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Abstract: We present results of an experimental study on single crystals of a 5d double perovskite Ba2CaReO6. Magnetization measurements reveal a weak splitting between zero-field-cooled and field-cooled protocols below 12 K. At magnetic fields above 1 T the splitting is absent and the magnetic susceptibility is featureless. A detailed specific heat study in a wide temperature range and comprising different heat pulses did not reveal any indication of a thermodynamic phase transition. At low temperatures we do observe specific heat deviating from a phonon background, leading to a total electronic entropy release of . Resonant and non-resonant x-ray diffraction of characteristic Bragg peaks indicates a significant presence of disorder, potentially related to random tilts and rotations of rigid ReO6 octahedra.

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Abstract: Four novel carbazole-based photopolymerizable liquid crystals (PLCs) incorporating diacrylates or nonconjugated dienes were designed and synthesized to study their mesomorphic behavior and photocuring properties, with a focus on future applications in 4D printing. A combined analysis protocol using polarized optical microscopy (POM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS) revealed a favorably wide range of nematic phases near room temperature and a slow tendency to crystallize. This should be advantageous in applications requiring good surface-alignment of the reactive mesogen in the nematic phase. This behavior could be attributed to the effects of polymerization under prolonged high temperatures for acrylates and the high entropy of long, branched, flexible alkyl chains in dienes. The polymerization process induces a kinetic competition between LC ordering and network formation. This work establishes protocols for real-time phase monitoring during polymerization, resolving longstanding ambiguities in LC phase identification under thermal polymerization. Furthermore, photocuring tests of the acrylate and diene monomers demonstrated high photopolymerization efficiency and good thermal stability, particularly for the acrylate monomers.

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Abstract: The unabating discovery of nanoskyrmions in centrosymmetric magnets challenges the conventional Dzyaloshinskii-Moriya (DM) skyrmion stabilization mechanism. We investigate Gd2⁢PdSi3 using polarized resonant x-ray scattering and find that the low-field incommensurate modulations are elliptical helices, evolving into spin-density waves at higher fields. Quasi-2D magnetism arises via local DM interactions generated by inversion symmetry breaking around Gd-Gd bonds, which we characterize using atomistic simulations. Our findings suggest a prominent “hidden” role of DM interactions even in centrosymmetric skyrmionic hosts.

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Abstract: We present a theoretical framework for understanding diffuse multiple scattering (DMS) in single crystals, focusing on diffuse scattering Bragg channels. These channels, when probed with high-flux low-divergence monochromatic synchrotron X-rays, provide well defined visualizations of Bragg cones. Our main contribution lies in modelling the intensity distribution along these lines by considering diffuse scattering (DS) around individual reciprocal-lattice nodes. The model incorporates contributions from both general DS and mosaicity, elucidating their connection to second-order scattering events. This comprehensive approach advances our understanding of DMS phenomena, enabling their use as probes for complex material behaviour, particularly under extreme conditions.

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Abstract: The performance and longevity of lithium-ion batteries depend critically on the structural and electrochemical dynamics of their constituent materials, particularly cathodes. Among these, LiCoO2 (LCO) is a benchmark material known for its high energy density. However, the structural evolution of LCO during electrochemical cycling, including strain, defects, and domain formation, remains poorly understood, largely due to the limitations of conventional imaging techniques in resolving nanoscale dynamics non-destructively. This thesis leverages Bragg Coherent X-ray Diffraction Imaging (Bragg CDI), a powerful, non-destructive technique, to probe the three-dimensional structural and strain dynamics of nanocrystalline LCO cathodes. By combining traditional phasing methods with machine learning-based strain reconstruction tools, and further enhancing data interpretation with advanced analysis techniques, this work provides unprecedented insights into the nanoscale behaviour of LCO under varying electrochemical and electric field conditions. The study reveals that during electrochemical cycling, LCO nanocrystals exhibit dynamic domain behaviour, including the formation and expansion of domains at the crystal edges in the charged state, followed by fragmentation into smaller domains bounded by dislocations. These processes are reversed during discharge, with domains shrinking and reassembling as the crystal approaches its discharged state. Additionally, under applied electric fields, polarised domains and significant phase changes are observed, with the field inducing phase uniformity along its direction. Notably, a migrating dislocation near the crystal edge exhibits depth invariance across varying field magnitudes, aligning with the domain expansion limit observed during cycling. These findings contribute to a deeper understanding of the structural and electrochemical interplay in LCO cathodes, offering valuable insights into the mechanisms underlying performance degradation and suggesting pathways for improving battery design and functionality.