I20-Scanning-X-ray spectroscopy (XAS/XES)
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Yuvraj
Vaishnav
,
Rohit K.
Rai
,
Walid
Al Maksoud
,
Fumitaka
Takeiri
,
Shusaku
Hayama
,
Hiroshi
Yaguchi
,
Samy
Ould-Chikh
,
Marcell
Toth
,
Raza Ullah Shah
Bacha
,
Bambar
Davaasuren
,
Maxim
Avdeev
,
Genki
Kobayashi
,
Yoji
Kobayashi
Diamond Proposal Number(s):
[31497]
Abstract: High-entropy materials have gained significant interest in many applications, but structural investigations of the effect on anions in the crystal structure are still scarce. Here, we study the effect of multicomponent cation disorder in the case of mixed-anion compounds. The distribution of mixed anions among various coordination sites is important given their implications for properties such as ionic conductivity and bulk diffusion in catalysis. Structural analysis in the fluorite-type (La,Ce,Pr,Nd,Y)H1.5O0.75 reveals that the disordered cationic effects create new interstitial sites, occupied selectively by hydride despite oxide and hydride disorder in other compositions and sites. In contrast, single-lanthanide oxyhydrides of analogous anion content, such as LaH1.5O0.75, or SmH2O0.5 lack the complex interstitial structure. Hydride ion conductivity measurements and bond valence sum energy maps show a considerably low activation energy of hydride migration due to the additional interstitial sites induced by high entropy. Such interstitials can be crucial in applications that involve hydride ion diffusion, such as ammonia synthesis catalysis and solid-state ionics, as further high-entropy compositions are explored.
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Oct 2024
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[35312]
Abstract: The electro-chemo-mechanic phenomena that play a crucial role in the stability of halide solid electrolytes with Li metal at the interface are unknown. Moreover, in a halide SE, the central M atom is known to dictate its reactivity with Li metal. To understand this chemical composition-dependent reactivity of halide SE, we have taken three halide solid electrolytes, namely Li3InCl6, Li2ZrCl6, and Li3YCl6. Here, we use operando X-ray photoelectron spectroscopy during Li plating to understand the reaction kinetics leading to the interphase evolution and interphase composition. The interphase evolution in symmetric cells was further monitored by operando electrochemical impedance spectroscopy and operando pressure measurements, showing the complex intertwining of molar volume change, void formation, and interphase growth. The as-grown interphase was visualized by focused ion beam scanning electron microscopy. The chemical reactivity was confirmed by bond strength calculations using operando synchrotron X-ray diffraction. We confirm volume changes due to molar volume mismatch leading to different microstructures of interphases for the three-halide solid electrolytes, which are correlated to the impedance growth during electrochemistry by operando impedance measurements, showing molar volume change has a drastic effect on the reactivity.
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Oct 2024
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B18-Core EXAFS
I10-Beamline for Advanced Dichroism - scattering
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[34243]
Open Access
Abstract: The increased capacity offered by oxygen-redox active cathode materials for rechargeable lithium- and sodium-ion batteries (LIBs and NIBs, respectively) offers a pathway to the next generation of high-gravimetric-capacity cathodes for use in devices, transportation and on the grid. Many of these materials, however, are plagued with voltage fade, voltage hysteresis and O2 loss, the origins of which can be traced back to changes in their electronic and chemical structures on cycling. Developing a detailed understanding of these changes is critical to mitigating these cathodes’ poor performance. In this work, we present an analysis of the redox mechanism of P2–Na0.67[Mg0.28Mn0.72]O2, a layered NIB cathode whose high capacity has previously been attributed to trapped O2 molecules. We examine a variety of charge compensation scenarios, calculate their corresponding densities of states and spectroscopic properties, and systematically compare the results to experimental data: 25Mg and 17O nuclear magnetic resonance (NMR) spectroscopy, operando X-band and ex situ high-frequency electron paramagnetic resonance (EPR), ex situ magnetometry, and O and Mn K-edge X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Spectroscopy (XANES). Via a process of elimination, we suggest that the mechanism for O redox in this material is dominated by a process that involves the formation of strongly antiferromagnetic, delocalized Mn–O states which form after Mg2+ migration at high voltages. Our results primarily rely on noninvasive techniques that are vital to understanding the electronic structure of metastable cycled cathode samples.
