The performance of monocrystalline silicon in ultraprecision manufacturing is strongly influenced by phase transformations under high strain rates. While extensive attention has been given to β -Si and Si-XIII, investigations on the bct5-Si phase remain limited, and no experimental validation of its existence has been reported to date. This study combines molecular dynamics (MD) analysis and nanoindentation experiments to uncover the mechanisms underlying bct5-Si nucleation and evolution. Results reveal that bct5-Si consistently emerges as the first high-pressure phase under shear-dominant stress states, regardless of indenter size or crystallographic orientation. On the (111) surface, higher shear stress along the 111110 slip systems accelerates its nucleation compared to (001) and (110) orientations. During unloading, bct5-Si exhibits dual pathways, reverting either to the diamond cubic structure or transforming into amorphous silicon. Importantly, the correspondence between MD-predicted electrical resistance changes and experimental measurements provides the first compelling evidence of bct5-Si formation. This work establishes bct5-Si as a universal and shear-driven transitional phase in silicon, offering new insights for tailoring phase pathways to optimize surface integrity in ultraprecision machining.
Li et al. (Fri,) studied this question.