An ordered twin boundary in this L10 alloy was investigated by means of computer modelling and high-resolution electron microscopy. The results demonstrated the importance of directional covalent bonding to the interfacial structure. Upon applying the  ab initio  full-potential linear muffin-tin orbital method, the stable structure exhibited a pronounced asymmetry. This structure was in excellent agreement with high-resolution electron microscopic observations. On the other hand, calculations which employed central-force many-body potentials predicted a structure whose asymmetry was so small that it was not discernible in high-resolution electron microscopic images. The preference for a strongly asymmetrical structure was explained in terms of covalent d-type bonding between Ti atoms in the alloy.

R.Siegl, V.Vitek, H.Inui, K.Kishida, M.Yamaguchi: Philosophical Magazine A, 1997, 75[5], 1447-59