I10-Beamline for Advanced Dichroism - scattering
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Diamond Proposal Number(s):
[38952]
Open Access
Abstract: High-entropy perovskite oxides offer a promising platform for tailoring magnetic functionality through compositional complexity; however, it remains unclear how targeted substitution of 4d transition metals modifies oxygen-mediated electronic structure and element-specific magnetic interactions. To address this question, we investigate the effect of Mo and Ru substitution on the electronic structure and magnetism of high-entropy perovskite oxide thin films using O K-edge and transition-metal L-edge X-ray absorption spectroscopy, X-ray magnetic circular dichroism (XMCD), and X-ray linear dichroism. O K-edge spectra reveal that Ru enhances O 2p–metal d hybridization, whereas Mo modifies charge distribution and local exchange pathways within the transition-metal sublattice. Multiplet analysis shows that Mn and Ni retain stable Mn4+ and Ni2+ states, while Co acts as the primary charge-compensation reservoir through changes in the Co2+/Co3+ ratio. Temperature-dependent XMCD demonstrates that these substitutions selectively reshape the magnetic exchange network, redistributing spin polarization among the constituent elements. Quantitative XMCD sum-rule analysis reveals that Mo substitution produces the highest reconstructed total magnetic moment across the measured temperature range, reaching values at low temperature that are nearly an order of magnitude larger than those observed in the Ru-containing compositions. These results establish a composition-driven strategy for tuning covalency, charge redistribution, and the balance between localized and itinerant magnetism in high-entropy oxide thin films, providing a pathway toward the design of tunable spintronic and multifunctional oxide materials.
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Aug 2026
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I15-Extreme Conditions
I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[41632, 36628, 38508]
Open Access
Abstract: Hybrid lead halide perovskites exhibit a delicate interplay between average crystallographic symmetry, local structural disorder and A-site orientational dynamics, giving rise to unusual vibrational and electronic behavior. Here, we combine large-scale molecular dynamics with a density-functional-theory-accurate machine learning force field to resolve the structural dynamics of perovskites across mesoscopic length scales. In formamidinium lead iodide (FAPbI3), we identify a high-temperature α phase with dynamic local order and correlated tilt nanodomains, an ordered γ phase with long-range a+a+a+ tilt coherence, and, below ∼100 K, a history-dependent γ′ state consisting of locally γ-like nanoscale regions separated by sharp twin-like boundaries. This low-temperature disordered state is not a distinct bulk polymorph, but a kinetically arrested metastable twin-domain network selected by the interplay between shallow tilt energetics and slowing FA reorientation. This picture is supported by our low-temperature X-ray diffuse scattering measurements and accounts for the broadened low-energy vibrational response found in the simulations. Furthermore, this unique structural landscape imprints a spatially varying electronic disorder with implications for macroscopic optoelectronic properties, reflected in substantial band-edge broadening retained at low temperature. Our results reconcile the debated low-temperature behavior of FAPbI3 in terms of competition between ordered and arrested structural states, and more broadly identify molecular reorientation as a kinetic selector of metastable framework topology in soft molecular crystals, placing thermal history on equal footing with composition as a determinant of structural and optoelectronic properties.
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Aug 2026
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[32893, 39378]
Open Access
Abstract: Systematic strategies to design properties such as ferroelectricity or magnetoelectric coupling are well-established in simple perovskite materials, but they remain scarce in more complex framework structures. Using a hexagonal polytype of the ternary Manganite AMnO3 (A= Ba, Sr, Ca) as a model system, we introduce a symmetry-guided design principle in which an inversion-breaking rigid-unit mode (RUM) serves as a single structural instability generating both polar and ferromagnetic orders within a bulk antiferromagnetic material. Symmetry analysis and first-principles calculations reveal that cooperative tilts of the Mn2O9 bioctahedral dimers generate a spontaneous polarization, and in the antiferromagnetically ordered state, they also induce a ferromagnetic moment. High-resolution diffraction and magnetic susceptibility measurements show that the structural and magnetic orders persist as high as 450 and 280 K, respectively, highlighting the untapped potential of framework structures that deviate from simple perovskite motifs to be designed to host useful ferroic properties. Our approach establishes a transferable symmetry-based framework for engineering ferroelectric and magnetoelectric states across chemically diverse framework architectures.
