The main binding phases of calcium aluminate cement (CAC) concrete, CaO·Al2O3·10H2O (CAH10) and 2CaO·Al2O3·8H2O (C2AH8), slowly convert to 3CaO·Al2O3·6H2O (C3AH6) and Al(OH)3 (AH3). This reaction significantly speeds up at a temperature higher than ∼30 °C, and over time leads to significant strength loss in CAC concrete. Because of the lack of direct evidence that simultaneously probes morphological and chemical/crystallographic information, intense debate remains whether the conversion is generated by a solid-state or through-solution reaction. The conversion of CAH10 at an elevated temperature is studied herein using synchrotron-radiation-based X-ray spectromicroscopy capable of acquiring near edge X-ray absorption fine structure data and ptychographic images with a resolution of ∼15 nm. We show that, when stored at 60 °C, CAH10 first converts to C2AH8 by solid-state decomposition, followed by the through-solution formation of C3AH6. The C3AH6 crystallizes from both the relics of dissolved C2AH8 and from the surface of existing C3AH6 crystals. The solid-state decomposition of CAH10 occurs in multiple sites inside the CAH10 crystals; the spatial range of each decomposition site spans a few tens of nanometers, which overcomes the kinetics barrier of ion transportation in the solid-state. Our work provides the first nanoscale crystal-chemical evidence to explain the microstructure evolution of converted CAC concrete.

Dicalcium silicate (C 2 S) is an important clinker mineral in Portland and belite-calcium sulfoaluminate cement. However, there is still a lack of information on the local degree of silicate polymerization and calcium coordination in C 2 S hydration products. This study aimed to fill this gap by characterizing the hydration of two C 2 S polymorphs, the β- and α′ H - types, using scanning transmission X-ray microscopy coupled with ptychographic imaging. The results showed that the coordination of the Ca species in β- and α′ H -C 2 S had a distorted, cubic-like symmetry, whereas the Ca coordination of calcium silicate hydrate (C-S-H), the main hydration product, was structurally similar to that of tobermorite. The outer hydration product (Op) of both polymorphs exhibited an increasing degree of silicate polymerization over time. The inner hydration product (Ip) of β-C 2 S polymerized slower than Op; however, the degree of silicate polymerization of both Ip and Op in the α′ H -C 2 S hydration system was comparable. The polymerization degree of Op was relatively heterogeneous, whereas, in α′ H -C 2 S, the polymerization degree was more homogeneous. Ptychographic imaging shows that the Op of α′ H -C 2 S exhibits coarser fibrils than the Op of β-C 2 S, and a clear Op-Ip interface of hydrated β-C 2 S is observed.

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The energy density of current batteries is limited by the practical capacity of the positive electrode, which is determined by the properties of the active material and its concentration in the composite electrode architecture. The observation in dynamic conditions of electrochemical transformations creates the opportunity of identifying design rules toward reaching the theoretical limits of battery electrodes. But these observations must occur during operation and at multiple scales. They are particularly critical at the single-particle level, where incomplete reactions and failure are prone to occur. Here, operando full-field transmission X-ray microscopy is coupled with X-ray spectroscopy to follow the chemical and microstructural evolution at the nanoscale of single crystals of Li1+xMn2-xO4, a technologically relevant Li-ion battery electrode material. The onset and crystallographic directionality of a series of complex phase transitions are followed and correlated with particle fracture. The dynamic character of this study reveals the existence of nonequilibrium pathways where phases at substantially different potentials can coexist at short length scales. The results can be used to inform the engineering of particle morphologies and electrode architectures that bypass the issues observed here and lead to optimized battery electrode properties.

The energy density of current batteries is limited by the practical capacity of the positive electrode, which is determined by the properties of the active material and its concentration in the composite electrode architecture. The observation in dynamic conditions of electrochemical transformations creates the opportunity of identifying design rules toward reaching the theoretical limits of battery electrodes. But these observations must occur during operation and at multiple scales. They are particularly critical at the single-particle level, where incomplete reactions and failure are prone to occur. Here, operando full-field transmission X-ray microscopy is coupled with X-ray spectroscopy to follow the chemical and microstructural evolution at the nanoscale of single crystals of Li1+xMn2-xO4, a technologically relevant Li-ion battery electrode material. The onset and crystallographic directionality of a series of complex phase transitions are followed and correlated with particle fracture. The dynamic character of this study reveals the existence of nonequilibrium pathways where phases at substantially different potentials can coexist at short length scales. The results can be used to inform the engineering of particle morphologies and electrode architectures that bypass the issues observed here and lead to optimized battery electrode properties. Compositional and morphological transitions during the electrochemical reaction of a single Li1+xMn2-xO4 microcrystal are successfully probed at the nanoscale using operando full-field transmission X-ray microscopy coupled with X-ray spectroscopy. It is possible to visualize the directionality of the transitions and correlate them with fracture. The approach reveals nonequilibrium pathways where phases at different potentials can coexist within a microcrystal.

