Crystal structure, microstructure and ionic conductivity of the cost-efficient sodium solid electrolyte Na5YSi4O12

There exist a number of solid-electrolyte materials for sodium battery technologies characterized by intermediate complexity of the corresponding crystal structures. Beside the well-known sodium solid-electrolytes, v''-alumina and NASICON, Na5YSi4O12 is another promising phase with a high ionic conductivity. Its main advantage over the two above-mentioned structures is a lower production complexity and thus associated costs. However, very little is known about the correlation between the complex crystal structure, with their one-dimensional ion migration pathways, the microstructure and the interplay with Na+ ionic conductivity. In this work, the phase content, the phase distribution, the migration pathways and the ionic conductivity of polycrystalline Na5YSi4O12-based materials, obtained by a glass-ceramic process, have been analyzed by means of X-ray powder diffraction, scanning electron microscopy, solid-state nuclear magnetic resonance and electrical impedance spectroscopy. These experimental results were discussed with respect to theoretical considerations of the crystal structure, based on the bond valence method and the Voronoi-Dirichlet approach, and other Na+ conductors.