The mechanochemical bromination of a heterocyclic sulfoximine is studied by ex-and in-situ solid-state NMR spectroscopy. A clean and fast reaction is observed in a mixer mill, which can alternatively be induced either using the centrifugal pressure of magic-angle spinning or by solely magnetic stirring the solid entities.
The structure of crystalline and amorphous materials in the sodium (Na) super-ionic conductor (NASICON) system Na1+xAlxGe2−x(PO4)3 with x = 0, 0.4 and 0.8 was investigated by combining (i) neutron and X-ray powder diffraction and pair-distribution function analysis with (ii) 27 Al and 31 P magic angle spinning (MAS) and 31 P/ 23 Na double-resonance nuclear magnetic resonance (NMR) spectroscopy. A Rietveld analysis of the powder diffraction patterns shows that the x = 0 and x = 0.4 compositions crystallize into space group type R 3 whereas the x = 0.8 composition crystallizes into space group type R 3c. For the as-prepared glass, the pair-distribution functions and 27 Al MAS NMR spectra show the formation of sub-octahedral Ge and Al centered units, which leads to the creation of non-bridging oxygen (NBO) atoms. The influence of these atoms on the ion mobility is discussed. When the as-prepared glass is relaxed by thermal annealing, there is an increase in the Ge and Al coordination numbers that leads to a decrease in the fraction of NBO atoms. A model is proposed for the x = 0 glass in which super-structural units containing octahedral Ge (6) and tetrahedral P (3) motifs are embedded in a matrix of tetrahedral Ge (4) units, where superscripts denote the number of bridging oxygen atoms. The super-structural units can grow in size by a reaction in which NBO atoms on the P (3) motifs are used to convert Ge (4) to Ge (6) units. The resultant P (4) motifs thereby provide the nucleation sites for crystal growth via a homogeneous nucleation mechanism.
This paper describes the preparation of a transparent glass‐ceramic from the SiO2‐K2O‐ZnO‐Al2O3‐TiO2 system containing a single crystalline phase, gahnite (ZnAl2O4). TiO2 was used as a nucleating agent for the heat‐induced precipitation of gahnite crystals of 5‐10 nm. The evolution of the ZnAl2O4 spinel structure through the gradual formation of Al‐O bonds was examined by infrared spectroscopy. The dark brown color of the transparent precursor glass and glass‐ceramic was eliminated using CeO2. The increase in transparency of the CeO2‐doped glass and glass‐ceramics was demonstrated by UV‐visible absorption spectroscopy. EPR measurements confirmed the presence of Ce3+ ions, indicating that CeO2 was effective in eliminating the brown color introduced by Ti3+ ions via oxidation to Ti+4. The hardness of the glass‐ceramic was 30% higher than that of the as‐prepared glasses. This work offers key guidelines to produce hard, transparent glass‐ceramics which may be potential candidates for a variety of technological applications, such as armor and display panels.
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