B18-Core EXAFS
I11-High Resolution Powder Diffraction
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James M. A.
Steele
,
Joshua D.
Bocarsly
,
Liam A. V.
Nagle-Cocco
,
George S.
Phillips
,
Farheen N.
Sayed
,
Giulio I.
Lampronti
,
Fabio
Orlandi
,
Pascal
Manuel
,
Iuliia
Mikulska
,
Clare P.
Grey
,
Sian E.
Dutton
Diamond Proposal Number(s):
[34243, 32018]
Open Access
Abstract: NaNiO2 is a promising cathode material for sodium-ion batteries due to its high theoretical capacity of 235.8 mAh.g–1. However, as with many Na-ion cathode materials, a series of poorly understood phase transitions occur on electrochemical cycling, inducing volume mismatch-based stress/strain, resulting in particle cracking, electrochemically disconnected particles and, therefore, irreversible capacity loss. This behavior is one key obstacle to developing long-lasting, high-performance Na-ion batteries. Although the series of phases that form as NaxNiO2 is electrochemically cycled have been previously identified, their structures remained unsolved, limiting our ability to understand and control the phase transition behavior. Here, we report structural solutions based on Rietveld refinement against high-resolution synchrotron x-ray diffraction (SXRD) and neutron powder diffraction (NPD) for the phases obtained on desodiation: P″3-Na1/2NiO2, O″3-Na2/5NiO2, and O‴3-Na1/3NiO2. Each phase contains a unique Na+/vacancy ordering, minimizing intralayer electrostatic repulsions between Na+ ions, and Nix+-charge ordering decreasing interlayer repulsions through the location of lower valence Nix+ nearer to vacancies. Using these structures, we conduct sequential Rietveld refinement against operando SXRD data, which supports prior identification of a transient P‴3-Na1/2<x<2/3NiO2 phase, not isolable ex situ. Operando data also identify the presence of a solid-solution phase O″3δ-Na1/3<x<2/5NiO2 and second-order behavior of the O″3-Na2/5NiO2 → O‴3-Na1/3NiO2 phase transition at the top of charge. This work provides unprecedented insight into structural evolution during electrochemical cycling in Ni-rich Na cathodes (and likely Li analogues), paving the way toward rational doping regimes designed to disrupt degradation-inducing phase transitions, increasing capacity and cycle lifetime, thus improving the performance of Co-free Na and Li cathodes.
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May 2026
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[40166]
Abstract: We report bulk magnetic properties of the monoclinic lanthanide tantalates, 𝑀′−𝐿𝑛TaO4 (𝐿𝑛= Tb, Dy, Ho, Er), where the magnetic 𝐿𝑛3+ ions are arranged on a distorted 2D square lattice. The heavier analog 𝑀′−YbTaO4 has been investigated as a spin-orbit-coupled, quasi-two-dimensional frustrated magnet, and the properties of the other 𝑀′−𝐿𝑛TaO4 are expected to vary depending on the electronic configuration of the 𝐿𝑛 ion, namely, Kramers vs non-Kramers behavior and different crystal electric field parameters. In this work, powder neutron diffraction is used to confirm the crystal structure for 𝐿𝑛= Tb, Ho, Er, and to determine the magnetic structure of 𝑀′−TbTaO4, which displays long-range antiferromagnetic (AFM) order below 𝑇N=2.1K. The Tb3+ moments are aligned primarily along the 𝑐 axis with AFM nearest-neighbor interactions. Susceptibility data suggest that 𝑀′−DyTaO4 may display short-range ordering around 2.7 K, while 𝑀′−HoTaO4 and 𝑀′−ErTaO4 show AFM correlations but do not order above 1.8 K. Measurements of the magnetic specific heat provide evidence for a Kramers doublet ground state in 𝑀′−ErTaO4, similar to its heavier analog 𝑀′−YbTaO.
