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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

An Aluminum-Based Metal–Organic Cage for Cesium Capture

Metal–organic cages are a class of supramolecular structures that often require the careful selection of organic linkers and metal nodes. Of this class, few examples of metal–organic cages exist where the nodes are composed of main group metals. Herein, we have prepared an aluminum-based metal–organic cage, H 8 [Al 8 (pdc) 8 (OAc) 8 O 4 ] (Al-pdc-AA), using inexpensive and commercially available materials. The cage formation was achieved via solvothermal self-assembly of solvated aluminum and pyridine-dicarboxylic linkers in the presence of a capping agent, acetic acid. The obtained supramolecular structure was characterized by single-crystal X-ray diffraction (SCXRD), thermogravimetric analysis, and NMR spectroscopy. Based on crystal structure and computational analyses, the cage has a 3.7 Å diameter electron-rich cavity suitable for the binding of cations such as cesium (ionic radius of 1.69 Å). Here, the host–guest interactions were probed with 1 H and 133 Cs NMR spectroscopy in DMSO, where at low concentrations, Cs + binds to Al-pdc-AA in a 1:1 ratio. The binding site was identified from the crystal structure of CsH 7 [Al 8 (pdc) 8 (OAc) 8 O 4 ] (Cs + Al-pdc-AA), and a binding affinity of ~10 6 –10 7 M –1 was determined from NMR titration experiments. The Al-pdc-AA showed improved selectivity for cesium binding over alkali metal cations (Cs + > Rb + > K + >> Na + ~ Li + ). Collectively, the study reports a novel aluminum cage that can serve as a promising host for efficient and selective cesium removal.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Sequential Bond Dissociation Energies of Th + (CO) x , x = 3–6: Guided Ion Beam Collision-Induced Dissociation and Quantum Computational Studies

Collision-induced dissociation (CID) of [Th,xC,xO] + , x = 3–6, with Xe is performed using a guided ion beam tandem mass spectrometer (GIBMS). Products are formed exclusively by the loss of CO ligands. Analyses of the kinetic energy-dependent CID product cross sections yield bond dissociation energies (BDEs) of (CO) x–1 Th + –CO at 0 K as 1.09 ± 0.05, 0.82 ± 0.07, 0.63 ± 0.05, and 0.70 ± 0.05 eV, respectively. Different structures of [Th,xC,xO] + were explored using various electronic structure methods, and BDEs for CO ligand loss from precursor [Th,xC,xO] + complexes were computed. Both experimental and theoretical results corroborate that the structures of [Th,xC,xO] + , x = 3–6, formed experimentally are homoleptic thorium cation carbonyl complexes, Th + (CO) x . The nonmonotonic trend in experimental BDEs is reproduced theoretically, although ambiguities in the spin states of the x = 4–6 complexes (doublet or quartet) remain. BDEs calculated at the coupled cluster with single, double, and perturbative triple excitations (CCSD(T))/cc-pVXZ//B3LYP/cc-PVXZ (X = T and Q) level and a complete basis set (CBS) extrapolation agree reasonably well with the experimental values for all complexes. Thorium oxide ketenylidene carbonyl cations, OTh + CCO(CO) y , y = 1–4, were calculated to be the most stable structures of [Th,xC,xO] + , x = 3–6, respectively; however, these are not observed in our experiment. Potential energy profiles (PEPs) having either quartet or doublet spin calculated at the B3LYP/cc-pVQZ level suggest that the failure to observe OTh + CCO(CO) y , y = 1–4, is the result of a barrier corresponding to the C–C bond formation, making the formation of OTh + CCO(CO) y inaccessible kinetically under the present experimental conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Multi-Ion Complexes and Competition from Bulky BArF – Anions for Chloride Binding in Ion Pairing Conditions

