I15-1-X-ray Pair Distribution Function (XPDF)
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Xiao
Hua
,
Alexander S.
Eggeman
,
Elizabeth
Castillo-Martinez
,
Rosa
Robert
,
Harry S.
Geddes
,
Ziheng
Lu
,
Chris J.
Pickard
,
Wei
Meng
,
Kamila M.
Wiaderek
,
Nathalie
Pereira
,
Glenn G.
Amatucci
,
Paul A.
Midgley
,
Karena W.
Chapman
,
Ullrich
Steiner
,
Andrew L.
Goodwin
,
Clare
Grey
Diamond Proposal Number(s):
[17315]
Abstract: Metal fluorides, promising lithium-ion battery cathode materials, have been classified as conversion materials due to the reconstructive phase transitions widely presumed to occur upon lithiation. We challenge this view by studying FeF3 using X-ray total scattering and electron diffraction techniques that measure structure over multiple length scales coupled with density functional theory calculations, and by revisiting prior experimental studies of FeF2 and CuF2. Metal fluoride lithiation is instead dominated by diffusion-controlled displacement mechanisms, and a clear topological relationship between the metal fluoride F− sublattices and that of LiF is established. Initial lithiation of FeF3 forms FeF2 on the particle’s surface, along with a cation-ordered and stacking-disordered phase, A-LixFeyF3, which is structurally related to α-/β-LiMn2+Fe3+F6 and which topotactically transforms to B- and then C-LixFeyF3, before forming LiF and Fe. Lithiation of FeF2 and CuF2 results in a buffer phase between FeF2/CuF2 and LiF. The resulting principles will aid future developments of a wider range of isomorphic metal fluorides.
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Jan 2021
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I09-Surface and Interface Structural Analysis
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Zachary W.
Lebens-Higgins
,
Nicholas V.
Faenza
,
Maxwell D.
Radin
,
Hao
Liu
,
Shawn
Sallis
,
Jatinkumar
Rana
,
Julija
Vinckeviciute
,
Philip J.
Reeves
,
Mateusz
Zuba
,
Fadwa
Badway
,
Nathalie
Pereira
,
Karena W.
Chapman
,
Tien-Lin
Lee
,
Tianpin
Wu
,
Clare P.
Grey
,
Brent
Melot
,
Anton
Van Der Ven
,
Glenn G.
Amatucci
,
Wanli
Yang
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[19162]
Open Access
Abstract: Oxygen participation, arising from increased transition metal–oxygen covalency during delithiation, is considered essential for the description of charge compensation in conventional layered oxides. The advent of high-resolution mapping of the O K-edge resonant inelastic X-ray scattering (RIXS) provides an opportunity to revisit the onset and extent of oxygen participation. Combining RIXS with an array of structural and electronic probes for the family of Ni-rich LiNi0.8Co0.2−yAlyO2 cathodes, we identify common charge compensation regimes that are assigned to formal transition metal redox (<4.25 V) and oxygen participation through covalency (>4.25 V). From O K-edge RIXS maps, we find the emergence of a sharp RIXS feature in these systems when approaching full delithiation, which has previously been associated with lattice oxidized oxygen in alkali-rich systems. The lack of transition metal redox signatures and strong covalency at these high degrees of delithiation suggest this RIXS feature is similarly attributed to lattice oxygen charge compensation as in the alkali-rich systems. The RIXS feature's evolution with state of charge in conventional layered oxides is evidence that this feature reflects the depopulation of occupied O 2p states associated with oxygen participation.
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Jul 2019
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I15-1-X-ray Pair Distribution Function (XPDF)
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Jiayang
Zhang
,
Louis
Longley
,
Hao
Liu
,
Christopher W.
Ashling
,
Philip A.
Chater
,
Kevin A.
Beyer
,
Karena W.
Chapman
,
Haizheng
Tao
,
David A.
Keen
,
Thomas D.
Bennett
,
Yuanzheng
Yue
Diamond Proposal Number(s):
[171151]
Abstract: A pronounced enthalpy release occurs around 1.38 Tg in the prototypical metal-organic framework glass formed from ZIF-4 [Zn(C3H3N2)2], but there is no sign for any crystallization (i.e., long-range ordering) taking place. This behavior is in strong contrast to that for other families of melt-quenched glasses.
