1208-1209.pdf - Google Drive
Complex structures can emerge from simple interactions (Ziman, 1979; Parsonage & Staveley, 1978; Welberry, 1985). Geometric frustration in the Ising triangular antiferromagnet (Wannier, 1950), the hydrogen-bonding-driven configurational degeneracy of cubic ice (Bernal & Fowler, 1933) and the long-period stacking phases of the anisotropic next-nearest-neighbour interaction (ANNNI) model (Bak, 1982) are all well studied examples. It is a natural corollary that complexity is not particularly uncommon, and indeed there is a growing realization that complexity of various types is not only present but important for the behaviour of many key classes of functional materials, from disordered rocksalt cathodes to high-temperature superconductors (Clément et al., 2020; Ji et al., 2019; Mydosh & Oppeneer, 2011; Welberry & Goossens, 2016; Simonov & Goodwin, 2020). Determining the structures of such systems is one of the key challenges of modern structural science (Billinge & Levin, 2007; Keen & Goodwin, 2015; Juhás et al., 2015).
1208-1209.pdf - Google Drive
For the specific procrystalline system Hg(NH3)2Cl2, and its 2D toy analogue, we have established that a mean-field refinement approach allows unambiguous determination from the diffuse scattering patterns of the microscopic interactions that drive their structural complexity. This link can be established without assuming the form of the interactions, and the process is even robust to (extreme) data incompleteness. We cautiously suggest that the interaction-space approach we have taken here might form the basis for a more general strategy for `solving' the structures of complex and/or disordered crystals (Goodwin, 2019). Certainly, the formalism as presented here is not limited to substitutional disorder in molecular systems with homogeneous average occupancies. The molecular form factors can be easily replaced by atomic form factors, and unequal average occupations are straightforwardly accommodated within the matrix [see equation (5)]. The formalism is easily extended to allow treatment of crystallographic space groups that contain several disordered sites in the unit cell, and such an extension would allow investigation of nonstoichiometric compounds as described by Gusev (2006) and Withers (2015).
Abstract:Cracks and defects, which could result in lower reflectivity and larger full width at half maximum (FWHM), are the major obstacles for obtaining highly ordered structures of colloidal crystals (CCs). The high-quality CCs with high reflectivity (more than 90%) and 9.2 nm narrow FWHM have been successfully fabricated using a fixed proportion of a soft matter system composed of silica particles (SPs), polyethylene glycol diacrylate (PEGDA), and ethanol. The influences of refractivity difference, volume fractions, and particle dimension on FWHM were illuminated. Firstly, we clarified the influences of the planar interface and the bending interface on the self-assembly. The CCs had been successfully fabricated on the planar interface and presented unfavorable results on the bending interface. Secondly, a hard sphere system consisting of SPs, PEGDA, and ethanol was established, and the entropy-driven phase transition mechanism of a polydisperse system was expounded. The FWHM and reflectivity of CCs showed an increasing trend with increasing temperature. Consequently, high-quality CCs were obtained by adjusting temperatures (ordered structure formed at 90 C and solidified at 0 C) based on the surface phase rule of the system. We acquired a profound understanding of the principle and process of self-assembly, which is significant for preparation and application of CCs such as optical filters.Keywords: soft matter; colloidal crystals; self-assembly; entropy-induced 041b061a72