Metal ion migration under operational gradients triggers irreversible decomposition and performance collapse in thermoelectric (TE) materials. β-Zn 4 Sb 3 has high TE performance but suffers from severe zinc (Zn) ion migration under an external field. This work uses powder atomic layer deposition (pALD) to engineer atomic-scale zinc oxide (ZnO) interfaces that simultaneously suppress Zn ion migration and enhance phonon scattering. Through precise ZnO coatings (50 to 200 cycles), we create continuous barriers that immobilize interstitial Zn ions, eliminating Zn motion and inhibiting phase decomposition. Optimized 100 ALD cycle coatings reduce lattice thermal conductivity by >20% through intensified boundary-phonon scattering, yielding a stabilized, nondegrading figure of merit compared to uncoated performance. Crucially, the thermal stability of 100-ALD-cycle-coated sample persists through 39,260 thermal cycles under gradients of 220 kelvin, and Seebeck coefficient mapping exhibits a uniform distribution along temperature difference. Our approach establishes pALD as a promising atomic-level interface design in migration-prone TE materials, bridging high performance with long-term operational reliability.

Iridium oxide is a promising catalyst for oxygen evolution reaction (OER) under acidic conditions due to its excellent ¬activity. However, the scarcity of iridium limits its large-scale industrial applications, prompting...

Despite extensive progress on two-dimensional (2D) materials, 2D lead oxides remain underexplored, limiting systematic structure-property studies. Here, we develop a bottom-up sol-gel synthesis route to 2D lead glycolate (PG) and oxide nanostructures via finely tuned hydrolysis-condensation of molecular metal alkoxides. The hydrolysis-condensation in ethylene glycol (EG), with controlled Pb-EG precursor/water and water/alcohol ratios, yields 2D-assembled nanoparticles, elongated nanostructures, and single-crystalline 2D hexagonal nanoplates. While calcination at 450 °C leads to a conversion of PG to tetragonal Pb3O4 with a significant collapse of 2D morphology, the introduction of a SiO2 overlayer can preserve the original 2D architecture of PG, affording 2D-assembled Pb3O4/SiO2 with minimal aggregation. The higher overpotential of 2D-assembled Pb3O4/SiO2, with a delayed current-onset potential, evidences its enhanced selectivity for electrochemical ozone production over oxygen evolution. This is further confirmed by a higher current density and a smaller Tafel slope in the high-potential region above ∼2.8 V. KI-starch assay and UV-Vis spectroscopy confirm more efficient ozone generation by 2D-assembled Pb3O4/SiO2 compared to aggregated Pb3O4. This morphology-preserving route offers a general strategy for synthesizing structurally defined 2D lead oxide catalysts with enhanced performance.

Compositionally complex solid solutions (frequently referred to as high entropy alloys) provide a unique route for designing high-performance electrocatalysts, where the polyelemental surface composition can be seamlessly tuned to optimize activity, selectivity, and stability. However, the mechanistic understanding of these electrocatalysts remains limited by the lack of a model system with a crystallographically defined surface that is compatible with correlative, multi-scale characterization. Here, we present epitaxial films as a model platform for studying compositionally complex electrocatalysts. Using magnetron sputtering, we realize (111) epitaxial Ir-Pd-Pt-Rh-Ru films on a (0001) sapphire substrate via a (111) Pt buffer layer, confirmed via X-ray diffraction and transmission electron microscopy. The growth approach is applicable across a broad composition range and produces smooth surfaces (root mean square roughness <1 nm) with micrometer-sized grains in the nanoscale films. For these films, we demonstrate direct structure-activity mapping at the nanoscale through precise co-localization using micro-indents and performing correlative atomic force microscopy, electron backscatter diffraction, and scanning electrochemical cell microscopy. Our work establishes a model platform for fundamental scale-bridging characterization and paves the way for rational design of compositionally complex electrocatalysts.

