Atomistic simulation of the effect of temperature and pressure on the [001] symmetric tilt grain boundaries of MgO

Computer simulation has been used to model a series of grain boundaries of MgO. The aim of the work is to establish a procedure for generating grain boundaries and to calculate the effect of high pressures and temperatures upon the structure, energies and ultimately diffusivities associated with these boundaries. The simulations predict that temperatures up to 1200 K have little effect upon the structure and energies, whereas pressures of up to 40 GPa have a large effect, causing the free energy of formation to increase with pressure for all the grain boundaries studied. In addition the (310), (410) and (510) grain boundaries undergo structural changes to minimize the dilation of the grain boundary. In the case of the (410) and (510) grain boundaries this structure change is found to be irreversible when the pressure is released.