Cationic charges have long been used to enhance anion binding. Embedding charge introduces strong ion pairing for target anions but also for off-target ions, ultimately generating a mixture of multi-ion species that are hard to identify and quantify. While many sidestep this problem using polar solvents and weakly coordinating ions, these approaches exclude a substantial cross-section of conditions found in applications spanning recognition, assembly, separations, templation, and catalysis. To confront this complexity, we study the binding of an anion to a cationic receptor featuring low shape complementarity in a low-polarity solvent to maximize ionic interactions. We prepared the receptor as a salt of the weakly coordinating tetrakis­[3,5-bis­(trifluoromethyl)­phenyl]­borate (BArF – ) anion and studied the binding of small chloride (Cl – ) and medium-sized iodide (I – ) anions. Surprisingly, the use of the bulky BArF – anion does not suppress ion pairing interactions, with 65% of the receptor being paired at 0.5 mM in dichloromethane. We observe multi-ion receptor-Cl – complexes (2:1, 1:1, 1:2), reinforcing the complexity that emerges when working in low-polarity media. Here, we reveal the dependence of affinity on anion charge density and size and that bulky BArF – counteranions compete for chloride binding. These studies reveal the noninnocence of BArF – anions and strategies to quantify multi-ion species.

Ion pairing↗
DOE OSTI2021

Characterization of Uranyl Coordinated by Equatorial Oxygen: Oxo in UO 3 versus Oxyl in UO 3 +

Uranium trioxide, UO 3 , has a T-shaped structure with bent uranyl, UO 2 2+ , coordinated by an equatorial oxo, O 2– . The structure of cation UO 3 + is similar but with an equatorial oxyl, O •– . Neutral and cationic uranium trioxide coordinated by nitrates were characterized by collision induced dissociation (CID), infrared multiple-photon dissociation (IRMPD) spectroscopy, and density functional theory. CID of uranyl nitrate, [UO 2 (NO 3 ) 3 ] – (complex A1), eliminates NO 2 to produce nitrate-coordinated UO 3 + , [UO 2 (O • )(NO 3 ) 2 ]– (B1), which ejects NO 3 to yield UO 3 in [UO 2 (O)(NO 3 )] – (C1). Finally, C1 associates with H 2 O to afford uranyl hydroxide in [UO 2 (OH) 2 (NO 3 )] – (D1). IRMPD of B1, C1, and D1 confirms uranyl equatorially coordinated by nitrate(s) along with the following ligands: (B1) radical oxyl O •– ; (C1) oxo O 2– ; and (D1) two hydroxyls, OH – . As the nitrates are bidentate, the equatorial coordination is six in A1, five in B1, four in D1, and three in C1. Ligand congestion in low-coordinate C1 suggests orbital-directed bonding. Hydrolysis of the equatorial oxo in C1 epitomizes the inverse trans influence in UO 3 , which is uranyl with inert axial oxos and a reactive equatorial oxo. The uranyl ν 3 IR frequencies indicate the following donor ordering: O 2– [best donor] >> O •– > OH – > NO 3 – .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Hydrogen Bond Network Disruption by Hydration Layers in Water Solutions with Salt and Hydrogen-Bonding Polymers (PEO)

A mean field theory model describing the interaction of ion hydration layers with the network of hydrogen bonds of both water and the nonionic polymer poly(ethylene oxide) (PEO) is presented. The predictions of the model for types and statistics of hydrogen bonds, the number of water molecules bound to PEO, or their dependence on temperature are successfully verified from all-atom simulations at different NaCl and PEO concentrations. Furthermore, our simulations show that the binding of cations to PEO increases monotonically with salt concentration, in agreement with recent experimental results, through a mechanism in which the sum of the number of bound water and cations is independent of salt concentration. Here, the model introduced is general and can describe any salt or hydrogen-bond-forming polymer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ultrafast Charge Transfer Dynamics at the Origin of Photoconductivity in Doped Organic Solids

In spite of their growing importance for optoelectronic devices, the fundamental properties and photophysics of molecularly doped organic solids remain poorly understood. Such doping typically leads to a small fraction of free conductive charges, with most electronic carriers remaining Coulombically bound to the ionized dopant. Recently, we have reported photocurrent for devices containing vacuum-deposited TAPC (1,1-bis(4-bis(4- methylphenyl)aminophenyl)cyclohexane) doped with MoO 3 , showing that photoexcitation of charged TAPC molecules increases the concentration of free holes that contribute to conduction. Here, we elucidate the excited-state dynamics of such doped TAPC films to unravel the key mechanisms responsible for this effect. We demonstrate that excitation of different electronic transitions in charged and neutral TAPC molecules allows bound holes to overcome the Coulombic attraction to their MoO 3 counterions, resulting in an enhanced yield of long-lived free carriers. This is caused by ultrafast back-and-forth shuffling of charges and excitation energy between adjacent cations and neutral molecules, competing with relatively slow nonradiative decay from higher excited states of TAPC •+ . The light-induced generation of conductive carriers requires the coexistence of cationic and neutral TAPC, a favorable energy level alignment, and intermolecular interactions in the solid state.