The formation of surface films and local alkalization during the aqueous corrosion of Mg alloys significantly influence their corrosion properties across various electrolytes. This study provides new insights into the layer formation on a Mg-1.06Al-0.046Ca alloy immersed in an alkaline electrolyte (pH = 11.5) for 72 h utilizing (electro-)chemical and microstructural analysis. Scanning transmission electron microscopy and atom probe tomography reveal a subsurface Al-enriched interlayer (similar to 4 at%) and the absence of Ca segregation at the metal and corrosion product interface. The corrosion product itself is a three-layer structure: next to the substrate a Mg(OH)2_dense layer, followed by an Al-enriched interlayer 2, and an outer Mg(OH)2_flake layer. Changes in diffusion-related transport properties are observed after 20.5 h of immersion, as indicated by the impedance response associated with the Mg(OH)2_dense layer and the subsurface Al interlayer 1. A similar to 1.5 mu m deformation layer persists after 72.0 h immersion in a pH of 11.5 and dominates the corrosion behavior.Subsurface Al enrichment (similar to 4 at%) occurs within the metallic substrate.Two distinct corrosion stages are identified with a transition from Ca- to Al-dominated dissolution.Capacitive layer properties appear diffusion-controlled according to Fick's law.

Thermoelectric (TE) materials with high efficiency near room temperature are crucial for low‐temperature waste‐heat recovery and solid‐state cooling applications. Among them, Mg3(Sb, Bi)2‐based Zintl compounds have emerged as leading n‐type materials due to their intrinsically low lattice thermal conductivity and favorable electronic structure. However, their performance is still constrained by the relatively low carrier mobility in the low‐temperature regime because of the dominated grain‐boundary charge scattering, which limits the achievable power factor and thus the overall figure of merit (zT). Hereby, we proposed an interface modification strategy based on powder atomic layer deposition (pALD) of metallic Cu to enhance the carrier mobility of n‐type Mg3(Sb, Bi)2. The ALD‐Cu addition is found to be beneficial for improving carrier mobility by promoting grain growth, compensating Mg deficiencies at some of the grain boundaries (particle boundaries), and thereby mitigating the interfacial transport barriers. Metallic Cu was precisely deposited on TE powders without introducing oxygen‐ or water‐based precursors, thereby avoiding surface oxidation and degradation of the powders. Simultaneously, despite the more than twofold increase in grain size, the formation of Cu‐rich domains near particle boundaries acts as effective phonon‐scattering centers, leading to a lower lattice thermal conductivity. Benefiting from this synergistic modification of electrical and thermal transport, both peak and average zT over 303–573 K were enhanced by 14% and 13.3%, respectively. This work demonstrates a feasible metallic pALD approach for interface modification and establishes a new strategy to decouple transport parameters in n‐type Mg3(Sb, Bi)2‐based alloys for near room temperature applications.

Active and reliable electrocatalysts are fundamental to renewable energy technologies. PdCoO2 is recently recognized as a promising catalyst template for the hydrogen evolution reaction (HER) in acidic media, thanks to the formation of exceptionally active PdHx. In this article, the transformation process of single PdCoO2 particles during HER is monitored and elucidated, confirming their almost complete transformation to PdHx. Using operando mass spectrometry, Co dissolution from the PdCoO2 template is observed under reductive potentials, with a partial current of 0.1% of the HER current, while PdHx is formed simultaneously. High HER activity of this phase is retained with long-term operation, dry storage, or vacuum exposure. Isotope labeling of hydrogen using D2O confirms the formation of a stable PdHx phase by secondary ion mass spectrometry and down to the near-atomic scale by atom probe tomography. A separation between D-poor alpha- and D-rich beta-Pd hydrides is observed with an overall composition of beta-PdD0.64. These findings highlight the critical role of a templated growth method for obtaining stabilized PdHx, enabling Pt-like efficient HER without the commonly slow activation processes observed in Pd due to rate-limiting material hydrogenation. This offer insights into the design of more efficient electrocatalysts for renewable energy technologies.

