Pressure- and plastic strain-induced phase transformations in silicon: drastic reduction of transformation pressures, change in transformation sequence, and particle size effect

The plastic strain-induced PTs differ qualitatively from pressure- and stress-induced transformations and require completely different experimental characterization and thermodynamic and kinetic description [1-2]. Pressure-induced phase transformations (PTs) between numerous phases of Si, the most important electronic material, have been studied for decades. Here, we revealed in-situ various unexpected plastic strain-induced PT phenomena with rotational diamond anvil cell. Thus, for 100-nm-Si, strain-induced PT Si-I to Si-II (and Si-I to Si-III) initiates at 0.4 GPa (0.6 GPa) versus 16.2 GPa (∞, since it does not occur) under hydrostatic conditions; for 30 nm-Si, it is 6.1 GPa versus ∞. The predicted theoretical correlation between the direct and reverse Hall-Petch effect of the grain size on the yield strength and the minimum pressure for strain-induced PT is confirmed for the appearance of Si-II and XI. Retaining Si-II at ambient pressure and obtaining reverse Si-II to Si-I PT was achieved, demonstrating the possibilities of manipulating different synthetic paths.