Colloid structure in polyethylene-wax/n-paraffin mixtures

The spherulite structure and its genesis in WAX PE130 are discussed on the basis of DSC, X-ray small-angle and raster-electron-microscopical measurements. Modifications of this superstructure in the presence of a low-molecular-weight solvent are shown. The role of thermodynamics and kinetics is reflected. Conclusions are drawn which imply general aspects that governs the growth of spherulites.     

An Unexpected New Member of the Family of Lithium Oxonitridosilicates – Li7Si2NO6

With Li₇Si₂NO₆, a new member of the family of lithium oxonitridosilicates with a so far unseen structure type could be synthesized. Using a high-temperature solid-state reaction in open nickel crucibles under nitrogen flow, it was possible to obtain single crystals from the starting materials SiO₂, Li₃N, and Li₂O at temperatures of 900 °C. Single crystal X-ray diffraction data yielded lattice parameters of a=5.0934(2), b=7.4128(2), c=8.5918(2) Å, α=75.16(1)°, β=87.36(1)°, γ=73.01(1)° and a cell volume of V=299.75(2) ų. The compound, crystallizing in the triclinic space group P (no. 2), consists of a highly condensed anionic network built up by [SiNO₃]-, [LiO₄]-, and [LiN₂O₂]-tetrahedra as well as lithium in octahedral coordination as completing cation. With an activation barrier of 695 meV for lithium migration, Li₇Si₂NO₆ is a potential lithium-ion conductor. The structure allows a classification not only as a sorosilicate but also as a tecto-lithosilicate and most precisely as a lithium oxonitridolithosilicate, when the different coordinations of the lithium ions are taken into account. Interestingly, the new compound is none of the several proposed representatives of the lithium oxonitridosilicates, thus expanding this substance class unexpectedly.     

Photodegradation of CuBi2O4 Films Evidenced by Fast Formation of Metallic Bi using Operando Surface-sensitive X-ray Scattering**

CuBi₂O₄ has recently emerged as a promising photocathode for photo-electrochemical (PEC) water splitting. However, its fast degradation under operation currently poses a limit to its application. Here, we report a novel method to study operando the semiconductor-electrolyte interface during PEC operation by surface-sensitive high-energy X-ray scattering. We find that a fast decrease in the generated photocurrents correlates directly with the formation of a metallic Bi phase. We further show that the slower formation of metallic Cu, as well as the dissolution of the electrode in contact with the electrolyte, further affect the CuBi₂O₄ activity and morphology. Our study provides a comprehensive picture of the degradation mechanisms affecting CuBi₂O₄ electrodes under operation and poses the methodological basis to investigate the photocorrosion processes affecting a wide range of PEC materials.