Characterizing microstructures of materials is essential for understanding the relationships with their properties. However, the microstructure can experience changes during operation at elevated temperatures and electrical biasing. Such conditions are standard for thermoelectric devices, which generate electricity from a temperature differential. To characterize these microstructural changes in situ in a transmission electron microscope (TEM), commercialized MEMS-based technology has been utilized. Operando conditions of thermoelectric devices, such as heat loads and electrical biasing, can be replicated by the chips during in situ TEM observation. Here, we show our approach to prepare TEM samples on in situ MEMS chips, suited for heating and biasing, using focused ion beam (FIB). The sample is first lifted out from a bulk material and then connected to the positive and negative electrodes of the chip. The contacts are established by ion beam deposition of a Pt-C composite. Finally, the TEM sample is thinned directly on the chip using FIB. To measure the electrical properties of the TEM sample, a voltage is applied between two electrodes. The current through the sample is measured to derive the total resistance at each temperature. Afterward, the resistivity of the sample and the contact resistance are determined from the measured resistances at different sample dimensions during different stages of FIB thinning. The results demonstrate that heating up to 200 °C causes a reduction in the contact resistance after each FIB thinning. After annealing of the contact, the electrical resistivity can be measured reliably with the presented approach from high temperature down to room temperature, free from the influence of contact resistance.

Compositionally complex solid solutions (CCSSs) consist of a randomly mixed single phase with the potential to enhance electrocatalytic activity through their polyelemental surface atom arrangements. However, microstructural complexity originating from multiple principal elements influences local structure, chemistry, and lattice strain, which might also affect electrocatalytic activity. Here, we investigate the effect of Ru content on electrochemistry and defect formation in Au-Pd-Pt-Ru CCSS thin films. Such defects could provide active sites when terminating at the CCSS surface or modify surface composition through preferential segregation. A thin-film material library covering a wide composition range was fabricated by room-temperature combinatorial co-sputtering. High-throughput compositional, structural and functional characterization, including electron microscopy equipped with energy dispersive X-ray spectroscopy, X-ray diffraction, and electrochemical screening, were used to correlate composition and microstructural features with catalytic activity. Three representative compositions selected from the library - Au68Pd13Pt15Ru4, Au27Pd24Pt23Ru26, and Au9Pd21Pt18Ru52 - were examined in detail. The three samples exhibit face-centered cubic structures, with lattice contraction occurring with increasing Ru content. In addition, with increasing Ru content, a transition from a high density of nanotwins to high-density, atomic-layer stacking faults was observed. Moreover, the hydrogen evolution reaction activity improves with higher Ru content. Atom probe tomography reveals local compositional fluctuations, including element-specific enrichment and depletion at grain boundaries. The findings provide a new insight into surface atom arrangement design in the CCSS electrocatalysts with enhanced performance.

TiO2 is widely applied as a photoanode material for the oxygen evolution reaction (OER), as well as for corrosion protection. However, its stability during photoelectrochemical (PEC) processes is still under debate. Here, we systematically investigate the effect of illumination, electrode potential, and electrolyte pH on the stability of rutile-type TiO2 nanowires during PEC OER. We provide operando insights into the photostability of TiO2, quantifying the photodissolution to identify degradation mechanisms in acidic and alkaline electrolytes. The structural evolution of TiO2 nanowires is correlated with their photodissolution as well as local pH changes during OER. Based on these findings, we propose a model that links the pH-dependent degradation of PEC performance with dissolution processes, thereby establishing a comprehensive understanding of the durabilities of TiO2 photoanodes in different electrolyte environments. Overall, this work identifies and rationalizes the PEC stability boundaries of TiO2, which is key for its practical application in photo/electro-catalysis and as a corrosion protection layer.

The practical application of Mg3Sb2-based thermoelectrics has been largely retarded by their poor thermal stability, mainly due to the rapid loss of Mg at elevated temperatures. Here, we prove that grain boundaries are fast diffusion channels for Mg, and we block these channels by forming Ga-rich grain boundary complexions. This design suppresses the formation of Mg vacancies at grain boundaries and inhibits the outward diffusion of Mg and the inward growth of MgO-related phases. Consequently, the thermal stability of Mg3Sb2-based materials is significantly improved at a high temperature of 718 K for at least 80 h. The corresponding single-leg Mg3Sb2-based device can maintain a conversion efficiency of 12.5% ± 0.6% for 7 days at a temperature difference of 423 K during the cycle test. Our findings provide an atomic-scale grain boundary engineering approach to enhance the thermal stability of thermoelectric devices and other functional materials operating at elevated temperatures.

