I21-Resonant Inelastic X-ray Scattering (RIXS)
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Daniel
Jost
,
Eder G.
Lomeli
,
Woo Jin
Kim
,
Emily M.
Been
,
Matteo
Rossi
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Chunjing
Jia
,
Brian
Moritz
,
Zhi-Xun
Shen
,
Harold Y.
Hwang
,
Thomas P.
Devereaux
,
Wei-Sheng
Lee
Open Access
Abstract: The layered cobaltate CaCoO2 exhibits a unique herringbone-like structure. Serving as a potential prototype for a new class of complex lattice patterns, we study the properties of CaCoO2 using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Our results reveal a significant inter-plane hybridization between the Ca 4s- and Co 3d- orbitals, leading to an inversion of the textbook orbital occupation of a square planar geometry. Further, our RIXS data reveal a strong low energy mode, with anomalous intensity modulations as a function of momentum transfer close to a quasi-static response. These findings indicate that the newly discovered herringbone structure exhibited in CaCoO2 may serve as a promising laboratory for the design of materials having strong electronic, orbital and lattice correlations.
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Jun 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[26777]
Open Access
Abstract: Resonant inelastic x-ray scattering (RIXS) has become a prominent technique to study quasiparticle excitations. With advances in polarization analysis capabilities at different facilities, RIXS offers exceptional potential for investigating symmetry-broken quasiparticles such as chiral phonons and magnons. At optical wavelengths, birefringence can severely affect polarization states in low-symmetry systems. Here we show its importance for soft x-ray resonances. Given the growing interest in circular dichroism (CD) in RIXS, it is important to evaluate how birefringence may affect the RIXS spectra of anisotropic systems. We investigate CuO, a well-known anisotropic material, using Cu 𝐿3-edge RIXS and detect significant CD in both magnetic and orbital excitations in the collinear antiferromagnetic phase. We demonstrate that the CD can be modeled by a proper treatment of RIXS scattering amplitudes derived from single-ion calculations with birefringence. Recognizing these effects is crucial for unambiguous identification of subtle dichroic effects induced by symmetry-broken quasiparticles. Furthermore, the combined sensitivity of RIXS and birefringence to local symmetry presents an opportunity to study microscopic changes driven by external perturbations.
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May 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Karin
Von Arx
,
Pascal
Rothenbühler
,
Qisi
Wang
,
Leonardo
Martinelli
,
Jaewon
Choi
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Antonio
Vecchione
,
Rosalba
Fittipaldi
,
Yasmine
Sassa
,
Mario
Cuoco
,
Filomena
Forte
,
Johan
Chang
Diamond Proposal Number(s):
[27638]
Open Access
Abstract: Multi-band Mott insulators with moderate spin-orbit and Hund’s coupling are key reference points for theoretical concept developments of correlated electron systems. The ruthenate Mott insulator Ca2RuO4 has therefore been intensively studied by spectroscopic probes. However, it has been challenging to resolve the fundamental excitations emerging from the hierarchy of electronic energy scales. Here we apply high resolution resonant inelastic x-ray scattering to probe deeper into the low-energy electronic excitations found in Ca2RuO4. In this fashion, we probe a series of spin-orbital excitations. By taking advantage of enhanced energy resolution, we probe a 40 meV mode through the oxygen K-edge. The polarization dependence of this low-energy excitations exposes a distinct orbital nature, originating from the interplay of spin-orbit coupling and octahedral rotations. Additionally, we discuss the role of magnetic correlations to describe the occurrence of excitations with amplitudes which are multiple of a given energy. Such direct determination of relevant electronic energy scales sharpens the target for theory developments of Mott insulators’ orbital degree of freedom.
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May 2025
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I15-1-X-ray Pair Distribution Function (XPDF)
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[35064, 39285, 40912]
Open Access
Abstract: Li-rich disordered rocksalts are promising next-generation cathode materials for Li-ion batteries. Recent reports have shown it is also possible to obtain Na-rich disordered rocksalts, however, it is currently poorly understood how the knowledge of the structural and redox chemistry translates from the Li-rich to the Na-rich analogs. Here, the properties of Li2MnO2F and Na2MnO2F are compared, which have different ion sizes (Li+ = 0.76 vs Na+ = 1.02 Å) but the same disordered rocksalt structure and stoichiometry. It is found that Na2MnO2F exhibits lower voltage Mn- and O-redox couples, opening access to a wider compositional range within the same voltage limits. Furthermore, the intercalation mechanism switches from predominantly single-phase solid solution behavior in Li2MnO2F to a two-phase transition in Na2MnO2F, accompanied by a greater decrease in the average Mn─O/F bond length. Li2MnO2F retains its long-range disordered rocksalt structure throughout the first cycle. In contrast, Na2MnO2F becomes completely amorphous during charge and develops a local structure characteristic of a post-spinel. This amorphization is partially reversible on discharge. The results show how the ion intercalation behavior of disordered rocksalts differs dramatically when changing from Li- to Na-ions and offers routes to control the electrochemical properties of these high-energy-density cathodes.