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Sep 2024
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18786, 25166, 32893]
Open Access
Abstract: wo new reduced phases derived from the topical excitonic insulator candidate Ta2NiSe5 have been synthesized via the intercalation of lithium and potassium from solutions of the metals in liquid ammonia. Li(NH3)Ta2NiSe5 and KTa2NiSe5 both crystallize in orthorhombic space group Pmnb with the following lattice parameters: a = 3.5175(1) Å, b = 18.7828(7) Å, and c = 15.7520(3) Å and a = 3.50247(3) Å, b = 13.4053(4) Å, and c = 15.7396(2) Å, respectively. They have increased unit cell volumes of 48% and 31%, respectively, relative to that of Ta2NiSe5. Significant rearrangement of the transition metal selenide layers is observed in both intercalates compared to the parent phase. In Li(NH3)Ta2NiSe5, neutron diffraction experiments confirm the location of the light Li, N, and H atoms, and solid-state nuclear magnetic resonance (NMR) experiments show that H, N, and Li each occupy a single environment at ambient temperature on the NMR time scale. Magnetometry data show that both intercalates have increased magnetic susceptibilities relative to that of Ta2NiSe5, consistent with the injection of electrons during intercalation and an enhancement of the Pauli paramagnetism.
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Sep 2024
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[26090]
Open Access
Abstract: Reorientational dynamics in solid electrolytes can significantly enhance the ionic conductivity, and understanding these dynamics can facilitate the rational design of improved solid electrolytes. Additionally, recent investigations on metal hydridoborate-based solid electrolytes have shown that the addition of a neutral ligand can also have a positive effect on the ionic conductivity. In this study, we investigate the dynamics in monomethylamine magnesium borohydride (Mg(BH4)2·CH3NH2) with quasielastic and inelastic neutron scattering, density functional theory calculations, and molecular dynamics simulations. The results suggest that the addition of methylamine significantly speeds up the reorientational frequency of the BH4– anion compared to Mg(BH4)2. This is likely part of the explanation for the high Mg-ion transport observed for Mg(BH4)2·CH3NH2. Furthermore, while the dynamics of both the BH4– anion and the CH3 group of the methylamine ligand is rapid, the NH2 group of the methylamine ligand exhibits much slower reorientations, as confirmed by both experimental and computational investigations. Notably, molecular dynamics calculations reveal mean square displacements of 0.387 Å2 for NH2, 1.503 Å2 for CH3, and 1.856 Å2 for BH4– using a trajectory of 10 ps. This study confirms the simultaneous presence of fast dynamics and high ionic conductivity in a metal borohydride-based system and can function as an experimental foundation for future studies on dynamics in hydrogen-rich solid electrolytes.
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Sep 2024
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I15-1-X-ray Pair Distribution Function (XPDF)
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Abstract: DUT-67 is a Zr-based metal–organic framework (MOF) that incorporates thiophene dicarboxylic acid linkers. In this study, we observed that DUT-67 underwent a striking structural order–disorder transition upon a dynamic heating process. We established a correlation between thermal responses and structural changes in DUT-67 during heating through both calorimetric analysis and structural characterization at various length scales. It was discovered that the chemical integrity of the DUT-67 linkers remained intact during heating. The morphology of DUT-67 was preserved after structural changes, while 50% of its porosity was retained, increasing the apparent density of the framework. The chemical changes caused by the heating were directly related to desolvation. The atomic pair distribution function analyses revealed that the structural disordering process occurred during heating. This was supported by a notable decrease in correlations between neighboring clusters, indicating a loss of structural order. The structural reordering in DUT-67 was found to involve multiple thermally induced phase transitions and then amorphization. The amorphous form of DUT-67 preserved both the high porosity and the functionality observed in its original crystalline state. This study implies that it is possible to find inherently unstable MOF structures for order–disorder engineering for creating new functionalities.
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Aug 2024
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I05-ARPES
I09-Surface and Interface Structural Analysis
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Brendan
Edwards
,
Darius-A.
Deaconu
,
Philip A. E.
Murgatroyd
,
Sebastian
Buchberger
,
Tommaso
Antonelli
,
Daniel
Halliday
,
Gesa-R.
Siemann
,
Andela
Zivanovic
,
Liam
Trzaska
,
Akhil
Rajan
,
Edgar
Abarca Morales
,
Daniel A.
Mayoh
,
Amelia E.
Hall
,
Rodion V.
Belosludov
,
Matthew D.
Watson
,
Timur K.
Kim
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Craig M.
Polley
,
Dina
Carbone
,
Mats
Leandersson
,
Geetha
Balakrishnan
,
Mohammad Saeed
Bahramy
,
Phil D. C.
King
Diamond Proposal Number(s):
[32937, 30125, 31465]
Open Access
Abstract: The addition of metal intercalants into the van der Waals gaps of transition metal dichalcogenides has shown great promise as a method for controlling their functional properties. For example, chiral helimagnetic states, current-induced magnetization switching, and a giant valley-Zeeman effect have all been demonstrated, generating significant renewed interest in this materials family. Here, we present a combined photoemission and density-functional theory study of three such compounds:
V1/3NbS2
,
Cr1/3NbS2
, and
Fe1/3NbS2
, to investigate chemical trends of the intercalant species on their bulk and surface electronic structure. Our resonant photoemission measurements indicate increased hybridization with the itinerant NbS2-derived conduction states with increasing atomic number of the intercalant, leading to pronounced mixing of the nominally localized intercalant states at the Fermi level. Using spatially and angle-resolved photoemission spectroscopy, we show how this impacts surface-termination-dependent charge transfers and leads to the formation of new dispersive states of mixed intercalant-Nb character at the Fermi level for the intercalant-terminated surfaces. This provides an explanation for the origin of anomalous states previously reported in this family of compounds and paves the way for tuning the nature of the magnetic interactions in these systems via control of the hybridization of the magnetic ions with the itinerant states.