36 MATERIALS SCIENCE↗
DOE OSTI2022

In Situ XAFS, XRD, and DFT Characterization of the Sulfur Adsorption Sites on Cu and Ce Exchanged Y Zeolites

Adsorptive desulfurization with Cu and Ce ion-exchanged Y zeolite (CuCeY) has proven to be an effective method for the removal of sulfur compounds from hydrocarbon fuels. In this study, Cu and Ce exchanged Y materials including CuY, CeY, and CuCeY were prepared and examined to investigate the mechanism behind the superior sulfur adsorption and selectivity of CuCeY. In situ conditions were used to study the materials as prepared for optimal desulfurization. X-ray diffraction (XRD) confirmed the absence of large well-ordered crystalline phases from metallic or oxide Cu and Ce after the reduction of the samples. The oxidation states and local environments of Cu and Ce were determined using X-ray adsorption fine structure (XAFS) analysis and correlated to theoretical findings obtained from density functional theory (DFT) calculations. XAFS data indicate the successful reduction of Cu species to Cu + and Cu o , and Ce to Ce 3+ . Analysis of XAFS spectra located Cu and Ce within the Y zeolite framework with Cu cations in the six-member ring sites and as small metallic Cu clusters. Ce cations were found to occupy both six-member ring and hexagonal prism sites. Furthermore, these results reveal the structure of CuCeY as prepared for desulfurization and provide insight into its superior sulfur adsorption performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Additive Molar Volumes in Amorphous Ca/Sr Carbonate Solid Solutions

The development of predictive models of minor element incorporation in crystalline carbonate end products requires an understanding of the fundamental controls on metastable intermediate phase composition. In this study, we used small-angle X-ray scattering (SAXS), X-ray pair distribution function (PDF), thermogravimetric analysis (TGA), inductively coupled plasma mass spectrometry (ICP-MS), and transmission electron microscopy (TEM) to determine the composition-dependent density of an amorphous calcium–strontium carbonate (ACSC) solid solution. The amorphous calcium carbonate (ACC) and strontium carbonate (ASC) measured densities were ρ ACC = 2.19 ± 0.04 g/cm 3 and ρ ASC = 2.97 ± 0.05 g/cm 3 . Throughout our work, the experiments showed a dependence of the water content of the amorphous solid solution on the Sr mole fraction. An equation that relates the molar volume to the average cation radius, the carbonate ion radius, and the water volume was parameterized for hydrated crystalline carbonates and predicted well the molar volume of the ACSC solid solution. This finding indicates that, as for hydrated crystalline carbonates, the molar volumes of amorphous carbonates are additive and that water is a structural component of ACSC. Ab initio molecular dynamics (AIMD) simulations of the ACSC solid solutions showed strong linear correlations between calculated molar volumes and Sr and H 2 O contents, thus supporting the experimental results. In conclusion, our findings highlight the need to consider the full CaCO 3 –MeCO 3 –H 2 O ternary when quantifying metal cation incorporation in ACC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Selective Oxidation and Cr Segregation in High-Entropy Oxide Thin Films

High-entropy oxides (HEOs) offer exceptional compositional flexibility and structural stability, making them promising materials for energy and catalytic applications. Here, in this study, we investigate Sr doping effects on B-site cation oxidation states, local composition, and structure in epitaxial La 1–x Sr x (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )O 3 thin films. X-ray spectroscopies reveal that Sr doping preferentially promotes Cr oxidation from Cr 3+ to Cr 6+ , partially oxidizes Co and Ni, while leaving Mn 4+ and Fe 3+ unchanged. Atomic-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy shows pronounced Cr segregation, with depletion at the interface and enrichment at the surface, along with partial amorphization in heavily Sr-doped samples. This segregation is likely driven by oxidation-induced migration of smaller, high-valence Cr cations during growth. These findings highlight the critical interplay between charge compensation, local strain, and compositional fluctuations in HEOs, indicating that precise control over growth conditions is critical for tuning their surface composition and electronic structure toward more robust electrocatalyst design.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Polytypic Zn–(In,Ga)–Se Nanocrystals with Tunable Emission

