Vibrational properties of a Σ5(3 1 0)[0 0 1] NiO grain boundary: a local analysis by molecular dynamics simulation

Using molecular dynamics and a rigid ion potential we studied the vibrational properties of a Σ5(3 1 0)[0 0 1] tilt grain boundary in NiO. We calculated the local density of states and the mean square displacement (MSD) of the cation and ion sublattice for a wide temperature range. We examined their behaviour in the directions parallel and normal to the boundary as a function from the grain boundary plane. We found that the local phonon density of states of the sites of the boundary are altered with comparison to the bulk presenting in general a shift towards lower frequencies in the direction normal to the boundary and toward higher frequencies in the direction parallel to the grain boundary. This anisotropy, which is conformed by the results of the MSDs, is maintained up to high temperatures. We have also observed that the increase of temperature leads to the gradual loosening of the binding of atoms.