Computer simulation of general grain boundaries in rocksalt oxides

The structures and energies of a series of tilt grain boundaries and corresponding surfaces were calculated to obtain a general relationship between the grain boundary energy and the tilt angle for NiO and MgO. We show that the simple elastic expressions for the grain boundary energy give reasonable results for low-angle grain boundaries. We investigate the assumptions that lie behind thermal grooving experiments and show that the torque terms should be large, even when far from a major pole [the (100), (110), or (111) directions]. However, the measured angles agree better with the calculations when torque terms are ignored. We discuss this effect in terms of faceting and oxidation of the surface. [S0163-1829(99)06627-8].