It was observed that internal oxidation of Ag-3at%Mn produced Mn3O4 precipitates which had a so-called parallel topotaxy with respect to the metal matrix, and an octahedral shape which was due to {111} facets. This orientation and shape did not give the lowest strain-energy state, thus indicating a predominance of interfacial energy over strain energy. On the basis of strain energy, the oxide precipitates should have had a plate-like shape with (001) as the dominant facet. Due to the tetragonality of the oxide, only a few planes and directions of the Ag and oxide could be parallel simultaneously. The precipitates exhibited a tendency to align their {111} planes parallel to the matrix for one pair of facets while, for another pair of planes, a tilt of 7.6º occurred which was relieved by the appearance of ledges in the Ag. An essentially 1-dimensional 10.4% resultant mismatch along <112> was usually accommodated by an array of dislocations with a <110> line direction and alternating Burgers vectors of 1/6<112> and 1/3<112>. At parts of the parallel and tilted interfaces, dislocations were observed which stood off from the interface by 1 or 2 atomic spacings into the Ag. On the basis of atomistic calculations, relaxation at the parallel {111} interfaces was attributed to the dissociation of unfavorable 1/3<112> Burgers vector into more favorable Shockley partials. At the tilted interfaces, ledges which corresponded to the tilt between the {111} planes could collapse and thus improve the parallelism of the {111} planes of the metal and oxide at the interface. The underlying mechanism of this collapse was the dissociation of a Frank partial into a Shockley partial which was then emitted into the Ag along {111} and made a large angle with respect to the interface and to a stair-rod which remained at the interface.

B.J.Kooi, H.B.Groen, J.T.M.De Hosson: Acta Materialia, 1997, 45[9], 3587-607