Grain boundary resistance was found to limit thermoelectric performance in Yb 14 MgSb 11 from room temperature to 1200 K. No similar resistance was observed in Yb 14 MnSb 11 , demonstrating the importance of composition in engineering boundary behavior.

Compositionally complex solid solutions provide a unique route for engineering high-performance electrocatalysts, where the polyelemental surface composition can be seamlessly tuned to optimize activity, selectivity, and stability. However, the mechanistic understanding of these electrocatalysts remains limited by the lack of a model system with a crystallographically-defined surface that is compatible with correlative, multi-scale characterization. Here, we present epitaxial films as a model platform for studying compositionally complex electrocatalysts. Using magnetron sputtering, we realize (111) epitaxial Ir-Pd-Pt-Rh-Ru films on (0001) sapphire substrate via a (111) Pt buffer layer, confirmed by X-ray diffraction and transmission electron microscopy. The growth approach is applicable across a broad composition range and produces smooth surfaces (root mean square roughness < 1 nm) with micrometer-sized grains in the nanoscale films. With these films, we demonstrate direct structure-activity mapping at the nanoscale through precise co-localization using micro-indents and performing correlative atomic force microscopy, electron backscatter diffraction, and scanning electrochemical cell microscopy. Our work establishes a model platform for fundamental scalebridging characterization and paves the way for rational design of compositionally complex electrocatalysts.

Grain-boundary (GB) engineering is a fundamental tool in materials design. Ever-increasing power to resolve the atomistic structure of GBs has enabled the discovery of new GB phases and their transitions. GB phase transitions are characterized by changes in the atomistic configuration of GBs, often together with variations in their chemical composition. Such transitions can be induced by temperature, local stress state and chemical potential of the constituent elements. In this article, we highlight some exciting new frontiers in this regard. The discussion is grouped into GB faceting (noncongruent) transitions, congruent transitions of structural units, chemical segregation-induced premelting, and chemical ordering. Based on atomic-scale characterizations, excess quantities of GBs can be derived to understand their thermodynamics. Moreover, new methodologies have been developed to characterize local properties of GBs, offering direct probes on their structure–property relationships and guiding the rational design of materials with superior structural and functional properties. Graphical abstract

Understanding the diagenesis of fossil teeth requires linking microstructure to chemistry across spatial scales to distinguish primary biogenic signals from diagenetic signals introduced by fluid-mineral interactions. Here, we investigate a Cretaceous theropod tooth using a multiscale analytical workflow that combines scanning and transmission electron microscopy with atom probe tomography. The results reveal a hierarchical pattern of diagenetic alteration in both enamel and dentine spanning from the microscale to the near-atomic scale. Enamel largely preserves its densely packed apatite crystallites yet contains sparsely distributed nanoscale precipitates enriched with secondary elements, indicating localized diagenetic modification. In contrast, dentine shows extensive diagenetic alteration, characterized by the infilling of dentinal tubules with secondary elements. Furthermore, both tissues exhibit intergranular segregation of C and Sr along apatite grain boundaries, a feature that has not been previously discussed in fossil dinosaur teeth. These observations demonstrate that diagenetic effects can extend down to the nanoscale, implying that bulk geochemical measurements with limited spatial resolution may integrate both preserved and altered domains. Our findings highlight the potential of atom probe tomography to advance the understanding of diagenesis and the biomineralization process.

Intermetallics often exhibit complex crystal structures, which give rise to intricate defect structures that critically influence their mechanical and functional properties. Despite studies on individual defect types, a comprehensive understanding of the defect landscape in μ-phases, a class of topologically close-packed phases, remains elusive. In this study, we investigated the planar defect structures in the Ta-Fe μ-phase across a compositional range of 46 to 58 at.% Ta using electron microscopy and density functional theory calculations. Electron backscatter diffraction and high-resolution scanning transmission electron microscopy reveal a transition from basal twin boundaries and planar faults containing C14 TaFe2 Laves phase layers at a low Ta content to pyramidal {1\bar{1}02} twins at a higher Ta content. Density functional theory calculations of defect formation energies confirm a chemical potential-driven stabilisation of Laves phase lamellae. The prevalence of pyramidal twins in Ta-rich μ-phase samples is attributed to the competitive nature of different planar defects during solidification. A defect landscape for μ-phases is proposed, illustrating the interplay between site occupancy, dislocation types and planar faults across the chemical potential space. These findings provide fundamental insights into defect engineering in structurally complex intermetallics and open pathways for optimising material properties through chemical tuning.

