Atomic structure of stoichiometric and non-stoichiometric grain boundaries in A 3B compounds with L1 2 structure

Abstract

Pair potentials are employed to investigate the similarities and differences between the boundaries in pure metals and L1 2 ordered compounds of the A BB type. Symmetrical σ = 5 (310) and (210) [001] tilt boundaries have been studied in detail. In addition, a limited study of the σ = 73 (830) boundary has also been performed. It turns out that the concepts of structural units and multiplicity of boundary structures, originally developed for pure metals, are still applicable. In general, the atomic structures of the boundaries in A BB-L1 2 compounds appear to be topologically similar to the structures of the boundaries of the same type in single-component f.c.c. materials. However, the multiplicity of boundary structures is much more extensive compared to pure materials since structures may differ not only topologically but also compositionally. The structural units in the stoichiometric boundaries are, in general, more distorted than those of either A or B rich boundaries (with respect to A 3B stoichiometry). Away from stoichiometry the structures resemble more closely the corresponding structures in single component systems. Possible consequences of these structural features for the grain boundary brittleness of the L1 2 compounds are discussed.