Christopher J. Kerr

This work introduces a completely rewritten version of the program RMCProfile (version 7), big-box, reverse Monte Carlo modelling software for analysis of total scattering data. The major new feature of RMCProfile7 is the ability to refine multiple phases simultaneously, which is relevant for many current research areas such as energy materials, catalysis and engineering. Other new features include improved support for molecular potentials and rigid-body refinements, as well as multiple different data sets. An empirical resolution correction and calculation of the pair distribution function as a back-Fourier transform are now also available. RMCProfile7 is freely available for download at https://rmcprofile.ornl.gov/.

We have developed a new class of lanthanide nano-clusters that self-assemble using flexible Schiff base ligands. Cd–Ln and Ni–Ln clusters, [Ln₈Cd₂₄(L¹)₁₂(OAc)₃₉Cl₇(OH)₂] (Ln = Nd, Eu), [Eu₈Cd₂₄(L¹)₁₂(OAc)₄₄], [Ln₈Cd₂₄(L²)₁₂(OAc)₄₄] (Ln = Nd, Yb, Sm) and [Nd₂Ni₄(L³)₂(acac)₆(NO₃)₂(OH)₂], were constructed using different types of flexible Schiff base ligands. These molecular nano-clusters exhibit anisotropic architectures that differ considerably depending upon the presence of Cd (nano-drum) or Ni (square-like nano-cluster). Structural characterization of the self-assembled particles has been undertaken using crystallography, transmission electron microscopy and small-angle X-ray scattering. Comparison of the metric dimensions of the nano-drums shows a consistency of size using these techniques, suggesting that these molecules may share similar structural features in both solid and solution states. Photophysical properties were studied by excitation of the ligand-centered absorption bands in the solid state and in solution, and using confocal microscopy of microspheres loaded with the compounds. The emissive properties of these compounds vary depending upon the combination of lanthanide and Cd or Ni present in these clusters. The results provide new insights into the construction of novel high-nuclearity nano-clusters and offer a promising foundation for the development of new functional nanomaterials.

Nano-structured silicon anodes are attractive alternatives to graphitic carbons in rechargeable Li-ion batteries, owing to their extremely high capacities. Despite their advantages, numerous issues remain to be addressed, the most basic being to understand the complex kinetics and thermodynamics that control the reactions and structural rearrangements. Elucidating this necessitates real-time in situ metrologies, which are highly challenging, if the whole electrode structure is studied at an atomistic level for multiple cycles under realistic cycling conditions. Here we report that Si nanowires grown on a conducting carbon-fibre support provide a robust model battery system that can be studied by ⁷Li in situ NMR spectroscopy. The method allows the (de)alloying reactions of the amorphous silicides to be followed in the 2nd cycle and beyond. In combination with density-functional theory calculations, the results provide insight into the amorphous and amorphous-to-crystalline lithium–silicide transformations, particularly those at low voltages, which are highly relevant to practical cycling strategies.

Subpercolated composites consisting of highly polar fillers in an insulating matrix have long been predicted to exhibit a large dielectric constant. In this study, we examine the feasibility of experimentally reproducing such an effect based on a multiwalled carbon nanotubes (MWNTs)-polydimethylsiloxane (PDMS) composite system. MWNTs of different diameters were subjected to high-power ultrasound. The sonication-induced scission of nanotubes shows saturation at a final length dependent on the tube diameter, in agreement with a theoretical model. Sonication allows us to produce MWNTs with a prescribed mean aspect ratio between 10 and 55. Composites were formed from these MWNTs with PDMS elastomer at a fixed 1 wt% doping level, using a common solution-processing method. Results from AC impedance spectroscopy indicate that the tube length minimally affects the dielectric response of these composites when the doping level is below the percolation threshold.