The mechanism and effect of defects in the B1-B2 phase transition of KCl under high pressure: molecular dynamics simulation

Molecular dynamics (MD) simulations of the pressure-induced phase transition of potassium chloride (KCl) were performed with 2744 and 9000 atoms to study crystalline states, the process and the effects of defects under high hydrostatic pressure. In this study, we adopted the Born-Mayer-Huggins-type potential function to describe the interatomic interaction. The potential parameters used in this study were empirically optimized on the basis of Hugoniot equation of state data. The simulation results for perfect crystals, (1372 K+ and 1372 Cl-) showed that the B1-B2 phase transition occurred with large hysteresis, and the thermodynamic transition pressure was calculated to be 3.5 GPa. The simulation results indicated that the phase transition proceeded through displacements of atomic lines parallel to the <100> axis direction of the B1-type structure, and that these lines corresponded to the atomic lines parallel to the <111> axis direction of the B2-type structure after the phase transition. In the case of the larger cells containing 9000 atoms with weak or strong van der Waals interactions, some clusters or dislocations, respectively, were generated in the resultant B2 phase. As regards dislocations, the phase transitions started around dislocations and the phase transition pressure decreased.