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Feb 2019
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B18-Core EXAFS
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Jatinkumar
Rana
,
Yong
Shi
,
Mateusz J.
Zuba
,
Kamila M
Wiaderek
,
Jun
Feng
,
Hui
Zhou
,
Jia
Ding
,
Tianpin
Wu
,
Giannantonio
Cibin
,
Mahalingam
Balasubramanian
,
Frederick O.
Omenya
,
Natasha
Chernova
,
Karena W.
Chapman
,
M. Stanley
Whittingham
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[18423]
Abstract: Recent advances in materials syntheses have enabled ε-LiVOPO4 to deliver capacities approaching, and in some cases exceeding the theoretical value of 305 mA h g-1 for 2Li intercalation, despite its poor electronic and ionic conductivity. However, not all of the capacity corresponds to the true electrochemical intercalation/deintercalation reactions as evidenced upon systematic tracking of V valence through combined operando and rate-dependent ex-situ X-ray absorption study presented herein. Structural disorder and defects introduced in the material by high-energy ball milling impede kinetics of the high-voltage V5+/V4+ redox more severely than the low-voltage V4+/V3+ redox, promoting significant side reaction contributions in the high-voltage region, irrespective of cycling conditions. The present work emphasizes the need for nanoengineering of active materials without compromising their bulk structural integrity in order to fully utilize high-energy density of multi-electron cathode materials.
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Sep 2018
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B18-Core EXAFS
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Diamond Proposal Number(s):
[13430]
Open Access
Abstract: Perovskite potassium sodium niobates, K1−xNaxNbO3, are promising lead-free piezoelectrics. Their dielectric and piezoelectric characteristics peak near x = 0.5, but the reasons for such property enhancement remain unclear. We addressed this uncertainty by analyzing changes in the local and average structures across the x = 0.5 composition, which have been determined using simultaneous Reverse Monte Carlo fitting of neutron and X-ray total-scattering data, potassium EXAFS, and diffuse-scattering patterns in electron diffraction. Within the A-sites, Na cations are found to be strongly off-centered along the polar axis as a result of oversized cube-octahedral cages determined by the larger K ions. These Na displacements promote off-centering of the neighboring Nb ions, so that the Curie temperature and spontaneous polarization remain largely unchanged with increasing x, despite the shrinking octahedral volumes. The enhancement of the properties near x = 0.5 is attributed to an abrupt increase in the magnitude and probability of the short-range ordered octahedral rotations, which resembles the pre-transition behavior. These rotations reduce the bond tension around Na and effectively soften the short Na-O bond along the polar axis – an effect that is proposed to facilitate reorientation of the polarization as external electric field is applied.
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Nov 2017
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[15676]
Abstract: Metal–organic frameworks (MOFs) are a family of chemically diverse materials, with applications in a wide range of fields, covering engineering, physics, chemistry, biology and medicine. Until recently, research has focused almost entirely on crystalline structures, yet now a clear trend is emerging, shifting the emphasis onto disordered states, including ‘defective by design’ crystals, as well as amorphous phases such as glasses and gels. Here we introduce a strongly associated MOF liquid, obtained by melting a zeolitic imidazolate framework. We combine in situ variable temperature X-ray, ex situ neutron pair distribution function experiments, and first-principles molecular dynamics simulations to study the melting phenomenon and the nature of the liquid obtained. We demonstrate from structural, dynamical, and thermodynamical information that the chemical configuration, coordinative bonding, and porosity of the parent crystalline framework survive upon formation of the MOF liquid.
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Oct 2017
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[12764, 16005]
Abstract: Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.
