It was shown that inhomogeneity of a grain boundary due, for instance, to the effect of a distribution of differing lattice sites on the heats of interaction with other species, led to non-linear grain boundary penetration plots (in Fisher’s coordinates). The sign of the curvature, and the degree of deviation from a straight concentration profile, depended upon the interaction parameters (maximum and minimum values of the interaction heat).

B.S.Bokstein, A.S.Ostrovsky, A.O.Rodin: Philosophical Magazine A, 1995, 72[4], 829-36