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Aug 2026
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[40151]
Open Access
Abstract: Pressure-driven phase transitions provide a means to modulate entropy in solids, although achieving large and reversible caloric responses remains a central challenge. The layered hybrid organic-inorganic perovskite (C9H19NH3)2CdCl4 exhibits two first-order transitions near room temperature that underpin its barocaloric response. High-pressure calorimetry combined with synchrotron X-ray diffraction shows that compression stabilizes a mixed-phase region over a wide pressure-temperature range rather than inducing a complete transformation. Consequently, the effective entropy change decreases with pressure, while a substantial reversible contribution is preserved, yielding reversible entropy and temperature changes of ΔSᵣeᵥ ≈ 136 J kg−1 K−1 and ΔTᵣeᵥ ≈ 17 K for a pressure change of 0.8 kbar. This leads to a refrigerant capacity exceeding 4 kJ kg−1 with a favorable coefficient of performance in the low-pressure regime. Notably, the large reversible temperature changes achieved at moderate pressures and close to room temperature highlight the potential of this material for solid-state cooling. Overall, these results demonstrate that high caloric performance can be achieved without complete phase transformation, reflecting a trade-off between entropy change and reversibility enabled by the structural flexibility of hybrid organic-inorganic materials.
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Aug 2026
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I07-Surface & interface diffraction
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Qichun
Gu
,
Tianjun
Liu
,
Yucheng
Xu
,
Xinjuan
Li
,
Yunzhou
Deng
,
Yang
Lu
,
Youcheng
Zhang
,
Zimu
Wei
,
Xinyu
Bai
,
Capucine
Mamak
,
Yutong
Han
,
Alessandro J.
Mirabelli
,
Weidong
Xu
,
Jian
Mao
,
Caterina
Ducati
,
Henning
Sirringhaus
,
Samuel D.
Stranks
,
Miguel
Anaya
Diamond Proposal Number(s):
[32266]
Open Access
Abstract: Perovskite light-emitting diodes (PeLEDs) are promising low-cost, solution-processable, and color-pure optoelectronic devices for display and lighting applications. However, blue PeLEDs continue to lag their green and red counterparts in terms of luminance and operational lifetime, limiting their practical implementation. The performance disparity primarily arises from charge injection imbalance, which accelerates degradation at the perovskite/hole transport layer (HTL) interface under electrical bias. Here, we design a polymer blend HTL comprising poly(N-vinyl-2,7-difluoro-carbazole) (PVK-F) and poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA), in which strengthened van der Waals interactions promote denser molecular packing. This optimized microstructure simultaneously enhances hole mobility and wettability, enabling high-quality perovskite film formation. Consequently, PeLEDs emitting at 485 nanometers achieve an external quantum efficiency of 24.1% and luminance exceeding 26,000 candela per square meter. Moreover, the improved hole injection mitigates interfacial degradation, yielding an operational half-lifetime exceeding 700 minutes at an initial luminance of 100 candela per square meter. This work establishes polymer blending as an effective strategy for advancing the performance and stability of blue PeLEDs.
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Aug 2026
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[38214]
Open Access
Abstract: Highly anisotropic platelet-shaped particles can be used to enhance both structural and functional applications. Anisotropic perovskites are especially in recent focus for their functional properties, including opto- and piezo-electric. Topochemical microcrystal conversion (TMC) in molten salt has been established as a scalable and robust way to fabricate anisotropic perovskite particles from templates. However, TMC often provides a low degree of control on the particle size and aspect ratio. The control over the particle shape is key to the crystallographic texture and mechanical properties of the final material. A comprehensive examination of the full reaction process is still lacking, leaving the underlying reaction mechanisms in large part unresolved. In this work, we employed in situ time-resolved synchrotron X-ray diffraction to monitor the TMC of Bi0.5Na0.5TiO3 (BNT) from Bi4Ti3O12 (BiT) templates under varying TiO2 deficiencies and uncovered new insights into the nucleation and growth mechanisms. We demonstrate that control over nucleation and initial anisotropic crystallite growth continuously dictates the final BNT particles’ morphologies. Based on these new insights, we produce BNT platelets with a 1.2- ∼2.1-times higher median aspect ratio than previously reported. In addition, we fabricated thin (170 nm) Bi0.5Na0.5TiO3–BaTiO3 platelets with a median and 90th percentile aspect ratio of up to 17 and 41, 1.4- and 2.9-fold higher than that of BiT templates (∼12 and 15), respectively, further ascertaining our growth model and its applicability to other BNT-based compositions. Our results expand our knowledge of the TMC process and open the way to producing high-aspect-ratio and quality perovskite platelets.
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Jul 2026
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[38966]
Open Access
Abstract: Mixed-cation lead mixed-halide perovskites are promising materials for applications in photovoltaics; however, it has been suggested that they exhibit instabilities linked to nanoscale heterogeneity. Directly probing the origins of this heterogeneity requires characterization with nanoscale spatial resolution, making transmission electron microscopy (TEM) an essential tool. However, characterizing these materials is challenging due to their extreme sensitivity to electron irradiation. Here, we develop a low-dose, concurrent methodology using four-dimensional scanning transmission electron microscopy (4D-STEM) and energy-dispersive x-ray spectroscopy (EDX) in order to map both the chemical and structural architecture of a (FA0.83Cs0.17)Pb(I0.8Br0.2)3 perovskite film without inducing damage. Our correlative analysis reveals a complex mosaic of coexisting crystal structures in this state-of-the-art LHP film. We establish a direct link between local chemical composition and crystal structure, showing that the formation of undesirable, photovoltaically inactive hexagonal polytypes is predominantly driven by local deficiencies in the stabilizing cesium cation. These findings provide crucial insight into one of the fundamental origins of structural instabilities in mixed composition perovskite thin-films, suggesting that achieving long-term device performance requires the development of fabrication routes that ensure compositional homogeneity at the nanoscale.
