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.

Coherent x-ray diffraction imaging is used to map the local three dimensional strain inhomogeneity and electron density distribution of two individual LiNi_0.5Mn_1.5O_4−δ cathode nanoparticles in both ex-situ and in-situ environments. Our reconstructed images revealed a maximum strain of 0.4%. We observed different variations in strain inhomogeneity due to multiple competing effects. The compressive/tensile component of the strain is connected to the local lithium content and, on the surface, interpreted in terms of a local Jahn-Teller distortion of Mn³⁺. Finally, the measured strain distributions are discussed in terms of their impact on competing theoretical models of the lithiation process.

Bragg coherent diffractive imaging is a powerful technique that can be used to explore the internal structure and strain of nanoscale crystalline objects. During the data collection process, the Bragg peak typically stays within a small range of pixels on the x-ray sensitive area detector. Here, we report abrupt and irreversible Bragg peak movement during the coherent x-ray data collection process for both Pd nanocubes and a Ni nanowire. We report that this phenomenon can be attributed to x-ray momentum transfer, also known as radiation pressure, to the nanocrystals. Understanding this effect is crucial given the anticipated coherent flux increases at next-generation synchrotron sources.

Nanocomposites of ferroelectric ceramic filler and polymer matrix show considerable promise as high energy-storage dielectric capacitors. However, the influence of the microstructure of the ferroelectric filler on the electric energy-storage performance in the nanocomposite has not been quantitatively studied, yet it is a key element in understanding the methods employed to improve the performance of capacitors. We demonstrate a strategy to enhance the energy-storage density with topological vortex structures in nanocomposites. Using three-dimensional phase field calculations, we show that multivortex structures can exist in ferroelectric nanowires without charge defects or free charges at the interface between the filler and matrix. The switching behavior of the topological structure (vortex and antivortex pair) under external electric field is calculated in nanocylinder wires. The small remnant polarization and very narrow hysteresis loop due to the vortex structure in the nanocomposites can lead to a large enhancement of energy density, as high as $5\mathrm{J}/{\mathrm{cm}}^3$ compared to $1–2\mathrm{J}/{\mathrm{cm}}^3$ for commercial capacitors, and high energy-storage efficiency (over 95%) at a relatively low electric field of $140\mathrm{MV}/\mathrm{m}$.

Magnetostriction is the emergence of a mechanical deformation induced by an external magnetic field. The conversion of magnetic energy into mechanical energy via magnetostriction at the nanoscale is the basis of many electromechanical systems such as sensors, transducers, actuators, and energy harvesters. However, cryogenic temperatures and large magnetic fields are often required to drive the magnetostriction in such systems, rendering this approach energetically inefficient and impractical for room-temperature device applications. Here, we report the experimental observation of giant magnetostriction in single-crystal nickel nanowires at room temperature. We determined the average values of the magnetostrictive constants of a Ni nanowire from the shifts of the measured diffraction patterns using the 002 and 111 Bragg reflections. At an applied magnetic field of 600 Oe, the magnetostrictive constants have values of λ₁₀₀ = −0.161% and λ₁₁₁ = −0.067%, two orders of magnitude larger than those in bulk nickel. Using Bragg coherent diffraction imaging (BCDI), we obtained the three-dimensional strain distribution inside the Ni nanowire, revealing nucleation of local strain fields at two different values of the external magnetic field. Our analysis indicates that the enhancement of the magnetostriction coefficients is mainly due to the increases in the shape, surface-induced, and stress-induced anisotropies, which facilitate magnetization along the nanowire axis and increase the total magnetoelastic energy of the system.