Novel developments in X-ray sources, optics and detectors have significantly advanced the capability of X-ray microscopy at the nanoscale. Depending on the imaging modality and the photon energy, state-of-the-art X-ray microscopes are routinely operated at a spatial resolution of tens of nanometres for hard X-rays or ∼10 nm for soft X-rays. The improvement in spatial resolution, however, has led to challenges in the tomographic reconstruction due to the fact that the imperfections of the mechanical system become clearly detectable in the projection images. Without proper registration of the projection images, a severe point spread function will be introduced into the tomographic reconstructions, causing the reduction of the three-dimensional (3D) spatial resolution as well as the enhancement of image artifacts. Here the development of a method that iteratively performs registration of the experimentally measured projection images to those that are numerically calculated by reprojecting the 3D matrix in the corresponding viewing angles is shown. Multiple algorithms are implemented to conduct the registration, which corrects the translational and/or the rotational errors. A sequence that offers a superior performance is presented and discussed. Going beyond the visual assessment of the reconstruction results, the morphological quantification of a battery electrode particle that has gone through substantial cycling is investigated. The results show that the presented method has led to a better quality tomographic reconstruction, which, subsequently, promotes the fidelity in the quantification of the sample morphology.

Total electron yield (TEY) imaging is an established scanning transmission X-ray microscopy (STXM) technique that gives varying contrast based on a sample's geometry, elemental composition, and electrical conductivity. However, the TEY-STXM signal is determined solely by the electrons that the beam ejects from the sample. A related technique, X-ray beam-induced current (XBIC) imaging, is sensitive to electrons and holes independently, but requires electric fields in the sample. Here we report that multi-electrode devices can be wired to produce differential electron yield (DEY) contrast, which is also independently sensitive to electrons and holes, but does not require an electric field. Depending on whether the region illuminated by the focused STXM beam is better connected to one electrode or another, the DEY-STXM contrast changes sign. DEY-STXM images thus provide a vivid map of a device's connectivity landscape, which can be key to understanding device function and failure. To demonstrate an application in the area of failure analysis, we image a 100 nm, lithographically-defined aluminum nanowire that has failed after being stressed with a large current density.

The success of ptychographic imaging experiments strongly depends on achieving high signal-to-noise ratio. This is particularly important in nanoscale imaging experiments when diffraction signals are very weak and the experiments are accompanied by significant parasitic scattering (background), outliers or correlated noise sources. It is also critical when rare events, such as cosmic rays, or bad frames caused by electronic glitches or shutter timing malfunction take place. In this paper, we propose a novel iterative algorithm with rigorous analysis that exploits the direct forward model for parasitic noise and sample smoothness to achieve a thorough characterization and removal of structured and random noise. We present a formal description of the proposed algorithm and prove its convergence under mild conditions. Numerical experiments from simulations and real data (both soft and hard X-ray beamlines) demonstrate that the proposed algorithms produce better results when compared to state-of-the-art methods.

We report the study of Mg cathodic electrochemical deposition on Ti and Au electrode using a multimodal approach by examining the sample area in-situ using liquid cell transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy (XAS). Magnesium Aluminum Chloride Complex was synthesized and utilized as electrolyte, where non-reversible features during in situ charging-discharging cycles were observed. During charging, a uniform Mg film was deposited on the electrode, which is consistent with the intrinsic non-dendritic nature of Mg deposition in Mg ion batteries. The Mg thin film was not dissolvable during the following discharge process. We found that such Mg thin film is hexacoordinated Mg compounds by in-situ STXM and XAS. This study provides insights on the non-reversibility issue and failure mechanism of Mg ion batteries. Also, our method provides a novel generic method to understand the in situ battery chemistry without any further sample processing, which can preserve the original nature of battery materials or electrodeposited materials. This multimodal in situ imaging and spectroscopy provides many opportunities to attack complex problems that span orders of magnitude in length and time scale, which can be applied to a broad range of the energy storage systems.