The diffusivity of Ge was measured in a series of bicrystals with symmetrical near-Σ7 38.2º (12¯3)[111] tilt grain boundaries (figure 2). The actual orientations were checked precisely by using the Kossel technique. The tilt angles ranged from 34.15 to 41.41º. Grain-boundary diffusion parallel to the tilt axis was measured in the type-B kinetic regime at 5 temperatures ranging from 518 to 680K. A characteristic non-monotonic behavior of the dependence of the grain boundary diffusivity upon the tilt angle was observed for all 5 temperatures. For the ideal Σ = 7 38.2º (12¯3)[111] tilt grain boundary, the diffusion was minimal. With increasing deviation from the coincidence site lattice grain boundary, the diffusivity increased and exhibited a broad maximum at about 38.2º. Opposite trends were observed in the pre-exponential factor and activation enthalpy for grain boundary diffusion. The Arrhenius parameters were highest for the ideal Σ = 7 coincidence site lattice grain boundary. The orientational dependence of the grain boundary diffusion supported the coincidence site lattice grain boundary diffusion model.

T.Surholt, D.A.Molodov, C.Herzig: Materials Science Forum, 1999, 294-296, 545-8