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May 2025
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[25166, 14239]
Open Access
Abstract: The high natural abundance and low toxicity of iron oxides provide a strong motivation to develop iron-based lithium-ion battery cathode materials. T-LiFeO2 adopts a cation-ordered wurtzite structure consisting of apex-linked LiO4 and FeO4 tetrahedra. Chemical or electrochemical lithium extraction rapidly converts T-LiFeO2 to the spinel LiFe5O8 and leads to poor energy storage performance. We have investigated the role of Al and Ga substitution on the stability of T-LiFeO2. Partial substitution of Fe by Al leads to the formation of cation-disordered solid solutions. In contrast, neutron diffraction data reveal that the Ga-substituted phase LiFe0.5Ga0.5O2 adopts an Fe/Ga cation-ordered structure. Chemical delithiation of LiFe1–xMxO2 phases reveals that 25% Al or 50% Ga substitution stabilizes the T-LiFe1–xMxO2 phases with respect to spinel conversion. The delithiated phases show no evidence of cation migration or oxygen loss. However, Fe-XANES, O-XAS, and O-RIXS data indicate that lithium extraction does not proceed via simple oxidation of Fe3+ to Fe4+ but rather via an anion redox process involving the formation of localized “FeIV–O” centers. Electrochemical data indicate that the formation of FeIV–O centers is irreversible, and so these oxidized species accumulate with continued electrochemical cycling, leading to a rapid decline in energy storage capacity. The electrochemical behavior of LiFe0.5Al0.5O2 and LiFe0.5Ga0.5O2 is discussed in terms of their crystal chemistry to account for the differing electrochemical performance of the Al- and Ga-substituted materials.
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Apr 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Jiarui
Li
,
Daniel
Jost
,
Ta
Tang
,
Ruohan
Wang
,
Yong
Zhong
,
Zhuoyu
Chen
,
Mirian
Garcia-Fernandez
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Brian
Moritz
,
Ke-Jin
Zhou
,
Yao
Wang
,
Thomas P.
Devereaux
,
Wei-Sheng
Lee
,
Zhi-Xun
Shen
Diamond Proposal Number(s):
[32900]
Abstract: Recent photoemission experiments on the quasi-one-dimensional Ba-based cuprates suggest that doped holes experience an attractive potential not captured using the simple Hubbard model. This observation has garnered significant attention due to its potential relevance to Cooper pair formation in high-𝑇𝑐 cuprate superconductors. To scrutinize this assertion, we examined signatures of such an attractive potential in doped 1D cuprates Ba2CuO3+𝛿 by measuring the dispersion of the 2-spinon excitations using Cu 𝐿3-edge resonant inelastic x-ray scattering (RIXS). Upon doping, the 2-spinon excitations appear to weaken, with a shift of the minimal position corresponding to the nesting vector of the Fermi points, 𝑞𝐹. Notably, we find that the energy scale of the 2-spinons near the Brillouin zone boundary is substantially softened compared to that predicted by the Hubbard model in one dimension. Such a discrepancy implies missing ingredients, which lends support for the presence of an additional attractive potential between holes.
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Apr 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Sophia F. R.
Tenhuisen
,
Grace A.
Pan
,
Qi
Song
,
Denitsa R.
Baykusheva
,
Dan
Ferenc Segedin
,
Berit H.
Goodge
,
Hanjong
Paik
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Yanhong
Gu
,
Stefano
Agrestini
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Lena F.
Kourkoutis
,
Charles M.
Brooks
,
Julia E. A.
Mundy
,
Mark P. M.
Dean
,
Matteo
Mitrano
Diamond Proposal Number(s):
[27484]
Abstract: Magnetic interactions are thought to play a key role in the properties of many unconventional superconductors, including cuprates, iron pnictides, and square-planar nickelates. Superconductivity was also recently observed in the bilayer and trilayer Ruddlesden-Popper nickelates, the electronic structure of which is expected to differ from that of cuprates and square-planar nickelates. Here we study how electronic structure and magnetic interactions evolve with the number of layers, 𝑛, in thin film Ruddlesden-Popper nickelates Nd𝑛+1Ni𝑛O3𝑛+1 with 𝑛=1,3, and 5 using resonant inelastic x-ray scattering (RIXS). The RIXS spectra are consistent with a high-spin |3𝑑8
𝐿
̲
⟩ electronic configuration, resembling that of La2−𝑥Sr𝑥NiO4 and the parent perovskite, NdNiO3. The magnetic excitations soften to lower energy in the structurally self-doped, higher-𝑛 films. Our observations confirm that structural tuning is an effective route for altering electronic properties, such as magnetic superexchange, in this prominent family of materials.