In ordered intermetallics, slight variations in lattice site occupancy and specific interlayer spacings have been identified as the sources of significant changes in critical resolved shear stress and therefore how a given phase may affect alloy properties. So far, atom positions and lattice site occupancies have traditionally been characterised by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD), which are methods that offer either local detail or high statistical significance but not both. Electron backscatter diffraction (EBSD), by contrast, provides high spatial resolution across large sample areas and therefore, has the potential to enable the local investigation of interlayer spacing and site lattice occupancy with improved statistical reliability. The objectives of the study are to benchmark EBSDs capability for resolving these subtle features and to correlate them with compositional and mechanical properties. In this case study, we therefore show that EBSD can resolve key crystallographic features of mu-phase intermetallics, specifically interlayer spacings. We combine pattern matching with large-scale dynamical simulations of template libraries guided by XRD based information on lattice parameters. For this, we generate structures that vary in the spacing between triple-layer and Kagome layer and in the site lattice occupancy of the 3a site. This approach successfully predicts the change of interlayer spacing between Kagome and triple layers in Nb-Co and Nb-Ni mu-phases, in good agreement with XRD and HR-TEM.

We present a three-dimensional (3D) electron backscatter diffraction (EBSD) study of oxidation induced microstructural evolution in 30 μm thick Cr2AlC coatings oxidized in air at 990 °C for 3 h. After Cr2AlC oxidation, correlative phase identification using site-specific atom probe tomography, energy dispersive X-ray spectroscopy, and selected area diffraction guided EBSD reindexing resolved the formation of two previously unreported phases: a Cr2Al-based phase, and a (Cr,Al)23C6 solid solution phase.The 3D volume was generated using serial focused ion beam sectioning, and the resulting phase fraction, grain shape, and texture data were benchmarked against those obtained from 2D EBSD sections. Notably, the individual 2D sections rarely capture the combined 3D phase fractions. 3D EBSD enabled phase neighborhood analysis, revealing a continuous Cr2AlC matrix containing clustered (Cr,Al)23C6 and isolated Cr7C3 grains, as well as a Cr2Al-based phase decorating Cr7C3-Cr2AlC interfaces. The large 3D dataset further enabled correlation analysis which revealed two distinct Cr7C3 grain populations differing in volume, Cr2AlC contact fraction, and texture. Overall, accurate phase identification using the aforementioned techniques enabled reliable reindexing of 3D EBSD data, yielding statistically robust information that cannot be captured by a single 2D cross-section.

Vanadyl acetylacetonate precursor oxidation with tert -butyl hydroperoxide reorganizes vanadyl complexes and directs nucleation pathways, enabling controlled synthesis of nanosized VO x materials with distinct morphologies and VO 2 -like phase behavior.

Grain boundary electrical resistance has been a limiting factor in the thermoelectric performance of many otherwise promising materials. For example, the recent emergence of Mg3Sb2 as a high performing low temperature thermoelectric material is a result of efforts to mitigate grain boundary electrical resistance. Many other materials including half Heuslers, oxides, Mg2Si and others have also seen improved thermoelectric performance after mitigating grain boundary electrical resistance. However, the focus of grain boundary engineering work has been on low and mid temperature materials. Grain boundary electrical resistance is typically strongest at room temperature, so it has been assumed that high temperature thermoelectrics do not need to be evaluated for detrimental grain boundary electrical resistance. In this study, we demonstrate the importance of grain boundary resistance in all temperature ranges by discovering large grain boundary resistance in the high temperature thermoelectric Yb14MgSb11. While the observed boundary resistance is still largest at room temperature, there is still significant boundary resistance in the measured temperature range. As a result, a 22% increase in thermoelectric figure of merit is acheived at 1000 degrees C by increasing the grain size. Further, we demonstrate the importance of bulk composition to grain boundary engineering, as substituting Mg for Mn completely removed all measurable grain boundary resistance. These results demonstrate that grain boundary resistance is important in all thermoelectric materials regardless of targeted operating temperature.