Topological defects of spontaneous polarization are extensively studied as templates for unique physical phenomena and in the design of reconfigurable electronic devices. Experimental investigations of the complex topologies of polarization have been limited to surface phenomena, which has restricted the probing of the dynamic volumetric domain morphology in operando. Here, we utilize Bragg coherent diffractive imaging of a single BaTiO₃ nanoparticle in a composite polymer/ferroelectric capacitor to study the behavior of a three-dimensional vortex formed due to competing interactions involving ferroelectric domains. Our investigation of the structural phase transitions under the influence of an external electric field shows a mobile vortex core exhibiting a reversible hysteretic transformation path. We also study the toroidal moment of the vortex under the action of the field. Our results open avenues for the study of the structure and evolution of polar vortices and other topological structures in operando in functional materials under cross field configurations.

Layered nickel-rich lithium transition-metal oxides (${\mathrm{Li}\mathrm{Ni}}_x{\mathrm{Mn}}_y{\mathrm{Co}}_{1-x-y}{\mathrm{O}}_2$; where x ≥ 0.8), with single-crystalline morphology, are promising future high-energy-density $\mathrm{Li}$-ion battery cathodes due to their ability to mitigate particle-cracking-induced degradation. This is due to the absence of grain boundaries in these materials, which prevents the build-up of bulk crystallographic strain during electrochemical cycling. Compared to their polycrystalline counterparts, there is a need to study single-crystalline $\mathrm{Ni}$-rich cathodes using operando x-ray methods in uncompromised machine-manufactured industrylike full cells to understand their bulk degradation mechanisms as a function of different electrochemical cycling protocols. This can help us identify factors to improve their long-term performance. Here, through in-house operando x-ray studies of pilot-line-built ${\mathrm{Li}\mathrm{Ni}}_{0.8}{\mathrm{Mn}}_{0.1}{\mathrm{Co}}_{0.1}{\mathrm{O}}_2$–graphite A7 pouch cells, it is shown that their electrochemical-capacity fade under harsh conditions (2.5–4.4 V and 40 °C for 100 cycles at a C/3 rate) primarily stems from the high-voltage reconstruction of the cathode surface from a layered to a cubic (rock-salt) phase that impedes the ${\mathrm{Li}}^{+}$ kinetics and increases cell impedance. Postmortem electron and x-ray microscopy show that these cathodes can withstand severe anisotropic structural changes and show no cracking when cycled under such conditions. Comparing these results to those from commercial $\mathrm{Li}$-ion cells with surface-modified single-crystalline $\mathrm{Ni}$-rich cathodes, it is identified that cathode surface passivation can mitigate this type of degradation and prolong cycle life. In addition to furthering our understanding of degradation in single-crystalline $\mathrm{Ni}$-rich cathodes, this work also accentuates the need for practically relevant and reproducible fundamental investigations of $\mathrm{Li}$-ion cells and presents a methodology for achieving this.

Strain engineering is a promising technology with potential application in memory devices, electronic elements, photoactive materials, etc. Nanoscale imaging of the strain is therefore important to better understand the operating condition of the device, growth processes, and influences of other factors. X-rays offer the advantage over electron-based techniques in that they offer high spatial resolution and access to volumetric information within nanostructured materials. This paper describes the basic physics behind strain at the nanoscale and provides a concise summary of the efforts in coherent diffractive imaging for the imaging of the displacement fields in nanocrystals. Although the approach is still under development, with instruments being continuously improved, a number of important results have already been demonstrated.

An array of compound refractive X-ray lenses (CRL) with 20 × 20 lenslets, a focal distance of 20cm and a visibility of 0.93 is presented. It can be used as a Shack-Hartmann sensor for hard X-rays (SHARX) for wavefront sensing and permits for true single-shot multi-contrast imaging the dynamics of materials with a spatial resolution in the micrometer range, sensitivity on nanosized structures and temporal resolution on the microsecond scale. The object’s absorption and its induced wavefront shift can be assessed simultaneously together with information from diffraction channels. In contrast to the established Hartmann sensors the SHARX has an increased flux efficiency through focusing of the beam rather than blocking parts of it. We investigated the spatiotemporal behavior of a cavitation bubble induced by laser pulses. Furthermore, we validated the SHARX by measuring refraction angles of a single diamond CRL, where we obtained an angular resolution better than 4 $\mathsf{\mu }$ rad.

We present iridium(iii) probes for bioorthogonal metabolic labeling, enabling versatile bioimaging applications including super-resolution X-ray fluorescence nanoscopy and photoluminescence lifetime imaging microscopy to advance sialylation studies.