Mechanisms of ductility improvement in L1₂ compounds

The present article first describes some characteristics of structure, chemistry, and electronic (bond) nature for grain boundaries in the A₃B Li₂-type intermetallic compounds. Next, the phenomenological aspects for the grain boundary brittleness of the Li₂-type intermetallic compounds are reviewed with respect to the combination of the constituent atoms, the alloying effect, the stoichiometry effect, and a role of impurity or gaseous atoms. It is emphasized that the brittleness of grain boundaries in the intermetallic compounds is directly controlled by the atomistic and electronic structures at grain boundary regions. Based on these systematic investigations, it is suggested that the brittleness of the Li₂-type intermetallic compounds can be manipulated by appropriate control of composition and the corresponding electrochemical bond environment at grain boundary planes and by control of test environment. Furthermore, some examples of the materials development are described.