While the polymorphism of chalcopyrite semiconductors has been widely studied, the wurtzite analogues of defect-chalcopyrite II–III 2 –VI 4 compositions, such as Zn(In,Ga) 2 (S,Se) 4 , remain underexplored. Here, we report the synthesis of polytypic Zn–(In,Ga)–Se multipods via cation exchange using ZnSe as a template. With cubic cores and wurtzite arms elongated along the hexagonal c-axis, the multipods retain the structure and morphology of the ZnSe template. Optical characterization reveals composition-dependent absorption and photoluminescence, tunable from the visible to the near-infrared region, with spectral features distinct from those of previously reported defect-chalcopyrite structures. Temperature-dependent measurements demonstrate strong emission at cryogenic temperatures, which is quenched near room temperature due to thermally activated nonradiative processes. Here, we illustrate the use of ZnSe as a platform for cation exchange toward wurtzite multinary chalcogenides, unlocking access to novel structures with colorful optical properties.

cation exchange↗
DOE OSTI2021

Long-Term Cycling of a Mn-Rich High-Voltage Spinel Cathode by Stabilizing the Surface with a Small Dose of Iron

The high-voltage, cobalt-free spinel cathode LiNi 0.5 Mn 1.5 O 4 (LNMO) is receiving extensive attention for lithium-ion batteries due to its low cost, high operating voltage and energy density, superior power density, and good thermal stability. However, its high operating voltage hampers its stability with commercial electrolytes and makes its practical viability challenging. We present here a Mn-rich LNMO cathode to encourage the disordering of Mn and Ni in the lattice and the incorporation of a small dose of Fe into Mn-rich LNMO (Fe-LNMO) to improve the cycling stability. The introduction of Fe further increases the cation disorder between Mn and Ni, thus enabling a better rate capability. Electron energy loss spectroscopy analysis indicates that Fe is concentrated on the surface, and X-ray photoelectron spectroscopy analysis shows that Fe-LNMO alleviates the aggressive reaction between the cathode surface and the electrolyte, thus stabilizing the interface and cycle life. Furthermore, a full cell assembled with a graphite anode with an areal capacity of 3 mA h cm –2 displays a capacity retention of 90% over 300 cycles. Furthermore, the present work demonstrates an effective way to promote cation disordering and lower the surface reactivity of LNMO with the electrolyte, thereby enhancing the conductivity, stabilizing the cathode–electrolyte interphase, and making LNMO promising for practical applications.

25 ENERGY STORAGE↗
DOE OSTI2020

Structure and Dynamics of Aqueous Electrolytes Confined in 2D-TiO 2 /Ti 3 C 2 T 2 MXene Heterostructures

The synthesis of heterostructures of different two-dimensional (2D) materials offers an approach to combine advantages of different materials constituting the heterostructure and ultimately enhance their performance for applications such as electrochemical energy storage, achieving high energy, and high-power densities. Understanding the behavior of ions and solvents in confinement between these dissimilar layers is critical to understand their performance and control. Considering aqueous electrolytes, we explore the heterostructure of 2D lepidocrocite-type TiO 2 (2D-TiO 2 ) and hydroxylated or O-terminated Ti 3 C 2 MXene using ReaxFF molecular dynamics simulations and elastic/quasielastic neutron scattering techniques. Simulating a bilayer water intercalation, we find that the extent of interlayer hydration is impacted most by the surface terminations on the MXene and is marginally affected by 2D-TiO 2 . However, the introduction of 2D-TiO 2 decreases the water self-diffusion due to the notch sites (i.e., surface oxygen ridges) entrapping water molecules. Intercalating alkali cations into the heterostructures, we find that Li + is predominantly adsorbed at the 2D-TiO 2 surface instead of the MXenes with the preferential occupation of the notch sites. In contrast, Na+ forms a planar solvation with water, while K + is adsorbed both at the O-terminated MXene and 2D-TiO 2 . This behavior is altered when OH-terminated MXene is involved—the repulsion from the protons on the MXene surface forces the K + ions to be adsorbed exclusively to 2D-TiO 2 , while Na + retains some of its solvation in the water layer due to its smaller size. In OH-terminated MXenes, we see a consistent transfer of protons from the MXene surface toward 2D-TiO 2 , implying a greater capacity to store protons in the heterostructures. Of the three cations simulated, Na + hinders the proton migration the least and Li + the most because of its position near the 2D-TiO 2 surface. Furthermore, 2D-TiO 2 /MXene heterostructures are likely to exhibit a higher energy density but lower power density, especially with Na + intercalation.