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Jul 2026
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166]
Abstract: Layered perovskite oxides continue to be the subject of intense research efforts due to their highly tunable crystal structures, which often arise from the competition between various lattice, spin, charge and orbital degrees of freedom. In particular, a number of recent works have focused on the mechanisms through which polar phases (those with globally broken inversion symmetry) emerge through the coupling of different structural distortions. The so-called hybrid improper mechanism, in which nonpolar structural distortions couple to break inversion symmetry, has been invoked to explain the appearance of polar structures in many different layered perovskite oxides. We use a combined experimental and computational approach to investigate the pseudo-Ruddlesden–Popper system Li2SrxCa1–xTa2O7 (0 < x < 1), which exhibits multiple competing polar phases that arise through distinct mechanisms. We untangle the complex interactions between various structural modes and find that, in contrast with previous work, the hybrid improper mechanism cannot by itself account for the observed polar phases. Our work demonstrates that there are significant differences in the mechanisms through which polar phases emerge in even nominally the same family of layered perovskites, suggesting a rich playground for further exploration and functional materials design.
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Jun 2026
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B18-Core EXAFS
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Diamond Proposal Number(s):
[37961]
Open Access
Abstract: In the present work, we report the exsolution of CoFe nanoalloy nanoparticles from Co and Fe co-doped lanthanum aluminate perovskite oxide, LaAl0.90Co0.05Fe0.05O3, and assess the perovskite oxide as an oxygen reduction reaction (ORR) electrocatalyst. We optimized both intrinsic and extrinsic material properties of perovskites to achieve good electrocatalytic performance in the kinetic and mass-transfer controlled region. Firstly, we demonstrated that the near surface segregation of B-site cation (Co) under reducing environment at low temperature (at 500 °C), believed to represent the initial stage of exsolution, led to high ORR activity in the mass-controlled region, with specific and mass activities of 4.9 mA/cm2 and 37.5 A/g (@0.4 V versus RHE), respectively. Secondly, reducing the particle size of perovskite oxide increased surface exposure to the reducing environment promoting the CoFe nanoalloy particle exsolution. The results demonstrate that cation enrichment in subsurface region, near grain boundaries contributes more effectively to ORR activity than exsolution in the form of nanoparticles in this perovskite oxide composition. Nevertheless, achieving fast charge transfer-kinetics without the use of precious metals still remains a challenge with lanthanum aluminates, as indicated by onset potentials of 0.84 V and 0.81 V (versus RHE) for the pristine and reduced perovskite oxide, respectively. Notably, impregnation of perovskite oxide with 0.2 wt. % Pt followed by heat treatment in reducing atmosphere at 500 °C increased the onset potential to 0.9 V. Overall, this study suggests that non-precious metal-doped lanthanum aluminate, LaAl0.90Co0.05Fe0.05O3, exhibits strong electrocatalytic activity and is further enhanced through impregnation treatment.
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Jun 2026
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[24600, 30866]
Open Access
Abstract: The electron in a solid can be considered a bound state of the three independent, fundamental degrees of freedom creating quasiparticles: spinons, carrying the electron spin; plasmons, carrying the collective charge mode; and orbitons, carrying its orbital degree of freedom. These fundamental degrees of freedom could form ordering states in which dynamics or collective motions could occur and manifest as low-energy excitations. The exotic properties that appear in the materials exhibiting these electronic orderings are associated with these low-energy excitations. Although the orbital order (OO) and its coupling to the spin system creates very interesting phenomena, the microscopic origin of OO has been much less explored than other electronic properties as it is very difficult to directly access experimentally. Due to the recent improvement in energy resolution and flux, soft-x-ray resonant inelastic scattering (RIXS) allows for a reexamination of orbital excitations in manganites. Here, we present a study of low-energy excitations in half doped 𝐴-site ordered SmBaMn2O6 through a combination of RIXS and soft-x-ray resonant elastic scattering measurements. We confirm the existence of OO at 𝐪 = (0.25, 0.25, 0) and find various low-energy excitations below 200 meV. While several excitations can be assigned to be of magnetic and phononic origin, a group of excitations between 80 and 200 meV show a temperature dependence closely following that of the OO, making them possible candidates for orbitons.
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Jun 2026
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