements provide a local probe of the magnetic fields inside this material over the t1/2 = 2.2 µs lifetime of a muon, indicating a slightly lower Néel transition temperature of 7.9(1) K. The dc susceptibility data do not show the loss of magnetization that should accompany the onset of the antiferromagnetic order; they indicate that a strongly antiferromagnetically coupled paramagnetic state [θ = −73(3) K] persists down to 4 K, at which temperature a weak transition occurs. The behavior of this material differs considerably from the closely related compositions Ba2MnMO6 (M = W, Te), which show collinear ordering arrangements and well defined antiferromagnetic transitions in the bulk susceptibility. This suggests that the Mo6+ cation leads to a fine balance between the nearest and next-nearest neighbor superexchange in these frustrated double perovskite structures.
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May 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Samuel W.
Coles
,
Viktoria
Falkowski
,
Harry S.
Geddes
,
Gabriel E.
Pérez
,
Samuel G.
Booth
,
Alexander G.
Squires
,
Conn
O'Rourke
,
Kit
Mccoll
,
Andrew L.
Goodwin
,
Serena A.
Cussen
,
Simon J.
Clarke
,
Saiful
Islam
,
Benjamin J.
Morgan
Diamond Proposal Number(s):
[27702]
Open Access
Abstract: Short-range ordering in cation-disordered cathodes can have a significant effect on their electrochemical properties. Here, we characterise the cation short-range order in the antiperovskite cathode material Li2FeSO, using density functional theory, Monte Carlo simulations, and synchrotron X-ray pair-distribution-function data. We predict partial short-range cation-ordering, characterised by favourable OLi4Fe2 oxygen coordination with a preference for polar cis-OLi4Fe2 over non-polar trans-OLi4Fe2 configurations. This preference for polar cation configurations produces long-range disorder, in agreement with experimental data. The predicted short-range-order preference contrasts with that for a simple point-charge model, which instead predicts preferential trans-OLi4Fe2 oxygen coordination and corresponding long-range crystallographic order. The absence of long-range order in Li2FeSO can therefore be attributed to the relative stability of cis-OLi4Fe2 and other non-OLi4Fe2 oxygen-coordination motifs. We show that this effect is associated with the polarisation of oxide and sulfide anions in polar coordination environments, which stabilises these polar short-range cation orderings. We propose similar anion-polarisation–directed short-range-ordering may be present in other heterocationic materials that contain cations with different formal charges. Our analysis also illustrates the limitations of using simple point-charge models to predict the structure of cation-disordered materials, where other factors, such as anion polarisation, may play a critical role in directing both short- and long-range structural correlations.
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Apr 2023
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I09-Surface and Interface Structural Analysis
I21-Resonant Inelastic X-ray Scattering (RIXS)
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A. S.
Menon
,
B. J.
Johnston
,
S. G.
Booth
,
L.
Zhang
,
K.
Kress
,
B. E.
Murdock
,
G.
Paez Fajardo
,
N. N.
Anthonisamy
,
N.
Tapia-Ruiz
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
K.
Zhou
,
P. K.
Thakur
,
T. L.
Lee
,
A. J.
Nedoma
,
S. A.
Cussen
,
L. F. J.
Piper
Diamond Proposal Number(s):
[29104, 29113]
Open Access
Abstract: The desire to increase the energy density of stoichiometric layered
Li
TM
O
2
(TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true
O
-redox, as observed in
Li
-excess cathodes. Through a high-resolution
O
K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the
Mn
-free
Ni
-rich layered oxide
Li
Ni
0.98
W
0.02
O
2
, we demonstrate that the same oxidized oxygen environment exists in both
Li
-excess and non-
Li
-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
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Mar 2023
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166]
Open Access
Abstract: Cation migration on electrochemical cycling can significantly influence the performance of li-ion cathode materials. Phases of composition LiFe2–xInxSbO6 (0 < x <1) adopt crystal structures described in space group Pnnm, consisting of a hexagonally close-packed array of oxide ions, with Fe/In and Sb cations ordered on octahedral sites, and lithium cations located within partially occupied tetrahedral sites. NPD, SXRD, and 57Fe Mössbauer data indicate that on reductive lithium insertion (either chemically or electrochemically), LiFe2SbO6 is converted to Li2Fe2SbO6 accompanied by large-scale cation migration, to form a partially Fe/Li cation-ordered and Fe2+/Fe3+ charge-ordered phase from which lithium cations cannot be easily removed, either chemically or electrochemically. Partial substitution of Fe with In suppresses the degree of cation migration that occurs on lithium insertion such that no structural change is observed when LiFeInSbO6 is converted into Li1.5FeInSbO6, allowing the system to be repeatedly electrochemically cycled between these two compositions. Phases with intermediate levels of In substitution exhibit low levels of Fe migration on Li insertion and electrochemical capacities which evolve on cycling. The mechanism by which the In3+ cations suppress the migration of Fe cations is discussed along with the cycling behavior of the LiFe1.5In0.5SbO6–Li1.75Fe1.5In0.5SbO6.