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Apr 2026
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[34243]
Open Access
Abstract: Lanthanide borates are widely studied for their optical and magnetic properties. A wide variety of structures are known with 3, 2, 1 and 0 dimensional connectivity of lanthanide ions. Here, we explore MgO10, with a quasi-1D arrangement of the Ln ions. Polycrystalline samples of MgO10 (Ln = La, Pr, Nd, Sm–Er) were synthesised via a solution-based method, which achieved higher purity than a solid-state method. Powder x-ray diffraction data confirmed the reported monoclinic space group (). The magnetic ions in MgO10 form relatively isolated zig-zag chains parallel to the b axis. Magnetic susceptibility and isothermal magnetisation were measured: all samples except (Eu, Sm) fit the Curie-Weiss Law in isothermal magnetisation at high temperatures, in broad agreement with theoretical expectations. (Nd, Tb, Dy, Ho, Er) exhibit signatures characteristic of Ising spin saturation, implying single ion anisotropy, while Gd exhibits characteristics of Heisenberg spins. Estimation of magnetic interactions suggests that MgO10 are candidate materials for quasi-1D magnetism. The magnetocaloric entropy change was also calculated, with MgGdB5O10 showing promise for application to solid-state refrigeration at liquid helium temperatures.
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Jan 2026
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[28349, 34243]
Open Access
Abstract: Ba2GdNbO6 has previously been reported to adopt either monoclinic, tetragonal, or cubic symmetry at room temperature. Using high-resolution synchrotron X-ray diffraction, neutron diffraction and neutron pair distribution function analysis we find that the compound adopts a tetragonal I4/m double-perovskite structure at room temperature (with a weak, temperature-independent second-order Jahn–Teller distortion in the NbO6 octahedra) and undergoes a phase transition to a monoclinic P21/n symmetry upon cooling to 2.4 K. Only upon heating above room temperature to T ≈ 450 K does Ba2GdNbO6 reversibly transition to a cubic Fm3̅m symmetry. Magnetic susceptibility measurements indicate predominant paramagnetic behavior down to 1.8 K, with minimal ferromagnetic short-range correlations (θ = 0.20(5) K) and a small exchange interaction (J1 = −0.0032(8) K). At 2 K and 9 T, the compound exhibits a maximum magnetic entropy change of −ΔSm = 15.75 J K–1 mol–1 and an adiabatic temperature change of ΔTad = 21 K, making it a promising candidate for low-temperature magnetocaloric applications. Heat capacity measurements confirm a rigid crystal lattice (TD = 267(3) K) and a corresponding small lattice entropy contribution in the low-temperature regime, highlighting the potential of Ba2GdNbO6 for effective cooling capability in magnetocaloric devices at cryogenic temperatures. This study elucidates the structural and magnetic characteristics of Ba2GdNbO6 and attests to its promise for low-temperature magnetocaloric refrigeration.
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Oct 2025
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[33172, 14239]
Open Access
Abstract: Recent reviews have highlighted borate polyanion systems as promising high-voltage cathode candidates for rechargeable Mg-ion batteries (RMBs) [Coordination Chemistry Reviews, 427, 213551 (2021)]. However, evaluating the electrochemical performance of cathodes for Mg-ion batteries is challenging, with many reports relying on an observed electrochemical capacity rather than demonstrating Mg-ion (de)intercalation. To address these two points, we study three classes of borate polyanions: orthoborates M3(BO3)2, ludwigites M3BO5, and pyroborates M2B2O5 and use a suite of experimental techniques to investigate de-magnesiation on charging vs Li metal with a Li electrolyte. We select five representative materials Mg2Mn(BO3)2, Mg2Ni(BO3)2, Mg2FeBO5, MgFeB2O5 and MgFe0.5Mn0.5B2O5. Whilst promising first charge capacities up to 200 mAh g−1 are observed for ball-milled cathodes cycled at 55°C in a Li containing electrolyte, extensive post-cycling analysis using ex-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Synchrotron Powder X-ray Diffraction (SXRD), combined with operando X-ray Absorption Spectroscopy (XAS) and operando Online Electrochemical Mass Spectrometry (OEMS), show that the capacities obtained are not associated with Mg2+ mobility in the cathodes, de-magnesiation or transition-metal redox. The observed capacity originates from a process enhanced by ball-milling, which is common to all borate polyanions investigated in this work. This process is in part attributed to the irreversible reaction of an amorphous surface layer on the polycrystalline particle, rich in carbonate and glassy borate phases. Here we present the first systematic study of the viability of transition-metal borate polyanions as intercalation cathode materials for RMBs and conclude that, despite the promising electrochemistry, these materials do not de-magnesiate under our tested conditions.
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Sep 2025
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I15-1-X-ray Pair Distribution Function (XPDF)
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Chumei
Ye
,
Lauren N.