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Aug 2017
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[13681]
Open Access
Abstract: The alloying mechanism of high-capacity tin anodes for sodium-ion batteries is investigated using a combined theoretical and experimental approach. Ab initio random structure searching (AIRSS) and high-throughput screening using a species-swap method provide insights into a range of possible sodium-tin structures. These structures are linked to experiments using both average and local structure probes in the form of operando pair distribution function analysis, X-ray diffraction, and 23Na solid-state nuclear magnetic resonance (ssNMR), and ex situ 119Sn ssNMR. Through this approach, we propose structures for the previously unidentified crystalline and amorphous intermediates. The first electrochemical process of sodium insertion into tin results in the conversion of crystalline tin into a layered structure consisting of mixed Na/Sn occupancy sites intercalated between planar hexagonal layers of Sn atoms (approximate stoichiometry NaSn3). Following this, NaSn2, which is predicted to be thermodynamically stable by AIRSS, forms; this contains hexagonal layers closely related to NaSn3, but has no tin atoms between the layers. NaSn2 is broken down into an amorphous phase of approximate composition Na1.2Sn. Reverse Monte Carlo refinements of an ab initio molecular dynamics model of this phase show that the predominant tin connectivity is chains. Further reaction with sodium results in the formation of structures containing Sn-Sn dumbbells, which interconvert through a solid-solution mechanism. These structures are based upon Na5-xSn2, with increasing occupancy of one of its sodium sites commensurate with the amount of sodium added. ssNMR results indicate that the final product, Na15Sn4, can store additional sodium atoms as an off-stoichiometry compound (Na15+xSn4) in a manner similar to Li15Si4.
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May 2017
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Huw R.
Marchbank
,
Adam H.
Clark
,
Timothy I.
Hyde
,
Helen Y.
Playford
,
Matthew G.
Tucker
,
David
Thompsett
,
Janet M.
Fisher
,
Karena W.
Chapman
,
Kevin A.
Beyer
,
Manuel
Monte
,
Alessandro
Longo
,
Gopinathan
Sankar
Abstract: The structure of several nano-sized ceria, CeO2, systems was investigated using neutron and X-ray diffraction and X-ray absorption spectroscopy. Whilst both diffraction and total pair distribution functions (PDFs) revealed that in all of the samples the occupancy of both Ce4+ and O2− are very close to the ideal stoichiometry, the analysis using Reverse Monte Carlo technique revealed significant disorder around oxygen atoms in the nano-sized ceria samples in comparison to the highly crystalline NIST standard. In addition, the analysis revealed that the main differences observed in the pair correlations from various X-ray and neutron diffraction techniques were attributable to the particle size of the CeO2 prepared by the reported three methods. Furthermore, detailed analysis of the Ce L3- and K-edge EXAFS data support this finding; in particular the decrease in higher shell coordination numbers with respect to the NIST standard, is attributed to differences in particle size.
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Nov 2016
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I09-Surface and Interface Structural Analysis
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Linda W.
Wangoh
,
Shawn
Sallis
,
Kamila M.
Wiaderek
,
Yuh-Chieh
Lin
,
Bohua
Wen
,
Nicholas
Quackenbush
,
Natasha A.
Chernova
,
Jinghua
Guo
,
Lu
Ma
,
Tianpin
Wu
,
Tien-Lin
Lee
,
Christoph
Schlueter
,
Shyue Ping
Ong
,
Karena W.
Chapman
,
M. Stanley
Whittingham
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[11246, 12546]
Abstract: Full, reversible intercalation of two Li+ has not yet been achieved in promising VOPO4 electrodes. A
pronounced Li+ gradient has been reported in the low voltage window (i.e., second lithium reaction)
that is thought to originate from disrupted kinetics in the high voltage regime (i.e., first lithium
reaction). Here, we employ a combination of hard and soft x–ray photoelectron and absorption
spectroscopy techniques to depth profile solid state synthesized LiVOPO4 cycled within the low
voltage window only. Analysis of the vanadium environment revealed no evidence of a Li+ gradient,
which combined with almost full theoretical capacity confirms that disrupted kinetics in the high
voltage window are responsible for hindering full two lithium insertion. Furthermore, we argue that
the uniform Li+ intercalation is a prerequisite for the formation of intermediate phases Li1.50VOPO4
and Li1.75VOPO4. The evolution from LiVOPO4 to Li2VOPO4 via the intermediate phases is
confirmed by direct comparison between O K–edge absorption spectroscopy and density functional
theory.
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Aug 2016
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