Instable Microdeformation\nand Strain Recovery in Amorphous\nLiPON Thin Layer

Lithium phosphorus oxynitride (LiPON) is a crucial electrolyte\nfor all-solid-state thin-film batteries due to its sufficient ionic\nconductivity. Understanding the mechanical behavior of LiPON films\nis crucial for further technological development. Previous studies\nnoted unexpected ductility and strain recovery in amorphous LiPON\nduring sharp-ended tip indentations revealing pile-up formation and\ndensification as the main deformation mechanisms. Our work presents\nnanoindentation experiments including spherical tips, revealing a\nnovel mechanical behavior of a sudden deformation event followed by\nslower but complete strain recovery during unloading. This unique\ndeformation phenomenon is likely linked to the material’s special\nstructure, featuring isolated phosphate tetrahedra P(O,N)<sub>4</sub> embedded in an amorphous Li matrix with occasional N bridge bonds\nbetween tetrahedra. In this study, the authors report on a range of\nnanoindentation experiments, examining how instability depends on\nstrain rate and the indenter’s tip geometry. It is found that\ninstability occurs only within a specific range of deformation velocities\nand strongly depends on the indenter’s tip sharpness. Assuming\nthe mobility and the capability of the cooperative movement of the\ntetrahedra, the measured novel deformation method, and other, deformation-attached\nproperties of the LiPON can be explained.