Polycrystalline material properties depend on the distribution and interactions of their crystalline grains. In particular, grain boundaries and defects are crucial in determining their response to ...external stimuli. A long-standing challenge is thus to observe individual grains, defects, and strain dynamics inside functional materials. Here we report a technique capable of revealing grain heterogeneity, including strain fields and individual dislocations, that can be used under operando conditions in reactive environments: grain Bragg coherent diffractive imaging (gBCDI). Using a polycrystalline gold thin film subjected to heating, we show how gBCDI resolves grain boundary and dislocation dynamics in individual grains in three-dimensional detail with 10-nanometer spatial and subangstrom displacement field resolution. These results pave the way for understanding polycrystalline material response under external stimuli and, ideally, engineering particular functions.
Oxidation of magnetite (Fe
O
) has broad implications in geochemistry, environmental science and materials science. Spatially resolving strain fields and defect evolution during oxidation of ...magnetite provides further insight into its reaction mechanisms. Here we show that the morphology and internal strain distributions within individual nano-sized (~400 nm) magnetite crystals can be visualized using Bragg coherent diffractive imaging (BCDI). Oxidative dissolution in acidic solutions leads to increases in the magnitude and heterogeneity of internal strains. This heterogeneous strain likely results from lattice distortion caused by Fe(II) diffusion that leads to the observed domains of increasing compressive and tensile strains. In contrast, strain evolution is less pronounced during magnetite oxidation at elevated temperature in air. These results demonstrate that oxidative dissolution of magnetite can induce a rich array of strain and defect structures, which could be an important factor that contributes to the high reactivity observed on magnetite particles in aqueous environment.
Topological defects are ubiquitous in physics and include crystallographic imperfections such as defects in condensed matter systems. Defects can determine many of the material’s properties, thus ...providing novel opportunities for defect engineering. However, it is difficult to track buried defects and their interfaces in three dimensions with nanoscale resolution. Here, we report three-dimensional visualization of gold nanocrystal twin domains using Bragg coherent X-ray diffractive imaging in an aqueous environment. We capture the size and location of twin domains, which appear as voids in the Bragg electron density, in addition to a component of the strain field. Twin domains can interrupt the stacking order of the parent crystal, leading to a phase offset between the separated parent crystal pieces. We utilize this phase offset to estimate the roughness of the twin boundary. We measure the diffraction signal from the crystal twin and show its Bragg electron density fits into the parent crystal void. Defect imaging will likely facilitate improvement and rational design of nanostructured materials.
We reveal three-dimensional strain evolution in situ of a single LiNi0.5Mn1.5O4 nanoparticle in a coin cell battery under operando conditions during charge/discharge cycles with coherent X-ray ...diffractive imaging. We report direct observation of both stripe morphologies and coherency strain at the nanoscale. Our results suggest the critical size for stripe formation is 50 nm. Surprisingly, the single nanoparticle elastic energy landscape, which we map with femtojoule precision, depends on charge versus discharge, indicating hysteresis at the single particle level. This approach opens a powerful new avenue for studying battery nanomechanics, phase transformations, and capacity fade under operando conditions at the single particle level that will enable profound insight into the nanoscale mechanisms that govern electrochemical energy storage systems.
Dealloying is a process whereby selective dissolution results in a porous, strained structure often with new properties. The process is of both intrinsic and applied interest, and recently has been ...used to make highly active catalysts. The porosity has been studied using electron microscopy while the dealloying‐induced strain has been studied at the ensemble level using X‐ray diffraction. Despite the importance of local, for example, at the individual particle or grain level, strain in controlling the properties of the dealloyed material, it remains unresolved due to the difficulty of imaging 3D strain distributions with nanometer resolution in reactive environments. This information could play an integral role in understanding and controlling lattice strain for a variety of applications. Here, 3D strain distributions in individual nanoparticles and thin film grains in silver–gold alloys undergoing nitric acid‐induced dealloying are imaged by Bragg coherent diffractive imaging. Particles exhibit dramatic changes in their local strains due to dealloying but grains do not. The average lattice in both grains and particles contracts during dealloying. In general, the results reveal significant dealloying‐induced strain heterogeneity at the nanoscale in both isolated and extended samples, which may be utilized to develop advanced nanostructures for a variety of important applications.
