Grain boundary tracer diffusion was treated as a correlated walk in a periodic system with multiple jump frequencies. Together with the usual defect-induced correlations, non-uniformity of the boundary structure itself gave rise to so-called structural correlations. These were also present in the interstitial mechanism of atomic migration and played an important role in boundary diffusion. In order to study them separately, a diffusion model was developed which took account only of structural correlations. On the basis of this model, a method was proposed for making exact or approximate calculations of the effective diffusion tensor and the correlation factors, using recursive relationships between displacement S-vectors which were associated with various sites in the boundary. By using this method, and Monte Carlo simulations, the diffusion behavior in a simplified grain boundary was investigated. Depending upon the distribution of easy and difficult jumps, and the tracer binding energies in the structure, the structural correlation effects ranged from very weak to very strong. In the latter case, they were associated with a trapping effect. Under certain conditions, the 2 types of correlation could be treated separately in terms of an encounter model.

J.M.Mishin, C.Herzig: Philosophical Magazine A, 1995, 71[3], 641-60