ИСТИНА

Silicon has a great importance as an optical, electronic and structural material. Modeling the impact of shock waves on silicon at room temperature is an important step toward understanding the various phenomena associated with phase transitions in Si [1]. Under the influence of pressure silicon undergoes a series of phase transitions caused by stress, accompanied by large changes in volume. Under high pressures SI undergo series of phase transitions. Si transforms to a primitive hexagonal (b-Sn) structure around 11 GPa, and to hcp (Si-VII) around 50 GPa [2]. Such high pressures could be achieved in laser-matter interactions. We used molecular dynamics simulation to investigate the pressure-induced phase transitions in Si both in static (fixed pressures) and dynamic (shock wave propagation) case. The simulations were performed in LAMMPS software package over 360000 atoms (TERSOFF interatomic potential). Fig.1. Histograms of atomic volume (a,b) during propagation of shock wave in Si (p=21.2 GPa) (a) and under constant pressures (b). XRD spectrum at constant pressure in SI. In the static pressure conditions (Fig.1b,c) we demonstrated that the phase transitions leads to the change of atomic volume, centrosymmetry parameter and XRD spectrum. The cubic diamond phase is stable up to 11GPa, -SN is stable in the pressure range from 11 to 50 GPa. In the dynamic phase the phase transition takes place only on the shock wave front on the ps timescale under pressures above 10 GPa. The phase is not stable and the structure returns to the initial state with a small number of defects. If pressure overcomes 30GPa the structure of Si becomes broken and it transmits to amorphous phase. The computed XRD spectra is a useful tool for compassion a numeric modeling data with experiments on synchrotron facilities.