Mchugh
,
Pierre
Florian
,
Ruohan
Yu
,
Celia
Castillo-Blas
,
Celia
Chen
,
Arad
Lang
,
Yuhang
Dai
,
Jingwei
Hou
,
David A.
Keen
,
Sian E.
Dutton
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[35405]
Open Access
Abstract: Hybrid organic-inorganic perovskites (HOIPs) have garnered significant attention for their crystalline properties, yet recent findings reveal that they can also form liquid and glassy phases, offering an alternative platform for understanding non-crystalline materials. In this study, we present a detailed investigation into the structural dynamics of the melting and glass formation process of a two-dimensional (2D) HOIP, (S−(−)−1-(1−naphthyl)ethylammonium)2PbBr4. Compared to its crystalline counterpart, the glass exhibits superior mechanical properties, including higher Young’s modulus and hardness. Our structural studies reveal that the liquid and glass formed from the 2D HOIP exhibit network-forming behaviour, featuring limited short-range order within individual octahedra, partial retention of metal-halide-metal connectivity between neighbouring octahedra, and residual structural correlations mediated by organic cations. We then combine in situ variable-temperature X-ray total scattering experiments, terahertz far-infrared absorption spectroscopy and solid-state nuclear magnetic resonance techniques to study the melting mechanism and the nature of the HOIP liquid obtained. Our results deepen the understanding of the structural evolution and property relationships in HOIP glasses, providing a foundation for their potential applications in advanced phase-change material technologies.
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Aug 2025
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I11-High Resolution Powder Diffraction
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George S.
Phillips
,
James M. A.
Steele
,
Farheen N.
Sayed
,
Leonhard
Karger
,
Liam A. V.
Nagle-Cocco
,
Annalena R.
Genreith-Schriever
,
Gabriel E.
Perez
,
David A.
Keen
,
Jürgen
Janek
,
Torsten
Brezesinski
,
Joshua D.
Bocarsly
,
Sian E.
Dutton
,
Clare P.
Grey
Diamond Proposal Number(s):
[34243]
Open Access
Abstract: Lithium nickel oxide, LiNiO2 (LNO), and its doped derivatives are promising battery cathode materials with high gravimetric capacity and operating voltages. They are also of interest to the field of quantum magnetism due to the presumed S = 1/2 triangular lattice and associated geometric frustration. However, the tendency for Li/Ni substitutional defects and off-stoichiometry makes fundamental studies challenging. In particular, there is still a discrepancy between the rhombohedral (R3̅m) bulk structure and the Jahn–Teller (JT) distortions of the NiO6 octahedra inferred on the basis of local structural probes. Karger et al. (Chem. Mater. 2023, 35, 648–657) recently used Na/Li ion exchange to synthesize “defect-free” LNO by exploiting the absence of antisite disorder in NaNiO2 (NNO). Here we characterize the short- and long-range structure of this ion-exchanged material and observe splittings of key Bragg reflections at 100 K in X-ray and neutron diffraction (XRD and NPD), indicative of a monoclinic distortion induced by a cooperative collinear JT distortion, similar to that seen in NNO. Variable temperature XRD reveals a second-order phase transition from the monoclinic (C2/m) low-temperature structure to a rhombohedral (R3̅m) structure above ∼400 K. We propose that this collinear JT ordering is also present in solid-state synthesized LNO with the domain size and extent of monoclinic distortion controlled by defect concentration. This new structural description of LNO will help advance our understanding of its electronic and magnetic properties and the series of phase transformations that this material undergoes upon electrochemical cycling in Li-ion batteries.
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Jul 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[31718]
Open Access
Abstract: NaNiO$_2$ is a Ni$^{3+}$-containing layered material consisting of alternating triangular networks of Ni and Na cations, separated by octahedrally-coordinated O anions. At ambient pressure, it features a collinear Jahn--Teller distortion below $T^\mathrm{JT}_\mathrm{onset}\approx480$\,K, which disappears in a broad first-order transition on heating to $T^\mathrm{JT}_\mathrm{end}\approx500$\,K, corresponding to the increase in symmetry from monoclinic to rhombohedral. It was previously studied by variable-pressure neutron diffraction [ACS Inorganic Chemistry 61.10 (2022): 4312-4321] and found to exhibit an increasing $T^\mathrm{JT}_\mathrm{onset}$ with pressure up to $\sim$5\,GPa. In this work, powdered NaNiO$_2$ was studied \textit{via} variable-pressure synchrotron x-ray diffraction up to pressures of $\sim$67\,GPa at 294\,K and 403\,K. Suppression of the collinear Jahn--Teller ordering is observed \textit{via} the emergence of a high-symmetry rhombohedral phase, with the onset pressure occurring at $\sim$18\,GPa at both studied temperatures. Further, a discontinuous decrease in unit cell volume is observed on transitioning from the monoclinic to the rhombohedral phase. These results taken together suggest that in the vicinity of the transition, application of pressure causes the Jahn--Teller transition temperature, $T^\mathrm{JT}_\mathrm{onset}$, to decrease rapidly. We conclude that the pressure-temperature phase diagram of the cooperative Jahn--Teller distortion in NaNiO$_2$ is dome-like.