The strain distribution in nanomaterials can significantly impact their properties. Using Bragg coherent diffractive imaging, the strain evolution due to dealloying in nanocrystals and grains is investigated. It is found that nanoparticles change their strain dramatically compared to their grain counterparts. These results have implications for strain tuning nanomaterials for a variety of applications.
Defects such as dislocations and grain boundaries often control the properties of polycrystalline materials. In nanocrystalline materials, investigating this structure–function relationship while ...preserving the sample remains challenging because of the short length scales and buried interfaces involved. Here we use Bragg coherent diffractive imaging to investigate the role of structural inhomogeneity on the hydriding phase transformation dynamics of individual Pd grains in polycrystalline films in three-dimensional detail. In contrast to previous reports on single- and polycrystalline nanoparticles, we observe no evidence of a hydrogen-rich surface layer and consequently no size dependence in the hydriding phase transformation pressure over a 125–325 nm size range. We do observe interesting grain boundary dynamics, including reversible rotations of grain lattices while the material remains in the hydrogen-poor phase. The mobility of the grain boundaries, combined with the lack of a hydrogen-rich surface layer, suggests that the grain boundaries are acting as fast diffusion sites for the hydrogen atoms. Such hydrogen-enhanced plasticity in the hydrogen-poor phase provides insight into the switch from the size-dependent behavior of single-crystal nanoparticles to the lower transformation pressures of polycrystalline materials and may play a role in hydrogen embrittlement.
Fundamental understanding of structural changes during catalytic reactions is crucial to understanding the underlying mechanisms and optimizing efficiencies. Surface energy and related catalytic ...mechanisms are widely studied. However, the catalyst lattice deformation induced by catalytic processes is not well understood. Here, we study the strain in an individual platinum (Pt) nanoparticle (NP) using Bragg coherent diffraction imaging under in situ oxidation and reduction reactions. When Pt NPs are exposed to H2O2, a typical oxidizer and an intermediate during the oxygen reduction reaction process, alternating overall strain distribution near the surface and inside the NP is observed at the (111) Bragg reflection. In contrast, relatively insignificant changes appear in the (200) reflection. Density functional theory calculations are employed to rationalize the anisotropic lattice strain in terms of induced stress by H2O2 adsorption and decomposition on the Pt NP surface. Our study provides deeper insight into the activity–structure relationship in this system.
Strain within grains and at grain boundaries (GBs) in polycrystalline thin-film absorber layers limits the overall performance because of higher defect concentrations and band fluctuations. However, ...the nanoscale strain distribution in operational devices is not easily accessible using standard methods. X-ray nanodiffraction offers the unique possibility to evaluate the strain or lattice spacing at nanoscale resolution. Furthermore, the combination of nanodiffraction with additional techniques in the framework of multimodal scanning X-ray microscopy enables the direct correlation of the strain with material and device parameters such as the elemental distribution or local performance. This approach is applied for the investigation of the strain distribution in CdTe grains in fully operational photovoltaic solar cells. It is found that the lattice spacing in the (111) direction remains fairly constant in the grain cores but systematically decreases at the GBs. The lower strain at GBs is accompanied by an increase of the total tilt. These observations are both compatible with the inhomogeneous incorporation of smaller atoms into the lattice, and local stress induced by neighboring grains.
Alloying anode materials offer high capacity for next-generation batteries, but the performance of these materials often decays rapidly with cycling because of volume changes and associated ...mechanical degradation or fracture. The direct measurement of crystallographic strain evolution in individual particles has not been reported, however, and this level of insight is critical for designing mechanically resilient materials. Here, we use operando X-ray diffraction to investigate strain evolution in individual germanium microparticles during electrochemical reaction with lithium. The diffraction peak was observed to shift in position and diminish in intensity during reaction because of the disappearance of the crystalline Ge phase. The compressive strain along the 111 direction was found to increase monotonically to a value of −0.21%. This finding is in agreement with a mechanical model that considers expansion and plastic deformation during reaction. This new insight into the mechanics of large-volume-change transformations in alloying anodes is important for improving the durability of high-capacity batteries.
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