SnCN₂: A Carbodiimide with an Innovative Approach for Energy Storage Systems and Phosphors in Modern LED Technology

The carbodiimide SnCN$_{2}$ was prepared at low temperatures (400 °C–550 °C) by using a patented urea precursor route. The crystal structure of SnCN$_{2}$ was determined from single‐crystal data in space group C2/c (no. 15) with a=9.1547(5), b=5.0209(3), c=6.0903(3) Å, β=117.672(3), V=247.92 Å$^{3}$ and Z=4. As carbodiimide compounds display remarkably high thermal and chemical resistivity, SnCN$_{2}$ has been doped with Eu and Tb to test it for its application in future phosphor‐converted LEDs. This doping of SnCN$_{2}$ proved that a color tuning of the carbodiimide host with different activator ions and the combination of the latter ones is possible. Additionally, as the search for novel high‐performing electrode materials is essential for current battery technologies, this carbodiimide has been investigated concerning its use in lithium‐ion batteries. To further elucidate its application possibilities in materials science, several characterization steps and physical measurements (XRD, in situ XANES, Sn Mössbauer spectroscopy, thermal expansion, IR spectroscopy, Mott‐Schottky analysis) were carried out. The electronic structure of the n‐type semiconductor SnCN$_{2}$ has been probed using X‐ray absorption spectroscopy and density functional theory (DFT) computations

29Si NMR Chemical Shifts in Crystalline and Amorphous Silicon Nitrides

We investigate 29Si nuclear magnetic resonance (NMR) chemical shifts, δiso, of silicon nitride. Our goal is to relate the local structure to the NMR signal and, thus, provide the means to extract more information from the experimental 29Si NMR spectra in this family of compounds. We apply structural modeling and the gauge-included projector augmented wave (GIPAW) method within density functional theory (DFT) calculations. Our models comprise known and hypothetical crystalline Si3N4, as well as amorphous Si3N4 structures. We find good agreement with available experimental 29Si NMR data for tetrahedral Si[4] and octahedral Si[6] in crystalline Si3N4, predict the chemical shift of a trigonal-bipyramidal Si[5] to be about −120 ppm, and quantify the impact of Si-N bond lengths on 29Si δiso. We show through computations that experimental 29Si NMR data indicates that silicon dicarbodiimide, Si(NCN)2 exhibits bent Si-N-C units with angles of about 143° in its structure. A detailed investigation of amorphous silicon nitride shows that an observed peak asymmetry relates to the proximity of a fifth N neighbor in non-bonding distance between 2.5 and 2.8 Å to Si. We reveal the impact of both Si-N(H)-Si bond angle and Si-N bond length on 29Si δiso in hydrogenated silicon nitride structure, silicon diimide Si(NH)2

Metal-Catalyst-Free Access to Multiwall Carbon Nanotubes/Silica Nanocomposites (MWCNT/SiO2) from a Single-Source Precursor

The present study introduces a facile single-source precursor preparative access to bamboo-like multiwalled carbon nanotubes (MWCNTs) highly dispersed within a mesoporous silica-rich matrix. The metal-free single-source precursor was synthesized via a one-pot sol-gel process using tetramethyl orthosilicate (TMOS) and 4,4′-dihydroxybiphenyl (DHBP) and converted subsequently via pyrolysis in argon atmosphere into MWCNT/silica nanocomposites. The in-situ segregation of the highly defective bamboo-like MWCNTs was carefully investigated and has been shown to occur within the mesopores of the silica-rich matrix at relatively low temperatures and without the use of a metal catalyst. The experimental results have been supported by extensive computational simulations, which correlate the molecular architecture of the single-source precursor with the structural features of the carbon phase segregating from the silica matrix. Furthermore, the role of hydrogen on the stability of the prepared nanocomposites as well as on the high-temperature evolution and morphology of the segregated MWCNTs has been discussed based on vibrational spectroscopy, calorimetric studies and empirical potential calculations. The results attained within the present study may allow for designing highly-defined nanocarbon-containing composites with tailored structural features and property profiles

Mechanisms of stress in the brain

The brain is the central organ involved in perceiving and adapting to social and physical stressors via multiple interacting mediators, from the cell surface to the cytoskeleton to epigenetic regulation and nongenomic mechanisms. A key result of stress is structural remodeling of neural architecture, which may be a sign of successful adaptation, whereas persistence of these changes when stress ends indicates failed resilience. Excitatory amino acids and glucocorticoids have key roles in these processes, along with a growing list of extra- and intracellular mediators that includes endocannabinoids and brain-derived neurotrophic factor (BDNF). The result is a continually changing pattern of gene expression mediated by epigenetic mechanisms involving histone modifications and CpG methylation and hydroxymethylation as well as by the activity of retrotransposons that may alter genomic stability. Elucidation of the underlying mechanisms of plasticity and vulnerability of the brain provides a basis for understanding the efficacy of interventions for anxiety and depressive disorders as well as age-related cognitive decline