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Apr 2025
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I11-High Resolution Powder Diffraction
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James M. A.
Steele
,
Annalena R.
Genreith-Schriever
,
Joshua D.
Bocarsly
,
Liam A. V.
Nagle-Cocco
,
Farheen N.
Sayed
,
Marie
Juramy
,
Christopher A.
O'Keefe
,
Fabio
Orlandi
,
Pascal
Manuel
,
Sian E.
Dutton
,
Clare P.
Grey
Diamond Proposal Number(s):
[34243]
Open Access
Abstract: NaNiO2 (NNO) has been investigated as a promising sodium-ion battery cathode material, but it is limited by degradation-induced capacity fade. On desodiation, NNO forms multiple phases with large superstructures due in part to Na+-ion vacancy ordering; however, their structures are unknown. Here, we report a structural solution to the Na2/3NiO2 (P′3) desodiated phase using combined Rietveld refinement of high-resolution synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) data, magnetic susceptibility, and 23Na solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Our experimental results are compared to ab initio molecular dynamics (AIMD) simulations, which indicate multiple low-energy structures that are dynamically populated. We observe a combination of competing effects that contribute to the resultant dynamic nature of the structure, including honeycomb ordering of mixed-valence Ni, orbital ordering of Jahn–Teller (JT) distorted Ni3+, and zigzag Na+/vacancy ordering. Our work provides evidence of multiple contributions to the structures of desodiated Na2/3NiO2, along with a framework for investigating the other unsolved desodiated structures. This work may also inform our understanding of the Jahn–Teller evolution in other nickel-rich lithium- and sodium-ion cathodes, such as LiNiO2.
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Mar 2025
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I15-1-X-ray Pair Distribution Function (XPDF)
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Bikash Kumar
Shaw
,
Lucia
Corti
,
Joshua M.
Tuffnell
,
Celia
Castillo-Blas
,
Patrick
Schlachta
,
Georgina P.
Robertson
,
Lauren
Mchugh
,
Adam F.
Sapnik
,
Sebastian A.
Hallweger
,
Philip A.
Chater
,
Gregor
Kieslich
,
David A.
Keen
,
Sian E.
Dutton
,
Frédéric
Blanc
,
Thomas D.
Bennett
Diamond Proposal Number(s):
[20038]
Open Access
Abstract: ABX3-type hybrid organic–inorganic structures have recently emerged as a new class of meltable materials. Here, by the use of phenylphosphonium derivatives as A cation, we study liquid- and glass-forming behavior of a new family of hybrid structures, (RPh3P)[Mn(dca)3] (R = Me, Et, Ph; dca = dicyanamide). These new compounds melt at 196–237 °C (Tm) and then vitrify upon cooling to room temperature, forming glasses. In situ glass formation of this new family of materials was probed on a large scale using a variable-temperature PXRD experiment. Structure analyses of the crystalline and the glasses were carried out by solid-state nuclear magnetic resonance spectroscopy and synchrotron X-ray total scattering techniques for using the pair distribution function. The mechanical properties of the glasses produced were evaluated showing promising durability. Thermal and electrical conductivities showed low thermal conductivities (κ ∼ 0.07–0.09 W m–1 K–1) and moderate electrical conductivities (σ ∼ 10–4–10–6 S m–1) at room temperature, suggesting that by the precise control of the A cation, we can tune meltable hybrid structures from moderate conductors to efficient thermal insulators. Our results raise attention on the practical use of this new hybrid material in applications including, e.g., photovoltaic devices to prevent light-deposited heat (owing to low κRT), energy harvesting thermoelectric, etc., and advance the structure–property understanding.
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Dec 2024
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