25 ENERGY STORAGE↗
DOE OSTI2024

Entropy-Stabilized Multication Fluorides as a Conversion-Type Cathode for Li-Ion Batteries–Impact of Element Selection

Metal fluorides (e.g., FeF 2 and FeF 3 ) have received attention as conversion-type cathode materials for Li-ion batteries due to their higher theoretical capacity compared to that of common intercalation materials. However, their practical use has been hindered by low round-trip efficiency, voltage hysteresis, and capacity fading. Cation substitution has been proposed to address these challenges, and recent advancements in battery performance involve the introduction of entropy stabilization in an attempt to facilitate reversible conversion reactions by increasing configurational entropy. Building on this concept, high entropy fluorides with five cations were synthesized by using a simple mechanochemical route. In order to examine the impact of element selection, Co 0.2 Cu 0.2 Ni 0.2 Zn 0.2 Fe 0.2 F 2 (HEF-Fe) was compared with Co 0.2 Cu 0.2 Ni 0.2 Zn 0.2 Mg 0.2 F 2 (HEF-Mg), replacing electrochemically inactive Mg with Fe as an active participant in the conversion reaction. Combining electrochemical measurements with first-principles calculations, high-resolution electron microscopy, and synchrotron X-ray analysis, HEFs’ battery performances and conversion reaction mechanisms were investigated in detail. The results highlighted that replacement of Mg with Fe was beneficial, with enhanced capacity, rate capability, and surface stability. In addition, it was found that HEF-Fe showed similar cycle stability without an electrochemically inactive element. In conclusion, these findings provide valuable insights for the design of high entropy multielement fluorides for improved Li-ion battery performance.

25 ENERGY STORAGE↗
DOE OSTI2025

Ionic Associations and Hydration in the Electrical Double Layer of Water-in-Salt Electrolytes

Water-in-Salt-Electrolytes (WiSEs) are an exciting class of concentrated electrolytes finding applications in energy storage devices because of their expanded electrochemical stability window, good conductivity and cation transference number, and fire-extinguishing properties. These distinct properties are thought to originate from the presence of an anion-dominated ionic network and interpenetrating water channels for cation transport, which indicates that associations in WiSEs are crucial to understanding their properties. Currently, associations have mainly been investigated in the bulk, while little attention has been given to the electrolyte structure near electrified interfaces. Here, we develop a theory for the electrical double layer (EDL) of WiSEs, where we consistently account for the thermoreversible associations of species into Cayley tree aggregates. The theory predicts an asymmetric structure of the EDL. At negative voltages, hydrated Li + dominates, and cluster aggregation is initially slightly enhanced before disintegration at larger voltages. At positive voltages, when compared to the bulk, clusters are strictly diminished. Performing atomistic molecular dynamics (MD) simulations of the EDL of WiSE provides EDL data for validation and bulk data for parametrization of our theory. Validating the predictions of our theory against MD showed good qualitative agreement. Furthermore, we performed electrochemical impedance measurements to determine the differential capacitance of the studied LiTFSI WiSE and also found reasonable agreement with our theory. Overall, the developed approach can be used to investigate ionic aggregation and solvation effects in the EDL, which, among other properties, can be used to understand the precursors for solid-electrolyte interphase formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Investigating Silver Nanoparticle Interactions with Quaternary Ammonium Functionalized Triblock Copolymers and Their Effect on Midblock Crystallinity

Interactions between silver nanoparticles and a cationic triblock copolymer significantly alter bulk material properties and can be tuned by functionalizing the polymer with different quaternary ammonium cations (QACs). In this work, poly-chloromethylstyrene-b-polycyclooctene-b-polychloromethylstyrene (PCMS-b-PCOE-b-PCMS) was quaternized with either methylpiperidinium (MPRD) or trimethylammonium (TMA). The surface interacting groups were identified using FT-IR to be the phenyl rings, the QACs from the outer blocks, and vinyl groups from the PCOE midblock. Changes in thermal characteristics and crystallinity were highly dependent on the QAC, uncovering differences in the nature of the interactions between silver and TMA or MPRD. Interactions induced by TMA greatly hinder crystalline domain formation and give rise to a higher water content, while MPRD promotes certain crystalline orientations and provides a greater degree of crystallinity with a lower water content. In this work, our findings demonstrate that bulk polymer characteristics can be tuned, a highly desirable attribute for many nanocomposite materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Vapor-Deposited n = 2 Ruddlesden–Popper Interface Layers Aid Charge Carrier Extraction in Perovskite Solar Cells

