Kinetically Stabilized Cation Arrangement in Li3YCl6 Superionic Conductor during Solid-State Reaction

The main approach for exploring metastable materials is via trial-and-error synthesis, and there is limited understanding of how metastable materials are kinetically stabilized. In this study, a metastable phase superionic conductor, beta-Li3YCl6, is discovered through in situ X-ray diffraction after heating a mixture of LiCl and YCl3 powders. While Cl- arrangement is represented as a hexagonal close packed structure in both metastable beta-Li3YCl6 synthesized below 600 K and stable alpha-Li3YCl6 above 600 K, the arrangement of Li+ and Y3+ in beta-Li3YCl6 determined by neutron diffraction brought about the cell with a 1/root 3 a-axis and a similar c-axis of stable alpha-Li3YCl6. Higher Li+ ion conductivity and lower activation energy for Li+ transport are observed in comparison with alpha-Li3YCl6. The computationally calculated low migration barrier of Li+ supports the low activation energy for Li+ conduction, and the calculated high migration barrier of Y3+ kinetically stabilizes this metastable phase by impeding phase transformation to alpha-Li3YCl6. This work shows that the combination of in situ observation of solid-state reactions and computation of the migration energy can facilitate the comprehension of the solid-state reactions allowing kinetic stabilization of metastable materials, and can enable the discovery of new metastable materials in a short time.

Automated summary

The study discovered a metastable phase superionic conductor through trial-and-error synthesis, showing improved ion conductivity compared to stable materials. Neutron diffraction and computational methods were utilized to determine the metastable structure and elucidate the mechanism of kinetic stabilization.