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Dec 2022
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[25542]
Open Access
Abstract: The realisation of post-combustion CO2 capture (PCCC) at industrial scale remains limited; one challenge is the concerns around capital costs and another concern is corrosion of the system itself. Corrosion resistance and mitigation against the amine solvent monoethanolamine (MEA) was studied, using the inhibitor copper (II) carbonate basic (CC). Carbon steel (C1018) was tested in CO2 loaded, 5M aqueous MEA solution, alone and in the presence of CC, to assess the corrosivity of the solution. Immersion testing used mass loss, Fe and Cu ion concentration in solution via ICP-MS, imaging (SEM) and analytical techniques (XRD and EDX) to investigate the effect of corrosion. Generally, the use of CC improved C1018 corrosion resistance relative to C1018 alone. Even at low concentrations (0.9 mM), CC was effective in inhibiting corrosion against CO2 loaded MEA, as the observed corrosion rate was effectively zero and no dissolved Fe was detected in solution. There was no evidence of copper surface adsorption. To clarify the solution chemistry resulting in corrosion inhibition, the local chemical environment of Fe and Cu were probed by Cu and Fe K-edge X-ray Absorption Spectroscopy, respectively. The Cu K- edge HERFD-XANES spectra reveal that a Cu2+ amine complex forms, critical to understanding the structure which is promoting significant corrosion inhibition.
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Dec 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[14239]
Open Access
Abstract: Garnet solid electrolytes, of the form Li7La3Zr2O12 (LLZO), remain an enticing prospect for solid-state batteries owing to their chemical and electrochemical stability in contact with metallic lithium. Dopants, often employed to stabilize the fast ion conducting cubic garnet phase, typically have no effect on the chemical stability of LLZO in contact with Li metal but have been found recently to impact the properties of the Li/garnet interface. For dopants more “reducible” than Zr (e.g., Nb and Ti), contradictory reports of either raised or reduced Li/garnet interfacial resistances have been attributed to the dopant. Here, we investigate the Li/LLZO interface in W-doped Li7La3Zr2O12 (LLZWO) to determine the influence of a “reducible” dopant on the electrochemical properties of the Li/garnet interface. Single-phase LLZWO is synthesized by a new sol–gel approach and densified by spark plasma sintering. Interrogating the resulting Li/LLZWO interface/interphase by impedance, muon spin relaxation and X-ray absorption spectroscopies uncover the significant impact of surface lithiation on electrochemical performance. Upon initial contact, an interfacial reaction occurs between LLZWO and Li metal, leading to the reduction of surface W6+ centers and an initial reduction of the Li/garnet interfacial resistance. Propagation of this surface reaction, driven by the high mobility of Li+ ions through the grain surfaces, thickens the resistive interphases throughout the material and impedes Li+ ion transport between the grains. The resulting high resistance accumulating in the system impedes cycling at high current densities. These insights shed light on the nature of lithiated interfaces in garnet solid electrolytes containing a reducible dopant where high Li+ ion mobility and the reducible nature of the dopant can significantly affect electrochemical performance.
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May 2022
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Nuria
Tapia-Ruiz
,
A. Robert
Armstrong
,
Hande
Alptekin
,
Marco A.
Amores
,
Heather
Au
,
Jerry
Barker
,
Rebecca
Boston
,
William R
Brant
,
Jake M.
Brittain
,
Yue
Chen
,
Manish
Chhowalla
,
Yong-Seok
Choi
,
Sara I. R.
Costa
,
Maria
Crespo Ribadeneyra
,
Serena A
Cussen
,
Edmund J.
Cussen
,
William I. F.
David
,
Aamod V
Desai
,
Stewart A. M.
Dickson
,
Emmanuel I.
Eweka
,
Juan D.
Forero-Saboya
,
Clare
Grey
,
John M.
Griffin
,
Peter
Gross
,
Xiao
Hua
,
John T. S.
Irvine
,
Patrik
Johansson
,
Martin O.
Jones
,
Martin
Karlsmo
,
Emma
Kendrick
,
Eunjeong
Kim
,
Oleg V
Kolosov
,
Zhuangnan
Li
,
Stijn F L
Mertens
,
Ronnie
Mogensen
,
Laure
Monconduit
,
Russell E
Morris
,
Andrew J.
Naylor
,
Shahin
Nikman
,
Christopher A
O’keefe
,
Darren M. C.
Ould
,
Robert G.
Palgrave
,
Philippe
Poizot
,
Alexandre
Ponrouch
,
Stéven
Renault
,
Emily M.
Reynolds
,
Ashish
Rudola
,
Ruth
Sayers
,
David O.
Scanlon
,
S.
Sen
,
Valerie R.
Seymour
,
Begoña
Silván
,
Moulay Tahar
Sougrati
,
Lorenzo
Stievano
,
Grant S.
Stone
,
Chris I.
Thomas
,
Maria-Magdalena
Titirici
,
Jincheng
Tong
,
Thomas J.
Wood
,
Dominic S
Wright
,
Reza
Younesi
Open Access
Abstract: Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.
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Jul 2021
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