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Apr 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Yanfang
Wang
,
Cheng
Li
,
Yingzhi
Li
,
Raquel
De Benito
,
Jacob
Williams
,
Joshua M.
Stratford
,
Zhiqiang
Li
,
Chun
Zeng
,
Ning
Qin
,
Hongzhi
Wang
,
Yulin
Cao
,
Dominic
Gardner
,
Wilgner
Lima Da Silva
,
Sahil
Tippireddy
,
Qingmeng
Gan
,
Fangchang
Zhang
,
Wen
Luo
,
Joshua W.
Makepeace
,
Ke-Jin
Zhou
,
Kaili
Zhang
,
Fucai
Zhang
,
Phoebe K.
Allan
,
Zhouguang
Lu
Diamond Proposal Number(s):
[35147]
Abstract: Simultaneously harnessing cation and anion redox activities in the cathode is crucial for the development of high energy-density lithium-ion batteries. However, achieving long-term stability for both mechanisms remains a significant challenge due to pronounced anisotropic volume changes at low lithium content, unfavorable cation migration, and oxygen loss. Here, we demonstrate exceptionally stable cation and anion redox behavior in a metastable, cobalt-free layered oxide, Li0.693[Li0.153Ni0.190Mn0.657]O2 (LLNMO). After 50 cycles at 50 mA/g (~0.2 C), the cathode retains 97.4% of its initial capacity (222.4 mAh/g) with negligible voltage decay. This remarkable stability is attributed to its metastable rhombohedral symmetry (R-3m) with unique local structures. The face-sharing connectivity between lithium layers and alternating transition metal (TM) layers effectively suppresses TM migration-induced voltage decay during anion redox. Additionally, the structure balances interlayer cation/cation and anion/anion repulsions, resulting in minimal expansion and contraction during de-/lithiation (< 2.3% along the c-axis) and excellent structural reversibility. These findings highlight that layered oxides with a metastable framework are promising cathode candidates for next-generation ultra-high-energy lithium-ion batteries.
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Feb 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[32023]
Open Access
Abstract: Activation of oxygen anion redox represents an effective method of increasing the specific capacity as well as raising the operating voltage of layered sodium transition metal oxides. However, these reactions are often accompanied by irreversible structural transformations and detrimental side‑reactions between the electrolyte and electrode interface which accelerate degradation, thereby impeding their practical application. To optimise the oxygen anion reversibility for practical use and compare the effects of dopants, we investigated Zn- and Ti-substitution both separately and combined in P3‑structure Na0.7Mn0.75Ni0.25O2, assisted by DFT calculations. The Zn-substituted materials, Na0.7Mn0.65Ni0.25Zn0.1O2 and Na0.7Mn0.58Ni0.25Zn0.07Ti0.1O2 present superior cycling stability over the high voltage range 3.8-4.3 V and enhanced rate capability, delivering a reversible capacity of ~80 mA h g‑1 at 500 mA g‑1 over the voltage window 2.2‑4.3 V compared with 58.6 mA h g-1 for the parent-phase. The improved electrochemical performance of the Zn-substituted materials is attributed to suppression of the P3 to O’3 phase transformation revealed by X‑ray diffraction and the lower electronegativity and filled d ‑band of Zn. The presence of TiO6 octahedra in the Ti-substituted materials relieves structural distortions/TM ordering, also improving the cycling stability. With Zn/Ti co-substitution these advantages may be combined, as demonstrated by the superior electrochemical performance observed for Na0.7Mn0.58Ni0.25Zn0.07Ti0.1O2.
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Jan 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Zhengang
Dong
,
Marios
Hadjimichael
,
Bernat
Mundet
,
Jaewon
Choi
,
Charles C.
Tam
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Claribel
Domínguez
,
Regan
Bhatta
,
Yue
Yu
,
Yufeng
Liang
,
Zhenping
Wu
,
Jean-Marc
Triscone
,
Chunjing
Jia
,
Ke-Jin
Zhou
,
Danfeng
Li
Diamond Proposal Number(s):
[32305]
Abstract: Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward to address these intricate questions is through the growth of high-crystallinity infinite-layer nickelates, including the “parent” phase. Here, we report the synthesis of a high-quality thin-film nickelate, NdNiO2. This is achieved through the growth of a perovskite precursor phase (NdNiO3) of superior crystallinity on the NdGaO3 substrate by off-axis RF magnetron sputtering and a low-temperature topochemical reduction using NaH. We observe a nonlinear Hall effect at low temperatures in this “non-doped” phase. We further study the electronic properties using advanced X-ray scattering and first-principles calculations. We observe spectroscopic indications of the enhanced two-dimensionality and a reduced hybridization of Nd 5d and Ni 3d orbitals. These findings unlock new pathways for preparing high-quality infinite-layer nickelates and provide new insights into the intrinsic features of these compounds.
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Jan 2025
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