Interfacial passivation with bulky organic cations such as phenetylammonium iodide has enabled high performance for metal halide perovskite optoelectronic devices. However, the homogeneity of these interfaces and their formation dynamics are poorly understood. Here we study how Ruddlesden-Popper 2D phases form at a 3D perovskite interface when the 2D precursors are introduced via solution or via vapor. When using vapor deposition, we observe uniform coverage of the capping layer and the formation of a predominantly n = 2 Ruddlesden-Popper phase. In contrast, when using solution deposition, we observe the presence of a mixture of n = 2 and n = 1 in the film and the formation of aggregates of the organic cations. As a result of the better phase purity and uniformity, vapor deposition enables higher median solar cell performance with narrower distribution compared to solution-treated films. This study provides fundamental information that the perovskite community can use to better design capping layers to achieve higher charge extraction efficiencies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Tunable n- and p-Type Behavior of Ruddlesden–Popper and Dion–Jacobson 2D Perovskites

Interfacial band alignment in two-dimensional (2D)/three-dimensional (3D) perovskite heterostructures is important for maximizing separation, extraction, and collection of charge carriers, which, in turn, stabilize the perovskite layer during solar cell operation. Despite the wide use of 2D spacer cations for stabilizing perovskite solar cells, spacer cation exchange across the 2D/3D interface induces structural transformation and degradation in performance and stability. We have now examined the electrochemical and photoelectrochemical behavior of 2D Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) perovskites to assess the impact of binding configuration on the interfacial charge separation and their operational stability. In-situ open circuit potential (OCP) responses of 2D perovskites under light illumination, paired with redox couples (ferrocene/ferrocenium), reveal different semiconducting polarizabilities of BA-RP (n-type) and BDA-DJ (p-type). The tunability of the Fermi energy level in 2D perovskites discussed in this study offers insight into the design of 2D/3D interfaces for optimizing charge transfer and enhancing charge neutrality and stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Unveiling Swift Heavy Ion Track Morphology in Sr-Based High-Entropy Perovskites

The incorporation of multiple cations on a single lattice site in the high-entropy oxides is considered the key driving factor for modifying the known atomic-level response to energetic ion irradiation due to the presence of structural disorder; however, these effects are not well-understood yet. In this work, we present atomic-level insight into irradiation-induced nanoscale phase transformations in a perovskite-structured high-entropy oxide, Sr(Zr 0.2 Sn 0.2 Ti 0.2 Hf 0.2 Nb 0.2 )O 3 (Sr(HE)O 3 ), subjected to 774 MeV swift Xe heavy ions, where damage is dominated by inelastic ion−lattice interactions. While these ions generally are known to create nanoscale disordered channels, “ion tracks”, along the penetration direction in the material, this study shows the formation of discontinuous and partially recrystallized ion tracks in Sr(HE)O 3 . Compared to SrTiO 3 irradiated under identical energy loss conditions, the ion tracks in Sr(HE)O 3 exhibit significantly reduced diameters and a markedly different interfacial structure. Notably, the crystalline−amorphous interface in Sr(HE)O 3 shows minimal lattice distortion, confined to approximately 2−3 monolayers, in contrast to the extended disordered shell commonly observed in SrTiO 3 . Using in situ atomic-resolution electron microscopy, we further demonstrate that the amorphous/disordered regions within Sr(HE)O 3 ion tracks remain highly stable under electron irradiation, whereas tracks in SrTiO 3 readily recrystallize. This enhanced stability is attributed to the dominance of structural and chemical complexity arising from multiple B-site cations, which suppress defect migration and templated recrystallization driven by electronic excitations and local heating. Overall, this study highlights how high-entropy oxide chemistry fundamentally reshapes irradiation damage evolution, offering insights into defect formation and phase stability under extreme conditions.

36 MATERIALS SCIENCE↗