Unexpected plastic strain-induced phase transformation phenomena in silicon

Pressure-induced phase transformations (PTs) in Si, the most important electronic material, have been broadly studied. However, strain-induced PTs in Si were never studied in situ . Here, we revealed in situ various important plastic strain-induced PT phenomena. A correlation between the particle size's direct and inverse Hall-Petch effect on yield strength and pressure for strain-induced PT is found. For 100 nm particles, strain-induced PT Si-I→Si-II initiates at 0.3 GPa versus 16.2 GPa under hydrostatic conditions; Si-I→Si-III PT starts at 0.6 GPa and does not occur under hydrostatic pressure. Pressure in small Si-II and Si-III regions is ~5-7 GPa higher than in Si-I. Retaining Si-II and single-phase Si-III at ambient pressure and obtaining reverse Si-II→Si-I PT demonstrates the possibilities of manipulating different synthetic paths. The obtained results corroborate the elaborated dislocation pileup-based mechanism and have numerous applications for developing economic defect-induced synthesis of nanostructured materials, surface treatment (polishing, turning, etc.), and friction.