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Jul 2024
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I07-Surface & interface diffraction
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Topias
Jussila
,
Anish
Philip
,
Victor
Rubio-Gimenez
,
Kim
Eklund
,
Sami
Vasala
,
Pieter
Glatzel
,
Johan
Lindén
,
Teruki
Motohashi
,
Antti J.
Karttunen
,
Rob
Ameloot
,
Maarit
Karppinen
Diamond Proposal Number(s):
[29967]
Open Access
Abstract: Advanced deposition routes are vital for the growth of functional metal–organic thin films. The gas-phase atomic/molecular layer deposition (ALD/MLD) technique provides solvent-free and uniform nanoscale thin films with unprecedented thickness control and allows straightforward device integration. Most excitingly, the ALD/MLD technique can enable the in situ growth of novel crystalline metal–organic materials. An exquisite example is iron-terephthalate (Fe-BDC), which is one of the most appealing metal–organic framework (MOF) type materials and thus widely studied in bulk form owing to its attractive potential in photocatalysis, biomedicine, and beyond. Resolving the chemistry and structural features of new thin film materials requires an extended selection of characterization and modeling techniques. Here we demonstrate how the unique features of the ALD/MLD grown in situ crystalline Fe-BDC thin films, different from the bulk Fe-BDC MOFs, can be resolved through techniques such as synchrotron grazing-incidence X-ray diffraction (GIXRD), Mössbauer spectroscopy, and resonant inelastic X-ray scattering (RIXS) and crystal structure predictions. The investigations of the Fe-BDC thin films, containing both trivalent and divalent iron, converge toward a novel crystalline Fe(III)-BDC monoclinic phase with space group C2/c and an amorphous Fe(II)-BDC phase. Finally, we demonstrate the excellent thermal stability of our Fe-BDC thin films.
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Jun 2024
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[26330]
Open Access
Abstract: We use a combination of X-ray pair distribution function (PDF) measurements, lattice dynamical calculations, and ab initio density functional theory (DFT) calculations to study the local structure and dynamics in various MPt(CN)6 Prussian blue analogues. In order to link directly the local distortions captured by the PDF with the lattice dynamics of this family, we develop and apply a new “interaction-space” PDF refinement approach. This approach yields effective harmonic force constants, from which the (experiment-derived) low-energy phonon dispersion relations can be approximated. Calculation of the corresponding Grüneisen parameters allows us to identify the key modes responsible for negative thermal expansion (NTE) as arising from correlated tilts of coordination octahedra. We compare our results against the phonon dispersion relations determined using DFT calculations, which identify the same NTE mechanism.
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May 2024
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166, 32893, 14239]
Open Access
Abstract: Recent advances in anion-redox topochemistry have enabled the synthesis of metastable mixed-anion solids. Synthesis of the new transition metal oxychalcogenide Sr2MnO2Na1.6Se2 by topochemical Na intercalation into Sr2MnO2Se2 is reported here. Na intercalation is enabled by the redox activity of [Se2]2– perselenide dimers, where the Se–Se bonds are cleaved and a [Na2–xSe2](2+x)– antifluorite layer is formed. Freshly prepared samples have 16(1) % Na-site vacancies corresponding to a formal oxidation state of Mn of +2.32, a mixed-valence between Mn2+ (d5) and Mn3+ (d4). Samples are highly prone to deintercalation of Na, and over two years, even in an argon glovebox environment, the Na content decreased by 4(1) %, leading to slight oxidation of Mn and a significantly increased long-range ordered moment on the Mn site as measured using neutron powder diffraction. The magnetic structure derived from neutron powder diffraction at 5 K reveals that the compound orders magnetically with ferromagnetic MnO2 sheets coupled antiferromagnetically. The aged sample shows a metamagnetic transition from bulk antiferromagnetic to ferromagnetic behavior in an applied magnetic field of 2 T, in contrast to the Cu analogue, Sr2MnO2Cu1.55Se2, where there is only a hint that such a transition may occur at fields exceeding 7 T. This is presumably due to the higher ionic character of [Na2–xSe2](2+x)– layers compared to [Cu2–xSe2](2+x)– layers, reducing the strength of the antiferromagnetic interactions between MnO2 sheets. Electrochemical Na intercalation into Sr2MnO2Se2 leads to the formation of multiphase sodiated products. The work shows the potential of anion redox to yield novel compounds with intriguing physical properties.
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May 2024
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