Comparison of ion sites and diffusion paths in glasses obtained by molecular dynamics simulations and bond valence analysis

Based on molecular dynamics simulations of a lithium metasilicate glass we study the potential of bond valence sum calculations to identify sites and diffusion pathways of mobile Li ions in a glassy silicate network. We find that the bond valence method is not well suitable to locate the sites, but allows one to estimate the number of sites. Spatial regions of the glass determined as accessible for the Li ions by the bond valence method can capture up to 90% of the diffusion path. These regions however entail a significant fraction that does not belong to the diffusion path. Because of this low specificity, care must be taken to determine the diffusive motion of particles in amorphous systems based on the bond valence method. The best identification of the diffusion path is achieved by using a modified valence mismatch in the BV analysis that takes into account that a Li ion favors equal partial valences to the neighboring oxygen ions. Using this modified valence mismatch it is possible to replace hard geometric constraints formerly applied in the BV method. Further investigations are necessary to better understand the relation between the complex structure of the host network and the ionic diffusion paths.Comment: 16 pages, 10 figure

Structure of glassy lithium sulfate films sputtered in nitrogen (LISON): Insight from Raman spectroscopy and ab initio calculations

Raman spectra of thin solid electrolyte films obtained by sputtering a lithium sulfate target in nitrogen plasma are measured and compared to ab initio electronic structure calculations for clusters composed of 28 atoms. Agreement between measured and calculated spectra is obtained when oxygen atoms are replaced by nitrogen atoms and when the nitrogen atoms form bonds with each other. This suggests that the incorporation of nitrogen during the sputtering process leads to structures in the film, which prevent crystallization of these thin film salt glasses.Comment: 5 pages, 4 figure

Mixed Barrier Model for the Mixed Glass Former Effect in Ion Conducting Glasses

Mixing two types of glass formers in ion conducting glasses can be exploited to lower conductivity activation energy and thereby increasing the ionic conductivity, a phenomenon known as the mixed glass former effect (MGFE). We develop a model for this MGFE, where activation barriers for individual ion jumps get lowered in inhomogeneous environments containing both types of network forming units. Fits of the model to experimental data allow one to estimate the strength of the barrier reduction, and they indicate a spatial clustering of the two types of network formers. The model predicts a time-temperature superposition of conductivity spectra onto a common master curve independent of the mixing ratio

Investigation of the Structures of Sodium Borophosphate Glasses by Reverse Monte Carlo Modeling to Examine the Origins of the Mixed Glass Former Effect

We present new results for the Reverse Monte Carlo modeling of 0.35Na2O + 0.65[xB2O3 + (1 –x)P2O5] glasses based on previously reported X-ray diffraction (XRD) data. Structural models have been generated that accurately reproduce the pair correlation functions and structure factors determined by XRD while maintaining nearly perfect charge neutrality between the positively charged cations and the negatively charged phosphate and borate oxyanion groups and while maintaining appropriate bond distances between the various atom pairs. These models, however, are not successful in accounting for the concentrations of network forming units (NFUs), as predicted by recent theoretical modeling and by magic-angle spinning nuclear magnetic resonance (MAS NMR) data for sodium borate glasses with similar stoichiometry. By a further refinement of the modeling, the NFU concentrations can be successfully reproduced as well. For the optimized structures, we investigate the question if the conductivity activation energy correlates with the volume fraction of the sodium long-range diffusion paths, as identified in the RMC modeling

Initial analysis of the impact of the Ukrainian power grid synchronization with Continental Europe

When Russia invaded Ukraine on the 24\textsuperscript{th} of February 2022, this led to many acts of solidarity with Ukraine, including support for its electricity system. Just 20 days after the invasion started, the Ukrainian and Moldovan power grids were synchronized to the Continental European power grid to provide stability to these grids. Here, we present an initial analysis of how this synchronization affected the statistics of the power grid frequency and cross-border flows of electric power within Continental Europe. We observe faster inter-area oscillations, an increase in fluctuations and changes in the cross-border flows in and out of Ukraine and surrounding countries as an effect of the synchronization with Continental Europe. Overall these changes are small such that the now connected system can be considered as stable as before the synchronization.Comment: 7 pages, 6 figure